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 layer highly stable against various magnetic fields during Joule heating of spin valve sensor stripes. Further, the PtMn synthetic-ferri-pinned-type dual spin valve films showed a large unidirectional exchange field of 2000 Oe and a giant magnetoresistance ratio of 11.0%.

Absstraci-Wle report that the spin-valve films using the antiferromagnetic cr-Fe203 layers show good nilR response due to the coercivity difference in an as-deposited state and due to the unidirectional biasing field after magnetic annealing. Both the high coercivity and the biasing field of the pinned layer is caused by an exchange coupling. The obtained MR ratio of 6.1% is higher than those of the other spin-valves using Fe-Mn or Ni-Mn owing to the high resistivity of the a-FezOs. Further higher MR ratio of 10% is achieved by imposing lnm-thick Co layers at the Ni-Fe/Cu interfaces. It was found that the free layer coercivity of these spin-valves is smaller than that in the Co-Pt/Cu/Ni-Fe sandwiches having the similar high coercivity of the pinned layer. High thermal stability and corrosion resistance were also confirmed in the a-FezOs spin-valves.

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 Å 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 Å)/NiFe SF free layers slightly increased after annealing at 250 °C for 4 h, and then the Hsf of the Co (3 Å)/NiFe(30 Å)/Ru(8 Å)/NiFe(20 Å) 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 Å)/NiFe(40 Å)/X/NiFe(25 Å), 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, were obtained both at Ir 3.8 Å and Rh 6.1 Å, which corresponded to the oscillatory first peak in the Co/NiFe/Ir/NiFe and Co/NiFe/Rh/NiFe sandwiches.

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 almost the same robustness as today’s non-NOL heads.

Herein, we investigated exchange coupling in PtCr/CoFe, PtCr/PtMn/CoFe, and PtMn/CoFe film structures, demonstrating that Pt51Cr49(30 nm)/Co90Fe10(10 nm), Pt51Cr49(27.2 nm)/Pt50Mn50/(2.8 nm)/Co90Fe10(10 nm), and Pt50Mn50(30 nm)/Co90Fe10(10 nm) structures annealed at 350 °C for 20 h in a 10-kOe field featured unidirectional anisotropy constants (Jk) of 0.09, 0.56, and 0.32 erg/cm2, respectively. In the case of the Ni50Fe12Cr38(4 nm)/Pt51Cr49(30 − X nm)/Pt50Mn50(X nm)/Co90Fe10(10 nm)/Ta(10 nm) [X = 0–30 nm] film system, Jk linearly and steeply increased with increasing X to reach a maximum of 0.56 erg/cm2 at X = 2.8 nm and then decreased in a complicated nonlinear fashion as X further increased to 30 nm. On the other hand, the blocking temperature of Pt51Cr49(28 nm)/Pt50Mn50/(2 nm)/Co90Fe10(10 nm) was determined as 500 °C and nearly equaled that of Pt51Cr49(30 nm)/Co90Fe10(10 nm), significantly exceeding the value of 400 °C determined for Pt50Mn50(30 nm)/Co90Fe10(10 nm). These results imply that the exchange bias field of the Ni50Fe12Cr38(4 nm)/Pt51Cr49(30 − X nm)/Pt50Mn50/(X nm)/Co90Fe10(10 nm)/Ta(10 nm) system is ultimately determined by the chemical composition and the modification of the antiferromagnetic spin structure at the ferromagnet–antiferromagnet interface, while the blocking temperature is almost entirely determined by the volume fraction of the PtCr component.