Specific heat and thermal expansion characteristics related to spin fluctuations in antiferromagnetic β-MnOs alloys

The temperature dependences of magnetic susceptibility, the specific heat and the thermal expansion of β-Mn_1-x Os_x alloys have been investigated. The electronic specific heat coefficient γ is significantly large and drastically decreases with increasing x. The specific heat peak associated with the Néel temperature T_N is clearly observed in high Os concentration regions. On the other hand, in low Os concentration regions, the peak is not clear and a linear relation between γ and T_N^3/4 is observed. Therefore, it is concluded that β-Mn_1-xOs_x alloys with low x are weak itinerant-electron antiferromagnets. The thermal expansion coefficient α in the paramagnetic state is remarkably large in the low Os concentration regions and becomes smaller with increasing x; that is, the larger the electronic specific heat coefficient γ, the larger the value of α in the paramagnetic region.