Magnetic moment distribution in Fe 3− xCr xSi alloys

Abstract

Polarized and unpolarized neutron diffraction and magnetization studies in the temperature range 10–300 K are report for the Fe 3− x Cr x Si ( x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 1.0) system. The experiments indicate that the single phase having the fcc DO 3-type structure is maintained for Fe 3 -x Cr x Si for x≤0.4, while the sample with x = 0.5 shows a small (<5%) contribution of an extra Cr 3Si-type phase, the amount of which increases linearly with Cr concentration. It is inferred from the dependence of the lattice constant on Cr content measured separately by X-ray diffraction that the phase with x = 0.35 ± 0.05 is always formed. Therefore, for the heat treatment reported here the concentration x = 0.4 seems to be the limit of solubility for Cr in DO 3-type Fe 3 -x Cr x Si system. It was found that Cr is randomly distributed among (A, C) and B sites, while D sites are fully occupied by Si. Room-temperature magnetization measurements show a linear dependence of magnetization on Cr concentration. The Curie temperature varies as (843.0 ± 1.5) K, (740.0 ± 1.5) K and (712.0 ± 1.5) K for x = 0.1, 03. and 0.4, respectively. Also a linear composition dependence of the one-site magnetic moments μ(A, C) and μ(B) was observed. At room temperature the μ(B) moment decreases from 2.61 μ B for x = 0.1 to 2.08 μ B for x = 0.4, while the μ(A, C) moments decrease from 0.95 μ B for x = 0.1 to 0.72 μ B for x = 0.4. Assuming the constancy of magnetic moments one obtains μ Fe A = (1.04±0.04) μ B and μ Fe B = (2.77±0.10) μ B , while μ A Cr = -(1.27±0.14) μ B and μ B Cr = −(2.57±0.38) μ B . A weak temperature dependence of μ(B) moment dμ(B)/d T = (-2.4±0.1)×10 -4 μ B/K in the range 10–300 K was found for samples with x = 0.1 and 0.3.