Mn2CoZ (Z=Al,Ga,In,Si,Ge,Sn,Sb) compounds:: Structural, electronic, and magnetic properties

We study the electronic structures and magnetic properties of Mn(2)CoZ (Z=Al,Ga,In,Si,Ge,Sn,Sb) compounds with Hg2CuTi-type structure using first-principles full-potential linearized-augmented plane-wave calculations. It is found that the compounds with Z=Al, Si, Ge, Sn, and Sb are half-metallic ferrimagnet. Experimentally, we successfully synthesized the Mn(2)CoZ (Z=Al,Ga,In,Ge,Sn,Sb) compounds. Using the x-ray diffraction method and Rietveld refinement, we confirm that these compounds form Hg2CuTi-type structure instead of the conventional L2(1) structure. Based on the analysis on the electronic structures, we find that there are two mechanisms to induce the minority-spin band gap near the Fermi level, but only the d-d band gap determines the final width of the band gap. The magnetic interaction is quite complex in these alloys. It is the hybridization between the Mn(C) and Co atom that dominates the magnitude of magnetic moment of the Co atom and the sign of the Mn(B)-Co exchange interaction. The Mn(2)CoZ alloys follow the Slater-Pauling rule M-H=N-V-24 with varying Z atom. It was further elucidated that the molecular magnetic moment M-H increases with increasing valence concentration only by decreasing the antiparallel magnetic moment of Mn(C), while the magnetic moments of Mn(B) and Co are unaffected.