Abstract
In this work, two kinds of competition between different Heusler structure types are considered, one is the competition between XA and L21 structures based on the cubic system of full-Heusler alloys, Pd2 YZ (Y = Co, Fe, Mn; Z = B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, Sb). Most alloys prefer the L21 structure; that is, Pd atoms tend to occupy the a (0, 0, 0) and c (0.5, 0.5, 0.5) Wyckoff sites, the Y atom is generally located at site b (0.25, 0.25, 0.25), and the main group element Z has a preference for site d (0.75, 0.75, 0.75), meeting the well known site-preference rule. The difference between these two cubic structures in terms of their magnetic and electronic properties is illustrated further by their phonon dispersion and density-of-states curves. The second type of competition that was subjected to systematic study was the competitive mechanism between the L21 cubic system and its L10 tetragonal system. A series of potential tetragonal distortions in cubic full-Heusler alloys (Pd2 YZ) have been predicted in this work. The valley-and-peak structure at, or in the vicinity of, the Fermi level in both spin channels is mainly attributed to the tetragonal ground states according to the density-of-states analysis. ΔE M is defined as the difference between the most stable energy values of the cubic and tetragonal states; the larger the value, the easier the occurrence of tetragonal distortion, and the corresponding tetragonal structure is stable. Compared with the ΔE M values of classic Mn2-based tetragonal Heusler alloys, the ΔE M values of most Pd2CoZ alloys in this study indicate that they can overcome the energy barriers between cubic and tetragonal states, and possess possible tetragonal transformations. The uniform strain has also been taken into consideration to further investigate the tetragonal distortion of these alloys in detail. This work aims to provide guidance for researchers to further explore and study new magnetic functional tetragonal materials among the full-Heusler alloys.
Highlights
Since the first series of Heusler compounds, of the general formula Cu2MnX (X = Al, In, Sn, Sb, Bi), was proposed by Heusler in 1903, the passion for research in Heusler alloys has continued to rise because of their numerous excellent properties and potential for many applications in numerous technical fields
The first is the L21 structure, where Pd atoms carrying more valence electrons than Mn and Al atoms occupy Wyckoff sites a (0, 0, 0) and c (0.5, 0.5, 0.5), while the Mn atom is at site b (0.25, 0.25, 0.25) and the Al atom is located at site d (0.75, 0.75, 0.75); this meets the well known site-preference rule
We investigated the atomic ordering competition between XA and L21 types, tetragonal transformation, and phase stability of full-Heusler alloys of Pd2YZ
Summary
Since the first series of Heusler compounds, of the general formula Cu2MnX (X = Al, In, Sn, Sb, Bi), was proposed by Heusler in 1903, the passion for research in Heusler alloys has continued to rise because of their numerous excellent properties and potential for many applications in numerous technical fields. They act as promising candidates for spin-gapless semiconductors (Wang, Chang, Liu et al, 2017; Bainsla et al, 2015; Wang et al, 2016; Gao & Yao, 2013; Skaftouros et al, 2013a), thermoelectric materials (Wehmeyer et al, 2017; Lue et al, 2007; Lue & Kuo, 2002), shape memory alloys (Li et al, 2018; Aksoy et al, 2009), superconductors The occupation of the atomic position has been confirmed to have a great influence on the properties of the Heusler alloy (Qin et al, 2017), so it is necessary to study the positioning in the X2YZ Heusler alloys for X with numerous valence electrons such as in Cu, Ni and Pd
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