Review of the magnetocaloric effect in manganite materials

Magnetocaloric effect and magnetic refrigeration

M Agnetocaloric M Aterials

Room temperature magnetic refrigeration is a new highly efficient and environmentally protective technology. Although it has not been maturely developed, it shows great applicable prosperity and seems to be a substitute for the traditional vapor compression technology. In this paper, the concept of magnetocaloric effect is explained. The development of the magnetic material, magnetic refrigeration cycles, magnetic field and the regenerator of room temperature magnetic refrigeration is introduced. Finally some typical room temperature magnetic refrigeration prototypes are reviewed.

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Review on research of room temperature magnetic refrigeration

A considerable magnetic entropy change has been observed in Ni51.5Mn22.7Ga25.8 alloys under a field of 0.9 T. This change originates from a sharp magnetization jump which is associated with a martensitic to austenitic structure transition. The large low field entropy change and the adjustable martensic–austensic transition temperature indicate a great potential of Ni–Mn–Ga as working materials for magnetic refrigerants in a wide temperature range.

Magnetic entropy change in Ni51.5Mn22.7Ga25.8 alloy

A large entropy variation (magnetocaloric effect) has been discovered in ceramic perovskites with the formulas La0.65Ca0.35Ti1−xMnxO3−z and La0.5+x+yLi0.5−3yTi1−3xMn3xO3−z. Both Curie temperature and entropy change were studied from 4.2 to 400 K for different stoichiometric compositions and applied magnetic fields. Our conclusion is that these materials are excellent candidates for working materials in magnetic refrigeration and liquefaction devices in a wide temperature range.

Tunable magnetocaloric effect in ceramic perovskites

We report experimental studies and suggest a quantitative model of spin relaxation in Mn12 acetate in a pulsed magnetic field in the temperature range 1.9‐5.0 K. When the field applied along the anisotropy axis is swept at 140 T/s through a nonmagnetized Mn12 acetate sample, the sample’s magnetization switches, within a few milliseconds, from zero to saturation at a well-defined field whose value depends on temperature but is quantized in units of 0.46 T. A quantitative explanation of the effect is given in terms of a spin-phonon avalanche combined with thermally assisted resonant spin tunneling. @S0163-1829~99!11529-7#

/pdf/spin-phonon-avalanches-in-mn-12-acetate-e2xd2ukynv.pdf

Spin-phonon avalanches in Mn 12 acetate

Magnetocaloric effect in La0.65Ca0.35Ti1 − xMnxO3 ceramic perovskites

In this paper we discuss both theoretical and experimental results on the time dependence of the heat capacity of oriented Mn12 magnetic clusters when a magnetic field is applied along their easy axis. Our calculations are based on the existence of two contributions. The first one is associated with the thermal populations of the 21 different Sz levels in the two potential wells of the magnetic uniaxial anisotropy and the second one is related to the transitions between the Sz levels. We compare our theoretical predictions with experimental data on the heat capacity for different resolution times at different fields and temperatures. @S0163-1829~99!01937-2#

/pdf/time-dependent-heat-capacity-of-mn-12-clusters-3d6dp85kb4.pdf

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Papers

Tunable magnetocaloric effect in ceramic perovskites

Spin-phonon avalanches in Mn 12 acetate

Magnetocaloric effect in La0.65Ca0.35Ti1 − xMnxO3 ceramic perovskites

Time-dependent heat capacity of Mn 12 clusters