Magnetocaloric materials: The search for new systems

Abstract

The prospect of efficient solid state refrigeration at room temperature is driving research into magnetic cooling engine design and magnetic phase transition-based refrigerants. In this Viewpoint an Ashby-style map of magnetic refrigerant properties is constructed, comparing popular materials with limits derived from an idealised first order transition model. This comparison demonstrates the potential for new magnetocaloric material systems to be established through structural control and optimisation at the atomic-, nano-and micro-scale.

Giant reversible magnetocaloric effect in flower-like β-Co(OH)2 hierarchical superstructures self-assembled by nanosheets

“…However, the value of -ΔS m increases with further increasing magnetic field due to the field-induced transition from the AFM to the FM state and becomes positive at 2.7 T. The field-induced AFM to FM transition is responsible for the conversion from the inverse to the conventional MCE in b-Co(OH) 2 . The maximum of -ΔS m of 13.4 J/kg K at K for ΔB = 5T, which is comparable with giant MCE reported for La-Fe-Si, MnAs and Mn-Fe-P based alloy 15 . The slope of the curve in Figure 2d is relatively small, and the smooth variation in -ΔS m with temperature is more useful than a sharp one, which is another property that makes it a promising magnetic refrigerant.…”

Tuning the giant inverse magnetocaloric effect in Mn2−xCrxSb compounds

“…In first order phase transitions where discontinuities in the thermal evolution of the crystal lattice are intrinsic, small volume changes are critical in keeping physical stability during cycling. This shift is not only important in determining the operating conditions for applications but it also provides an upper bound to the value of the adiabatic temperature change ∆T ad max 22 . The upper bound to ∆T ad can be calculated using δT t /δB, M S and the specific heat value just before (or after) the latent heat peak of the first order phase transition (see figure 5).…”

Large magnetocaloric effects in magnetic intermetallics: First-principles and Monte Carlo studies

“…The resulting adiabatic temperature change ∆T ad for this alloy is still quite small (1.6 K) in spite of the large change of M showing that the magnetocaloric effect (MCE) needs further optimization compared to the classical Gd-Si-Ge, Fe-Rh and La-Fe-Si MCE materials, which all display ∆T ad of about 13 K and a large isothermal entropy change ∆S iso . There have been many attempts to improve the MCE in Heusler and other intermetallics which has been highlighted in the literature [31]. A discussion of the magnetostructural transition and adiabatic temperature variation in poly-crystal and single crystal Ni-Mn-Ga alloys can be found in [32].…”