K. Ramesh Kumar

Disordered ferromagnetism in Ho2NiMnO6 double perovskite

Magnetic and dielectric properties of the double perovskite Ho2NiMnO6 are reported. The compound is synthesized by nitrate route and is found to crystallize in monoclinic P21/n space group. Lattice parameters obtained by refining powder x-ray diffraction data are; a  =  5.218(2) Å, b  =  5.543(2) Å, c  =  7.480(3) Å and the monoclinic angle is [Formula: see text](4). A phase transition is observed at [Formula: see text] K in the temperature-dependent magnetization curve, M(T). The inverse magnetic susceptibility, (1/[Formula: see text]) fits reasonably well with modified Curie-Weiss law by incorporating the paramagnetic response of Ho3+. 1/[Formula: see text] manifests as an upward deviation from ideal Curie-Weiss behaviour well above the ferromagnetic transition. Signs of inherent Griffiths phase pertaining to the Ni/Mn subsystem are visible when one subtracts the Ho3+ paramagnetic contribution from total susceptibility and does the power-law analysis. The magnetic hysteresis at 2 K gives the maximum value of magnetization [Formula: see text] [Formula: see text]/f.u. at 50 kOe. Field-derivative of magnetization at 2 K shows discontinuities which indicates the existence of metamagnetic transitions in this compound. This needs to be probed further. Out of the two dielectric relaxations observed, the one at low temperature may be attributed to phononic frequencies and that at higher temperature may be due to Maxwell-Wagner relaxation. A correlation between magnetic and lattice degrees of freedom is plausible since the anomaly in dielectric constant coincides with T C.

Magnetocaloric effect in the metamagnet ErRhSi compound

The magnetocaloric effect is observed in the 1:1:1 compound ErRhSi, which is a metamagnet is reported in this paper. ErRhSi crystallizes in the orthorhombic space group Pnma, adopting the TiNiSi structure type, with lattice parameters a(A) = 6.7903(5), b(A) = 4.1881(3), and c(A) = 7.3847(4). Our magnetic measurements confirm an antiferromagnetic phase transition at TN ≈ 8.5 K, also supported by the specific heat measurement. Crystal field effects of Er3+ are suggested by the inverse magnetic susceptibility data which do not conform to an ideal Curie-Weiss behaviour and also by the total entropy that attains Rln (2) at TN. Although the magnetic hysteresis indicates ErRhSi to be a soft magnet, several clear metamagnetic features are observed at 2 K. Magnetic entropy change ΔSM = − 8.7 J/kg-K is observed at about 9 K with the application of 5 T magnetic field. The corresponding adiabatic temperature change ΔTad is about 4 K. Large magnetocaloric effects suggest that this material is suitable for the low temp...

Double-phase transition and giant positive magnetoresistance in the quasi-skutterudite Gd3Ir4Sn13

The magnetic, thermodynamic, and electrical/thermal transport properties of the caged-structure quasi-skutterudite Gd3Ir4Sn13 are re-investigated. The magnetization M(T), the specific heat Cp(T), and the resistivity ρ(T) reveal a double-phase transition—at TN1 ∼ 10 K and at TN2 ∼ 8.8 K—which was not observed in the previous report on this compound. The antiferromagnetic transition is also visible in the thermal transport data, thereby suggesting a close connection between the electronic and lattice degrees of freedom in this Sn-based quasi-skutterudite. The temperature dependence of ρ(T) is analyzed in terms of a power-law for resistivity pertinent to Fermi liquid picture. Giant, positive magnetoresistance (MR) ≈ 80% is observed in Gd3Ir4Sn13 at 2 K with the application of 9 T. The giant MR and the double magnetic transition can be attributed to the quasi-cages and layered antiferromagnetic structure of Gd3Ir4Sn13 vulnerable to structural distortions and/or dipolar or spin-reorientation effects. The giant...

Van Hove scenario and superconductivity in full Heusler alloy Pd2ZrGa

Ab-initio band structure calculation using the state-of-the-art density functional theory was carried out for the sample Pd2ZrGa. The equilibrium lattice parameter was found by fitting the energy vs volume data to Murnaghan equation of state and the value was observed to be 6.467 A. Non analytical behavior of the energy functional was observed in band structure as well as in density of states diagram near the Fermi level. Polycrystalline sample synthesized using arc-furnace showed compositional variation in X-ray diffraction and energy dispersive analysis of X-ray spectrum studies. Magnetic measurements showed Meissner diamagnetic shielding in the as-cast sample below 2 K. From the Zero Field Cooled (ZFC) and Field Cooled (FC) measurements, we observed that the system is a type II BCS superconductor. The volume susceptibility at 2 K was observed to be 3.1 emu/Oe cm3.

Large magnetocaloric effect and critical behaviour analysis in Gd2Cu2In

The ternary intermetallic compound Gd2Cu2In crystallizes in the Mo2Fe2B-type structure with the space group . The compound undergoes a ferromagnetic-paramagnetic (FM-PM) phase transition at 94.1 K and large magnetocaloric effect has been observed over a wide range of temperature. The isothermal magnetic entropy change and adiabatic temperature change were observed to be 13.8 J/kg K and 6.5 K for 7 T applied field. We have employed a modified Arrott plot (MAP) and Kouvel-Fisher (KF) procedures to estimate the critical exponents near the FM-PM phase transition. Critical exponents and are estimated through a non-linear fitting. The β value is close to the three-dimensional (3D) Ising value, whereas γ and δ values lie closer to the mean-field values. Scaled magnetic isotherms collapse into two branches below and above T C in accordance with a single scaling equation. Specific-heat measurements show a λ-type peak near 94 K indicating long-range magnetic ordering. The specific-heat exponent α was estimated by a non-linear fitting using the function . The fitting in the temperature range yields .

Field-insensitive heavy fermion features and phase transition in the caged-structure quasi-skutterudite Sm3 Ru4 Ge13

The robust field-insensitive heavy fermion features in Sm

Magnetic, specific heat and electrical transport properties of Frank-Kasper cage compounds RTM2Al20 [R = Eu, Gd and La; TM = V, Ti].

_3

Spin freezing in the spin-liquid compound FeAl2O4

Ru

Magnetic ordering and crystal field effects in quasi-caged structure compound PrFe2Al8

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Metamagnetism, sign reversal and low temperature magnetocaloric effect in single-crystalline EuV2Al20

Ge