Thermal expansion anomaly and pressure effect on the Curie temperature of Lu₆(Mn_1-xFe_x)₂₃ compounds

The thermal expansion and specific heat measurements under ambient pressure and the thermomagnetization measurement under applied pressure for new Lu₆(Mn_1-xFe_x)₂₃ compounds have been carried out in order to discuss the relationship between the thermal expansion anomaly and the spin fluctuations. The thermal expansion coefficient α significantly increases above the Curie temperature T_C. The electronic specific heat coefficient increases with increasing x, accompanied by the decrease of the spin fluctuation spectral width. The value of the pressure dependence of T_C, ∂T_C/∂ P, is large at about -50 K GPa^-1. The anti-invar effect and the pressure effect of T_C are closely related to a significant thermal variation of the amplitude of spin fluctuations.