Chemical properties and GMR improvement of specular spin valves with nano-oxide layers, formed in ambient mixed gases

Abstract

Specular spin valves (SVs) containing nano-oxide layers (NOLs) structured as substrate/seed/AF/P1/NOL/P2/Cu/F/NOL, have been fabricated. The NOLs were formed by natural oxidation in different ambient atmospheres of pure oxygen, oxygen/nitrogen and oxygen/argon gas mixtures. The fabrication conditions were optimized to enhance the magnetoresistance (MR) ratio, to suppress the interlayer coupling fields (Hf) between the free and pinned layers, to suppress the high interface density of the NOL, to ease the control of the NOL thickness and to form a smooth NOL/P2 interface for promoting specular electron scattering. The characteristics of our specular SVs are the MR ratio of 14.1%, the exchange bias field of 44–45 mT, and Hf weaker than 1.0 mT. The optimal conditions for oxidation time, total oxidation pressure and the annealing temperature were found to be 300 s, 0.14 Pa (oxygen/argon = 80/20) and 250°C, respectively. Also, the origin of thermal stability of MMn-based (M = Fe, Pt, Ir, etc) specular SVs has been explained in detail by chemical properties of NOL using secondary-ion mass spectroscopy and x-ray photoelectron spectroscopy depth profile analyses. Thermal stability turns out to be caused by a decrease in MR ratios at high temperatures (>250°C), which is a serious problem for device applications using the SV structure as a high density read head device.

Micro-structural change and high temperature properties of constituent elements (Fe, Co, Mn, Cu) in spin valves containing oxide layers

“…the serious thermal stability problem at high temperatures (>250 ˚C), which has to be solved in this article. Nevertheless, the MR ratio for the SV with an OXL 1 is better than that of the SV without an OXL 1 [9,10].…”

“…The decrease in MR ratio at high temperatures is presumably due to chemical elements present in the SVs [9]. However, it is just one of the many possible reasons for the MR ratio behaviour at high temperatures (>250 ˚C).…”

“…Strong exchange biasing with higher blocking temperature was found in specular SVs utilizing metallic Mn-based antiferromagnetic (AF) layers. These SVs showed serious thermal degradation in the multilayer structures, which originated from Mn diffusion at temperatures above 250 ˚C [4,6,9]. More specifically, in the IrMn-based SVs, the main cause of thermal degradation of MR at 250 ˚C was the interdiffusion of Mn atoms along the grain boundary.…”

“…Here, XRD and XTEM are useful in analysing the change in the micro-structure of specular SVs at high temperatures compared with as-deposited samples. The authors of [9] analysed the effect of the OXL as a thermal stabilizer of FeMn-based SVs through SIMS and XPS analysis. We would like to extend the previously mentioned analyses to IrMn-based SVs with OXLs.…”

Study of the areal density in the read heads with spin valves with nano-oxide-layer insertion

“…The spin-polarized electrons scatter at the NOL surfaces, placed above the free layer and inside the pinned magnetic layer. The mean free path of majority spinpolarized electrons is consistently extended due to specular reflection at metal and insulator interfaces, on NOLs [7], [8], and [9]. In the same time, an improvement of the resistivity of the current-confined-path occurs [9], [10].…”