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: XMn₂V (Mn-rich type) and X ₂MnV (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 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 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 ₂MnV (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.

Projected density of states of Mn₂CoCrP₂/GaAs/Mn₂CoCrP₂ magnetic tunnel junction along the transport direction (z-axis).

A highly lattice-matched all-Heusler-alloy magnetic tunnel junction (MTJ) is proposed by associating half metallic CoFeTiSi electrode and non-magnetic semiconductor Fe₂TiSi barrier. Based on the non-equilibrium Green's function combined with first-principles calculations, spin transport mechanism is studied by analyzing the transmission coefficient, local density of states, and scattering states. The calculated equilibrium tunnel magnetoresistance (TMR) ratio in CoFeTiSi/Fe₂TiSi/CoFeTiSi reaches up to about 3.30 × 10⁸%, which is much higher than in CoFeTiSi/MgO/CoFeTiSi. The calculated scattering states reveal that CoFeTiSi/Fe₂TiSi/CoFeTiSi MTJ possesses two transport channels, and the contribution of channel I to the total transport is about 80%, which plays a dominate role. The analyses on non-equilibrium spin transport properties reveal that CoFeTiSi/MgO/CoFeTiSi MTJ can output a high intensity transport current with complete spin polarization, and it can output a stable and highly efficient signal. The TMR ratio possesses an extremely large value of about 2.4 × 10⁸% and even the bias voltage increases to 0.2 V, exhibiting a robust current-driven stability.

Equiatomic quaternary Heusler compounds (EQHCs) generally have the advantages of high Curie temperature, large spin polarization and long spin diffusion length, and they are regarded as one of the most promising candidates for spintronics devices. Herein, we report a theoretical investigation on an EQHC CoRhMnGe based magnetic tunnel junction (MTJ) with (i) MnGe-terminated interface and (ii) modified pure Mn terminated interface, i.e., MnMn-terminated interface. By employing first principle calculations combined with non-equilibrium Green's function, the local density of states (LDOS), transmission coefficient, spin-polarized current, tunnel magnetoresistance (TMR) ratio and spin injection efficiency (SIE) as a function of bias voltage are studied. It reveals that when the MTJ under equilibrium state, TMR ratio of MnGe-terminated structure is as high as 3,438%. When the MTJ is modified to MnMn-terminated interface, TMR ratio at equilibrium is enhanced to 2 × 10⁵%, and spin filtering effects are also strengthened. When bias voltage is applied to the MTJ, the TMR ratio of the MnGe-terminated structure suffers a dramatic loss. While the modified MnMn-terminated structure could preserve a large TMR value of 1 × 10⁵%, even bias voltage rises up to 0.1 V, showing a robust bias endurance. These excellent spin transport properties make the CoRhMnGe a promising candidate material for spintronics devices.