Effect of finite magnetic film thickness on Néel coupling in spin valves

Abstract

Spin valves are widely studied due to their application as magnetoresistive material in magnetic recording heads and other magnetic field sensors. An important film property is the interlayer coupling field (called offset field Ho or ferromagnetic coupling field Hf). It has been shown that the Néel model for orange-peel coupling can be applied successfully to describe this interlayer coupling. The waviness associated with the developing granular structure is thereby taken as the relevant waviness. The original Néel model describes the ferromagnetic magnetostatic interaction between two ferromagnetic layers, of infinite thickness, separated by a nonmagnetic spacer with a correlated interface waviness. In this article, this physical picture is refined to account for the effect of the finite thickness of the magnetic films in a spin valve. Magnetic poles created at the outer surfaces of the magnetic layers result in an antiferromagnetic interaction with the poles at the inner surface of the opposite layer. A simple model is presented for the different interactions in a top spin valve (columnar structure with cumulative waviness on a flat substrate) and for a bottom spin valve (columnar structure with conformal waviness on a way substrate). Comparison to experimental data, shows that the free and pinned layer thickness dependence can be understood from this refined picture.

Spin-polarized tunneling with Au impurity layers

“…Hence, if this topography were covered with a Co layer, we would expect that Co would be in direct contact with the barrier only in this area fraction, and we ought to observe no more 11 % of the TMR or TSP of a junction without Au. Nevertheless, we can see from by to explain the reduction in TMR and TSP using this island-growth hypothesis, the huge additional roughness for the thicker Au layers, a few nm in amplitude, would lead to a substantial increase in the orange-peel coupling field for the free layer, 18 , whereas we see no observable change in Fig. 1.…”

Interlayer exchange coupling and current induced magnetization switching in magnetic tunnel junctions with MgO wedge barrier

“…We estimated the influence of the interface roughness using the model in Ref. 12. The roughness amplitude of the bottom CoFeB electrode after annealing was measured with AFM and do not exceed 0.25 nm.…”

Influence of annealing on the bias voltage dependence of tunneling magnetoresistance in MgO double-barrier magnetic tunnel junctions with CoFeB electrodes

“…The hysteresis loop shift, which is detrimental to practical applications, is predominantly due to Néel orange peel coupling between the CoFeB electrodes. 20,21 This magnetostatic effect is associated with conformal roughness in the ferromagnetic electrodes and is generally found to be strongest for rough magnetic tunnel barrier interfaces. 22 The decrease of the coupling field in our DMTJ structures with increasing annealing temperature therefore suggests that annealing at elevated temperatures not only crystallizes the CoFeB electrodes but also smoothens the CoFeB / MgO interfaces.…”