Characteristic spin fluctuations in Y(Mn_1-xAl_x) ₂

The thermal expansion and magnetic susceptibility have been measured for Y(Mn_1-xAl_x)₂ pseudobinary Laves phase intermetallic compounds. A large volume change at T_N and a remarkable enhancement of the thermal expansion coefficient above T_N were observed in YMn₂. The substitution of Al for Mn makes these anomalies less clear. The temperature dependence of the susceptibility, being almost temperature independent for YMn₂, becomes of the Curie-Weiss type as the Al content increases. Such behaviour is explained as the characteristic features of spin fluctuations. The amplitude of local spin fluctuations at the Mn site has been estimated on the basis of the phenomenological theory of magnetovolume effects. It has been revealed that the magnetic ground state of Al-substituted compounds is a spin glass.