Thin films of magnetic materials have attracted a great deal of interest due to the possibility of unique and desirable magnetic properties which promote valuable technological applications, particularly in the data storage industry. The magnetic properties of Fe thin films were known to be complicated on different substrates due to its structure transition from fcc to bcc and also many kinds of anisotropy competitions. Fe film growth on W(111) surface was carried out to probe the fcc structure according to earlier report. However, our structure investigations by low energy electron microscopy (LEEM) and diffraction (LEED) show no evidence of the formation of fcc Fe over the entire thickness range studied, up to 18 monolayers (ML). Observations are instead consistent with the formation...[ Read more ]

Thin films of magnetic materials have attracted a great deal of interest due to the possibility of unique and desirable magnetic properties which promote valuable technological applications, particularly in the data storage industry. The magnetic properties of Fe thin films were known to be complicated on different substrates due to its structure transition from fcc to bcc and also many kinds of anisotropy competitions. Fe film growth on W(111) surface was carried out to probe the fcc structure according to earlier report. However, our structure investigations by low energy electron microscopy (LEEM) and diffraction (LEED) show no evidence of the formation of fcc Fe over the entire thickness range studied, up to 18 monolayers (ML). Observations are instead consistent with the formation of a well-ordered, laterally (tensile) strained bcc Fe layer that gradually relaxes vertically and develops increasing disorder with increasing thickness. Magnetic measurements of the Fe film on W(111) using spin polarized low energy electron microscopy (SPLEEM) show ferromagnetic order appears at 6 ML, but surprisingly vanishes at 8 ML and reappears just as suddenly at 9 ML during Fe deposition at room temperature. The evolution of magnetism and exchange asymmetry with increasing thickness and the appearance of the ferromagnetic gap are attributed to structural and morphological changes in the strained Fe layer, which eventually lead to a relaxed although highly disordered bcc Fe layer. The magnetization direction of a mono-domain structure remains constant before and after the magnetization “gap” at 8-9 ML until the formation of a multi-domain structure at about 12 ML. Ferromagnetism between 6-8 ML also vanishes at only five degrees above room temperature. Spin-resolved quantum size effect (QSE) in electron reflectivity from Fe films grown on 1ML and 2ML Cu layer pre-covered W(110) surface is studied with SPLEEM. The analysis of the intensity oscillations using the phase accumulation model provides information on the unoccupied spin polarized band structure in the Fe film above the vacuum level. Compared to Fe / W(110) films, the presence of one non-magnetic Cu layer shifts spin polarized quantum well resonances in the Fe layer uniformly downward in energy by 1.1 eV. The QSE induced intensity oscillations from Fe films on Cu (2ML) / W(110) are obviously weaker than that from Fe films on Cu (1ML) / W(110), and this is attributed to the film roughness caused by the interdiffusion when the Fe is deposited on the fcc Cu(111) surface of Cu (2ML) / W(110). In-plane spin reorientation transition (SRT) is observed at the early stage of Fe growth on Au (2ML) / W(110) substrate, and this indicates the thickness related non-collinear magnetization of Fe thin film. The SRT phenomenon results from that the interaction between the Fe film and the W(110) substrate forces the magnetization of Fe film along [11̄0] direction, with Fe film thickness increasing the magnetization of Fe film would prefer to along the easy axis of bcc Fe, which is [001] . The inserted Au layers weaken the Fe-W interaction, so that the SRT could happen when the Fe film is still quite thin.