Micromagnetism of epitaxial ferromagnetic microelements

• Main Author: Ahmad, E.
• Published: University of Cambridge 1998
• Subjects: 530.412
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595380

We have developed processes for fabricating microelements from epitaxial Fe films and thin electron transparent membranes for Lorentz microscopy. Square and rectangular microelements of two different edge-orientations, parallel to the <100> and the <110> directions were fabricated from Fe(150 Å)/GaAs(001) films. The unique magnetocrystalline anisotropy property of a thin Fe(35Å)/GaAs(001) film gives rise to both the classical single-jump and the two-jump hysteresis loops. Macroscopically, these jumps are considered as abrupt reorientations of the magnetization vector over a hard axis. However, microscopically these jumps correspond to 90° in-plane reorientations of the magnetization vector by domain wall displacements. Patterning a continuous epitaxial thin film into microelements introduces competition between the shape and magnetocrystalline anisotropies. This competition results in new features in the static and dynamic micromagnetic structures. The formation of <I>edge-domains </I>at remanence for both the square and rectangular shaped microelements is a direct consequence of such competition. A transition from the single domain to the multidomain remanent state when a square element is reduced below a critical size of ˜10 μm is also attributed to the interplay between the in-plane shape and magnetocrystalline anisotropies. Such interplay gives rise to distinct microscopic magnetization reversal processes in square elements, depending on the relative orientation of the applied filed with respect to the element-edges. The reversal processes in larger (55 μm x 55 μm) square elements only differ slightly from the continuous film. However, the reversal processes of smaller (12 μm x 12 μm) square elements differ significantly as the in-plane dipolar contribution to the total energy is comparable with that of the magnetocrystalline anisotropy at this size.