Neutron scattering study of spin fluctuations in Y(Mn1-xAlx)2

Elastic and inelastic neutron-scattering measurements have been made on a series of pseudobinary intermetallic compounds Y(Mn1-xAlx)2. Long-range antiferromagnetic order below TN∼100 K in YMn2 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 YMn2 it drops by more than 30% at TN and then increases gradually with increasing temperature. A considerable degree of spatial correlations of spin fluctuations persists up to at least 760 K, which is similar to the behavior observed in YMn2 but quite different from the characteristics of simple localized-electron magnets.