Magnetocaloric effect (MCE) is the change in isothermal magnetic entropy (ΔSm)and adiabatic temperature (ΔTad) that accompany magnetic transitions in materials during the application or the removal of magnetic field under adiabatic conditions. The physics of MCE gets enriched by correlated spin-lattice degrees of freedom. This phenomenon has been actively investigated over the past few decades as it holds a promise for an alternate method of refrigeration/heat pumping. This has already resulted in several reviews on this topic. This paper focusses on some recent trends in this field and prospects of using rare-earth-based materials as active magnetic refrigerants over a broad temperature range that includes gas liquefaction and near-room temperature refrigeration/heating. © Indian Academy of Sciences.

R. Nirmala

Department Of Physics

Degrees of freedom (mechanics)

Inert gases

INTERMETALLICS

Magnetic properties

Magnetism

Rare earth alloys

Rare earths

Refrigeration

Single crystals

Adiabatic conditions

Adiabatic temperature

Broad temperature ranges

Magnetic refrigerants

Magnetic transitions

magnetocaloric effect (MCE)

Near room temperature

rare earth intermetallics

Magnetocaloric effects

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IIT Madras

Pramana - Journal of Physics

Magnetic and magnetocaloric properties of polycrystalline Ho5Ge4 (orthorhombic, Sm5Ge4-type, Space group Pnma, No. 62, oP36) compound have been studied. This compound orders antiferromagnetically at ~24 K (TN). From the magnetization vs field isotherms obtained close to the magnetic transition temperature, magnetocaloric effect (MCE) has been estimated. The isothermal magnetic entropy change (ΔSM) reaches a maximum value of ~−27 J/kg-K at ~30 K for a field change of 140 kOe. A metamagnetic transition is observed in the field dependent magnetization data at temperatures below 20 K, for critical fields above 20 kOe, giving rise to a ferromagnetic order and hence a large MCE. The magnetic moment value at 2.5 K is ~8μB/Ho3+ in 90 kOe field. © 2016 Elsevier B.V.

Journal of Magnetism and Magnetic Materials

Metamagnetism-enhanced magnetocaloric effect in the rare earth intermetallic compound Ho5Ge4

Magnetic and magnetocaloric properties of cubic Laves phase RCoNi (R Gd, Tb, Dy, and Ho) compounds have been studied. The RCoNi (R Gd, Tb, Dy, and Ho) compounds order ferromagnetically at ∼200 K, ∼113 K, ∼68 K, and ∼42 K (TC), respectively. Field dependent magnetization data of RCoNi at 5 K in fields up to 7 T reveal saturation behaviour with minimal hysteresis. Magnetocaloric effect in terms of isothermal magnetic entropy change has been calculated. Maximum isothermal magnetic entropy change values of ∼-7.2 J/kg/K, ∼-10.1 J/kg/K, ∼-15.5 J/kg/K, and ∼-19.6 J/kg/K are obtained for RCoNi (R Gd, Tb, Dy, and Ho) compounds for 7 T field change close to TC. Substitution of 50 at. Ni in Co-site of RCo2 has led to the reduction of TC of the parent compounds by nearly one-half, but broadened the magnetic entropy change vs T curve and hence improved the relative cooling power. The large magnetocaloric effect associated with RCoNi compounds makes them potential candidates for low temperature magnetic refrigeration applications. © 2013 American Institute of Physics.

Fulltext

Journal of Applied Physics

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

The magnetic structure of the Fe2P-type R6CoTe2 phases (R=Gd-Er, space group P6-2m) has been investigated through magnetization measurement and neutron powder diffraction. All phases demonstrate high-temperature ferromagnetic and low-temperature transitions: TC=220 K and TCN=180 K for Gd6CoTe2, TC=174 K and TCN=52 K for Tb6CoTe2, TC=125 K and TCN=26 K for Dy6CoTe2, TCN=60 K and TN=22 K for Ho6CoTe2 and TCN∼30 K and TN∼14 K for Er6CoTe2. Between 174 and 52 K Tb6CoTe2 has a collinear magnetic structure with K0=[0, 0, 0] and with magnetic moments along the c-axis, whereas below 52 K it adopts a non-collinear ferromagnetic one. Below 60 K the magnetic structure of Ho6CoTe2 is that of a non-collinear ferromagnet. The holmium magnetic components with a K0=[0, 0, 0] wave vector are aligned ferromagneticaly along the c-axis, whereas the magnetic component with a K1=[1/2, 1/2, 0] wave vector are arranged in the ab plane. The low-temperature magnetic transition at ∼22 K coincides with the reorientation of the Ho magnetic component with the K0 vector from the collinear to the non-collinear state. Below 30 K Er6CoTe2 shows an amplitude-modulate magnetic structure with a collinear arrangement of magnetic components with K0=[0, 0, 0] and K1=[1/2, 1/2, 0]. The low-temperature magnetic transition at ∼14 K corresponds to the variation in the magnitudes of the MErK0 and MErK1 magnetic components. In these phases, no local moment was detected on the cobalt site. The magnetic entropy of Gd6CoTe2 increases from ΔSmag=-4.5 J/kg K at 220 K up to ΔSmag=-6.5 J/kg K at 180 K for the field change Δμ0H=0-5 T. © 2010 Elsevier Inc. All rights reserved.

Journal of Solid State Chemistry

Magnetic properties of Fe2P-type R6CoTe2 compounds (R=Gd-Er)

The rare earth intermetallic compound, Tb5Si2Sb2 (orthorhombic Tm5Si2Sb2-type, space group Cmca), has been synthesized and characterized by means of magnetization measurements. This compound orders ferromagnetically at ∼181 K (TC). Using magnetization vs. field data, the isothermal magnetic entropy change (Δ SM) has been computed in the vicinity of TC in applied fields up to 5 T. A maximum value of magnetic entropy change ∼4.4 J/kg/K has been achieved for a field change of 5 T close to the magnetic ordering temperature. The magnetocaloric effect in this compound is thus moderate and spread over a broad temperature range of ∼30 K near TC which is useful for Ericsson-cycle magnetic refrigeration. © 2008 Elsevier Ltd. All rights reserved.

Journal	Pramana - Journal of Physics
Publisher	Indian Academy of Sciences
ISSN	03044289
Open Access	No