Hysteresis Design of Magnetocaloric Materials—From Basic Mechanisms to Applications

Abstract

Magnetic refrigeration relies on a substantial entropy change in a magnetocaloric material when a magnetic field is applied. Such entropy changes are present at first‐order magnetostructural transitions around a specific temperature at which the applied magnetic field induces a magnetostructural phase transition and causes a conventional or inverse magnetocaloric effect (MCE). First‐order magnetostructural transitions show large effects, but involve transitional hysteresis, which is a loss source that hinders the reversibility of the adiabatic temperature change ΔTad. However, reversibility is required for the efficient operation of the heat pump. Thus, it is the mastering of that hysteresis that is the key challenge to advance magnetocaloric materials. We review the origin of the large MCE and of the hysteresis in the most promising first‐order magnetocaloric materials such as Ni–Mn‐based Heusler alloys, FeRh, La(FeSi)13‐based compounds, Mn3GaC antiperovskites, and Fe2P compounds. We discuss the microscopic contributions of the entropy change, the magnetic interactions, the effect of hysteresis on the reversible MCE, and the size‐ and time‐dependence of the MCE at magnetostructural transitions.

Energy Applications of Magnetocaloric Materials

“…They also achieved a significant reduction of the thermal hysteresis. The fine‐tuning of the Curie temperature by varying the Mn concentration of hydrogenated La(Fe‐Mn‐Si) 13 ‐H compounds was reported by Basso et al The tuning of Heusler alloys can also be achieved by varying the composition or the microstructures of thin films, which strongly impact the phase transformation temperature . If the tuning of a magnetocaloric material belonging to a certain group fails to broaden the temperature span, materials from different groups can still be used to produce the magnetocaloric regenerators.…”

“…The adiabatic temperature change and the isothermal entropy change of the magnetocaloric material should be correctly indicated under the cycling conditions and realistic conditions for any refrigeration or heat pumping system. This important fact actually concerns hysteretic materials and was excellently addressed in a recent publication by Gottschall et al This is also the reason why low‐cost and rare‐earth‐free Heusler alloys, despite having been the focus of intensive research, are currently not being considered for the development of magnetic refrigeration and heat pumping systems, except there are relevant new findings …”

“…An investigation of the thermal hysteresis of different magnetocaloric materials such as La‐Fe‐Si‐based, Heusler‐based, and Fe 2 P‐based compounds was performed by Gutfleisch et al The work included an examination of the causes of the hysteresis and possible methods for reducing it. Another comprehensive study was conducted by Scheibel et al, who investigated the origin of the large magnetocaloric effect and hysteresis of several first‐order magnetocaloric materials such as Ni‐Mn‐based Heusler alloys, FeRh, La(FeSi) 13 ‐based compounds, Mn 3 GaC anti‐perovskites, and Fe 2 P compounds.…”

“…Nanostructuring of Gd‐Ti into multilayers has been used to enhance the magnetic field responsiveness, and this may be also interesting for other types of materials . Much effort has likewise been invested in minimizing the hysteresis and improving the magnetocaloric effect of Heusler alloys over the last few years . The mastering of hysteresis requires a very good knowledge of its intrinsic and extrinsic origins, supported by theoretical and experimental investigations toward tailoring the material with a reversible magnetocaloric effect …”

On the Optimization of Magneto‐Volume Coupling for Practical Applied Field Magnetic Refrigeration

“…In contrast, the SOPT materials despite their lower maximum entropy change, do not present significant magnetic/thermal hysteresis and exhibit much lower fatigue – enabling their mechanical stability under several magnetic/thermal cycles. Hence, one of the followed approaches nowadays is to make the best out of the two regimes and focus on materials lying at the border between the first and the second‐order – the tri‐critical point materials to take advantage of the entropic superiority of first order transition together with no reduction of MCE under cycling . Therefore, as recently highlighted, many studies were focused on understanding the mechanisms of phase transition and predicting the tri‐critcal composition for various family of magnetocaloric materials, like La(FeSi) 13 , Nd 1−x Sr x MnO 3 , MnFePSi, Sn 1−x CMn 3.x , and CoMnSi 0.92 Ge 0.08 …”