First-principles study on the structural, electronic and magnetic properties of the Ti₂VZ (Z = Si, Ge, Sn) full-Heusler compounds

Highlights

• Structural properties of Ti₂VZ (Z = Si, Ge, Sn) have been achieved by ab initio.

• The calculations proved Ti₂VSi and Ti₂VGe to be half-metallic compounds.

• The total magnetic moments of Ti₂VSi and Ti₂VGe followed the SP rule M_t = Z_t − 18.

• Their magnetic and half-metallic properties changed with lattice distortion.

Abstract

In the present work, we have investigated the structural, electronic and magnetic properties of Ti₂VZ (Z = Si, Ge, Sn) alloys with Hg₂CuTi-type structure in the framework of density functional theory with generalized gradient approximation (GGA). The calculated results show that Ti₂VSi and Ti₂VGe alloys belong to half-metallic compounds with a perfect 100% spin polarization at the Fermi level while Ti₂VSn alloy is just a conventional ferrimagnetism compound. And the total magnetic moment of Ti₂VSi and Ti₂VGe obey the Slater–Pauling (SP) rule. In a moderate variation range of lattice distortion, Ti₂VSi and Ti₂VGe remain half-metallicity. We expect that our calculated results may trigger Ti₂VZ (Z = Si, Ge, Sn) applying in the future spintronics field.

Introduction

Recent years, the half-metallic compounds have attracted growing attention due to their great potential in the field of spintronics device application [1], [2]. The concept of half-metallic property was initially proposed by de Groot et al. basing on NiMnSb half-Heusler alloy calculations in 1983, which behaved as metal for one spin direction and as semiconductor or insulator for the opposite spin direction [3]. The half-metallic compound shows a peculiar 100% spin polarization at the Fermi level. Apart from Heusler alloys, many other compounds are also observed theoretically or experimentally to behave half-metallic nature, for example, double perovskites [4], some oxides [5], [6], dilute magnetic semiconductor [7], [8] and materials possessing zincblende structure [9], [10]. In fact, investigating and searching for new half-metallic materials are mostly focused on the Heusler alloys due to their high spin polarization, high Curie temperature and simultaneously a low saturation magnetization, which are suitable for ultrahigh density magnetic memory storage devices [11], [12], [13].

The outstanding material was first discovered by Fritz Heusler in 1903 when he found that Cu₂MnAl alloy behaved ferromagnetic even without magnetic constituent elements [14]. Generally, the class of ternary Heusler alloy family includes two possible variations, called half-Heusler and full-Heusler alloy, with chemical formula XYZ and X₂YZ, respectively. X and Y represent different transition elements, while Z refers to the main group Ⅲ, Ⅳ or Ⅴ element. The full-Heusler alloy crystallizes either in the Cu₂MnAl prototype (space group $\text{Fm}\overline{3}\text{m}$) or in the Hg₂CuTi prototype (space group $\text{F}\overline{4}3\text{m}$) known as inverse Heusler structure [15]. In the case when the number of 3d valence electrons of Y atom is larger than that of X in full-Heusler alloy, the later structure will be preferential choice.

Up to now, many Ti₂-based full-Heusler compounds have been investigated for future spintronics applications. Zheng et al. applied first-principles to study the Ti₂-based full-Heusler Ti₂YAl (Y = V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) compounds [16], and they predicted that the Ti₂YAl (Y = Fe, Co, and Ni) alloys were half-metallic ferrimagnets and Ti₂MnAl alloy was found to be a half-metallic antiferromagnet while the Ti₂YAl (Y = V, Cr, Cu, and Zn) alloys were conventional ferromagnets. Mao et al. proposed that Ti₂FeZ (Z = Al, Ga, Ge) alloys with Hg₂CuTi-type structure were half-metallic ferrimagnets, following the M_t = Z_t − 18 rule and agreeing with the Slater–Pauling curve quite well [17]. Very recently, S. Galehgirian with his colleague have studied Ti₂VZ (Z = Al, Ga, and In) alloys which exhibited half-metallic characteristic in their electronic structures basing on first-principles calculation [18].

To our best knowledge, due to the difficulty in synthesizing the stoichiometric compositions, there is no comprehensive experimental study on Ti₂VZ (Z = Si, Ge, and Sn) compounds. However, the theoretical study is still desirable and helpful for future investigations. Therefore, we present a systematic study the structural, electronic and magnetic properties of the series Ti₂VZ (Z = Si, Ge, Sn) full-Heusler compounds with Hg₂CuTi prototype for the first time, based on first-principles calculations and group theory in the present work. The paper is organized as follows: in Section 2 it includes the calculation methods; in Section 3, the structural, magnetic and electronic properties are discussed; finally in Section 4, we summarize our calculated results and conclusions.