Yoichi Ishida

Magnetic domain observation in writer pole tip for perpendicular recording head by electron holography

Electron holographic observations were performed in order to clarify the magnetic domain structures in nanosized pole tips for perpendicular recording heads made from Ni–Fe and Co–Ni–Fe. While an external magnetic field was applied, the magnetic fields leaking from the pole tips as well as the detailed magnetic flux distribution inside them were visualized for the first time. In addition, we report the direct observation result that implies the pole erasure characteristic of the Co–Ni–Fe pole tip. The observations have revealed that electron holography provides useful information for understanding the magnetic characteristics of nanosized pole tips for perpendicular recording heads.

Nanoscale Magnetic Characterization of Tunneling Magnetoresistance Spin Valve Head by Electron Holography

Nanostructured magnetic materials play an important role in increasing miniaturized devices. For the studies of their magnetic properties and behaviors, nanoscale imaging of magnetic field is indispensible. Here, using electron holography, the magnetization distribution of a TMR spin valve head of commercial design is investigated without and with a magnetic field applied. Characterized is the magnetic flux distribution in complex hetero-nanostructures by averaging the phase images and separating their component magnetic vectors and electric potentials. The magnetic flux densities of the NiFe (shield and 5 nm-free layers) and the CoPt (20 nm-bias layer) are estimated to be 1.0 T and 0.9 T, respectively. The changes in the magnetization distribution of the shield, bias, and free layers are visualized in situ for an applied field of 14 kOe. This study demonstrates the promise of electron holography for characterizing the magnetic properties of hetero-interfaces, nanostructures, and catalysts.

Quantitative evaluation of magnetic flux density in a magnetic recording head and pseudo soft underlayer by electron holography

The magnetic interaction between the pole tip of a single-pole head and a pseudo soft underlayer in perpendicular magnetic recording was observed by electron holography. The magnetic flux density inside the soft underlayer was quantitatively evaluated. The distribution of magnetic flux density was calculated using the finite element method, and the influences of the modulation of the reference wave and stray fields were investigated by comparison with experimental results. The flux density observed was found to be underestimated due to the modulation of the phase shift in reference wave. The magnetic flux measured experimentally was larger than that inside the specimen because of the relatively large stray fields above and below the specimen in the direction of the electron beam.

Elemental Distribution in Multilayer Systems by Laser-Assisted Atom Probe Tomography with Various Analysis Directions.

Elemental distributions in a magnetic multilayer system with the structure Si substrate/Ta/NiFe/Ru/CoFeB/Ru/NiFe were studied using atom probe tomography (APT) along different analysis directions. The distributions of Ru and B atoms, which require a high evaporation field, were strongly influenced by the APT analysis direction. In particular, B in the CoFeB layer appeared near the interface with the lower Ru layer when the analysis was anti-parallel to the film growth direction, while B atoms were observed at the other side of the CoFeB layer when the analysis was parallel to the film growth direction. Moreover, when the analysis was perpendicular to the film growth direction, a homogenous distribution of B atoms was found within the CoFeB layer. Owing to this B behavior, the underlying Ru layer was affected in both of these analysis directions. In APT measurements of such a multilayer system composed of a stack of different evaporation field materials, evaluation of the elemental distribution around interfaces should be performed from more than one analysis direction.

Observing the Magnetization Distribution in the Pseudo Soft Underlayer of Perpendicular Magnetic Recording Media by Electron Holography

We visualized the magnetic flux density of the cross track direction in the pseudo soft underlayer (SUL) of perpendicular magnetic recording media. We deposited a pseudo-SUL on the fabricated slider of a perpendicular magnetic recording head, and used electron holography to visualize and quantify the magnetic flux magnitude and distribution in the pseudo-SUL. We observed the pseudo-SUL magnetized by the write field from the writer pole tip. The magnetic flux magnitude and full width at half maximum increased with an increasing write field. We observed a correspondence between an actual recording situation and the electron holography observation.

Observation of Magnetization Distribution in Soft Underlayer of Perpendicular Magnetic Recording Media by Electron Holography

The magnetic properties of the soft underlayer (SUL) of perpendicular recording media affect the recording performance significantly. We visualized and quantified the distribution and magnitude of magnetic flux in the recording layer and SULs of perpendicular recording media by electron holography. Pseudo-SULs with different permeability were deposited on the slider of perpendicular recording heads. The SUL with higher permeability produced higher write magnetic flux (By) as compared to the SUL with lower permeability, which results higher overwrite performance. Further, the magnitude profile of Bx in the SUL thickness direction was different for the two SULs; the magnitude of magnetic flux in SUL is related to the occurrence of adjacent track erasure.