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- d -metal Heusler alloys, X 2 − x Mn 1 + x V ( X = Pd, Ni, Pt, Ag, Au, Ir, Co; x ; = 1, 0), were predicted by first principles. The series can be roughly divided into two categories: X Mn 2 V (Mn-rich type) and X 2 MnV (Mn-poor type). Using optimized structural analysis, it is shown that the ground state of these all- d -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 L2 1 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 c / a 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 X 2 MnV ( X = 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- d -metal Heusler alloys. This work provides relevant experimental guidance in the search for possible martensitic Heusler alloys in all- d -metal materials with less Mn and new spintronic and magnetic intelligent materials among all- d -metal Heusler alloys.