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

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

A new energy paradigm, consisting of greater reliance on renewable energy sources and increased concern for energy effi ciency in the total energy lifecycle, has accelerated research into energy-related technologies. Due to their ubiquity, magnetic materials play an important role in improving the effi ciency and performance of devices in electric power generation, conditioning, conversion, transportation, and other energy-use sectors of the economy. This review focuses on the state-of-the-art hard and soft magnets and magnetocaloric materials, with an emphasis on their optimization for energy applications. Specifi cally, the impact of hard magnets on electric motor and transportation technologies, of soft magnetic materials on electricity generation and conversion technologies, and of magnetocaloric materials for refrigeration technologies, are discussed. The synthesis, characterization, and property evaluation of the materials, with an emphasis on structure‐property relationships, are discussed in the context of their respective markets, as well as their potential impact on energy effi ciency. Finally, considering future bottlenecks in raw materials, options for the recycling of rare-earth intermetallics for hard magnets will be discussed.

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Magnetic materials and devices for the 21st century: Stronger, lighter, and more energy efficient

Simple rules for the understanding of Heusler compounds

Magnetocaloric effect: From materials research to refrigeration devices

MnFeP1−xSix compounds with x=0.10,0.20,0.24,0.28,…,0.80,1 were prepared by high-energy ball milling and solid-state reaction. The structural, magnetic, and magnetocaloric properties are investigated as a function of temperature and magnetic field. X-ray diffraction studies show that the samples in the range from x=0.28 to 0.64 adopt the hexagonal Fe2P-type structure with a small amount of second phase which increases with increasing Si content. The samples with lower Si content show the orthorhombic Co2P-type structure. Magnetic measurements show that the paramagnetic-ferromagnetic transition temperatures range from 214to377K. Of much importance is the fact that these compounds do not contain any toxic components and exhibit excellent magnetocaloric properties.

https://pure.uva.nl/ws/files/1088517/69767_301639.pdf

Structure, magnetism, and magnetocaloric properties of MnFeP1−xSix compounds

The structural and magnetic properties of MnFe1-xCoxGe compounds with x=0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.85,0.9, and 1.0 were investigated by means of X-ray diffraction (XRD) and magnetization measurements. XRD shows that the MnFe1-xCoxGe compounds crystallize in the hexagonal Ni2In-type crystal structure for xles0.8 and in the orthorhombic NiTiSi-type structure for x>0.8. The magnetization measurements show that the MnFe1-xCoxGe compounds exhibit a complex magnetic behavior. The Curie temperature increases with increasing of x. The saturation magnetization of the compounds with Ni2In type structure increase with increasing of x and the saturation of the magnetization in the NiTiSi-type structure also increases with increasing x. We investigated the magnetocaloric effects in these compounds by means of magnetization measurements. The maximum magnetic-entropy change observed in these compounds reaches 9 J/kgK for x=0.8 in a field change from 0 to 5 T at around 289 K

Structural and Magnetic Properties of MnFe $_1 - rm x$ Co $_rm x$ Ge Compounds

We report unconventional exchange bias in oxide-coated manganese nanoparticles, in which the Curie temperature of Mn3O4 shell is lower than the Neel temperature of the antiferromagnetic core. The coercivity (873 kA/m) of the nanoparticles, which is more than four times greater than that of bulk Mn3O4, has been enhanced significantly. A considerable enhancement in Curie temperature compared to the bulk was also observed for Mn3O4 in nanoscale. An exchange bias field as large as 400 kA/m was observed due to the strong interfacial exchange coupling. A simple phenomenological model is given to understand these phenomena in this ferri/antiferromagnetic system. (C) 2005 American Institute of Physics.

Unconventional exchange bias in oxide-coated manganese nanoparticles

In this article we report on the magnetic and transport properties of FexRh1−x thin films, prepared by evaporation in high vacuum, in the composition range 0.41<xFe<0.59. Upon annealing (at a temperature of 870 K or higher) a certain volume fraction transforms to the ordered CsCl-type (α′) FeRh phase. Close to room temperature this phase shows a hysteretic transition between the antiferromagnetic (AF) and the ferromagnetic (F) state for samples with xFe<0.5, which gives rise to a magnetoresistance (MR) effect. Although the magnetic transition was never found to be complete, it is shown that the full MR ratio can be obtained by extrapolation of the measured MR ratio as a function of the relative change of the magnetization at the transition. The AF→F transition is only observed for films with xFe<0.505±0.015, for which the α′ phase with this (fixed) composition is present together with a nonmagnetic Rh-rich fcc-type phase, as is shown from a combination of x-ray diffraction, Mossbauer spectroscopy, and mag...

/pdf/compositional-dependence-of-the-giant-magnetoresistance-in-5bpcvy6tkl.pdf

E.H. Brück

Papers

Structure, magnetism, and magnetocaloric properties of MnFeP1−xSix compounds

Structural and Magnetic Properties of MnFe $_1 - rm x$ Co $_rm x$ Ge Compounds

Unconventional exchange bias in oxide-coated manganese nanoparticles

Compositional dependence of the giant magnetoresistance in FexRh1−x thin films

Magnetic and magnetocaloric properties of Mn5Ge3−xSbx