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.

/pdf/magnetic-materials-and-devices-for-the-21st-century-stronger-xvi5miqu1p.pdf

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

Atomic-level structure and structure–property relationship in metallic glasses

Thermodynamic and kinetic aspects of the crystal to glass transformation in metallic materials

We present the results of a crystallization study in glassy Ni‐Zr. The alloys were prepared by melt spinning over the continuous range Ni20Zr80 to Ni70Zr30 including for the first time the region between Ni40Zr60 and Ni60Zr40. As expected we find that the glasses are most stable at and around the eutectic compositions, except that at the extreme Zr‐rich eutectic the glasses are destabilized by the premature precipitation of ω‐Zr. The products of crystallization indicate that the current crystalline phase diagram is incomplete: a new peritectoid phase must be added at the composition Ni2Zr.

Crystallization characteristics of Ni‐Zr metallic glasses from Ni20Zr80 to Ni70Zr30

The superconducting transition temperature, upper critical field, and magnetic susceptibility have been measured in four binary metallic glass systems: Cu-Zr, Ni-Zr, Co-Zr, and Fe-Zr For each alloy system, a full and continuous range of Zr-rich compositions accessible by melt spinning has been examined For Cu-Zr, the range is $075gxg030$; for Ni-Zr, $080gxg030$; for Co-Zr, $080gxg048$, and for Fe-Zr, $080gxg055$ ($x$ being the concentration of Zr in at%) The results show clearly the influence of spin fluctuations in reducing the superconducting transition temperature The data have been successfully analyzed using a modified form of the McMillan equation together with expressions for the Stoner enhanced magnetic susceptibility and the Ginsburg-Landau-Abrikosov-Gor'kov expression for the upper critical field

Superconductivity and spin fluctuations in M − Z r metallic glasses ( M = C u , N i , C o , a n d F e )

The crystallization characteristics of glassy Cu‐Zr has been studied by differential scanning calorimetry, x‐ray diffraction, and measurement of electrical resistance and magnetic susceptibility. Our results allow us to remove many discrepancies between previously published data; they also suggest that the equiatomic Cu‐Zr does not exist as a single phase in the crystalline state. We observe parallel changes on crystallization between the magnetic susceptibility and the electrical resistance, which we interpret through changes in the d density of states.

Crystallization characteristics of Cu‐Zr metallic glasses from Cu70Zr30 to Cu25Zr75

The role of oxygen and other impurities on the crystallization characteristics of Ni‐Zr glasses near the composition NiZr2, as well as for FeZr2, CoZr2, and NiHf2, has been investigated. For NiZr2 glasses with 1 at. % oxygen, the first crystallization product is the metastable E93 structure with a =1.227 nm instead of the equilibrium C16 structure. A similar effect is found for samples containing ≳3 at. % B. For FeZr2, CoZr2, and NiHf2 the first crystallization product is also E93 structure, even with very small levels of oxygen (≤0.2 at. %). The formation of the E93 structure is always accompanied by an increase in the electrical resistivity, an increase which transmission electron microscopy shows is intrinsic to the phase and unrelated to crystallite size. For Ni36.5Zr63.5 and Ni42Zr58 the crystallization is also accompanied by an increase in electrical resistance and the evolution of a crystal structure similar to the E93 structure in the size of the unit cell and packing fraction but with a different...

The influence of oxygen and other impurities on the crystallization of NiZr2 and related metallic glasses

The magnetic properties of the low-temperature phase of MnBi, prepared by rapid solidification, have been measured in a pulsed field over the temperature range 80--625 K. The anisotropy field, obtained by the singular-point-detection technique, is found to increase with temperature and has a maximum value of 9 T at 530 K. A fit to the saturation-magnetization measurement gives a virtual Curie point of 775 K. The coercive field is fitted by a hybrid domain-wall-pinning theory which yields, at 300 K, a domain-wall energy of 15.6 erg/${\mathrm{cm}}^{2}$ and a wall thickness of 70 \AA{}. Below 200 K, the presence of a ferrimagnetic phase is detected. Its critical field associated with spin reversal is a convex function of temperature having a maximum value of 8 T at 120 K.

Z. Altounian

Papers

Crystallization characteristics of Ni‐Zr metallic glasses from Ni20Zr80 to Ni70Zr30

Superconductivity and spin fluctuations in M − Z r metallic glasses ( M = C u , N i , C o , a n d F e )

Crystallization characteristics of Cu‐Zr metallic glasses from Cu70Zr30 to Cu25Zr75

The influence of oxygen and other impurities on the crystallization of NiZr2 and related metallic glasses

Magnetic properties of MnBi prepared by rapid solidification.