Yuzo Kamiguchi

Spin-valve giant magnetoresistive films with antiferromagnetic Ir-Mn layers

We succeeded in developing CoFe spin valves with an antiferromagnetic Ir-Mn film. Ir-Mn single-layer films and spin valves of Ta(5 nm)/Ir-Mn(8 or 9 nm)/Co90Fe10(x nm)/Cu(3 nm)/Co90Fe10(3 nm)/NiFe(2 nm)/CoZrNb(10 nm)/ (x=2, 2.3, 2.6 nm), prepared by the sputtering method, showed the crystal structure of a fcc (111) preferred orientation. As-deposited CoFe spin valves with Ir-Mn exhibited an interfacial exchange coupling energy of J=0.192 erg/cm2 (Hua∼640 Oe at tCoFe=2 nm), that was the highest ever reported for as-deposited antiferromagnetic films, such as NiO, NiMn, and FeMn. Furthermore, CoFe spin valves with Ir-Mn exhibited a higher blocking temperature of 260 °C, and a higher MR ratio of 6.37% than the spin valves with FeMn film. After annealing, the MR ratio increased to 7.82%. On the other hand, the Hua decreased about 100 Oe after annealing. The Hua-T curve was, however, improved and the Hua at 100 °C increased to 400 Oe. The decrease in Hua was not observed after second annealing and seems to be st...

Output enhancement of spin-valve giant magnetoresistance in current-perpendicular-to-plane geometry

In this work, we present a suitable material for metal-based spin-valve in current-perpendicular-to-plane (CPP) geometry. The AΔR (A is the element size and ΔR is the change in resistance) was investigated for three kinds of free and pinned layers material, that is, Co90Fe10, Fe50Co50, and Fe50Co50 with half-atomic Cu layers. When the free and pinned layers are 5 nm, AΔR is 1.0 mΩ μm2, 1.6 mΩ μm2, and 2.9 mΩ μm2, respectively. Moreover, the dual-type spin valve having Fe50Co50 with half-atomic Cu layers achieved 5.2 mΩ μm2. According to the free and pinned layers thickness dependence of AΔR, the spin-dependent resistance at the interfaces between ferromagnetic layers and spacer Cu is enhanced mainly by changing from Co90Fe10 to Fe50Co50, and the spin-dependent bulk resistance in free and pinned layers is enlarged by inserting half-atomic Cu layers.

Giant magnetoresistance and soft magnetic properties of Co90Fe10/Cu spin‐valve structures

Spin‐valve structures with a magnetic material buffer layer, CoNbZr/NiFe/Co90Fe10/Cu/Co90Fe10/Fe50Mn50, were prepared on a oxidized Si substrate. From x‐ray diffraction analysis, it was shown that the CoNbZr/NiFe buffer layer enhances the fcc (111) orientation of the spin‐valve structure on oxidized Si. After annealing, the giant magnetoresistance (GMR) ratio of Δρ/ρ=8% and the soft magnetic properties of Hc=0.1 Oe and Hk=2.8 Oe were obtained. The sensitivity of GMR, Δ(Δρ/ρ)/ΔH, of 1.4%/Oe is achieved.

All-metallic nonlocal spin valves using polycrystalline Co2(FeMn)Si Heusler alloy with large output

A large output voltage of 0.7 mV at 1 mA charge current is demonstrated for all-metallic nonlocal spin valves using Co2(FeMn)Si Heusler alloy and Cu with a junction area of about 50 nm2. The output is attributed to the junction size reduction as well as to the high spin polarization in the Heusler alloy. An analysis using a one-dimensional model reveals that the spin diffusion length in the Cu layer shows no clear degradation even in the case of a 50 nm2 junction. When the junction is reduced further to 10 nm2, an output voltage of about 10 mV is expected.

Saturation magnetostriction of an ultrathin CoFe free-layer on double-layered underlayers

We investigated the saturation magnetostriction (λs) of an ultrathin CoFe free-layer on double-layered underlayers of Ru/Cu. By increasing the Ru underlayer thickness, λs becomes positively large; on the other hand, λs becomes negatively large by increasing the Cu underlayer thickness. This tendency can be explained by the model where λs is changed by the film strain. The λs sensitivity on the Cu underlayer thickness becomes large with increasing the Co concentration of the CoFe free-layer. This indicates that CoFe λs becomes sensitive to strain with increasing Co concentration. In order to realize small magnetostriction spin-valve films with an ultrathin CoFe free-layer, we have to take care of the lattice strain of the film.

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 anti...

Voltage-control spintronics memory (VoCSM) having potentials of ultra-low energy-consumption and high-density

We propose a new spintronics-based memory employing the voltage-control-magnetic-anisotropy effect as a bit selecting principle and the spin-orbit-torque effect as a writing principle. We have fabricated the prototype structure, and successfully demonstrated the writing scheme specific to this memory architecture.

Dual spin valves with nano-oxide layers

A novel method is proposed for increasing the giant magnetoresistance (GMR) of dual spin valves of the CoFe/Cu/CoFe/Cu/CoFe type by inserting nano-oxide layers (NOLs) into the pinned layers. Using this method, MR ratio of 23.5% was obtained, a value equal to those of specular spin valves with antiferromagnetic oxide, e.g., NiO. This method allows the selection of metallic materials for the antiferromagnetic layer. In addition, we obtained the specularity factor of upper NOLs, 0.8, and that of lower NOLs, 0.7, by calculating Boltzmann equations taking into account the roughness of each interlayer. This model shows that the MR ratio would be 27.5% for dual spin valves with ideal NOLs.

Precise Damage Observation in Ion-Beam Etched MTJ

Patterning damage at the sidewall in a magnetic tunnel junction (MTJ) was observed precisely using a rectangular MTJ where deterioration in crystallinity is easier to identify than in the case of a dot-shaped conventional MTJ. A 200-500 nm-square rectangular MTJ was patterned by a 200 eV ion beam (IB). Cross-sectional transmission electron microscopy was used for damage observation. A bright-field image showed that crystallinity deteriorated to a depth of

Improved read disturb and write error rates in voltage-control spintronics memory (VoCSM) by controlling energy barrier height

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