Neutron polarization analysis study of the frustrated magnetic ground state ofβ-Mn1−xAlx

Abstract

We have performed a neutron polarization analysis study of the short-range nuclear and magnetic correlations present in the dilute alloy, $\ensuremath{\beta}{\text{-Mn}}_{1\ensuremath{-}x}{\text{Al}}_{x}$ with $0.03\ensuremath{\le}x\ensuremath{\le}0.16$, in order to study the evolution of the magnetic ground state of this system as it achieves static spin-glass order at concentrations $x>0.09$. To this end we have developed a reverse--Monte Carlo algorithm which has enabled us to extract Warren-Cowley nuclear short-range order parameters and magnetic spin correlations. Using conventional neutron powder diffraction, we show that the nonmagnetic Al substituents preferentially occupy the magnetic site II Wyckoff positions in the $\ensuremath{\beta}\text{-Mn}$ structure---resulting in a reduction of the magnetic topological frustration of the Mn atoms. These Al impurities are found to display strong anticlustering behavior. The magnetic spin correlations are predominantly antiferromagnetic, persisting over a short range which is similar for all the samples studied---above and below the spin-liquid-spin-glass boundary---while the observed static (disordered) moment is shown to increase with increasing Al concentration.