Neutron polarization analysis study of the frustrated magnetic ground state of β-Mn_{1−x}Al_{x}

We have performed a neutron polarization analysis study of the short-range nuclear and magnetic correlations present in the dilute alloy, -Mn1−xAlx with 0.03x0.16, 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 -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.