Study of paramagnetic phase of metallic magnet by means of microscopic methods

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Elastic and inelastic neutron scattering measurements have been made on a series of pseudobinary intermetallic compounds Y(Mn_<1-x>Al_x)_2. Long range antiferronagnetic order below T_N - 100K in YMn_2 has been shown to collapse by substitution of only 5% of the manganese atoms by aluminum atoms. In these compounds, a spin glass transition has been clearly indicated by a change in the energy width of the scattered neutron spectrum, as well as by the onset of field hysteresis in susceptibility measurements. In the compound with x = 0.10, the amplitude of spin fluctuations S does not change appreciably with temperature, whereas in YMn_2 it drops by more than 30% at T_N and then increases gradually with increasing temperature. A considerable degree of spatial correlations of spin fluctuations persists up to at least 760K, which is similar to the behavior observed in YMn_2 but quite different from the characteristics of simple localized electron magnets.