Eiji Makino

Thermal degradation of spin valve multilayers caused by Mn migration

We have investigated the thermal degradation of spin valve multilayers caused by annealing at 250–300u200a°C, and determined that it significantly depended on selection of antiferromagnetic layers. Spin valves with a CuAu-I type ordered PtMn antiferromagnetic layer exhibited better thermal stability than those with a disordered Rh17–Mn83 or an Ir20–Mn80 layer. Comparing the magnetoresistance ratio dR/R of those spin valves after annealing at 280u200a°C for 5 h, that of PtMn spin valves was more than 60% higher than the others, even though the same stack of layers was used, except the antiferromagnetic layer. Such an excellent thermal stability of PtMn spin valves was attributed to less Mn migration over the existing layers after annealing. This indicated that Mn impurities in ferromagnetic layers such as Co90–Fe10 or Ni81–Fe19 deleteriously affected the spin-dependent scattering of conduction electrons.

Film structure dependence of the magnetoresistive properties in current perpendicular to plane spin valves and its relation with current in plane magnetoresistive properties

The magnetoresistive properties of current perpendicular to plane (CPP) spin valves (SV) were investigated for various film structures. CPP-SV elements were fabricated by photolithography and ion-beam etching. As an unexpected result, resistivity change-area product (dRA) improved up to 60% with increasing the PtMn layer thickness from 20 to 40 nm in the bottom synthetic spin valve structure, even though the PtMn layer cannot contribute to the spin dependent scattering. For the free layers, dRA improved with increasing the free layer thickness, although a saturation magnetization (Ms) and free layer thickness were restricted for the head application. Aiming at the enhancement of the spin dependent scattering on the interface, CoFe/NiFe multilayer is adopted as the free layer. Although NiFe improves dR, dRA was not improved with increasing the number of interfaces between CoFe and NiFe when total thickness is kept constant. It also becomes clear that NiFe is the appropriate material in terms of the bulk sc...

Reduction of interlayer coupling in bottom synthetic spin valves through a gas exposure process

The magnetoresistance (MR) ratio of spin valves can be improved by reducing the thickness of the nonmagnetic interlayer, such as Cu, due to not only reducing the shunt, but also increasing the probability of electrons scattered through the Cu. However, at small thickness, interlayer coupling between the free and pinned layer is increased, which makes it difficult to control the bias point. The minimum thickness of the interlayer Cu was thereby limited to around 3 nm. On the other hand, it is reported that the ferromagnetic interlayer coupling that arises from the film roughness can be reduced by controlling the residual gas inside the deposition chamber. The same effect can also be achieved by exposing the wafer into an oxygen gas atmosphere right after the deposition of the high conductive Cu interlayer. By this method the thickness of the interlayer Cu was reduced successfully from 3.0 to 2.0 nm without increasing the interlayer coupling. As a result, the MR ratio and dRsq was improved by 12% and 48%, a...