Competition between cubic and tetragonal phases in all--metal Heusler alloys, Mn V ( = Pd, Ni, Pt, Ag, Au, Ir, Co; = 1, 0): a new potential direction of the Heusler family.

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