We have measured temperature-dependent magnetic Compton profiles (MCPs) from a single crystal of ${\mathrm{L}\mathrm{a}}_{1.2}{\mathrm{S}\mathrm{r}}_{1.8}{\mathrm{M}\mathrm{n}}_2{\mathrm{O}}_7$. The MCPs, which involved the scattering of circularly polarized $x$ rays, are in general related to the momentum density of all the unpaired spins in the system. Nevertheless, we show that when the x-ray scattering vector lies along the [110] direction, the number of magnetic electrons of a specific symmetry, i.e., $d$ electrons of $x^2-y^2$ symmetry, yield a distinct signature in the MCP, allowing us to monitor substantial changes in the occupancy of the $d_{x^2-y^2}$ states over the investigated temperature range of 5–200 K. This study indicates that magnetic Compton scattering can provide a powerful window on the properties of specific magnetic electrons in complex materials.

• Received 9 January 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.207206