Magnetic anisotropy in the electron momentum density of iron

Abstract

The existence of magnetic terms in the X-ray scattering cross-section is well established^1–3, and the suggestion that X-ray studies of magnetization density would be viable dates from 1970⁴. But despite pioneering diffraction studies with conventional X-ray sources^5–7, measurements proved difficult until the advent of synchrotrons producing high X-ray flux. This is because of the weakness of these contributions and the general need to use polarized beams or polarization analysis⁸. In recent years, diffraction studies of rare-earth antiferromagnets⁹ and interfacial magnetic layers¹⁰ undertaken with synchrotron radiation have established the viability of the approach and the magnetic terms in the cross-section. In ferromagnets the demonstration of these effects has been predominantly through inelastic Compton scattering, rather than elastic Bragg diffraction studies. The Compton experiment is interpreted in terms of the electron's momentum distribution¹¹, rather than its more familiar spatial counterpart studied in polarized neutron diffraction experiments. Here we report the measurement of the [111], [110] and [100] directional Compton profiles of the unpaired spin electrons in a single crystal of iron, obtained with a 60-keV circularly polarized beam extracted from the Dares-bury storage ring. The data provide a more critical test of band theory than is possible with polycrystalline samples (for which the scattering geometry is much simpler), and indicate the potential of this new technique.