Spin fluctuation, thermal expansion anomaly, and pressure effects on the Neel temperature of β-MnM (M=Ru, Os, and Ir) alloys -: art. no. 054420

The specific heat and the thermal expansion under ambient pressure and the temperature dependence of magnetic susceptibility under applied pressure have been investigated for beta-Mn1-xMx (M=Ru, Os, and Ir) alloys by taking spin fluctuations into consideration. From powder neutron diffractions for beta-Mn0.75Os0.25 alloys, the magnetic Bragg peaks was observed at 10 K, which is the first direct confirmation of a long-range magnetic order in beta-Mn alloys. The relationship between the pressure dependence of the Neel temperature dT(N)/dP and T-N is explained by the Ehrenfest equation. A significantly large thermal expansion coefficient in a wide range of temperature above T-N is clearly correlated with spin fluctuations. At low and finite temperatures, the effects of spin fluctuations as a function of the Neel temperature in both the weak itinerant-electron antiferromagnetic state and intermediate antiferromagnetic state are common to beta-Mn alloys, regardless of the kinds of additional elements.