Temperature-dependent magnetic properties of ultrathin Fe films: Interplay between local environment and itinerant ferromagnetism

The magnetic properties of ultrathin Fe films are determined as a function of temperature in the framework of a functional-integral itinerant-electron theory. The environment-dependent electronic structure is derived from a realistic $d$-band model and a real-space recursive expansion of the local Green's functions. The statistical average of spin fluctuations is performed within the static approximation and a layer-resolved alloy analogy by treating disorder in the virtual crystal approximation and in the coherent potential approximation. Results are given for the temperature dependence of the local moments, layer magnetizations ${M}_{l}(T)$, and spin fluctuation energies of ultrathin bcc (001) films. These are compared with the corresponding bulk results in order to quantify the role of dimensionality. Strain and local environment effects are quantified by varying the interatomic bond length $d$. A strong nonmonotonous dependence of ${M}_{l}(T)$ as a function of $d$ is revealed, which can be correlated with the environment dependence of the electronic structure and with the resulting changes in the ground-state magnetic moments and spin fluctuation energies. Finally, goals, limitations, and possible extensions are briefly discussed.