Competition between cubic and tetragonal phases in all-<i>d</i>-metal Heusler alloys, <i>X</i> _2−<i>x</i>Mn_1+<i>x</i>V (<i>X</i> = Pd, Ni, Pt, Ag, Au, Ir, Co; <i>x</i> = 1, 0): a new potential direction of the Heusler family

Abstract

In this work, a series of all-<i>d</i>-metal Heusler alloys, <i>X</i> _{2 - <i>x</i>} Mn_{1 + <i>x</i>} V (<i>X</i> = Pd, Ni, Pt, Ag, Au, Ir, Co; <i>x</i>; = 1, 0), were predicted by first principles. The series can be roughly divided into two categories: <i>X</i>Mn₂V (Mn-rich type) and <i>X</i> ₂MnV (Mn-poor type). Using optimized structural analysis, it is shown that the ground state of these all-<i>d</i>-metal Heusler alloys does not fully meet the site-preference rule for classic full-Heusler alloys. All the Mn-rich type alloys tend to form the L2₁ structure, where the two Mn atoms prefer to occupy the A (0, 0, 0) and C (0.5, 0.5, 0.5) Wyckoff sites, whereas for the Mn-poor-type alloys, some are stable with XA structures and some are not. The <i>c</i>/<i>a</i> ratio was also changed while maintaining the volume the same as in the cubic state to investigate the possible tetragonal transformation of these alloys. The Mn-rich Heusler alloys have strong cubic resistance; however, all the Mn-poor alloys prefer to have a tetragonal state instead of a cubic phase through tetragonal transformations. The origin of the tetragonal state and the competition between the cubic and tetragonal phases in Mn-poor alloys are discussed in detail. Results show that broader and shallower density-of-states structures at or in the vicinity of the Fermi level lower the total energy and stabilize the tetragonal phases of <i>X</i> ₂MnV (<i>X</i> = Pd, Ni, Pt, Ag, Au, Ir, Co). Furthermore, the lack of virtual frequency in the phonon spectra confirms the stability of the tetragonal states of these Mn-poor all-<i>d</i>-metal Heusler alloys. This work provides relevant experimental guidance in the search for possible martensitic Heusler alloys in all-<i>d</i>-metal materials with less Mn and new spintronic and magnetic intelligent materials among all-<i>d</i>-metal Heusler alloys.