Magnetic order and critical behavior at surfaces of ultrathin Fe(100)p(11) films on Pd(100) substrates

The magnetic order and critical behavior at well-defined surfaces of ultrathin ( 1.9-2.1) monolayer Fe{ lOO)p( 1 X 1) films, deposited at room temperature on atomically flat Pd( 100) substrate crystals, is investigated using electron-capture spectroscopy { ECS). Ferromagnetic order sets in at a surface Curie temperature Tc,=613.1 K. At room temperature, the long-ranged electron-spin polarization (ESP) amounts to 34% and is oriented in-plane for well-annealed films. Near T,, the ESP follows the power law ( TCsr)4 with a critical exponent. /3=0.1X AO.01 evaluated near TC-, This result is in good agreement with the exact value &=a of the two-dimensional Ising model with short-ranged forces. For temperatures far from TCs the ESP follows precisely the temperature dependence of the magnetization as predicted by Yang’s exact solution of the two-dimensional Ising model including long-ranged forces.