Possible evidence for a first-order magnetic phase transition on the Gd(0001) surface

The magnetic phase transition at the Gd(0001) surface is found to be strongly dependent on the presence of an external magnetic field during cooling across the surface critical temperature TC,s. Surface enhanced magnetic order on Gd(0001), present at up to 22 K above the bulk Curie temperature TC,b can be almost quenched if cooling is performed under zero magnetic field conditions. These observations are found on the surface of bulklike epitaxial, remanently magnetized Gd(0001) films probed with spin-polarized low-energy electron diffraction. In connection with recent theoretical work of Sanchez and Moran-Lopez, who predict magnetic-field-dependent surface first-order phase transitions on close-packed (111) surfaces of fcc spin-1/2 Ising ferromagnets, the above observations provide perhaps evidence for the existence of surface first-order phase transitions on the hcp(0001) surface of Gd. © 1988 The American Physical Society.