Effective Exchange Constant and Electronic Structure of Pseudo-Gap-Type L1_0-MnPd Alloys(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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The electrical resistivity, magnetic and low-temperature specific heat measurements, and theoretical calculations for L1_0-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 Neel 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 J_0 which gives the value of T_N. In the temperature dependence of electrical resistivity for the L1_0-type MnPd alloys, a characteristic behavior of a hump just below T_N was observed, which is associated with the pseudo-gaptype antiferromagnets. In addition, the value of the electronic specific heat coefficient γ_e is significantly small below 1 mJmol^<-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.
2006-10-15