Advanced materials for solid-state refrigeration Mañosa, Lluís; Planes, Antoni; Acet, Mehmet
Journal of materials chemistry. A, Materials for energy and sustainability,
01/2013, Volume:
1, Issue:
16
Journal Article
Peer reviewed
Recent progress on caloric effects are reviewed. The application of external stimuli such as magnetic field, hydrostatic pressure, uniaxial stress and electric field give rise respectively to ...magnetocaloric, barocaloric, elastocaloric and electrocaloric effects. The values of the relevant quantities such as isothermal entropy and adiabatic temperature-changes are compiled for selected materials. Large values for these quantities are found when the material is in the vicinity of a phase transition. Quite often there is coupling between different degrees of freedom, and the material can exhibit cross-response to different external fields. In this case, the material can exhibit either conventional or inverse caloric effects when a field is applied. The values reported for the many caloric effects at moderate fields are large enough to envisage future application of these materials in efficient and environmental friendly refrigeration.
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.
Application of hydrostatic pressure under adiabatic conditions causes a change in temperature in any substance. This effect is known as the barocaloric effect and the vast majority of materials heat ...up when adiabatically squeezed, and they cool down when pressure is released (conventional barocaloric effect). There are, however, materials exhibiting an inverse barocaloric effect: they cool when pressure is applied, and they warm when it is released. Materials exhibiting the inverse barocaloric effect are rather uncommon. Here we report an inverse barocaloric effect in the intermetallic compound La-Fe-Co-Si, which is one of the most promising candidates for magnetic refrigeration through its giant magnetocaloric effect. We have found that application of a pressure of only 1 kbar causes a temperature change of about 1.5 K. This value is larger than the magnetocaloric effect in this compound for magnetic fields that are available with permanent magnets.
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.
Understanding hysteresis: Materials with magnetostructural phase transitions (MSPT) show a large magnetocaloric effect (MCE). The understanding of MSPT and its thermal hysteresis requires the knowledge about the electronic, magnetic, and lattice entropy contributions. In this Review, we provide an overview of the properties of MSPT in La–Fe–Si, Heusler alloys, Mn3GaC, and Fe2P‐type materials with respect to the MCE and its reversibility based on studies under static/dynamic conditions at micro‐ and mesoscopic scales.
In this study, we investigate the enhancement of exchange bias in core/shell/shell structures by synthesizing single inverted core/shell (Co-oxide/Co) and core/shell/shell (Co-oxide/Co/Co-oxide) ...nanostructures through a two-step reduction and oxidation method. We evaluate the magnetic properties of the structures and study the effect of shell thickness on the exchange bias by synthesizing various shell thicknesses of Co-oxide/Co/Co-oxide nanostructures. The extra exchange coupling formed at the shell-shell interface in the core/shell/shell structure leads to a remarkable increase in the coercivity and the strength of the exchange bias by three and four orders, respectively. The strongest exchange bias is achieved for the sample comprising the thinnest outer Co-oxide shell. Despite the general declining trend of the exchange bias with Co-oxide shell thickness, we also observe a nonmonotonic behavior in which the exchange bias oscillates slightly as the shell thickness increases. This phenomenon is ascribed to the dependence of the antiferromagnetic outer shell thickness variation at the expense of the simultaneous opposite variation in the ferromagnetic inner shell.
The structural and magnetic properties of Heusler alloy series Ni
50 Mn
50−
x
Sn
x
(numbers indicate at. %) and Ni
50 Mn
50−
x
In
x
have been studied. Magnetization and calorimetric measurements have ...been carried out in order to study the magnetic and structural transitions properties. The behaviour of the studied compounds is compared with that of the Ni–Mn–Ga alloy. Data for entropy and magnetization changes at the martensitic transition are reported. It is found that, as opposed to Ni–Mn–Ga, for Ni–Mn–In and Ni–Mn–Sn the magnetic moment in martensite is lower than in austenite.
Next to the multifunctional properties of Ni-Mn-based Heusler alloys new functionalities related to shell-ferromagnetism are emerging. To understand in more detail the properties of ...shell-ferromagnetism we examine a decomposed Ni50.0Mn45.1In4.9 off-stoichiometric compound using magnetic resonance techniques which provides details on magnetic interactions. We find that the ferromagnetic resonance profile of the shell-ferromagnetic state is symmetric for positive and negative fields and is independent of the direction of the field-sweep except for the hysteresis observed at small fields.
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