Efficient parameterisation of non-collinear energy landscapes in itinerant magnets

Magnetic exchange interactions determine the magnetic groundstate, as well as magnetic excitations of materials and are thus essential to the emerging and fast evolving fields of spintronics and magnonics. The magnetic force theorem has been used extensively for studying magnetic exchange interactions. However, short-ranged interactions in itinerant magnetic systems are poorly described by this method and numerous strategies have been developed over the years to overcome this deficiency. The present study supplies a fully self-consistent method for systematic investigations of exchange interactions beyond the standard Heisenberg model. In order to better describe finite deviations from the magnetic ground state, an extended Heisenberg model, including multi-spin interactions, is suggested. Using cross-validation analysis, we show that this extended Heisenberg model gives a superior description for non-collinear magnetic configurations. This parameterisation method allows us to describe many different itinerant magnetic systems and can be useful for high-throughput calculations.

Interface control of electronic transport across the magnetic phase transition in SrRuO3/SrTiO3 heterointerface

The emerging material class of complex-oxides, where manipulation of physical properties lead to new functionalities at their heterointerfaces, is expected to open new frontiers in Spintronics. For example, SrRuO3 is a promising material where external stimuli like strain, temperature and structural distortions control the stability of electronic and magnetic states, across its magnetic phase transition, useful for Spintronics. Despite this, not much has been studied to understand such correlations in SrRuO3. Here we explore the influence of electron-lattice correlation to electron-transport, at interfaces between SrRuO3 and Nb:SrTiO3 across its ferromagnetic transition, using a nanoscale transport probe and first-principles calculations. We find that the geometrical reconstructions at the interface and hence modifications in electronic structures dominate the transmission across its ferromagnetic transition, eventually flipping the charge-transport length-scale in SrRuO3. This approach can be easily extended to other devices where competing ground states can lead to different functional properties across their heterointerfaces.

Small hole polaron in CdTe: Cd-vacancy revisited

The characteristics of electronic states of Cd-vacancies in CdTe, an important semiconductor for various technological applications, are under debate both from theoretical and experimental points of view. Experimentally, the Cd-vacancy in its negative charge state is found to have C3v symmetry and a (-1/-2) transition level at 0.4 eV. Our first principles density functional calculations with hybrid functionals confirm for the first time these experimental findings. Additionally, we find that the C3v symmetry and the position of the (-1/-2) transition level are caused by the formation of a hole polaron localised at an anionic site around the vacancy.

The dipole moment of the spin density as a local indicator for phase transitions

The intra-atomic magnetic dipole moment - frequently called 〈T_z〉 term - plays an important role in the determination of spin magnetic moments by x-ray absorption spectroscopy for systems with nonspherical spin density distributions. In this work, we present the dipole moment as a sensitive monitor to changes in the electronic structure in the vicinity of a phase transiton. In particular, we studied the dipole moment at the Fe²⁺ and Fe³⁺ sites of magnetite as an indicator for the Verwey transition by a combination of x-ray magnetic circular dichroism and density functional theory. Our experimental results prove that there exists a local change in the electronic structure at temperatures above the Verwey transition correlated to the known spin reorientation. Furthermore, it is shown that measurement of the dipole moment is a powerful tool to observe this transition in small magnetite nanoparticles for which it is usually screened by blocking effects in classical magnetometry.

Emergence of spin spiral magnetic order in Mn based inverse Heusler alloys

In this article we demonstrate, by first principles density functional calculations, the emergence of spin-spiral magnetic order in Mn₂NiX(X=Al,Ga,In,Sn) inverse Heusler alloys with the application of pressure. This noncollinearity originates from the features in the band structures and the nesting of fermi surfaces of collinear spin bands. The calculated interatomic magnetic exchange parameters suggest that the frustrations in the Mn sublattice with octahedral symmetry are responsible for the stabilization of a noncollinear state. We propose that the pressure induced stabilization of spin-spiral magnetic order is a general feature of magnetic alloys crystallizing in inverse Heusler structures.

Tailoring of defect levels by deformations: Te-antisite in CdTe

The properties of the Te-antisite defect in the neutral state in CdTe were examined using ab initio calculations. The influence of three types of deformations (1D, 2D and 3D) on the defect energy levels and formation energies was investigated. It was found that the 2D deformation is the most effective for pushing the defect levels towards the band edges and opening up the bandgap of the semiconductor, and hence may improve the performance of CdTe as a detector material. We studied the defect levels and their occupancies including Jahn-Teller distortions. The Jahn-Teller distorted configuration places the 2A1(a) defect level closer to the valence band and this defect level position coincides with the 'unknown deep donor' measured in some experiments. Partial densities of states and band structures have been analysed to understand the arrangement of the defect bonds.

Epitaxial Fe films on ZnSe(001): effect of the substrate surface reconstruction on the magnetic anisotropy

It is well known that Fe films deposited on a c(2 × 2)-reconstructed ZnSe(001) surface show a strong in-plane uniaxial magnetic anisotropy. Here, the effect of the substrate reconstruction on the magnetic anisotropy of Fe has been studied by in situ Brillouin light scattering. We found that the in-plane uniaxial anisotropy is strongly reduced for Fe films grown on a (1 × 1)-unreconstructed ZnSe substrate while the in-plane biaxial one is nearly unaffected by the substrate reconstruction. Calculations of magnetic anisotropy energies within the framework of ab initio density functional theory reveal that the strong suppression of anisotropy at the (1 × 1) interface occurs due to complex atomic relaxations as well as the competing effects originating from magnetocrystalline anisotropy and dipole-dipole interactions. For both sharp and intermixed c(2 × 2) interfaces, the magnetic anisotropy is enhanced compared to the (1 × 1) case due to the further lowering of symmetry. The theoretical results are in agreement with the experimental findings.

Evolving properties of two-dimensional materials: from graphene to graphite

We have studied theoretically, using density functional theory, several material properties when going from one C layer in graphene to two and three graphene layers and on to graphite. The properties we have focused on are the elastic constants, electronic structure (energy bands and density of states), and the dielectric properties. For any of the properties we have investigated the modification due to an increase in the number of graphene layers is within a few per cent. Our results are in agreement with the analysis presented recently by Kopelevich and Esquinazi (unpublished).

Tailoring the nature of magnetic coupling of Fe-porphyrin molecules to ferromagnetic substrates

We demonstrate that an antiferromagnetic coupling between paramagnetic Fe-porphyrin molecules and ultrathin Co and Ni magnetic films on Cu(100) substrates can be established by an intermediate layer of atomic oxygen. The coupling energies have been determined from the temperature dependence of x-ray magnetic circular dichroism measurements. By density functional theory+U calculations the coupling mechanism is shown to be superexchange between the Fe center of the molecules and Co surface-atoms, mediated by oxygen.

Dual nature of improper ferroelectricity in a magnetoelectric multiferroic

Using first-principles calculations, we study the microscopic origin of ferroelectricity (FE) induced by magnetic order in the orthorhombic HoMnO3. We obtain the largest ferroelectric polarization observed in the whole class of improper magnetic ferroelectrics to date. We find that the two proposed mechanisms for FE in multiferroics, lattice and electronic based, are simultaneously active in this compound: a large portion of the ferroelectric polarization arises due to quantum-mechanical effects of electron orbital polarization, in addition to the conventional polar atomic displacements. An interesting mechanism for switching the magnetoelectric domains by an electric field via a 180 degrees coherent rotation of Mn spins is also proposed.

Influence of ligand states on the relationship between orbital moment and magnetocrystalline anisotropy

The spin and orbital moments of Au/Co/Au trilayers grown on a W(110) single crystal substrate have been investigated by means of x-ray magnetic circular dichroism. Our findings suggest that the orbital moment of Co does not obtain a maximum value along the easy axis, in contrast with previous experience. This is attributed to the large spin-orbit interaction within the Au caps. Both second order perturbation theory and first principles calculations show how the magnetocrystalline anisotropy (MCA) is dramatically influenced by this effect, and how this leads to the fact that the orbital moment anisotropy is not proportional to the MCA.

Substrate-induced magnetic ordering and switching of iron porphyrin molecules

To realize molecular spintronic devices, it is important to externally control the magnetization of a molecular magnet. One class of materials particularly promising as building blocks for molecular electronic devices is the paramagnetic porphyrin molecule in contact with a metallic substrate. Here, we study the structural orientation and the magnetic coupling of in-situ-sublimated Fe porphyrin molecules on ferromagnetic Ni and Co films on Cu(100). Our studies involve X-ray absorption spectroscopy and X-ray magnetic circular dichroism experiments. In a combined experimental and computational study we demonstrate that owing to an indirect, superexchange interaction between Fe atoms in the molecules and atoms in the substrate (Co or Ni) the paramagnetic molecules can be made to order ferromagnetically. The Fe magnetic moment can be rotated along directions in plane as well as out of plane by a magnetization reversal of the substrate, thereby opening up an avenue for spin-dependent molecular electronics.

Vanishing magnetic interactions in ferromagnetic thin films

We have used element-specific hysteresis measurements, based on the x-ray magnetic circular dichroism technique, to investigate magnetic trilayer structures composed of Fe and Ni layers. Within a critical regime we have discovered a class of structures in which the exchange interaction, the mechanism responsible for the macroscopic magnetism, can become vanishingly small. The experimental observations are supported by first principles theory and are explained as arising from a cancellation of several competing magnetic interactions. Hence, we have discovered a system with a novel exchange interaction between magnetic layers in direct contact that replaces the conventional exchange interaction in ferromagnets.

Cloning and characterization of a novel protein kinase that impairs osteoblast differentiation in vitro

The bone morphogenic proteins (BMPs) play a key role in skeletal development and patterning. Using the technique of differential display polymerase chain reaction (ddPCR), we have identified a novel gene whose expression is increased during BMP-2-induced differentiation of the prechondroblastic cell line, MLB13MYC clone 17, to an osteoblastic phenotype. The 6.5-kilobase mRNA recognized by this ddPCR product is increased 10-fold by BMP-2 treatment of the MLB13MYC clone 17 cells. The mRNA recognized by this ddPCR product is also increased as MC3T3-E1 cells recapitulate the program of osteoblast differentiation during prolonged culture. The full-length transcript corresponding to this ddPCR product was cloned from a MLB13MYC clone 17 cell cDNA library. Analysis of the deduced amino acid sequence demonstrated that this gene encodes a novel 126-kDa putative serine/threonine protein kinase containing a nuclear localization signal. The kinase domain, expressed in Escherichia coli, is capable of autophosphorylation as well as phosphorylation of myelin basic protein. The gene was, therefore, named BIKe (BMP-2-Inducible Kinase). The BIKe nuclear localization signal is able to direct green fluorescent protein to the nucleus in transfected COS-7 cells. When stably expressed in MC3T3-E1 cells, BIKe significantly decreases alkaline phosphatase activity and osteocalcin mRNA levels and retards mineral deposition relative to vector control. This novel kinase, therefore, is likely to play an important regulatory role in attenuating the program of osteoblast differentiation.

Autoamputation of the tongue

Autoamputation is an uncommon phenomenon that has been reported for the fingers, toes, appendix, ovary, spleen, etc. Autoamputation of the tongue has never been reported. An elderly man with carcinoma of lateral pharyngeal wall and tonsil presented with an autoamputated tongue that was attached to the oral cavity with a thin band. The patient required detachment of the tongue and tracheostomy followed by radiotherapy for the primary tumour.

Receptor-mediated transport of human amyloid beta-protein 1-40 and 1-42 at the blood-brain barrier

Since amyloid beta-protein (A beta) is the primary component of both vascular and parenchymal amyloid deposits in Alzheimer's disease, information regarding its permeability at the blood-brain barrier (BBB) will help elucidate the contribution of circulating A beta to vascular and parenchymal A beta deposition in this disease and in brain aging. The permeability of the D- and L-enantiomers of A beta 1-40 and L-A beta 1-42 at the BBB was determined in the normal adult rat by quantifying the permeability coefficient-surface area product (PS) for each protein after correction for the residual plasma volume (Vp) occupied by the protein [labeled with a different isotope of iodine (125I vs 131I)] in blood vessels of different brain regions. After a single i.v. bolus injection, the plasma pharmacokinetics determined by TCA precipitation, paper chromatography, and SDS-PAGE were similar for both 125I-L-A beta 1-40 and 125I-L-A beta 1-42. The PS at the BBB for L-A beta 1-42 was significantly (1.4- to 1.8-fold) higher than for L-A beta 1-40 and ranged from 17.7 to 26.4 x 10(-6) ml/g/s for different brain regions. A comparison of the PS values at the BBB for L-A beta 1-40 showed no significant difference when determined at 15 or 30 min after i.v. bolus injection, times that reflect different levels of degradation in plasma (37.9% at 15 min and 65.5% at 30 min). The PS values obtained, therefore, were representative of the intact protein rather than degradation products. The PS values obtained for the all-D-enantiomer of A beta 1-40 were very low and comparable to that of albumin and IgG, whose mechanism of transport is by passive diffusion. Taken together, these data imply a stereoisomer-specific, ligand-receptor interaction at the BBB for the L-A beta proteins. The high PS values observed for L-A beta 1-40 and 1-42 compare to insulin, whose uptake is decidedly by a receptor-mediated transport process, and suggest a similar mechanism for L-A beta entry into the brain.

Differential expression of the heavy-chain ferritin gene in non-adhered and adhered oligodendrocytes

Oligodendrocytes (OLGs) synthesize and maintain central nervous system myelin. Little is known about the molecules and pathways involved in signaling the commencement of myelination; yet myelination is spatially and temporally controlled. We are interested in deciphering the signaling events that control the on and off switch of myelination. To address these questions we are using an in vitro model system consisting of pure cultures of OLGs, isolated from postmyelination brains. We have shown that in vitro, these OLGs regenerate and reenact the ontogenic development of myelin upon adhesion to a substratum; we have also shown that when transplanted in vivo, they can form myelin. Hence, identifying the genes that are turned on upon OLG adhesion seemed a worthwhile approach to singling out those genes that are critical to the differentiation process. For this we adopted a novel technique-differential display-that permits the comparison of gene expression under two sets of conditions; in our case between non-adhered and adhered OLGs. Using the differential display method in conjunction with a set of five arbitrary primers, we have identified five cDNAs that are activated upon OLG substratum adhesion. Four of these cDNAs proved to be fragments of the heavy (H)-chain ferritin cDNA. H-chain ferritin is involved in the rapid sequestration and delivery of iron; it is also a cytoprotectant. Brain iron is localized predominantly in OLGs. Our finding that the expression of H-chain ferritin is upregulated upon OLG regeneration/differentiation agrees with reports, in other cell types, that H-chain ferritin transcription is modulated by factors that control cell growth and differentiation. The enhanced transcription results in a twofold augmentation in ferritin synthesis. This is the first demonstration of an adherence-mediated activation of the H-chain ferritin gene. The observation has interesting implications. The transcription of the H-chain ferritin gene is associated with tissue stress such as might occur during rapid cell growth. The fact that this transcription takes place upon OLG-substratum adhesion can be viewed as another manifestation of the anchorage-induced signal that drives OLGs toward a differentiation program. This entails the synthesis of all the necessary components for the assembly of large quantities of membranes, hence constituting a period of rapid growth and considerable cell stress. We have sequenced the full-length ferritin cDNA of ovine OLGs; the cDNA is 775 bp long. The coding sequence starts at residue 57 with the ATG codon and terminates at residue 602, with the stop codon TAA. The cDNA codes for 181 amino acids with a predicted size for the protein of 22 kD. The deduced amino acid sequence is 93% identical to human ferritin. We postulate that OLG H-chain ferritin may function at more than one level: 1) it provides the iron required to sustain an oxidative metabolism; and 2) it acts as a cytoprotectant against oxidant-mediated injury.

Serum copper levels in gastrointestinal tract (GIT) cancer

Cancer of the gastrointestinal tract (GIT) is very commonly encountered in Kashmir Valley of India. Serum copper and ceruloplasmin levels were investigated in 75 patients with GIT cancer, 42 non-GIT cancer and 75 normal healthy controls. The mean serum copper in the control group was 1,078 (S.D. 0,296) mg/L, while in patients with GIT and non-GIT cancers, it was 1,738 (S.D. 0,675) and 1,449 (S.D. 0,501) mg/L. Copper in both types of cancers showed significant increase (p less than 0.001). It was significantly higher in GIT cancers (p less than 0.01) as compared to non-GIT cancers. Ceruloplasmin in controls was 379 (S.D. 51) mg/L, while in GIT and non-GIT cancer patients the values were 363 (S.D. 75) and 364 (S.D. 77) mg/L, respectively. No significant difference could be found in either of the groups. In Kashmir Valley, the copper content in body tissues is likely to be on the high side because copper utensils are widely used by the general population. Water and milk samples stored in copper vessels and salt tea prepared in copper vessels showed markedly high levels of copper.

Desquamation of malignant cells in carcinoma of the uterine cervix: its role in prognosis

Percentage of malignant cell exfoliation in relation to that of benign epithelial cells was studied in pretreatment vaginal smears of 251 patients of squamous cell carcinoma of the cervix. The rate of exfoliation did not increase with increasing clinical severity. Also, the various cell types of squamous cell carcinoma and clinical radiation response were independent of number of malignant cells shed in the vagina. However, the group of patients having a fewer number of malignant cells in their vaginal smears had a statistically significantly better five-year survival.

Radiation changes in vaginal and cervical cytology in carcinoma of the cervix uteri

Radiation changes are observed in all postirradiated smears of squamous cell carcinoma of the cervix from 56 females, although to a variable degree. After 1 year the changes subside gradually. A high cornification index is a good guide for recurrence. The significance of dysplastic cells as premonition for recurrence is debatable. The presence of malignant cells at any stage was considered of grave significance, and indicates poor radiation response or recurrence.

Ewing's sarcoma: A combined approach in the management

Twenty-seven histologically confirmed cases of localised Ewing's sarcoma were treated by two different regimes. Radiotherapy alone was used in 13 cases and a combination of chemotherapy and radiotherapy in 14. Single agent chemotherapy (cyclophosphamide) was given sequentially in nine patients and cyclophosphamide and actinomycin-D in five. There is a significant difference in the response to these different regimes. Only 69.2% of patients treated by radiotherapy alone were disease-free, for a median period of 10.4 months and metastases were noticed in 53.8% of cases. The disease-free survival in patients treated by combination therapy (radiotherapy and chemotherapy) was 18.4 months and metastases were seen in only 42.9%. However, no metastases were seen in patients who received cyclophosphamide and actinomycin-D, during a period of 14 months and only one patient showed residual disease. It is concluded that the addition of cyclophosphamide alone is not adequate in the management of Ewing's sarcoma. Actinomycin-D in addition to cyclophosphamide has improved the disease-free survival period significantly. The optimum dose of radiotherapy and its combination with other chemotherapeutic agents needs further trials to find the best and most suitable schedule.

Blood group specific substances in saliva of patients with cervical carcinoma

Secretion of blood group specific substances in saliva of 380 patients with carcinoma of the cervix was studied, along with age-matched controls. The study shows that carcinoma of the uterine cervix is much more common in non-secretors (55.0%) than in secretors (45.0%). Statistically, this difference was found to be highly significant (P less than 0.001).+

Histiocytes in vaginal smears: as prognostic parameter in carcinoma of the uterine cervix

Pretreatment vaginal smears of 251 patients with carcinoma of the cervix were counted for the percentage of histiocyte count in relation to benign squamous epithelial cells. No correlation was found between the percentage of histiocyte count and the age of the patient, clinical stage, cell type of squamous cell carcinoma, and clinical radiation response. Also a high histiocyte count is found to be unrelated to 5-year survival, recurrence, metastasis, or death of these patients. The present study indicates that the histiocyte number appears to have no relationship with immediate or remote prognosis in patients with carcinoma of cervix uteri.

Primary tumours and tumour-like conditions of the mandible

Reports on comprehensive mandibular tumours are very rare. The present article describes a total of 81 primary tumour and tumour-like lesions of the mandible seen at the University Hospital, Banaras Hindu University, during last 16 years. In the mandible the ratio of odontogenic to nonodontogenic tumors is 1.6:1. Ameloblastomas constitute 56% of the odontogenic tumors. Among the benign mesenchymal tumours of the jaw 58% are neoplastic and 42% are nonneoplastic in which cementoostoid tissue is laid down secondary to inflammatory process. Over all 40 cases are benign 28 potentially malignant (ameloblastoma) and 13 are malignant lesions. Among the malignant mandibular tumours, bone tumours are more common than the soft tissue sarcomas. Microscopically mandibular osteosarcomas are better differentiated than similar tumours in the long bones. Local, segmental, or radical surgery seems to be the treatment of choice in the mandibular tumours.

Carcinoma of breast associated with pregnancy and lactation

Out of 840 cases of breast carcinoma seen over a period of ten years, 18 were found to be associated with pregnancy and lactation. According to the mode of onset and presentation of the disease, these patients were divided into four groups. The average age of these patients was 31.9 years old. Thirteen out of 18 patients presented in a very advanced stage of the disease. In a short period, involvement of liver was noticed in 8, brain in 3, and bones and lung in 2 each. The disease was bilaterally simultaneous in two patients. The acceleration of growth was noticed during second and third trimesters of pregnancy as well as during lactation. The termination of pregnancy in three patients did not alter the clinical course of the disease.

Tissue isoantigens A, B, and H in carcinoma of the cervix uteri: their clinical significance

A specific red cell adhesion test was done in 243 patients with carcinoma of the cervix uteri and showed the presence of isoantigens in only 27.16% of the patients with infiltrating squamous cell carcinoma. There was a gradual loss of isoantigens during the development of carcinoma. The test can be usefully employed in studying the evolution of the disease. The negativity of the test was found to increase as clinical severity of the disease increases. Also, the highest percentage (57.57%) of retained isoantigen was found in large-cell nonkeratinizing carcinoma, a well-differentiated type for the cervix. Follow-up studies suggest that the loss of antigen indicates probably metastasis and a poor prognosis.

Symptomatic vertebral haemangiomas

Twelve cases of symptomatic vertebral haemangioma are reported in respect of their clinical presentation and radiological findings. One patient was only 10 years old, the youngest patient ever reported. Less commonly known findings of associated paravertebral mass and the displacement of the thoracic paraspinal line are discussed.

Extramedullary plasmacytoma: simulating a soft tissue sarcoma of the chest wall

Extramedullary plasmacytoma occurs infrequently as compared to osseous myoloma. A single case of extramedullary plasmacytoma was seen during the last 10 years whose initial presentation was that of a soft tissue sarcoma of the chest wall. Clinical data along with relevent investigation and treatment results are discussed with a review of the literature.