Half-Heusler compounds are an impressive class of materials with a huge potential for different applications such as future energy applications and for spintronics. The semiconducting Heusler compounds can be identified by the number of valence electrons. The band gap can be tuned between 0 and 4 eV by the electronegativity difference of the constituents. Magnetism can be introduced in these compounds by using rare-earth elements, manganese or ‘electron’ doping. Thus, there is a great interest in the fields of thermoelectrics, solar cells and diluted magnetic semiconductors. The combination of different properties such as superconductivity and topological edge states leads to new multifunctional materials, which have the potential to revolutionize technological applications. Here, we review the structure, the origin of the band gap and the functionalities of semiconducting half-Heusler compounds.

https://iopscience.iop.org/article/10.1088/0268-1242/27/6/063001/pdf

Half-Heusler compounds: Novel materials for energy and spintronic applications

Magnetic interactions in Pr1−xTbxMn2Ge2

Large reversible magnetocaloric effect, which is associated with a second-order magnetic transition at 28 K, has been observed in DyCuAl compound. The maximum values of magnetic entropy change −ΔSM and adiabatic temperature change ΔTad are 20.4 J kg−1 K−1 and 7.7 K for a field change of 0–5 T, respectively. Especially, the large values of −ΔSM (10.9 J kg−1 K−1) and ΔTad (3.6 K) with a considerable refrigerant capacity value of 150 J kg−1 are also obtained for a relatively low field change of 0–2 T, suggesting that DyCuAl compound could be considered as a good candidate for low-temperature magnetic refrigerant.

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Large reversible magnetocaloric effect in DyCuAl compound

The effect of four different dopants (Ca, Sr, Ba, and Yb) on the structural and physical properties of the ternary rare-earth transition metal compound, Eu14MnSb11, has been investigated. The compounds, Eu14-xAxMnSb11 (A = Ca, Sr, Ba, and Yb, x = 1), have been prepared by heating the mixture of stoichiometric amounts of the elements, sealed in a quartz jacketed Ta tube, in a two-zone furnace with Thigh = 1100 °C and Tlow = 1050 °C for 10 days. These compounds are isostructural with the Zintl compound Ca14AlSb11 and crystallize in the tetragonal space group I41/acd, Z = 8. The lattice parameters of the doped compound increase correspondingly as the radius of the metal dopant (A2+) increases. The preference of the dopants onto the four crystallographically inequivalent sites of Eu was examined by single-crystal X-ray diffraction. The magnetization of the compounds has been measured as a function of temperature and applied magnetic field. Temperature-dependent magnetic susceptibility measurement of powder sa...

Structure, magnetism, and magnetoresistance of the rare-earth transition metal compounds Eu13AMnSb11 (A = Ca, Sr, Ba, and Yb)

Publisher Summary Metallic systems containing rare earth or actinide elements exhibit a particularly rich variety of magnetic properties and phenomena that are caused by the incompletely filled 4f or 5f shells, respectively. The elemental metal dysprosium possesses the largest saturation magnetic moment per unit mass among all elements, being about 60% higher than that of iron. On the other hand, it is possible to obtain a ferromagnetic system with vanishing magnetization, if the compound SmA1 2 is doped with small amounts of Gd. Special attention is paid to new developments in the field, but the presentation is based on a broad tutorial discussion. In particular, density functional theory (DFT) is introduced on a level that will allow the reader to judge the most important details of the presented calculations.

Chapter 2 Density functional theory applied to 4f and 5f elements and metallic compounds

Publisher Summary This chapter discusses the magnetic properties of ternary intermetallic rare-earth compounds. The values of the effective moments are deduced from the temperature dependence of the magnetic susceptibility. The disagreement between the experimental moments and the rare earth's free-ion moments is a result of a strong coupling of the conduction electrons with the localized moments. In the RKKY theory, the magnetic effective moment is given by the formula, described in the chapter. In the ternary rare-earth compounds discussed, the magnetic properties are determined by the rare-earth moments. The transition metal atoms T, except for Mn, do not carry magnetic moments. These materials have a metallic character and the interatomic distances between the rare-earth atoms are fairly large. The magnetic interaction between the highly localized 4f electrons is realized by their conduction electrons mediating in an exchange interaction, and by the effects of crystalline electric fields (CEF) acting on the 4f electrons. The chapter also reviews the influence of these factors on the magnetic properties. In metallic compounds of rare earths, exchange interactions between rare-earth moments are mediated by the spin polarization of conduction electrons. This leads to long-range exchange interactions with an oscillatory dependence of the interaction strength on the distance between the moments.

A. Szytuła

Papers

Chapter 2 Magnetic properties of ternary intermetallic rare-earth compounds