$4f$ spin density in the reentrant ferromagnet ${\mathrm{SmMn}}_2{\mathrm{Ge}}_2$

The spin contribution to the magnetic moment in ${\mathrm{SmMn}}_2{\mathrm{Ge}}_2$ has been measured by magnetic Compton scattering in both the low- and high-temperature ferromagnetic phases. At low temperature, the Sm site is shown to possess a large $4f$ spin moment of $3.4\pm 0.1{\mu }_B,$ aligned antiparallel to the total magnetic moment. At high temperature, the data show conclusively that ordered magnetic moments are present on the samarium site.