Tailoring of magnetic properties of giant magnetoresistance spin valves via insertion of ultrathin non-magnetic spacers between pinned and pinning layers

Si Nyeon Kim,Jun Woo Choi,Sang Ho Lim

doi:10.1038/s41598-018-38269-w

Si Nyeon Kim, Jun Woo Choi + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-38269-w

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Abstract

The low-field sensitivity of a giant magnetoresistance (GMR) spin valve can be enhanced by tailoring the bias field of the free layer because this sensitivity and bias field are known to show a strong correlation. In this study, the free-layer bias field is reduced considerably to almost zero via the insertion of an ultrathin nonmagnetic spacer between the pinned layer and the pinning layer. The spacer promotes an increase in the density of Néel walls in the pinned layer. This increase, in turn, induces domain-wall-induced magnetostatic interactions of the free poles formed on the Néel walls inside the free and pinned layers. The magnetostatic interactions result in the formation of flux closures that act as pinning sites during the magnetization reversal process and stabilize the antiparallel magnetization state between the free layer and the pinned layer by suppressing the switching of the free layer from the antiparallel state to the parallel state. Furthermore, the spacer offers an additional advantage of increasing the GMR ratio by inducing a specular scattering effect at its top and bottom interfaces. A highly improved low-field sensitivity of 12.01 mV/mA·Oe is achieved in the sample with a Cu/Pt dual spacer.

Highlights

Giant magnetoresistance (GMR) spin valves (SVs) are extensively used in magnetic sensors such as biosensors[1], hard-disk read heads[2,3], and detectors of oscillations in microelectromechanical systems[4] because of their beneficial properties of a high signal-to-noise ratio and thermal stability
The loops of the free layer are shifted in the negative direction, and it is well known that the interlayer exchange coupling between the free layer and the pinned layer is P coupling owing to the dominant effect of Néel orange-peel coupling in giant magnetoresistance (GMR) SVs12,13
The obtained quantitative values (1.22 and 0.487 nm) are possibly overestimated, but the relative difference between the values from Cu and Pt can qualitatively describe the interfacial quality. These results indicate that the interfacial quality is better for the Pt spacer than for the Cu spacer, explaining the high GMR values for the samples with the Pt spacer

Summary

Introduction

Giant magnetoresistance (GMR) spin valves (SVs) are extensively used in magnetic sensors such as biosensors[1], hard-disk read heads[2,3], and detectors of oscillations in microelectromechanical systems[4] because of their beneficial properties of a high signal-to-noise ratio and thermal stability. These SVs are multilayered structures comprised of two ferromagnetic (FM) layers separated by a non-magnetic (NM) spacer.

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