Half-metallic properties of Zr2CrAl ferrimagnetic full-Heusler compound, investigated in tetragonal, orthorhombic and rhombohedral crystal structures

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Highlights

  • The half-metallic and magnetic properties of Zr2CrAl were investigated.

  • The cubic, tetragonal, orthorhombic and rhombohedral structures were considered.

  • The total magnetic moment of Zr2CrAl, for all distortions analyzed is 1μB/ f.u.

  • Complete spin polarization is present, in all crystal structures investigated.

Abstract

The research efforts focused on the implementation of Heusler materials into spintronic heterostructures triggered the investigations on the half-metallic and magnetic properties on Zr2CrAl ferrimagnetic compound. The theoretical investigations based on Density Functional Theory were performed on the tetragonal, orthorhombic and rhombohedral distortions of the typical inverse-Heusler cubic crystalline structure, previously reported. The compound exhibits half-metallic characteristics for all deformations considered. The slight variations in volume of the unit cell do not destroy the high spin polarization state. The band gap from minority spin channel slightly decreases in orthorhombic and rhombohedral deformations. The total magnetic moment calculated per formula unit is integer (equal to 1μB/f.u.) and follows the Slater-Pauling rule for all cases investigated. The antiferromagnetic coupling between the Zr and Cr atoms was preserved. The functionality of ferrimagnetic full-Heusler alloys to be used as overlayers in the production of epitaxially deposited heterostructures on substrates with crystalline structures other than cubic was proven.

Introduction

The overwhelming advances in computer science, medicine or biotechnology would have not be possible without the cutting-edge studies in magnetism. To date, an abundant literature has been devoted to thousands of multifunctional materials already used in spintronic applications [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11].

The peculiar property of half-metallicity [12], [13] implies a semiconducting gap in one spin channel of densities of state and a metallic character in the other spin channel, which leads to a high spin polarization, useful to increase the performance in magnetic tunnel junctions or spin-valves.

The current research progress in half-metallic materials includes several computational approaches, like formation energy, Slater-Pauling rule [1], [3], [4], [8], phonon [3], [7], [4], [9] and convex hull calculations [1] or exchange coupling interaction [2], [3], [9], [10], [11] to investigate the material stability with tunable properties for targeted applications.

In this respect, Heusler compounds [14] exhibit high tunability of magnetic properties, due to the bcc-like structure composed from four interpenetrating fcc lattices. They often exhibit half-metalicity in the cubic C1b structure for the half-Heusler XYZ variants and in Cu2MnAl or Hg2CuTi prototypes for full-Heusler X2YZ compounds; X is a transition metal, Y may be a rare-metal or a transition metal and Z is a main group element [3], [10], [15], [16] In addition, desirable compounds should be corrosion resistant and should exhibit low toxicity, such are Zirconium based Heusler compounds[17], [18], [19].

Ferromagnetism produces energy losses and high stray fields in spintronic devices, impeding the optimal operation and decreasing the device’s performance. However, in ferrimagnetism, where the partial magnetic moments are uncompleted compensated, the total magnetic moment in the unit cell significantly decreases, producing lower stray fields, being therefore less sensitive to external fields and allowing higher storage densities. A unique property of some Heusler alloys, classified as spin gapless semiconductors was first reported by [20]. In these materials, to excite electrons from valence to conduction band, almost no threshold energy is required [10].

Nevertheless, growing thin epitaxial heterostructures often lead to change of the typical cubic structure, due to the mismatch between the involved lattice parameters. The traditional time-consuming and costly trial-and-error approaches to design and develop novel magnetic materials with particular properties are being overtaken by advanced strategies based on a comprehensive understanding of the magnetic phenomena up to the structure-property relationship on the level of individual atoms, through theoretical modeling.

In one of our previous study [21] was demonstrated that small distortions of unit cell, may lead to interesting changes of the half-metallic properties in ferromagnetic Heusler alloys. However, ferrimagnetic coupling lead to significant lower total magnetic moments, therefore ab initio electronic structure calculations based on DFT have been highly successful in predicting the properties of new systems and explaining existing phenomena. In order to identify the influence of symmetry decrease due to the mismatches appeared in heretostructures as a result of the growing conditions and to substantially reduce the experimental efforts employed, first principle investigations were performed to study the electronic and magnetic properties in tetragonal, orthorombic and triclinic structures, with respect to potential application of Zr2CrAl ferrimagnetic compound [17], [18], [19], as epitaxial layer grown on a substrate. Either distortions of the films or growing on substrates with other symmetry than cubic could be mentioned at the origin of such structures.

Section snippets

Method of calculation

Theoretical investigations, based on first-principle density functional calculations were performed by applying the Full Potential Linearized Augmented Plane Wave (FPLAPW) method, from Wien2k code [22]. The exchange and correlation interaction was modeled with the Perdew-Burke-Ernzehof (PBE) functional and the Generalized Gradient Approximation (GGA) [23], [24].

The wavefunctions were approximated by Fourier series, in the interstitial regions of the muffin-tin (MT) model (in which the unit cell

Results and discussions

Theoretical investigations reported in literature for Zr2CrAl compound present as the most energetically favorable structure, not only Hg2CuTi -type [17] but also Cu2MnAl -type [18]. The inverse-Heusler structure ( the Hg2CuTi -type) with a lattice parameter a = 6.59 A˙ was obtained by using the scalar relativistic approximation within full-potential local-orbital basis method [26], [27], [28] while the L21 structure (Cu2MnAl -type) with a = 6.66 A˙ was calculated based on pseudopotential

Conclusions

The electronic and magnetic structure of cubic, tetragonal, orthorhombic and rhombohedral Heusler compound with the composition Zr2CrAl were investigated by ab initio calculations. The optimum unit cell volume was expended/contracted by± 1%,± 3%,± 5% to investigate the stability of half-metallic and magnetic properties. The partial and total magnetic moments were calculated and the results proved that the ferrimagnetic coupling between the Zr and Cr atoms was not affected by the symmetry

CRediT authorship contribution statement

A. Birsan: Conceptualization, Methodology, Software, Data curation, Writing − original draft preparation. V. Kuncser: Conceptualization, Supervision, Writing- Reviewing, Project administration.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors acknowledge the financial support provided by the Romanian National Authority for Scientific Research through the Core Program PN19–03 and the PED306/2020 project.

References (30)

  • S. Jiang et al.

    J. Alloy. Compd.

    (2021)
  • M. Carpentieri et al.

    Encycl. Smart Mater.

    (2022)
  • A. Hirohata et al.

    J. Magn. Magn. Mater.

    (2020)
  • X. Wang et al.

    Phys. Rep.

    (2020)
  • J. Goraus et al.

    J. Alloy. Compd.

    (2021)
  • Xiao-Ping Wei et al.

    Mater. Res. Bull.

    (2017)
  • F. Meng et al.

    J. Alloy. Compd.

    (2017)
  • A. Birsan

    J. Alloy. Compd.

    (2017)
  • K. Elphick et al.

    Sci. Technol. Adv. Mater.

    (2021)
  • Wei Yang Samuel Lim et al.

    Ady Suwardi Front. Mater.

    (2021)
  • S. Chatterjee et al.

    J. Condens. Matter Phys.

    (2022)
  • VG. de Paula et al.

    Chem. Mater.

    (2021)
  • J. Barker et al.

    J. Phys. Soc. Jpn.

    (2021)
  • C. Felser et al.

    Heusler alloys: Properties, Growth, Applications ISSN 0933-033X

    (2016)
  • ZJ. Yue et al.

    Small

    (2020)
  • Cited by (4)

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