Abstract
The magnetic behavior of Co-Mn and Ni-Mn alloys is typical of competing interaction systems with regions of ferromagnetism and antiferromagnetism enclosing an intermediate concentration region in which only magnetic short-range order (MSRO) occurs. Neutron diffuse scattering measurements were made on alloys from this intermediate region to characterize the MSRO and to determine the associated magnetic moments. Diffuse peaks indicative of antiferromagnetic short-range order were observed and average sublattice moments were determined by comparison of the integrated diffuse peak intensities with the cross section for Bragg scattering from the alloys with assumed antiferromagnetic long-range order. The average sublattice moment of the Co-Mn alloys is appreciably smaller than that for the Ni-Mn alloys. Recent local density calculations indicate vanishing moments for Ni and Co atoms in fcc antiferromagnets with large wave vectors. If this applies to these alloys, then all of the moment resides at the Mn sites and corresponds to about 1${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/Mn for the Co-Mn alloys and 4${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/Mn for Ni-Mn alloys. This moment difference for these otherwise similar systems is attributed to a moment-volume instability of the type more commonly associated with fcc Fe.
Published Version
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