R. Nirmala

Effect of magnetic polarons on the magnetic, magnetocaloric, and magnetoresistance properties of the intermetallic compound HoNiAl

The magnetic, magnetocaloric, and magnetoresistive properties of the polycrystalline compound HoNiAl have been studied. The temperature variations of magnetization and heat capacity show that the compound undergoes two magnetic transitions, one at 14K and the other at 5K. The former is due to the paramagnetic-ferromagnetic transition, while the latter is attributed to the onset of an antiferromagnetic ordering, as the temperature is lowered. The M-H isotherm obtained at 2K shows a metamagnetic transition with a critical filed of about 13kOe. The maximum values of isothermal magnetic entropy change and adiabatic temperature change, for a field change of 50kOe, are estimated to be 23.6J∕kgK and 8.7K, respectively. The relative cooling power is found to be about 500J∕kg for a field change of 50kOe. A large magnetoresistance of about 16%, near the ordering temperature of 14K, is observed for a field of 50kOe. The magnetic, magnetocaloric, and magnetoresistance data seem to suggest the presence of magnetic pol...

Correlation between magnetism and magnetocaloric effect in the intermetallic compound DyNiAl

Magnetization studies carried out in polycrystalline sample of DyNiAl show the presence of two magnetic transitions, one at 15 K and the other at 30 K. The low-temperature transition is attributed to the onset of antiferromagnetic ordering, while the other one corresponds to the ferro-para transition. Thermomagnetic irreversibility found in the temperature dependence of magnetization data is attributed to the domain-wall pinning effect and also to the magnetic frustration. Magnetocaloric effect is found to be negative in the antiferromagnetic phase and positive above the Neel temperature.

Observation of spin glass state in weakly ferromagnetic Sr2FeCoO6 double perovskite

A spin glass state is observed in the double perovskite oxide Sr2FeCoO6 prepared through sol-gel technique. Initial structural studies using x rays reveal that the compound crystallizes in tetragonal I4/m structure with lattice parameters, a = 5.4609(2) A and c = 7.7113(7) A. The temperature dependent powder x ray diffraction data reveal no structural phase transition in the temperature range 10-300 K. However, the unit cell volume shows an anomaly coinciding with the magnetic transition temperature thereby suggesting a close connection between lattice and magnetism. Neutron diffraction studies and subsequent bond valence sums analysis show that in Sr2FeCoO6, the B site is randomly occupied by Fe and Co in the mixed valence states of Fe3 + /Fe4+ and Co3+/Co4+. The random occupancy and mixed valence sets the stage for inhomogeneous magnetic exchange interactions and in turn, for the spin glass state in this double perovskite, which is observed as an irreversibility in temperature dependent dc magnetization...

Large magnetic entropy change in nanocrystalline Pr0.7Sr0.3MnO3

Nanocrystalline Pr0.7Sr0.3MnO3 sample has been prepared by sol-gel method. The room temperature powder x-ray diffraction data show single phase nature of the sample and confirm the cubic crystal structure with Fm3¯m space group. The average crystallite size is calculated using Scherrer formula, and it is found to be ∼25 nm. Transmission electron microscopy image shows that the particles are spherical in shape and the average particle size is ∼35 nm. The sample undergoes ferromagnetic ordering at 235 K (TC) and obeys the Curie–Weiss law in the paramagnetic region. The maximum value of the magnetic entropy change |ΔSM|max is ∼6.3 J kg−1 K−1, and the relative cooling power is ∼385 J kg−1 for a field change of 50 kOe. The Arrott plot confirms that the magnetic ordering is of second order nature. The experimentally observed magnetic entropy change of the sample obeys Landau theory of phase transition well.

Competition between superconductivity and charge-density-wave ordering in the Lu 5 Ir 4 ( Si 1 − x Ge x ) 10 alloy system

We have performed bulk measurements such as dc magnetic susceptibility, electrical resistivity, and heat capacity on the pseudoternary alloys

Magnetic, transport, and magnetocaloric properties of double perovskite oxide LaCaMnCoO6

{\mathrm{Lu}}_{5}{\mathrm{Ir}}_{4}{({\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x})}_{10}

Magnetocaloric effect in the rare earth intermetallic compounds RCoNi (R = Gd, Tb, Dy, and Ho)

to study the interplay and competition between superconductivity and the charge-density-wave- (CDW) ordering transition. We track the evolution of the superconducting transition temperature

Magnetization and neutron diffraction studies on Sr2TiMnO6

{T}_{\mathrm{SC}}

Study of the magnetic behavior of single-crystalline Nd0.5Sr0.5MnO3

and the CDW-ordering temperature

Resistivity and thermoelectric power of NaxCoO2 (x=1.0, 0.7, and 0.6) system

{T}_{\mathrm{CDW}}