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

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

Magnetocaloric effect: From materials research to refrigeration devices

Modern society relies on readily available refrigeration. Magnetic refrigeration has three prominent advantages compared with compressor-based refrigeration. First, there are no harmful gases involved; second, it may be built more compactly as the working material is a solid; and third, magnetic refrigerators generate much less noise. Recently a new class of magnetic refrigerant-materials for room-temperature applications was discovered. These new materials have important advantages over existing magnetic coolants: they exhibit a large magnetocaloric effect (MCE) in conjunction with a magnetic phase-transition of first order. This MCE is larger than that of Gd metal, which is used in the demonstration refrigerators built to explore the potential of this evolving technology. In the present review we compare the different materials considering both scientific aspects and industrial applicability. Because fundamental aspects of MCE are not so widely discussed, we also give some theoretical considerations.

https://iopscience.iop.org/article/10.1088/0022-3727/38/23/R01/pdf

Developments in magnetocaloric refrigeration

The magnetic refrigeration technique based on the magnetocaloric effect (MCE) has attracted increasing interest because of its high efficiency and environment friendliness. in this article, our recent progress in exploring effective MCE materials is reviewed with emphasis on the MCE in the LaFe13-xSix-based alloys discovered by us. These alloys show large entropy changes over a wide temperature range near room temperature. The effects of magnetic rare-earth doping, interstitial atoms and high pressure on the MCE have been systematically studied. Special issues, such as appropriate approaches to determining the MCE associated with the first-order magnetic transition, the depression of magnetic and thermal hysteresis, and the key factors determining the magnetic exchange in alloys of this kind, are discussed. The applicability of giant MCE materials to magnetic refrigeration near ambient temperature is evaluated. A brief review of other materials with significant MCE is also presented.

Recent Progress in Exploring Magnetocaloric Materials

We have discovered that the substitution of Ga or Si for Fe in Sm2Fe17Cx helps the formation of high‐carbon rare‐earth iron compounds with 2:17‐type structure. We have succeeded in preparing Sm2Fe15M2Cx (M=Ga, x=0, 1.0, 2.0, and 3.0; M=Si, x=0, 0.5, 1.0, and 1.5) compounds with Th2Zn17‐type structure by arc melting. The carbides are single phase except for Sm2Fe15Ga2C3.0, which contains a few percent of α‐Fe. The Curie temperature TC of Sm2Fe15Si2Cx compounds is found to increase from 550 to 590 K, as x increases from 0 to 1.5. For Sm2Fe15Ga2Cx, TC increases with x from 565 K for x=0 to 635 K for x=2.0, and then decreases with x. Room‐temperature saturation magnetization of these carbides is in excess of 100 emu/g and has a small dependence on carbon content. All compounds of Sm2Fe15M2Cx studied in this work except for Sm2Fe15Si2 exhibit an easy c‐axis anisotropy at room temperature and show an anisotropy field of higher than 90 kOe for x≥1.0. The present work suggests the possibility of producing high‐pe...

A novel hard magnetic material for sintering permanent magnets

Crystallographic and magnetic structures of the cubic NaZn13-type intermetallic compound LaFe11.4Si1.6 have been studied by means of powder neutron diffraction. Rietveld analysis indicates that Si atoms substitute for Fe atoms randomly on two different Fe sites. All spins in the unit cell are aligned ferromagnetically with the FeI?(8b) moment smaller than the FeII?(96i) one. The long-range ferromagnetic ordering induces a drastic expansion of the lattice and the coexistence of the large and small volume phases near the Curie temperature. Even in the ferromagnetic state, the lattice expansion still correlates strongly with the spontaneous magnetic moment, marked by a large positive magnetovolume coupling constant kC = 1.14 ? 10?8 cm6?emu?2. From the temperature dependence of Fe?Fe bond lengths, we suggest that the Fe?Fe exchange interaction between the clusters (each formed by a central FeI atom and 12 surrounding FeII atoms) plays an important role in the magnetic properties of La(Fe1?xAl/Six)13, as does that within the clusters.

https://iopscience.iop.org/article/10.1088/0953-8984/15/30/309/pdf

Strong interplay between structure and magnetism in the giant magnetocaloric intermetallic compound LaFe11.4Si1.6: a neutron diffraction study

The structure and intrinsic magnetic properties of Sm2Fe17-xGax (0 5 exhibit easy-plane anisotropy while samples with 1 < x < 5 exhibit easy c-axis anisotropy. The samples with x = 1 and 5 show a mixture of easy-plane and easy-axis behaviour.

Magnetic anisotropy of Sm2Fe17-xGax compounds with 0 < or = x < or = 6

The magnetic and transport properties of layered manganese oxides La12 Sr18 Mn2 - x Tx O7 (T = Fe, Co, Cr) are reported The undoped oxide La12 Sr18 Mn2 O7 is ferromagnetic (FM) below 125 K where an insulating-metallic (I-M) transition occurs Fe and Co doping have similar effects on the properties of La12 Sr18 Mn2 O7 , resulting in quick weakening of FM ordering, occurrence of a cluster-glass or spin-glass state for x > 007, immediate disappearance of the I-M transition and enhancement of low-temperature magnetoresistance But a different effect is observed for Cr doping In La12 Sr18 Mn2 - x Crx O7 , although the I-M transition also disappears quickly, FM ordering is maintained even for x = 05 These doping effects could be understood by considering the different exchange interactions between Mn and T (Fe, Co, Cr) and the corresponding change of the double-exchange interaction in La12 Sr18 Mn2 - x Tx O7 

Magnetic and transport properties of layered La1.2Sr1.8Mn2 - xTxO7 (T = Fe, Co, Cr)

We report the effect of Fe doping on magnetic properties and magnetoresistance (MR) in the layered perovskite La1.2Sr1.8Mn2O7. Fe doping results in the weakening of ferromagnetic (FM) ordering, and the occurrence of a low-temperature spin-glass state in La1.2Sr1.8Mn2−xFexO7. Resistivity increases sharply with increasing Fe concentration. The metal–insulator transition disappears at a very low doping level (x=0.01), but the low-temperature MR effect is enhanced. These effects result from the replacement of Mn3+ by the doped Fe ions, which interrupts the path of double–exchange interaction and destroys the FM metallic state. Due to the anisotropic interaction in the layered perovskite, the magnetic properties and MR effect are more sensitive to Fe doping than those in ABO3-type perovskites.

Fang-wei Wang

Papers

A novel hard magnetic material for sintering permanent magnets

Strong interplay between structure and magnetism in the giant magnetocaloric intermetallic compound LaFe11.4Si1.6: a neutron diffraction study

Magnetic anisotropy of Sm2Fe17-xGax compounds with 0 < or = x < or = 6

Magnetic and transport properties of layered La1.2Sr1.8Mn2 - xTxO7 (T = Fe, Co, Cr)

Effect of Fe doping on magnetic properties and magnetoresistance in La1.2Sr1.8Mn2O7