Fumihito Koike

PTMN SINGLE AND DUAL SPIN VALVES WITH SYNTHETIC FERRIMAGNET PINNED LAYERS

Spin valve films with the PtMn/Co/Ru/Co synthetic ferrimagnet pinned layer, in which the magnetization of the two Co layers is strongly coupled in an antiparallel orientation and the magnetization direction of one of the Co layers is pinned by unidirectional exchange coupling with PtMn, were investigated. PtMn synthetic ferrimagnet pinned layers were demonstrated to exhibit strong unidirectional exchange field Hex exceeding 2500 Oe at an optimum PtMn/Co/Ru/Co thickness combination for either PtMn on top or at the bottom. The Hex of PtMn/Co/Ru/Co rapidly increased at the PtMn layer thickness around 10–12 nm and was nearly constant from 12 to 30 nm. It was also found that the saturation field of the Co(3 nm)/Ru(0.8 nm)/Co(2 nm) sandwich, which represents the antiparallel interlayer coupling strength through Ru, remained 2200 Oe even at 300 °C. Thus the combination of the high blocking temperature of 380 °C for PtMn and the large antiparallel exchange interaction of Co/Ru/Co up to 300 °C makes the pinned lay...

PtMn spin valve with synthetic ferrimagnet free and pinned layers

Spin valve films with a laminated antiparallel Co/NiFe/Ru/NiFe synthetic ferrimagnet (SF) free layer combined with PtMn/Co/Ru/Co SF pinned layers were demonstrated to maintain large magnetoresistance ratio of ∼8.0% even below ∼10 A of effective thickness of the Co/NiFe/Ru/NiFe SF free layers, defined as the thickness difference of the two ferromagnetic layers antiferromagnetically coupled through Ru. Spin flopping field Hsf and saturation field Hs of the Co/NiFe/Ru (8 A)/NiFe SF free layers slightly increased after annealing at 250 °C for 4 h, and then the Hsf of the Co (3 A)/NiFe(30 A)/Ru(8 A)/NiFe(20 A) SF free layer after annealing remained 600 Oe, even at 200 °C. Further, antiferromagnetic coupling interlayer materials and their thickness dependence of Hsf and Hs were investigated in the Co(3 A)/NiFe(40 A)/X/NiFe(25 A), X=Ru, Cr, Ir, and Rh, sandwich stacks. The oscillatory antiferromagnetic exchange coupling was clearly observed, and the large Hsf and Hs exceeding 2000 Oe and 7 kOe, respectively, wer...

Nano-oxide-layer specular spin valve heads with synthetic pinned layer: Head performance and reliability

To implement the specular nano-oxide-layer (NOL) spin valve (SV) heads for use in practical applications, it is key to simultaneously achieve a good specular effect of the NOL inserted in the synthetic ferrimagnet pinned layer (i.e., high magnetoresistance MR performance) and a strong pinning field through the NOL. By using CoFe+X as a substance to be subjected to oxidation, we obtained the NOL specular SV films simultaneously achieving a high MR ratio of 17%–18% and a high pinning field of 1100–1500 Oe. Narrow track (0.12 μm) heads were fabricated and they showed a high sensitivity of 10 mV/μm. Several reliability tests were done both at the sheet film level and the actual head level. The oxygen inside NOL was found to be stable up to 350 °C, and pinned layer magnetization canting after orthogonal field annealing was found to be almost the same as today’s non-NOL SV films. An electrostatic discharge test and accelerated lifetime test were also performed and NOL specular heads were demonstrated to have al...

Soft Magnetic Properties and Corrosion Resistance of Nanocrystalline Fe-Al-Ta-C Films

The effect of addition of Al to sputtered nanocrystalline Fe-Ta-C films on the film structure, soft magnetic properties and corrosion resistance were investigated. Films were crystallized from an amorphous state to a nanocrystalline state in which ultra-fine TaC particles were dispersed. Most of the Al in the films was dissolved in ¿-Fe after crystallization. When the Al concentration was increased, the high-frequency permeability improved owing to the increase in electrical resistivity. The thermal stability of the soft magnetic properties was also improved over that of Fe-Ta-C films, and the film corrosion resistance improved sufficiently, probably because of the Al dissolved in ¿-Fe. An Fe66.6Al10.6Ta10.5C12.3 nanocrystalline film after annealing at 823K exhibited a high saturation point of 1.25 T, a high permeability of 3200 at 1 MHz, a high electrical resistivity of 1.32 ¿¿-m, and excellent corrosion resistance and noble pitting potential.