Giant magnetoresistance effect and magnetic anisotropy in Co₉Fe{plus 45 degree rule}Cu{plus 45 degree rule}Co₉Fe trilayers on MgO(110) substrates

Magnetoresistive properties were investigated for Co₉Fe/Cu/Co₉Fe trilayers with a 21 Å Cu layer thickness and different Co₉Fe layer thickness which were prepared on MgO(110) substrates using ion beam sputter deposition. The influence of a 50 Å Fe buffer was also investigated. The films grew with epitaxial relations of MgO(110) [110] {norm of matrix} Co₉Fe(110)[110] and MgO(110)[110] {norm of matrix} bccFe(211)[111] {norm of matrix} Co₉Fe(110)[110] without and with a Fe buffer layer, respectively. In-plane uniaxial magnetic anisotropy (K_u) in addition to cubic anisotropy (K₁) was induced, of which the easy axis was along MgO[001] and MgO[110] without and with a 50 Å Fe buffer layer, respectively. The magnetoresistance (MR) ratio decreased monotonically with increasing Co₉Fe layer thickness in the investigated thickness range, 25-70 Å. The maximum value obtained was 11.5% at room temperature. With increasing field the MR saturated with a gentle slope after a steep drop at a small field without a Fe buffer layer, but rapidly saturated at a small field with a Fe buffer. These behaviours can be understood by magnetization processes taking into account both K_u and K₁.