Kazuhiro Saito

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...

Influence of crystal structure and oxygen content on exchange-coupling properties of IrMn/CoFe spin-valve films

Investigations were made into the relationship between the exchange-coupling properties and the IrMn crystal grain size for CoFe/IrMn spin valves. The IrMn crystal grain size increased with increasing thickness and decreasing oxygen content of the IrMn layer. The increase in the IrMn grain size resulted in a higher blocking temperature (TB) but a lower unidirectional anisotropy field (HUA). This opposite dependence of TB and HUA on the IrMn grain size is different from those of other antiferromagnetic films such as FeMn, NiMn, and CrMnPt. An HUA of 400 Oe at room temperature and a TB of 300 °C are obtained for CoFe (2 nm)/IrMn (10 nm) spin valves by controlling the oxygen content of the IrMn layer.

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.

Fretting Fatigue in Slot Dovetail of Turbo-generator Rotor Shaft

This paper describes the fretting fatigue of slot-dovetails in turbo-generator rotor including typical examples and repairs of fretting fatigue cracks, results of fretting fatigue tests, factors affecting fretting fatigue strength, fretting fatigue preventive technologies, and UT inspection methods.