The recent literature concerning the magnetocaloric effect (MCE) has been reviewed. The MCE properties have been compiled and correlations have been made comparing the behaviours of the different families of magnetic materials which exhibit large or unusual MCE values. These families include: the lanthanide (R) Laves phases (RM2, where M = Al, Co and Ni), Gd5(Si1−xGex)4 ,M n(As1−xSbx), MnFe(P1−xAsx), La(Fe13−xSix) and their hydrides and the manganites (R1−xMxMnO3, where R = lanthanide and M = Ca, Sr and Ba). The potential for use of these materials in magnetic refrigeration is discussed, including a comparison with Gd as a near room temperature active magnetic regenerator material. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0034-4885/68/6/R04/pdf

Recent developments in magnetocaloric materials

Magnetocaloric effect: From materials research to refrigeration devices

In the past 20 years, there has been a surge in research on the magnetocaloric response of materials, due mainly to the possibility of applying this effect for magnetic refrigeration close to room temperature. This review is devoted to the main families of materials suitable for this application and to the procedures proposed to predict their response. Apart from the possible technological applications, we also discuss the use of magnetocaloric characterization to gain fundamental insight into the nature of the underlying phase transition.

The Magnetocaloric Effect and Magnetic Refrigeration Near Room Temperature: Materials and Models

The search for materials showing large caloric effects close to room temperature has become a challenge in modern materials physics and it is expected that such a class of materials will provide a way to renew present cooling devices that are based on the vapour compression of hazardous gases. Up to now, the most promising materials are giant magnetocaloric materials. The discovery of materials showing a giant magnetocaloric effect at temperatures close to ambient has opened up the possibility of using them for refrigeration. As caloric effects refer to the isothermal entropy change achieved by application of an external field, several caloric effects can take place on tuning different external parameters such as pressure and electric field. Indeed the occurrence of large electrocaloric and elastocaloric effects has recently been reported. Here we show that the application of a moderate hydrostatic pressure to a magnetic shape-memory alloy gives rise to a caloric effect with a magnitude that is comparable to the giant magnetocaloric effect reported in this class of materials. We anticipate that similar barocaloric effects will occur in many giant-magnetocaloric materials undergoing magnetostructural transitions involving a volume change.

Giant solid-state barocaloric effect in the Ni-Mn-In magnetic shape-memory alloy

Theoretical aspects of the magnetocaloric effect

The inverse magnetocaloric effect occurs when a magnetic material cools down under applied magnetic field in an adiabatic process. Although the existence of the inverse magnetocaloric effect was recently reported experimentally, a theoretical microscopic description is almost nonexistent. In this paper we theoretically describe the inverse magnetocaloric effect in antiferro- and ferrimagnetic systems. The inverse magnetocaloric effects were systematically investigated as a function of the model parameters. The influence of the Neel and the compensation temperature on the magnetocaloric effect is also analyzed using a microscopic model.

/pdf/understanding-the-inverse-magnetocaloric-effect-in-antiferro-4hzzgxx4ef.pdf

Understanding the inverse magnetocaloric effect in antiferro- and ferrimagnetic arrangements

In this work we discuss the thermodynamics of the magnetocaloric effect around the first- and second-order magnetic phase transitions. We show that, around the second-order phase transition, the magnetocaloric potential $\ensuremath{\Delta}S$ can indeed be determined by using magnetization data through the Maxwell relation. However, around the first-order phase transition, the Maxwell relation is not valid so that the determination of $\ensuremath{\Delta}S$ by using magnetization data is somewhat more complex and should be done very carefully. These statements were verified in a simple model of interacting spins with two energy levels including an extra term to account for the first-order phase transition.

Magnetocaloric effect around a magnetic phase transition

In this paper, the magnetocaloric effect in the hexagonal intermetallic compounds belonging to the $R{\mathrm{Ni}}_{5}$ series was calculated using a Hamiltonian including the crystalline electrical field, exchange interaction, and the Zeeman effect. Experimental work was performed and the two thermodynamics quantities, namely, isothermal entropy change and adiabatic temperature change were obtained for polycrystalline samples, using heat capacity measurements, and compared to the theoretical predictions.

Magnetocaloric effect in the R Ni 5 ( R = Pr , Nd, Gd, Tb, Dy, Ho, Er) series

We report the theoretical investigations on the colossal magnetocaloric effect using a simple model that couples the lattice entropy and magnetic entropy through the magnetoelastic deformation. Analytical expressions were obtained for the thermodynamic magnetic state equation as well as for the total entropy and heat capacity. The coupled magnetic lattice model predicts high isothermal entropy changes due to the lattice contribution for external magnetic field change, overcoming the magnetic entropy change limit.

N.A. de Oliveira

Papers

Theoretical aspects of the magnetocaloric effect

Understanding the inverse magnetocaloric effect in antiferro- and ferrimagnetic arrangements

Magnetocaloric effect around a magnetic phase transition

Magnetocaloric effect in the R Ni 5 ( R = Pr , Nd, Gd, Tb, Dy, Ho, Er) series

Analytical model to understand the colossal magnetocaloric effect