Roger Ward

Abstract:

Epitaxial Fe/Co bilayers were grown on MgO (001) substrates by molecular beam epitaxy, characterized in situ by reflection high-energy electron diffraction and ex situ by x-ray diffraction (XRD), as well as high-resolution transmission electron microscopy (HRTEM). The hexagonal close packed (hcp) structure in two perpendicular domains was identified for the Co layer using XRD and HRTEM techniques. Co is found to grow in the (11-20) orientation with the c axis in plane, parallel either to Fe[110] or Fe[1-10] The magnetic properties as a function of Co thickness in Fe (10 nm)/Co (t) (t=5-20 nm) bilayers were investigated. The Fe/Co bilayers exhibit in plane magnetization with easy axes parallel to Fe[100] and Fe[010] axes. The magnetic behavior is consistent with the orientation relationship between the Fe and Co layers.

Abstract:

Single crystal 400 nm thick Laves phase [20 Å∈DyFe 2/80 Å∈YFe2]40 superlattice have been grown by MBE with a (110) growth direction. VSM measurements performed at room temperature with an applied field range of ±1.2×10⁵ Oe, directed along the [001] direction, reveal a unique single-phase-liked ferrimagnetic behavior. A dominant exchange spring behavior is revealed by MOKE measurement along the [-110] direction. Furthermore, for striped arrays patterned along the [001] direction with height-to-width ratio of 0.05, a shape anisotropy of the order of 10⁴ erg/cm³ is induced, resulting into a pronounced change of coercivity due to the comparable magnitude with intrinsic anisotropies. The results demonstrate the feasibility of engineering both single-phase-liked and exchange-spring magnet behavior in Laves phase epitaxial hard/soft superlattices by patterning. © Springer-Verlag 2007.