MICROMAGNETIC STRUCTURES AND MICROSCOPIC MAGNETIZATION-REVERSAL PROCESSES IN EPITAXIAL FE GAAS(001) ELEMENTS/

The in-plane size and orientation-dependent micromagnetic structures o f thin epitaxial Fe(001) elements were studied by Lorentz electron mic roscopy. It is found that the single-domain remanent state supported b y continuous epitaxial films with in-plane anisotropy decays into a mu ltidomain configuration upon reducing the film lateral dimensions. For 150-Angstrom-thick Fe(001) elements, such drastic changes in the rema nent domain structure and reversal processes occur when the element si ze is reduced to similar to 10 mu m. This transition can be explained as a consequence of the in-plane dipolar (shape anisotropy) contributi on to the total energy becoming comparable with that of the magnetocry stalline anisotropy at this size. Due to the interplay between in-plan e shape and magnetocrystalline anisotropies, novel micromagnetic pheno mena were observed. Distinct microscopic reversal processes arise acco rding to not only the crystallographic direction along which the field is applied but also the orientation of the element edges. For magneti zation reversal along the in-plane [100] directions (easy axes), domai ns nucleate at either element edges or corners depending on the orient ation of element edges. For applied fields aligned along the in-plane [110] directions (hard axes), a fine-scale stripe (width less than or equal to 200 nm) domain structure develops upon reducing the applied f ield from saturation. In addition to coherent rotation and domain-wall displacement, a 90 degrees coherent jump reversal process has been ob served for the elements with edges parallel to the [110] directions. T he micromagnetic behavior of these epitaxial elements is substantially different from those of either continuous epitaxial Fe(001) films [E. Gu et al., Phys. Rev. B 51, 3596 (1995), C. Daboo et al., Phys. Rev. B 51, 15 964; (1995)] or polycrystalline elements in which the magneto crystalline anisotropy is negligibly small. As the relative contributi ons of the in-plane shape and magnetocrystalline anisotropies can be m odified by varying the element size, shape and orientation, these meso scopic epitaxial elements not only offer an ideal model to study the r oles of anisotropies in determining the micromagnetic structures but a lso allow the magnetic spin configuration to be controlled which could be useful for device applications, e.g., spin-polarized injection con tacts and magnetic memory elements.