Small-angle neutron scattering from magnetic correlations in Fe0.7Al0.3

Abstract

Ordered Fe_0.7Al_0.3 becomes ferromagnetic below 400 K but paramagnetic on cooling below 170 K and then is mictomagnetic below 92 K. A previous neutron study of this material showed magnetic diffuse scattering over this entire temperature range and we present here an extension of this study to very small angles (6×10⁻³?κ?30×10⁻³ Å⁻¹). We find that the scattering measured at constant K shows a hump at T_c as a function of temperature but also peaks near the inverse Curie temperature and these peaks occur at different temperatures for different κ. This result is reminiscent of spin glass behavior. No significant change occurs in the scattering at the mictomagnetic transition at 92 K. The κ dependence of the scattering can be described by both a Lorentzian (Ornstein‐Zernike type) and by the square of a Lorentzian (Debye type) but a more reasonable fit is found for the latter form. The application of a field of a few kilogauss eliminates the small angle scattering at all temperatures, and for scattering directions not only parallel, but also perpendicular to the applied field direction.