Monolayer ferromagnetism of Fe(110) on W(110) studied by Mössbauer spectroscopy

Fe(110) films in the monolayer regime were prepared at 300 K in UHV on W(110). Pseudomorphic structure and layer-by-layer growth were established using LEED, AES, and conversion electron Mössbauer spectroscopy (CEMS). For the pseudomorphic monolayer, ferromagnetic order was established using CEMS below a monolayer Curie temperature TC (1)=(210±10) K=0.20TC(∞) for a free monolayer and TC(1)=(296±1) K=0.28TC(∞) for a Ag-coated monolayer, respectively. Magnetic hyperfine fields Bhf(T) could be measured for T≥90 K. Ground-state values could be determined by extrapolation to Bhf(0)=(10±1) T for the free and Bhf(0)=(11.9±0.3) T for the Ag-coated monolayer, respectively. A critical region 270<T<300 K was analyzed to some detail for the Ag-coated monolayer. In this region, the CEMS spectrum contains a magnetic and a nonmagnetic component. Transition to the paramagnetic phase occurs by transition of intensity from the magnetic to the nonmagnetic line, whereas Bhf of the magnetic component remains finite with approach to TC. Beyond the true monolayer, double layer and monolayer components can be distinguished in the CEMS spectra.