We have synthesized a new intermetallic compound Ho2Ni0.95Si2.95 in a single phase with a defect crystal structure. The magnetic ground state of this material found to be highly frustrated without any long range order or glassy feature as investigated through magnetic, heat capacity and neutron diffraction measurements. The interest in this material stems from the fact that despite the absence of true long range order, large magnetocaloric effect (isothermal magnetic entropy change, −ΔSM ~ 28.65 J/Kg K (~205.78 mJ/cm3 K), relative cooling power, RCP ~ 696 J/Kg (~5 J/cm3) and adiabatic temperature change, ΔTad ~ 9.32 K for a field change of 70 kOe) has been observed which is rather hard to find in nature.
Half-metallic ferromagnets (HMF) are on one of the most promising materials in the field of spintronics due to their unique band structure consisting of one spin sub-band having metallic characteristics along with another sub-band with semiconductor-like behavior. In this work, we report the synthesis of a novel quaternary Heusler alloy FeMnVAl and have studied the structural, magnetic, transport, and electronic properties complemented with first-principles calculations. Among different possible structurally ordered arrangements, the optimal structure is identified by theoretical energy minimization. The corresponding spin-polarized band structure calculations indicates the presence of a half-metallic ferromagnetic ground state. A detailed and careful investigation of the x-ray diffraction data, Mössbauer and nuclear magnetic resonance spectra suggest the presence of site-disorder between the Fe and Mn atoms in the stable ordered structure of the system. The magnetic susceptibility measurement clearly establishes a ferromagnetic-like transition below ∼213 K. The 57 Fe Mössbauer spectrometry measurements suggest only the Mn-spins could be responsible for the magnetic order, which is consistent with our theoretical calculation. Surprisingly, the density-functional-theory calculations reveal that the spin-polarization value is almost immunized (92.4% → 90.4%) from the Mn-Fe structural disorder, even when nonmagnetic Fe and moment carrying Mn sites are entangled inseparably. Robustness of spin polarization and half metallicity in the studied FeMnVAl compound comprising structural disorder is thus quite interesting and could provide a new direction to investigate and understand the exact role of disorders on spin polarization in these class of materials, over the available knowledge.
In this work, we report successful synthesis of a new intermetallic compound Tm<sub>2</sub>Ni<sub>0.93</sub>Si<sub>2.93</sub> that forms in single phase only in defect crystal structure. The compound does not show any long range magnetic ordering down to 2 K. The material exhibits large magnetic entropy change (-ΔS<sub>M</sub> ~ 13.7 J/kg K) and adiabatic temperature change (ΔT<sub>ad</sub> ~ 4.4 K) at 2.2 K for a field change of 20 kOe which can be realized by permanent magnets, thus being very beneficial for application purpose. In the absence of long range magnetic ordering down to 2 K, metastable nature of the low temperature spin dynamics and short range magnetic correlations are considered to be responsible for such large magnetocaloric effect (MCE) over a wide temperature region.
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