What Are the Effects Of La Doping On The Properties of MnCoGe Heusler Alloys? (Material Science)

Yifei Bi and colleagues carried out study on the effects of La Doping on the crystal structure and magnetic properties of Ni2In phase MnCoGe1-xLax (x = 0, 0.01, 0.03) alloys. They showed that the doping of La results in decreased Curie temperature, unchanged magnetic entropy and slightly decreased refrigeration capacities. Their study recently appeared in the Journal Materials.

Heusler alloy is an intermetallic compound characterized by a highly ordered arrangement of atoms. It can be divided into full Heusler alloy and half-Heusler alloy, which provides the material with rich physical properties and application functions. Heusler alloy has not only the properties of a metal alloy but also significant magnetic properties. MM’X alloy is a kind of Heusler alloy, of which the MM’X alloy MnCoGe (half-Heusler) has attracted wide attention. The MnCoGe Heusler alloy can be applied to refrigeration equipment and zero-expansion materials due to its unique magnetic refrigeration, magnetocaloric and negative thermal expansion effects. It has huge development potential. However, most of the samples currently studied are not single-phase, and most of the research samples are two-phase. There are few studies on the doping of high-temperature Ni2In-phase MnCoGe single-phase samples, and the doping of rare earth La atoms in high-temperature Ni2Inphase MnCoGe alloy has not previously been studied. As such, the study of the magnetic properties of La-doped high-temperature Ni2In phase MnCoGe alloy is meaningful for its potential application.

Thus, Yifei Bi and colleagues carried out study on the effects of La Doping on the crystal structure and magnetic properties of Ni2In phase MnCoGe1-xLax (x = 0, 0.01, 0.03) alloys.

Figure 1. XRD pattern of MnCoGe11xLax alloy at room temperature © Yifei Bi et al.

They performed a experiment for which they prepared a series of MnCoGe1−xLax (x = 0, 0.01, 0.03) alloy samples using a vacuum arc melting method. Later, they investigated the crystal structure and magnetic properties of alloys using X-ray diffraction (XRD), Rietveld method, physical property measurement system (PPMS), and vibrating sample magnetometer (VSM) analyses.

Figure 2. Rietveld refinement results for MnCoGe11xLax.: (a) MnCoGe; (b) MnCoGe0.99La0.01; (c) MnCoGe0.97La0.03 © Yifei Bi et al.

Their results showed that all samples were of high-temperature Ni2 In-type phases, belonging to space group P63/mmc (194) after 1373 K annealing. In MnCoGe1−xLax, the lattice constant gradually increases and the unit cell volume becomes larger with an increase in doped La content.

They also found that MnCoGe1−xLax is ferromagnetic at low temperatures and paramagnetic at room temperature. With an increase in doped content, the Curie temperature decreased and the Curie temperature of the MnCoGe_1−xLa_x (x = 0, 0.01, 0.03) series alloys were 294, 281, and 278 K, respectively.

In addition, it has been found that, with an increase in doped La content, the saturation magnetization at 80 K decreased slightly; being 88.75 emu/g for MnCoG, 87.55 emu/g for MnCoGe_0.99La_0.01, and 80.91 emu/g for MnCoGe_0.97La_0.03 at 5K.

Moreover, the maximum magnetic entropy changes in MnCoGe_1−xLa_x series alloys at 1.5T were 1.64, 1.52, and 1.56 J·kg¯1 ·K¯1, respectively, and the refrigeration capacities (RC) were 60.68, 59.28, and 57.72 J·kg¯1, respectively, with a slight decrease along the series.

“These changes can be observed in our study, the findings of which can serve as a reference for future research into the application of rare earth element-doped MnCoGe series alloys in magnetic refrigeration.”

— they concluded.

The authors gratefully acknowledge financial support from: The Institution of National Nature Science Foundations of China (51861003).

Featured image: MnCoGe0.97La0.03 crystal structure: (a) the crystal structure of the MnCoGe0.97La0.03; (b) the atomic environments of Mn; (c) Co and (d) M2 © Yifei Bi et al.

Reference: Bi, Y.; He, W.; Yang, T.; Wu, W.; Wen, J.; Yu, X.; Chen, F., “The Effects of La Doping on the Crystal Structure and Magnetic Properties of Ni2In-Type MnCoGe11xLax (x = 0, 0.01, 0.03) Alloys. Materials 2021, 14, 3998. https://doi.org/10.3390/ma14143998

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