Koji Shimazawa

CPP-GMR Film With ZnO-Based Novel Spacer for Future High-Density Magnetic Recording

A new type of CPP-GMR film, which has ZnO-based novel spacer, was studied. A high MR ratio of 21.4% at RA of about 0.2 ¿¿m2 at room temperature was obtained by optimization of the fabrication condition of ZnO layer. Based on HRTEM observation, the ZnO spacer is crystalline which have c-axis orientation with wurtzite structure, and there are no metallic portions. The measured noise is in good agreement with Johnson noise fitted at T = 400(K). This result suggests that the contact at our ZnO-based spacer interface with magnetic electrode is ohmic. First principle calculations that used a simple model supported the existence of large spin dependent scattering at the interface of ZnO layer. These results indicate that higher signal to noise ratio can be achieved in this type of CPP GMR head even with lower MR ratio than MTJ head and it is very attractive candidate of future magnetic read sensor in HDDs.

Canting of exchange coupling direction in spin valve with various pinned layers

One of the problems in spin valve (SV) is the thermal stability of exchange coupling between the pinned magnetic layer and the antiferromagnetic (AFM) layer. During operating in actual hard disk drives, the pinned direction tends to cant toward the longitudinal hard magnet direction and as a result, the output voltage drops. In this study we examine the amount of the cant by the heat and field in SV which used different pinned layer material. The sample we used is Ta(5)/NiFe(9)/Co(1)/Cu(2.7)/pinned layer/AFM/Ta(5) unit nanometers. The pinned layer is three kinds—Co(2), Co(1)/NiFe(1.7), NiFe(3.5), and AFM is two kinds of Ru3Rh15Mn(12 nm), Ru3Rh15Mn(8 nm). The pinned-Co–SV has a larger increase of canting degree than the pinned-Co/NiFe–SV and the pinned-NiFe–SV. The longer the SV is exposed to heat and magnetic field, the more the cant increases. It is likely due to the change of the local pinned direction which in turn may be due to the aftereffect in the minute AFM grains during the heating process.