Interlayer exchange coupling in spin valves with specularly reflective oxide layers

Abstract

We found that capping a spin valve with thin oxide can make the interlayer coupling oscillatory as a function of thickness of the Cu spacer. The coupling was antiferromagnetic and it allowed us to reduce the thickness of the Cu spacer down to 20 Å without sacrificing the good properties of the spin valve. In addition, the oxide layer enhanced specular reflection of conduction electrons at the interface. As a result, we could greatly increase the giant magnetoresistance (GMR) value of the spin valve. The fact that less current shunted through the thinned Cu spacer and the enhancement of specular reflection contributed to the large GMR value. We also report the observation of the oscillation of interlayer coupling as a function of thickness of the magnetic layer in a spin valve.

Electrical and magnetic properties of nano-oxide added spin valves

“…That means it is still ferromagnetic coupling between the free layer and the pinned layer. The fact that the interlayer coupling oscillates from positive to negative has already been reported by Hong et al [10,14] and Lin et al [15]. We believe that this is very much dependent on the smoothness of the interface between the spacer and the pinned and free CoFe layers.…”

“…Since the surface roughness at the interface between the magnetic layer and the spacer can be also improved after incorporating NOL layer inside the SV, the quantum size effect can be amplified due to the electron confinement inside the spacer. For example, the oscillation of the interlayer coupling field between the free and pinned layers with respect to the thickness of the spacer, even with respect to the thickness of the free layer can be easily observed in the nano-oxide added SVs [9,10]. Here, we will mainly focus on our recent work related to the performance enhancement after incorporating the NOL in the SVs.…”

Exchange coupling between ferromagnetic and laminated antiferromagnetic layers and its application

“…Another way to reduce the ferromagnetic coupling field is to increase the Ruderman-Kittel-Kasuya-Yosida type antiferromagnetic coupling, e.g., by inserting a high conductive capping layer above the free layer and by improving the surface roughness. 28,29 This capping layer can also enhance the MR ratio because of the spin filter effect. We have fabricated a bottom type uniaxial spin valve with the structure of Ta5/NiFe2/(IrMn2/CoFe2) 3 / IrMn2/NiFe4/CoFe0.5/Cu2.2/NOL/CoFe2.5/Cu1/Al 2 O 3 /Ta1.…”