Formation of quaternary all-d-metal Heusler alloy by Co doping fcc type Ni2MnV and mechanical grinding induced B2-fcc transformation

The structure of the all-d-metal alloy Ni$_{50-x}$Co$_{x}$Mn$_{25}$V$_{25}$ ($x = 0$-50) is investigated by using theoretical and experimental methods. The first-principles calculations indicate that the most stable structure of the Ni$_{2}$MnV alloy is face-centered cubic (fcc) type structure with ferrimagnetic state and the equilibrium lattice constant is 3.60 Å, which is in agreement with the experimental result. It is remarkable that replacing partial Ni with Co can turn the alloy from the fcc structure to the B2-type Heusler structure as Co content $x > 37$ by using the melting spinning method, implying that the d-d hybridization between Co/Mn elements and low-valent elements V stabilizes the Heusler structure. The Curie temperature $T_{\rm C}$ of all-d-metal Heuser alloy Ni$_{50-x}$Co$_{x}$Mn$_{25}$V$_{25}$ ($x > 37$) increases almost linearly with the increase of Co due to that the interaction of Co-Mn is stronger than that of Ni-Mn. A magnetic transition from ferromagnetic state to weak magnetic state accompanying with grinding stress induced transformation from B2 to the dual-phase of B2 and fcc has been observed in these all-d-metal Heusler alloys. This phase transformation and magnetic change provide a guide to overcome the brittleness and make the all-d-metal Heusler alloy interesting in stress and magnetic driving structural transition.