Insight into the negative magnetization and anomalous exchange-bias in DyFe5Al7 through neutron depolarization and neutron diffraction studies

We have provided the mesoscopic and microscopic understandings of polarity reversal of the magnetization or negative magnetization (NM) below TCOMP = 93 K in an exotic magnetic material containing three magnetic sublattices, viz., DyFe5Al7 crystallizing in ThMn12 structure, using neutron depolarization and neutron diffraction techniques. A full recovery of the neutron beam polarization at the TCOMP in a neutron depolarization experiment reveals a total compensation of magnetization inside the magnetic domains in the sample. The temperature-dependent neutron diffraction study under zero magnetic field has provided temperature dependencies of antiparallelly coupled Dy (MDy(2a)) and Fe (MFe(8f) and MFe(8j)) sublattice magnetic moments along [100] direction.Thedominance of |MDy(2a)| over total Fe moment, MFetotal = 4*|MFe(8f)| + |MFe(8j)|, below TCOMP leads to the NM in the compound. The magnetization versusmagnetic field curves below the TCOMP indicate the presence of field-induced spin reorientation in the compound. The magnetic field required for spin reorientation (HSR) is maximum at the lowest temperature and it decreases to zero as the temperature is increased to TCOMP. Interestingly, the compound shows a finite exchange-bias (HEB) below the TCOMP only, as evident from the field-cooled hysteresis loops, while at T > TCOMP,HEB is almost zero. The cooling-field (HCOOL) dependent study of HEB shows a slope change at HCOOL ~ HSR indicating a correlation of exchange-bias with spin-reorientation in the compound. This study, apart from revealing microscopic understanding of magnetic behavior of an exotic three magnetic sublattice system, provides a correlation among exchange-bias, magnetic compensation, and spin-reorientation phenomena.

Effective Formation of a Mn-ZIF-67 Nanofibrous Network via Electrospinning: An Active Electrocatalyst for OER in Alkaline Medium

Finding the active center in a bimetallic zeolite imidazolate framework (ZIF) is highly crucial for the electrocatalytic oxygen evolution reaction (OER). In the present study, we constructed a bimetallic ZIF system with cobalt and manganese metal ions and subjected it to an electrospinning technique for feasible fiber formation. The obtained nanofibers delivered a lower overpotential value of 302 mV at a benchmarking current density of 10 mA cm^-2 in an electrocatalytic OER study under alkaline conditions. The obtained Tafel slope and charge-transfer resistance values were 125 mV dec^-1 and 4 Ω, respectively. The kinetics of the reaction is mainly attributed from the ratio of metals (Co and Mn) present in the catalyst. Jahn-Teller distortion reveals that the electrocatalytic active center on the Mn-incorporated ZIF-67 nanofibers (Mn-ZIF-67-NFs) was found to be Mn³⁺ along with the Mn²⁺ and Co²⁺ ions on the octahedral and tetrahedral sites, respectively, where Co²⁺ ions tend to suppress the distortion, which is well supported by density functional theory analysis, molecular orbital study, and magnetic studies.

Double glassy states and large spontaneous and conventional exchange bias in La1.5Ca0.5CoFeO6ferrimagnetic double perovskite

The structural and magnetic properties of hole doped double perovskite La_1.5Ca_0.5CoFeO₆have been investigated by measuring x-ray photoemission spectroscopy, neutron powder diffraction and magnetization. A ferrimagnetic transition is observed atT_C∼ 167 K. The presence of anti-site disorder (ASD) in La_1.5Ca_0.5CoFeO₆has also been demonstrated. Double re-entrant cluster glass transitions (T₁∼ 11 K andT_S∼ 35 K) were observed which has been attributed to the ASD effect. The presence of both large spontaneous exchange biasH_SEB∼ 2.106 kOe and giant conventional exchange biasH_CEB∼ 1.56 T at 5 K has also been observed which can be attributed to the coexistence of long range magnetic ordering and glassy state. The experimental observations were explained with the results obtained by the density functional theory calculation. The presence of double glassy states, large exchange-bias effect and different magnetic phases make this system a potential candidate for spintronic applications.

High cubicity of D2O ice inside spherical nanopores of MIL-101(Cr) framework: a neutron diffraction study

Although cubic ice (ice I_c) is considered to be an important phase of water that impacts ice cloud formation in the Earth's upper atmosphere, its properties have not been studied to the same extent as those of hexagonal ice (ice I_h). This is because pristine ice I_c is not formed in simple laboratory conditions. Ice I_c formed in ambient conditions has a stacking disordered array of both hexagonal and cubic-structured hydrogen-bonded water molecules. It is therefore an active area of research to find ways of developing stacking disorder-free pure ice I_c. We demonstrate the evolution of almost pure ice I_c structure within the spherical nanopores of a hydrostable Cr-based metal-organic framework MIL-101(Cr) with an average pore size of 1 nm by low-temperature neutron diffraction study on D₂O. It is observed that at temperatures below 230 K a fraction of liquid D₂O transforms into ice and more than 94% of ice crystals evolved inside the pore are cubic in shape. This is a significantly high fraction of ice I_c formed under simple conditions inside the spherical pores of a Cr-based MOF. It is also observed that upon increasing the temperature, i_ce I_c remains stable until its melting point, without being transformed into ice I_h. This observation is in contrast to our previous observation of ice structure in the 2D cylindrical nanopores of MCM-41, where H₂O ice after creeping out from the cylindrical channel was seen to be dominated by hexagonal shape. In the present study, the D₂O molecules were confined into well-defined spherical nanopores, which hindered the growth of crystals above a certain size, thus minimizing the stacking disordered array. Nanoconfinement of water inside uniform spherical pores is therefore a promising method for the evolution of a significantly large fraction of cubic ice by minimizing the stacking disorder. This finding may open up the possibility of forming ice I_c with 100% cubicity under simple laboratory conditions, which will help in exploring the microphysics of ice cloud formation in the upper atmosphere.

Observation of Anisotropic Thermal Expansion and the Jahn-Teller Effect in Double Perovskites Sr2-xLaxCoNbO6 Using Neutron Diffraction

We use temperature dependent neutron powder diffraction (NPD) to investigate the structural changes and magnetic interactions in double perovskite Sr_2-xLa_xCoNbO₆ (x = 0.4 and 0.6). A structural phase transition from tetragonal (I4/m) to monoclinic (P2₁/n) is observed between x = 0.4 and 0.6 samples. Interestingly, the temperature evolution of the unit cell parameters follows the Grüneisen approximation, and the analysis suggests an isotropic thermal expansion in the case of the x = 0.4 sample, whereas the x = 0.6 sample shows the anisotropy where the thermal expansion along the c-axis significantly deviates from the Grüneisen function. We observe the z-out Jahn-Teller distortion in the CoO₆ and consequently z-in distortion in the adjacent NbO₆ octahedra. With an increase in the La substitution, a decrease in the degree of octahedral distortion is evident from the significant reduction in the local distortion parameter Δ around the B-site atoms.

Cluster spin-glass-like dynamics in Mn-rich La2Ni0.5Mn1.5O6ferromagnetic insulator

We report on the physical properties of Mn-rich, nonstoichiometric La₂Ni_0.5Mn_1.5O₆ferromagnetic insulator, prepared by sol-gel method. The single-phase orthorhombicPbnmstructure for the compound was confirmed by x-ray diffraction measurements. Dc magnetization measurements revealed a high saturation magnetization of ∼5.95 μ_B/f.u. at 5 K, and a ferromagnetic to paramagnetic transition at ∼162 K. Ac magnetic susceptibility measurements confirmed a broad frequency-dependent anomaly at lower temperatures indicating the presence of spin-glass type magnetic interactions. The ac susceptibility data have been discussed within the framework of the critical slowing down model and Vogel-Fulcher law, and confirmed the cluster spin-glass dynamics with a relaxation time of the order of 10^-5 s. The valence of Ni and Mn ions was verified from the x-ray absorption near edge structure spectroscopy. The origin of cluster spin-glass state was discussed in terms of several possible magnetic exchange interaction pathways among Ni and Mn ions.

Effect of crystallite size on the phase transition behavior of heterosite FePO4

For advanced lithium-ion battery technology, olivine-based cathodes are considered to be the most dominant and technologically recognized materials. The extraction of lithium ions from olivine LiFePO₄ results in the two-phase mixture with heterosite FePO₄ exhibiting a deintercalation potential of 3.45 V vs. Li⁺/Li over a wide range of lithium content. Here, we report the synthesis and characterization of chemically deintercalated heterosite FePO₄ with varying crystallite sizes using different analytical techniques. The decrease in the crystallite size of heterosite FePO₄ leads to an increase in the lattice parameters including the unit cell volume. The characteristic behavior in the structural properties of heterosite FePO₄ shows a strong dependency on the crystallite size which is correlated with the change in the chemical bonding. The volume expansion of the nano-sized heterosite FePO₄ with respect to the bulk counterpart is suggested to be a direct consequence of reduced hybridization between the Fe3d and O2p states. Furthermore, the combined X-ray diffraction and Mössbauer spectroscopic studies reveal the appearance of a new phase namely trigonal FePO₄ at the lower crystallite sizes due to the enhanced surface energy kinetics. We also find that the observed trigonal FePO₄ phase is more magnetically active than the paramagnetic olivine FePO₄. For the unique structural advantage of the heterosite phase as an electrode material, the change in bonding characteristics is very useful and can have strong implications on the electronic properties of heterosite FePO₄ at the nanoscale level.

Evolution of confined ice nano structures at different levels of pore filling: a synchrotron based X-ray diffraction study

We have thoroughly investigated the crystal structure of ice evolved from super cooled water confined in MCM-41 cylindrical nano pores through a synchrotron-based X-ray diffraction (XRD) technique for two different levels of pore filling. A rigorous analysis of XRD data shows that the nucleation dynamics and the structure of nucleated ice highly depend on the level of pore filling. In the nearly fully hydrated pores, ice crystallites start nucleating inside the pores below 240 K and creep out of the pores to form bulk crystals having crystalline structure of a mixed phase of hexagonal and cubic forms. In the partially hydrated pores, on the other hand, ice crystals cannot creep out of the pore crossing the energy barrier. The crystalline ice particles remaining inside the cylindrical pore show a short range "cubic rich" structure. The "pure cubic" phase has not been identified at either of the pore fillings in these 2.5 nm average size pores. A large fraction of water inside the pores remains in the super cooled liquid phase even at 180 K. This observation is relevant for understanding the ice nucleation through the pore condensation and freezing mechanism, which is a major pathway for the formation of cirrus clouds in the upper atmosphere.

Exploring Magnetic XY Behavior in a Quasi-2D Anisotropic Triangular Lattice of Cu(II) by Functionalized Graphene

Study on magnetism in two-dimensional (2D) spin-lattices is advancing rapidly. In this work, phase-pure botallackite (Bo) (Cu₂(OH)₃Br), a quasi-2D S = 1/2 anisotropic triangular spin-lattice is stabilized over 2D reduced graphene oxide (rGO) nanosheets via simple oxidation-reduction reaction chemistry. In comparison to polycrystalline Bo, such an anchoring resulted in the oriented growth of Bo crystallites in the Bo-rGO system. The Bo-rGO nanocomposite was found to be magnetically active with a Néel transition at ∼8.9 K, crossing over to possible XY anisotropy at ∼5 K-as revealed by complementary dc and ac susceptibility measurements-an unprecedented observation in the field assigned to an interfacial effect. This work demonstrates the potential usage of nonmagnetic 2D functionalized graphene to significantly modulate the magnetic properties of 2D spin-lattices.

Metamagnetism in Nanosheets of CoII-MOF with TN at 26 K and a Giant Hysteretic Effect at 5 K

Herein, we have synthesized at room-temperature two-dimensional nanosheets of a MOF comprised of cobalt(II) ion with benzenedicarboxylic acid  ligand, which exhibited unusual magnetic properties. Direct-current magnetic susceptibility revealed an antiferromagnetic (AFM) transition at 26 K (Néel temperature,  T_N) followed by a canting of the spin moments along with the concomitant appearance of a sigmoidal-shaped magnetization versus field ( M- H) curve at 15 K. Such a canted AFM ordering led to nonzero remnant magnetization with a remarkably high coercive field of ∼10 kOe at 5 K. Metamagnetism was further substantiated by the alternating-current magnetic susceptibility measurements.

Magnetic Exchange Interaction in Nitronyl Nitroxide Radical-Based Single Crystals of 3d Metal Complexes: A Combined Experimental and Theoretical Study

Two stable nitronyl nitroxide free radicals {R ¹ = 4'-methoxy-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (NNPhOMe) and R ² = 2-(2'-thienyl)-4,4,5,5-tetramethylimidazoline 3-oxide 1-oxyl (NNT)} are successfully synthesized using Ullmann condensation. The reactions of these two radicals with 3d transition metal ions, in the form of M(hfac)₂ (where M = Co or Mn, hfac: hexafluoroacetylacetone), result in four metal-organic complexes Co(hfac)₂(NNPhOMe)₂, 1; Co(hfac)₂(NNT)₂·(H₂O), 2; Mn(hfac)₂(NNPhOMe)·x(C₇H₁₆), 3; and Mn(hfac)₂(NNT)₂, 4. The crystal structure and magnetic properties of these complexes are investigated by single-crystal X-ray diffraction, dc magnetization, infrared, and electron paramagnetic resonance spectroscopies. The compounds 1 and 4 crystallize in the triclinic, P1̅, space group, whereas complex 3 crystallizes in the monoclinic structure with the C2/c space group and forms chain-like structure along the c direction. The complex 2 crystallizes in the monoclinic symmetry with the P2₁/c space group in which the N-O unit of the radical coordinates with the Co ion through hydrogen bonding of a water molecule. All compounds exhibit antiferromagnetic interactions between the transition metal ions and nitronyl nitroxide radicals. The magnetic exchange interactions (J/K _B) are derived using isotropic spin Hamiltonian H = -2J∑(S _metal S _radical) for the model fitting to the magnetic susceptibility data for 1, 2, 3, and 4. The exchange interaction strengths are found to be -328, -1.25, -248, and -256 K, for the 1, 2, 3, and 4 metal-organic complexes, respectively. Quantum chemical density functional theory (DFT) computations are carried out on several models of the metal-radical complexes to elucidate the magnetic interactions at the molecular level. The calculations show that a small part of the inorganic spins are delocalized over the oxygens from hfac {∼0.03 for Co(II) and ∼0.015 for Mn(II)}, whereas a more significant fraction {∼0.24 for Mn(II) and ∼0.13 for Co(II)} of delocalized spins from the metal ion is transferred to the coordinated oxygen atom(s) of nitronyl nitroxide.

Revealing magnetic ordering and spin-phonon coupling in Y1-x Tb x MnO3 (0.1 ⩽ x ⩽ 0.3) compounds

The structural and magnetic properties of the Y_1-x Tb _x MnO₃ (0.1  ⩽  x  ⩽  0.3) compounds were investigated. Neutron diffraction patterns for all three samples, recorded at room temperature (RT), were fitted to the nuclear structure confirming the paramagnetic nature of the compounds. At 2.8 K, for the x  =  0.1 sample magnetic moments of the Tb³⁺ ionic as well as Mn³⁺ ionic were ordered. At 5 K for the x  =  0.2 sample only the Mn³⁺ ionic magnetic moments were ordered. There were six sites for Mn atoms. Three on the z  =  0 plane and three on the z  =  0.5 plane (where z corresponds to  +c axis).The Mn³⁺ionic moments were confined to the a-b plane with a net magnitude of 2.78(3) µ _B, and 2.90(3) µ _B for the x  =  0.1 and the x  =  0.2 samples. The Tb³⁺ionic moments had a magnitude of 1.36(4) µ _B at 2.8 K and were aligned antiferromagnetically along the crystallographic c-axis for the x  =  0.1 sample. The low moment in comparison with Mn³⁺ free ions has been attributed to crystalline electric fields similar to that found in the parent compound YMnO₃ and also in another rare earth manganite viz HoMnO₃. The x  =  0.3 sample was found to be a canonical spin glass. To investigate the role of the above spin ordering in Y_1-x Tb _x MnO₃ in governing the phonon dynamics, temperature dependent Raman measurements were carried out. We observed the deviation of the phonon frequency near 685 cm^-1 and its line-width from the expected anharmonic behaviour around magnetic ordering temperature for Tb substituted compounds with x  =  0.1 and 0.2. This was attributed to the spin-phonon coupling in these systems. The anomalous behaviour of this phonon mode in the canonical spin glass compound with x  =  0.3, indicated that the coupling sustained even in the presence of only local magnetic ordering.

Synthesis, Characterization and Exploration of Multiferroic Properties in Nano-Crystalline Tb1-xYxMnO3 (0 ≤ x ≤ 0.4)

We report the synthesis and electric properties of nano-crystalline Tb1-xYxMnO3 (x = 0, 0.1, 0.2, 0.3 and 0.4) compounds prepared by gel-combustion method. These samples were characterized by a number of techniques including X-ray diffraction (XRD), Raman spectroscopy, specific-heat measurement, neutron diffraction, and magnetic field dependent pyrocurrent measurement. All the samples crystallize in the orthorhombic structure with space group Pnma at room temperature. Anomalies were observed in low temperature specific-heat measurement corresponding to magnetic and electric phase transitions. The magnetic phase transitions occurred at ~35, ~22-28 and ~7 K for all the samples. Signatures of coupling between magnetic and electric order parameters were revealed by pyrocurrent measurements carried out in presence of magnetic fields.

Dyslipidemia: Prevalence and associated risk factors among patients with Lichen Planus in Kano, North-West Nigeria

BACKGROUND

Lichen planus (LP) is a chronic inflammatory disorder. Recently, there are suggestions that LP is associated with dyslipidemia in a large series of patients independent of other causes.

OBJECTIVE

The objective of this study was to investigate the prevalence and associated risk factors for dyslipidaemia among patients with LP.

METHODS

This case-control study included 180.subjects, 90 with lichen planus (39 men and 51 Women) and 90 (44 men and 46 women) controls consecutively recruited from the outpatient Dermatology clinic of Amnihu Kano Teaching Hospital Kano-Nigeria.

RESULTS

The prevalence of dyslipidemia was found to be higher among LP patients (32%) than the corol group (24%), p=0.208. Our study showed that male patients with LP have higher tendencies to develop dyslipidemia (OR 5.66, CI 1.73-19.59). Equally the duration of illness t 2 months was found to be a strong predictor of developing dyslipidemia (OR 5.65, CI 1.12-38.3). No significant differences were observed in glucose levels, body mass index, or blood pressure between the two study groups.

CONCLUSION

The prevalence of dyslipidaemia among patients with LP in this study was high with male gender and increased-duration of illness being strong predictors. There is need for further studies on a larger scale to establish the prevalence and independent predictors of dyslipidaemia in patients with LP in our setting.

Structural, magnetic, and dielectric studies on Gd0.7Y0.3MnO3

Structural, magnetic, specific heat, and dielectric studies were carried out on Y substituted (30 at. %) GdMnO(3) compound as a function of temperature. Anomalies occur at ~41 and 18 K, in the specific heat measurements and are ascribed to paramagnetic, to sinusoidal incommensurate antiferromagnetic transition (ICAFM) and ICAFM to commensurate antiferromagnetic transitions, respectively. Changes in the lattice parameters across these temperatures indicate magneto-elastic coupling present in the compound. However, in the dielectric measurements, an anomaly at 18 K alone is observed and is ascribed to a ferroelectric transition, giving rise to spontaneous ferroelectric ordering at low temperatures. This observation is supported by an anomaly in lattice parameters, across the transition temperature. From the frequency dependent dielectric studies, a strong coupling between Gd(3+) and Mn(3+) magnetic sublattices is inferred and Y substitution results in substantial changes in the relaxation process compared to that of GdMnO(3).

Correspondence between neutron depolarization and higher order magnetic susceptibility to investigate ferromagnetic clusters in phase separated systems

It is a tough task to distinguish a short-range ferromagnetically correlated cluster-glass phase from a canonical spin-glass-like phase in many magnetic oxide systems using conventional magnetometry measurements. As a case study, we investigate the magnetic ground state of La0.85Sr0.15CoO3, which is often debated based on phase separation issues. We report the results of two samples of La0.85Sr0.15CoO3 (S-1 and S-2) prepared under different conditions. Neutron depolarization, higher harmonic ac susceptibility and magnetic relaxation studies were carried out along with conventional magnetometry measurements to differentiate subtle changes at the microscopic level. There is no evidence of ferromagnetic correlation in the sample S-2 attributed to a spin-glass phase, and this is compounded by the lack of existence of a second order component of higher harmonic ac susceptibility and neutron depolarization. A magnetic relaxation experiment at different temperatures complements the spin glass characteristic in S-2. All these signal a sharp variance when we consider the cluster-glass-like phase (phase separated) in S-1, especially when prepared from an improper chemical synthesis process. This shows that the nonlinear ac susceptibility is a viable tool to detect ferromagnetic clusters such as those the neutron depolarization study can reveal.

Fabrication of porous β-Co(OH)2 architecture at room temperature: a high performance supercapacitor

A facile, cost-effective, surfactant-free chemical route has been demonstrated for the fabrication of porous β-Co(OH)2 hierarchical nanostructure in gram level simply by adopting cobalt acetate as a precursor salt and ethanolamine as a hydrolyzing agent at room temperature. A couple of different morphologies of β-Co(OH)2 have been distinctly identified by varying the mole ratio of the precursor and hydrolyzing agent. The cyclic voltammetry measurements on β-Co(OH)2 displayed significantly high capacitance. The specific capacitance obtained from charge-discharge measurements made at a discharge current of 1 A/g is 416 F/g for the Co(OH)2 sample obtained at room temperature. The charge-discharge stability measurements indicate retention of specific capacitance about 93% after 500 continuous charge-discharge cycles at a current density of 1 A g(-1). The capacitive behavior of the other synthesized morphology was also accounted. The nanoflower-shaped porous β-Co(OH)2 with a characteristic three-dimensional architecture accompanied highest pore volume which made it promising electrode material for supercapacitor application. The porous nanostructures accompanied by high surface area facilitates the contact and transport of electrolyte, providing longer electron pathways and therefore giving rise to highest capacitance in nanoflower morphology. From a broad view, this study reveals a low-temperature synthetic route of β-Co(OH)2 of various morphologies, qualifying it as supercapacitor electrode material.

Field induced incommensurate-to-commensurate magnetic phase transition in Ca₃Co₁.₈Fe₀.₂O₆: a neutron diffraction study

Neutron powder diffraction experiments have been performed to investigate the nature of magnetic ordering, as a function of temperature (1.5-100 K) and magnetic field (0, 2 and 4 T), in the compound Ca3Co1.8Fe0.2O6. In zero applied field, the compound orders magnetically in the incommensurate spin density wave (SDW) structure (TN ∼ 20 K). Under an applied field of ∼2 T, an incommensurate-to-commensurate magnetic phase transition has been observed. With a further increase in the magnetic field (∼4 T), the commensurate magnetic structure transforms into a ferrimagnetic structure. In zero applied field, magnetic short-range ordering (SRO) coexists with the SDW long-range ordering (LRO) at all temperatures below TN. In an applied magnetic field (2 and 4 T), SRO is converted into LRO only over the temperature range 12-20 K; however, below ∼12 K, an increase in the volume fraction of the SRO has been observed. The correlation length for the SRO (below ∼12 K) also gets affected by the application of a field.

The magnetic proximity effect in a ferrimagnetic Fe3O4 core/ferrimagnetic γ-Mn2O3 shell nanoparticle system

We report the magnetic proximity effect in a ferrimagnetic Fe(3)O(4) core/ferrimagnetic γ-Mn(2)O(3) shell nanoparticle system, in terms of an enhancement of the Curie temperature (T(c)) of the γ-Mn(2)O(3) shell (~66 K) compared to its bulk value (~40 K), and the presence of magnetic ordering in its so-called paramagnetic region (i.e. above 66 K). The ferrimagnetic nature of both core and shell has been found from a neutron diffraction study. The origin of these two features of the magnetic proximity effect has been ascribed to the proximity of the γ-Mn(2)O(3) shell with a high-T(c) Fe(3)O(4) core (~858 K in bulk form) and an interface exchange coupling between core and shell. Interestingly, we did not observe any exchange bias effect, which has been interpreted as a signature of a weak interface exchange coupling between core and shell. The present study brings out the importance of the relative strength of the interface coupling in governing the simultaneous occurrence of the magnetic proximity effect and the exchange bias phenomenon in a single system.

Diffusion of water in molecular magnet Cu(0.75)Mn(0.75)[Fe(CN)6]·7H2O

Here we report the dynamical behaviour of water in Prussian blue analogue (PBA) Cu(0.75)Mn(0.75)[Fe(CN)(6)]·7H(2)O molecular magnet in the temperature range 260-360 K as studied using the quasielastic neutron scattering technique. While significant quasielastic broadening is observed in the hydrated sample, no broadening was observed in the dehydrated one. Data analysis showed that the observed quasielastic broadening in Cu(0.75)Mn(0.75)[Fe(CN)(6)]·7H(2)O corresponds to the dynamics of the non-coordinated water molecules at the 32f site and the coordinated water molecules at the 24e site, existing in the cavities created by the absence of Fe(CN)(6) units. The non-coordinated water molecules at 8c interstitial sites do not contribute to the broadening, suggesting that they are immobile at least within the time window of the spectrometer used. Behaviour of the elastic incoherent structure factor is consistent with the model where the water molecules undergo translational diffusion localized within the cavity of 5.1 Å. While all the non-coordinated water molecules at the 32f site are dynamic over the entire range of temperatures, the coordinated ones at the 24e site become progressively dynamic with temperature. The water molecules were found to undergo hindered (~1.16 × 10(-5) cm(2) s(-1) at 300 K) diffusion compared to bulk water and the diffusivity followed Arrhenius behaviour within the measured temperature range with an activation energy of 1.26 kcal mol(-1).

Effect of electron doping on the magnetic correlations in the bilayered brownmillerite compound Ca(2.5-x)La(x)Sr(0.5)GaMn2O8: a neutron diffraction study

The effect of electron doping on the magnetic properties of the brownmillerite type bilayered compounds has been investigated by neutron powder diffraction in La substituted Ca(2.5-x)La(x)Sr(0.5)GaMn(2)O(8) compounds (x = 0.05 and 0.1), in comparison with the undoped compound (x = 0). In all compounds, a long-range three-dimensional collinear antiferromagnetic (AFM) structure is found below the Néel temperature T(N) of the respective compound, whereas, well above T(N), three-dimensional short-range magnetic ordering is observed. In the intermediate temperature range just above T(N), a strong effect of electron doping (La substitution) on the magnetic correlations has been observed. Here, a short-range AFM correlation with a possible dimensionality of three has been found for substituted compounds (x = 0.05 and 0.1) as compared to the reported two-dimensional long-range AFM ordering in the parent compound. With increasing electron doping, a decrease in T(N) is also observed. The short-range magnetic correlations set in over a large temperature range above T(N). A magnetic phase diagram in the x-T plane is proposed from these results.

Idiopathic scrotal calcinosis; a rare scrotal tumour: a case report and review of literature

Idiopathic scrotal calcinosis is a rare benign disease characterized by multiple, asymptomatic and painless nodules on the scrotum. We herein report this rare disease in a Nigerian adult male and briefly review the relevant literature.

Influence of lattice distortion on the Curie temperature and spin-phonon coupling in LaMn0.5Co0.5O3

Two distinct ferromagnetic phases of LaMn(0.5)Co(0.5)O(3) having monoclinic structure with distinct physical properties have been studied. The ferromagnetic ordering temperature T(c) is found to be different for both the phases. The origin of such contrasting characteristics is assigned to the changes in the distance(s) and angle(s) between Mn-O-Co resulting from distortions observed from neutron diffraction studies. Investigations on the temperature dependent Raman spectroscopy provide evidence for such structural characteristics, which affects the exchange interaction. The difference in B-site ordering which is evident from the neutron diffraction is also responsible for the difference in T(c). Raman scattering suggests the presence of spin-phonon coupling for both the phases around the T(c). Electrical transport properties of both the phases have been investigated based on the lattice distortion.

Ichthyosis hystrix Curth-Macklin type in an African girl

Ichthyosis hystrix Curth-Macklin type is a rare autosomal dominant skin disorder characterized by extensive hyperkeratosis and palmo-plantar keratoderma. It results from heterozygous frameshift mutation in keratin 1 gene (KRT1). Histological features, showing perinuclear vacuolization and binucleated cells, are similar to those of epidermolytic hyperkeratosis except for the absence of epidermolysis. The present report describes the condition in a 16-year-old African girl where available treatment was disappointing.

Hierarchical superparamagnetic magnetite nanowafers from a resin-bound [Fe(bpy)3]2+ matrix

The brilliant red [Fe(bpy)(3)](2+) complex upon immobilization on a strongly acidic cation exchanger or in situ formation of the same cationic complex onto a resin matrix and subsequent modified hydrothermolysis (MHT) at approximately 110 degrees C produces unusually stable hierarchical magnetite (Fe(3)O(4)) nanowafers. The slow hydrothermolysis, oxidation, and subsequent dehydration of the complex on the solid-liquid interface produce stable hierarchical nanostructures. The isolation of neat Fe(3)O(4) (uncapped) particles from the resin matrix as hierarchical nanowafers was achieved by magnetically stirring a CH(3)CN suspension of nanocomposites. The solid resin support not only aids nanowafer formation on its surface but also provides unique stability to the magnetite particles, where nanowafer oxidation is largely retarded. The utility of the as-prepared porous nanocomposite and characterization of the nanoparticles are promising for nanotechnological and soft ferromagnetic applications.

Disseminated cutaneous leishmaniasis in HIV positive patient--a case report

Disseminated cutaneous leishmaniasis and HIV dual-infection is seldom reported. Leishmaniasis and HIV co-infection may intensify the immune defect and is the chief reason for atypical presentation and widespread progression of cutaneous leishmaniasis and its defiance to conventional therapy. Here we report a 38-year-old HIV-positive lady who presented with a 6-month history of a progressive papule and nodular eruptions of leishmaniasis on face, trunk and extremities that was recalcitrant to treatment.

Type 2 segmental Darier's disease in a twelve-year-old Nigerian male--a case report

Darier's disease is an autosomal dominant disorder characterized clinically by presence of keratotic papules in a seborrheic distribution, nail involvement and mucosal lesions. There are several clinical variants of Darier's disease, but few cases of segmental Darier's disease have been described in the literature. We describe a 12-year-old boy with type 2 mosaic phenotype. This unique clinical variant of Darier's disease has been described very rarely.

Krukenberg's tumour

BACKGROUND

Krukenburg's tumour, a metastatic cancer to the ovary can pose difficulties in early diagnosis. The paucity of reports from our environment coupled with the difficulties we encountered makes it imperative that we report this case.

METHODS

We present a 32-year-old lady who presented with mucoid and bloody diarrhoea associated with menstrual irregularity, weight loss and lower abdominal pains 2 years after surgical treatment for gastric cancer. Literature on Krukenburg's tumour was also reviewed.

RESULTS

While serum level of CEA was found to be elevated and colonoscopy showed an ulcerated mass obliterating the lumen of the sigmoid colon, abdominal CT scan revealed bilateral adnexal masses. The histology of the colonic lesion showed signet ring carcinoma while the enlarged ovaries turned out to have evidence of metastatic adenocarcinoma.

CONCLUSION

Early diagnosis of KT can be difficult. Periodic surveillance is, therefore, essential especially in those who have had a gastrointestinal malignancy.

Dyschromatosis universalis hereditaria in a young Nigerian female

Dyschromatosis universalis hereditaria (DUH) is a clinically heterogeneous disorder that shows generalized mottled pigmentation. It occurs most commonly in Japanese persons, with sporadic reports from South Africa, India, and Iraq. Histopathology reveals a variable degree of pigmentary incontinence. Although the precise etiology of this disorder is not yet known, the clinicopathological findings implicate an inherent abnormality of melanosomes or melanin processing. We describe a case in a young Nigerian girl.

Nanocrystalline HoCrO4: facile synthesis and magnetic properties

Nanocrystalline HoCrO4 powder was synthesized by a combustion technique using glycine and citric acid as the fuels in different oxidant-to-fuel ratios. Fuel-deficient glycine-nitrate combustion reaction resulted in zircon type HoCrO4 free from HoCrO3 phase. The crystallite size for the phase pure product after calcination at 575 degrees C in oxygen atmosphere was found to be 34 nm by X-ray line broadening. The TEM observations showed highly porous structure. Magnetic measurements reveal the ferromagnetic nature of HoCrO4 nano particles with Tc = 18 K. The compound shows high remanence of 30.4 emu x g(-1) and low coercivity of -0.0343 T.

Microscopic understanding of negative magnetization in Cu, Mn, and Fe based Prussian blue analogues

A crossover of the field-cooled magnetization from positive to negative has been observed below the magnetic ordering temperature (17.9 K) in a multimetal Prussian Blue analogue (PBA), Cu_{0.73}Mn_{0.77}[Fe(CN)_{6}].zH_{2}O. The reverse Monte Carlo (RMC) modeling (using the program RMCPOW) has been used to derive the various scattering contributions (e.g., nuclear diffuse, nuclear Bragg, magnetic diffuse, and magnetic Bragg) from the observed neutron diffraction patterns. The RMC analysis combined with the Rietveld refinement technique show an antiferromagnetic ordering of Mn moments with respect to the Cu as well as the Fe moments. Our study gives the first neutron magnetic structure evidence towards the microscopic understanding of the negative magnetization in the PBAs. This information can be effectively utilized to design suitable PBAs for making multifunctional devices.

Room temperature ferromagnetism in CoO nanoparticles obtained from sonochemically synthesized precursors

In this paper we report the magnetic properties of nanosized CoO particles, prepared from sonochemically synthesized precursors and characterized using x-ray diffraction (XRD), conventional transmission electron microscopy (TEM) and scanning tunneling electron microscopy combined with energy dispersive x-ray analysis (STEM-EDX) techniques. The nanoparticles were faceted and the sizes varied between 30 and 60 nm depending on the time of annealing. They were stable even in the absence of any organic coating on them. Magnetic measurements reveal the presence of ferromagnetic interactions at low temperatures in the CoO nanoparticles synthesized after 2 and 4 h of annealing of the sonochemically synthesized precursor under nitrogen. However, after 6 h of annealing, the nanoparticles show hysteresis not only at low temperatures (1.5 K) but also at higher temperatures (100 K and room temperature), indicating the presence of room temperature ferromagnetism.

Magnetite nanoparticles with tunable gold or silver shell

Fe3O4 nanoparticles with size approximately 13 nm have been prepared successfully in aqueous micellar medium at approximately 80 degrees C. To make Fe3O4 nanoparticles resistant to surface poisoning a new route is developed for coating Fe3O4 nanoparticles with noble metals such as gold or silver as shell. The shell thickness of the core-shell particles becomes tunable through the adjustment of the ratio of the constituents. Thus, the route yields well-defined core-shell structures of size from 18 to 30 nm with varying proportion of Fe3O4 to the noble metal precursor salts. These magnetic nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), FTIR, differential scanning calorimetry (DSC), Raman and temperature-dependent magnetic studies.

Structural study of La(0.75)Sr(0.25)CrO(3) at high temperatures

A high-temperature neutron diffraction study has been carried out on La(0.75)Sr(0.25)CrO(3) compound in the temperature range 300-1400 K. On doping the parent compound LaCrO(3) with Sr at the La site, the orthorhombic (Pbnm) to rhombohedral ([Formula: see text]) structural transition shifts to lower temperatures. From quantitative Rietveld analysis it is found unequivocally that there is a two-phase coexistence (orthorhombic and rhombohedral phases with ∼89 and 11 weight%, respectively) in the temperature range 300-470 K and a three-phase coexistence (with a new cubic phase with space group Pm3m) in the temperature range 480-1400 K. The weight percentages of the orthorhombic, rhombohedral and cubic phases were found to be ∼49%, 37% and 14%, respectively, in the temperature range 480-1300 K, while over 1350-1400 K, the average weight percentages of orthorhombic, rhombohedral and cubic phases were found to be ∼41%, 41% and 18%, respectively. The coefficients of volume thermal expansion and linear thermal expansion have been determined for all three phases. The importance of the present study has been discussed for practical applications of the studied compound in solid oxide fuel cells.

Extracellular biosynthesis of magnetite using fungi

The development of synthetic processes for oxide nanomaterials is an issue of considerable topical interest. While a number of chemical methods are available and are extensively used, the collaborations are often energy intensive and employ toxic chemicals. On the other hand, the synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures and pressures, and at neutral pH (examples include magnetotactic bacteria, diatoms, and S-layer bacteria). Here we show that nanoparticulate magnetite may be produced at room temperature extracellularly by challenging the fungi, Fusarium oxysporum and Verticillium sp., with mixtures of ferric and ferrous salts. Extracellular hydrolysis of the anionic iron complexes by cationic proteins secreted by the fungi results in the room-temperature synthesis of crystalline magnetite particles that exhibit a signature of a ferrimagnetic transition with a negligible amount of spontaneous magnetization at low temperature.

Wet chemical method for synthesis of superparamagnetic alloyed Ni--Pd and Ni--Pt nanomagnets in micelles

The evolution of sphere- and rod-shaped superparamagnetic Ni--Pd and Ni--Pt nanoparticles by wet chemical methods is reported. It has been shown that increased CTAB (cetyltrimethylammonium bromide) concentration at room temperature promotes the formation of a higher proportion of rod-shaped nanomagnets over spherical particles. Temperature-dependent magnetic properties, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electron dispersive X-ray (EDX) studies reveal the superparamagnetic behavior, size distribution, and percentage composition of the alloyed structures.

Effects of noradrenaline and metaraminol on isolated aortic strips and auricles obtained from untreated and reserpine-treated rabbits

The isolated aortic strips of the untreated rabbits responded to noradrenaline in concentrations ranging from 20 to 160 ng/mL, whereas similar preparations from reserpine-treated animals responded to lower concentrations (from 2.5 to 10 ng/mL) and larger effects were produced by concentrations ranging from 20 to 160 ng/mL. Comparatively stronger concentrations (from 0.4 to 1.6 microgram/mL) of metaraminol were required to produce suitable contractile responses, which were not modified by reserpine pretreatment. On the isolated auricles obtained from untreated rabbits, noradrenaline was used in concentrations of 20 and 80 ng/mL, but these concentrations were reduced to 2.5 and 10 ngmL in the case of tissues obtained from reserpinized rabbits. Comparatively stronger (0.2 and 0.8 microgram/mL) concentrations of metaraminol were required to produce a stimulant effect on this preparation, and the sensitivity was not altered by reserpine pretreatment. These observations lead to the conclusions that though reserpine pretreatment produces a well-marked increase in the sensitivity of isolated rabbit aortic strips and auricles to noradrenaline, it does not modify the sensitivity of these preparations to metaraminol. Reserpine was used in 0.3 mg/kg doses injected subcutaneously for 3 successive days.

Reserpine induced supersensitivity to isoprenaline on the blood pressure and heart rate of anaesthetized rabbits

Reserpine, when administered intraperitoneally in 0.25, 0.5 and 1 mg/kg doses, produced a decrease in the mean blood pressure and heart rate of the pentobarbitone anaesthetized rabbits. In these animals reserpine pretreatment produced supersensitivity to the hypotensive and positive chronotropic effects of isoprenaline.