Magnetic anisotropy of epitaxial Fe layers grown on Si(001)

The magnetic properties of epitaxial iron films up to 80 monolayers (ML) th ickness grown on Si(001) by using a template technique were investigated by means of superconducting quantum interference device and magneto-optic Ker r effect techniques. The thinnest films investigated (similar to3 ML) exhib it a composition close to Fe3Si with a Curie temperature below room tempera ture (RT) and strong out-of-plane remanent magnetization that reflects the presence of a dominant second order surface anisotropy term. Thicker films (greater than or equal to4 ML) are ferromagnetic at RT with remanent magnet ization in film-plane and a composition closer to pure Fe with typically 8- 10% silicon content. When deposited at normal incidence such films show sim ple in-plane fourfold anisotropy without uniaxial contribution. The relevan t fourth-order effective anisotropy constant K-4(eff) was measured versus f ilm thickness and found to change its sign near 18 ML. The origin of this r emarkable behavior is investigated by means of a Neel model and mainly trac ed back to fourth-order surface anisotropy and magneto-elastic effects rela ted to the large biaxial in-plane compressive strain up to 3.5% in the thin nest (less than or equal to 25 ML) films. (C) 2001 Elsevier Science B.V. Ai l rights reserved.