Evidence for ferromagnetic order at gadolinium surfaces above the bulk Curie temperature

The electron-spin polarization P at the topmost layer of atomically clean, magnetized gadolinium (Gd) surfaces is measured by using electron capture spectroscopy. P varies almost linearly with temperature between 160 K (P=-42%) and 315 K (P=0). It is found that the surface Curie temperature $T_{\mathrm{Cs}}$ is far above—lying near 310 K—the bulk Curie temperature $T_{\mathrm{Cb}}$=292.5 K, indicating uniaxial anisotropic magnetic exchange interactions at the topmost surface layer of Gd.