| Popis: |
The torque curves, T (α), of PtCo/TbFeCo (RE-dominated) bilayers behave unexpectedly when the applied field H is directed close to the perpendicular ( α =0). The Pt/Co and TbFeCo films separately are characterized by positive effective magnetic uniaxial anisotropy. Consequently we expect T (α)/α to be negative near α = 0. However, we find T (α)/α to be large, positive and approximately constant near α = 0. In this angular region the relaxation of the wall associated with the bilayer exchange coupling drives the Pt/Co and TbFeCo layer magnetizations in opposite directions. On the thin wall model basis, the wall energy, σ w , inferred from the ensuing torque slope is about two and a half times the σ w computed from Kerr loop shifts. The bilayer magnetic energy density, E (α), must be even [ E ( α ) = E (− α )] and in the form of an inverted parabola near α = 0. Physically more realistic distributed wall models must conform to the required symmetry as well as to fit experimental data. |
