Observation of short range order driven large refrigerant capacity in chemically disordered single phase compound Dy2Ni0.87Si2.95

Complex magnetic properties associated with competing local and itinerant magnetism in [Formula: see text]

Ternary intermetallic compound [Formula: see text] has been synthesized in single phase and characterized by x-ray diffraction, scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX) analysis, magnetization, heat capacity, neutron diffraction and muon spin rotation/relaxation ([Formula: see text]SR) measurements. The polycrystalline compound was synthesized in single phase by introducing necessary vacancies in Co/Si sites. Magnetic, heat capacity, and zero-field neutron diffraction studies reveal that the system undergoes magnetic transition below [Formula: see text]4 K. Neutron diffraction measurement further reveals that the magnetic ordering is antiferromagnetic in nature with an weak ordered moment. The high temperature magnetic phase has been attributed to glassy in nature consisting of ferromagnetic clusters of itinerant (3d) Co moments as evident by the development of internal field in zero-field [Formula: see text]SR below 50 K. The density-functional theory (DFT) calculations suggest that the low temperature magnetic transition is associated with antiferromagnetic coupling between Pr 4f and Co 3d spins. Pr moments show spin fluctuation along with unconventional orbital moment quenching due to crystal field. The evolution of the symmetry and the crystalline electric field environment of Pr-ions are also studied and compared theoretically between the elemental Pr and when it is coupled with other elements such as Co. The localized moment of Pr 4f and itinerant moment of Co 3d compete with each other below [Formula: see text]20 K resulting in an unusual temperature dependence of magnetic coercivity in the system.

Studies on magnetocaloric effect of Tb2Ni0.90Si2.94 compound

A comparative study has been carried out on the magnetocaloric properties of as-cast and annealed Tb₂Ni_0.90Si_2.94 intermetallic compound. While the as-cast material exhibits ferromagnetic cluster-glass behaviour below 9.9 K coexisting with antiferromagnetic (AFM) interaction, the annealed system shows AFM ordering below 13.5 K and spin freezing occurs below 4 K. The compound exhibits moderate magnetocaloric performance with maximum isothermal entropy changes (-ΔS _M) 8.8 and 10.9 J kg^-1 K^-1, relative cooling power (RCP) 306 and 365 J kg^-1, along with adiabatic temperature change (ΔT _ad) 5.5 and 8.15 K for 70 kOe magnetic field change in as-cast and annealed forms, respectively. The estimated magnetic entropy change is found to be larger for annealed sample in comparison to that of as-cast analogue. However, the full width at half maxima (FWHM) of -ΔS _M(T) behaviour is larger in as-cast compound due to the presence of inherent structural disorder which reduces with thermal annealing. A positive isothermal entropy change (-ΔS _M) and adiabatic temperature change (ΔT _ad) is observed for the as-cast compound in the measured field and temperature region. In contrast, the annealed system exhibits inverse magnetocaloric effect in the low field and temperature region where AFM interactions dominate. Magnetocaloric effect (MCE) is used as a tool to establish a subtle correlation between the observed magnetocaloric effect and the reported magnetic properties of the system.

Physical properties of RIr3 (R = Gd, Tb, Ho) compounds with coexisting polymorphic phases

The binary compounds GdIr₃, TbIr₃ and HoIr₃ are synthesized successfully and found to form with macroscopic co-existence of two polymorphic phases: AuBe₅ (C15b) and AuCu₃-type. The dc magnetization and heat capacity studies confirm that the C15b phase orders ferromagnetically, whereas the AuCu₃ phase remains paramagnetic down to 2 K. The frequency dependent ac-susceptibility data, time dependent magnetic relaxation behavior and magnetic memory effect studies suggest that TbIr₃ and HoIr₃ are cannonical spin-glass systems, but no glassy feature could be found in GdIr₃. The critical behavior of all three compounds has been investigated using the magnetization and heat capacity measurements around the transition temperature (T_C). The critical exponents α, β, γ and δ have been estimated using different techniques such as the Arrott-Noakes plot, Kouvel-Fisher plot and critical isotherm as well as analysis of specific heat data and study of magnetocaloric effect. The critical analysis study identifies the type of universal magnetic class in which the three compounds belong.

Unusual bidirectional frequency dependence of dynamical susceptibility in hexagonal intermetallic Pr2Ni0.95Si2.95

In this study, the synthesis of a novel ternary intermetallic compound Pr₂Ni_0.95Si_2.95 forming in single phase only by deliberately introducing vacancies in Ni/Si site is reported. The detailed studies on dc magnetization, heat capacity, ac magnetization & associated dynamical scaling, different types of non-equilibrium dynamical behaviour, viz., magnetic relaxation behaviour as a function of wait time and temperature, aging phenomena, and magnetic memory effect firmly establish that the compound exhibits spin freezing behaviour below 3.3 K (T_f). However, below T_f, temperature dependence of ac susceptibility data exhibit an additional peak that shows reverse frequency dependence to that generally observed in a glassy system. The unusual bidirectional frequency dependence in a single magnetic system is of significant interest and rarely reported in literature. Competing exchange interaction arising from c/a ~ 1 and crystallographic randomness driven magnetic phase separation has been argued to be responsible for such observation. The reverse frequency shift of the low temperature peak has been described on the basis of a simple phenomenological model proposed in this work.