Magnetic Critical Scattering from an Itinerant Antiferromagnet of γFe0.5Mn0.5 Alloy I. Quasi Elastic Scattering

The magnetic critical scattering from a single crystal of γ-Fe 0.537 Mn 0.463 has been studied around the (001) and (110) reciprocal lattice points. It has been found that the longitudinal spin correlation becomes divergent at the Néel temperature T N of 479.0±1.5 K, the parallel staggered susceptibility χ // ( Q ) obeys a power law of α( T - T N ) -1.35±0.05 , in contrast with the temperature independent static susceptibility. The transverse spin correlation, however, remains finite at T N with the inverse correlation length of about 0.038 Å -1 . The anisotropy of the spin correlation has been suggested not due to the crystal anisotropy, but to either the anisotropic exchange interaction or the anisotropy of the non-interacting spin susceptibility of d bands. The anisotropy of the scattering profile with respect to the wave vector around the reciprocal lattice points has been found much smaller than that expected for the type I antiferromagnet with the short range interactions.