Effective exchange constant and electronic structure of pseudo-gap-type L1₀-MnPd alloys

The electrical resistivity, magnetic and low-temperature specific heat measurements, and theoretical calculations for L1₀-type MnPd alloy system were carried out in a wide range of composition from 40 to 60% Pd. In the present antiferromagnetic alloy system, the highest Néel temperature T_N was observed in the vicinity of 53% Pd concentration, deviating from the equiatomic concentration. This behavior was also conformed by the theoretical calculations for the effective exchange constant J₀ which gives the value of T_N. In the temperature dependence of electrical resistivity for the L1₀-type MnPd alloys, a characteristic behavior of a hump just below T_N was observed, which is associated with the pseudo-gap-type antiferromagnets. In addition, the value of the electronic specific heat coefficient γ_e is significantly small below 1 mJ mol^-1 K^-2 above 50% Pd, reflecting the very low density of states at the Fermi energy E_F. The linear relation between the magnetic moment and the Pauling valence has been confirmed in the L1 ₀-type Mn alloy systems, together with that of other Mn alloy systems. The present several results strongly imply that the characteristic electronic structure with the pseudo-gap and the Pauling valence (PV) associated with the covalent bonding state is closely interrelated in the L1 ₀-type Mn alloy systems.