Neutron scattering study of spin fluctuations in Y(${\mathrm{Mn}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$${)}_2$

Elastic and inelastic neutron-scattering measurements have been made on a series of pseudobinary intermetallic compounds Y(${\mathrm{Mn}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$ ${)}_2$. Long-range antiferromagnetic order below $T_N$∼100 K in ${\mathrm{YMn}}_2$ 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 ${\mathrm{YMn}}_2$ 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 760 K, which is similar to the behavior observed in ${\mathrm{YMn}}_2$ but quite different from the characteristics of simple localized-electron magnets.