The thermodynamic, electronic and magnetic properties of Ni_2MnX (X=Ge, Sn, Sb) Heusler alloys: a quasi-hormonic Debye model and first principles study

摘要

The thermodynamic, electronic and magnetic properties of Ni_2MnX (X=Ge,Sn, Sb) Heusler alloys are investigated using the quasi-hormonic Debye model and the first principles calculation based on the density-functional-theory. The calculated results of the temperature dependent bulk modulus, coefficient of thermal expansion and the P-V relation for Ni_2MnX (X=Ge,Sn, Sb) indicate that the bonding strength becomes stronger along the sequence of Ni_2MnSb→ Ni_2MnSn → Ni_2MnGe. The slower change trend of temperature dependent heat capacity of Ni_2MnGe than that of Ni_2MnSn and Ni_2MnSb stems from the larger contribution of electronic heat capacity and smaller contribution of lattice heat capacity compared to the other two alloys. The ferromagnetic coupling order between the Ni and Mn is confirmed by our first principles calculations. The total moments in one primitive cell for the three alloys are all about 4.0 μB which are mainly carried by Mn atom with about 3.5 μB as can be seen from the magnetization density distribution.