CoFe Free Layer Research Articles

Spin-filter spin-valve films with an ultrathin CoFe free layer

The concept of spin-filter spin-valve (SFSV) films is reviewed. The dependence of the free layer structure on the spin-filter effect was investigated by using model films and two types of free layers were compared, a single CoFe layer and a conventional NiFe/Co free layer. At the same magnetic thickness of the free layer, the SFSV films with a CoFe free layer showed a larger magnetoresistance (MR) ratio than those with a NiFe/Co free layer. This is partly attributed to the thinner CoFe free layer thickness, which is due to the fact that the CoFe free layer has higher Bs than the NiFe/Co free layer. Moreover, SFSV films with a CoFe free layer still showed a larger MR ratio when the free layer thickness was the same. It suggests that other factors contribute to the high MR performance, such as the quality of the interface between a free layer and a high conductance layer. Film performance of MR 9% to 10%, ΔRs 1.5–2.0 Ω, Hcea∼3 Oe, and λs⩽±0.5 ppm was obtained with a single CoFe free layer and synthetic antiferromagnetic pinned structure.

スピンバルブ膜の背後膜／保護膜構成に依存する磁気抵抗効果と層間結合

We investigated the giant magnetoresistance (GMR) effect and interlayer coupling field (Hint) for spin-valve films, which were fabricated as a back layer (Cu and NiCr) and a thin Ta cap layer on a CoFe free layer. As the Cu back layer was thickened, the GMR ratio was enhanced and the Hint oscillated. This behavior may be understood as a result of the spin-dependent potential created by the CoFe/Cu interface. On the other hand, the thin Ta cap layer enhanced the GMR effect.

IrMn based spin-filter spin-valves

As recording densities increase, the sense layer (free layer) thickness in a recording head (whether spin-valve or otherwise) must also decrease so that the sense layer can be effectively saturated by the transitions on the media. However, in a traditional spin-valve structure, reducing the sense layer (free layer) thickness below ∼50 Å results in a rapid reduction in ΔR/R. One of the solutions for this is the spin-filter spin-valve, having a free layer composed of a very thin magnetic layer and an adjacent thin enhancing conduction layer. The advantage of the spin-filter spin-valve is high ΔR/R and easy control of the bias point while keeping the free layer very thin (10–30 Å). The present work reports the results on sputtered IrMn top and bottom spin-filter spin-valves. The data clearly show that ΔR/R has been significantly improved when reducing the free layer CoFe down to 10 Å. ΔR/R>8.0% remains for free layer thickness between 10 and 20 Å using a Cu enhancing layer, while ΔR/R decreased rapidly to 4.0% with no Cu enhancing layer for the same free layer thickness range. An optimized ΔR/R of ∼10% was obtained for an enhancing layer of tCu∼13 Å, as a result of the balance between the increase in electron mean free path difference and current shunting through the very conducting enhancement layer. It was also found that the softness of the CoFe free layer was improved when sandwiched by Cu layers, showing similar soft properties and magnetostriction to conventional free layers. Such a soft, thin CoFe free layer is particularly attractive for high density (30–50 Gb/in2) read sensor applications.

MR Characteristics of Spin-Valve Films Coupled with CoAlO Soft Magnetic Layers

Giant magnetoresistance (GMR) in spin-valve structures is attracting much attention for its potential application in MR sensors and MR heads. We propose a new spin-valve structure, in which the free layer is coupled with soft magnetic CoAlO layers, and investigate the MR characteristics and sensor performance of the spin-valve structure NiO/CoFe/Cu/CoFe/CoAlO. Owing to the soft magnetic properties and high electrical resistivity of a CoAlO layer coupled with the CoFe free layer, the coercivity of the spin valve was dramatically reduced and the large MR ratio remained. An MR ratio of 9.4% and a coercivity of 3.1 Oe were achieved for a spin-valve structure of NiO (500 Å)/CoFe (50 Å)/Cu (11 Å)/CoFe (50 Å)/CoAlO (1000 Å).

GMR in CoFe/IrMn Spin-Valves Prepared by Ion Beam Sputtering Using Xe-H2 Mixture Gas

Co90Fe10/Cu/Co90Fe10/Ir25Mn75 spin-valves with Ta buffer layer were prepared by ion beam sputtering. Improvements in physical properties were obtained by adding H2 to Xe sputtering gas. Specifically, coercivity in the CoFe free layer considerably decreased with increasing H2-flow rate. In addition, exchange coupling between the IrMn and pinned CoFe layers became stronger in the preparation under the higher H2-flow rate. X-ray diffraction, transmission electron microscope, and secondary ion mass spectroscopy observations suggest that micro-crystallization of each layer is responsible for improving the physical properties.