Shigeki Nakagawa

Effect of multilayer configuration of [Fe/Pt] multilayer to attain (001) oriented FePt ordered alloy thin films

L10-FePt ordered alloy thin films with (001) preferential orientation were fabricated from [Pt(1 nm)/Fe(1 nm)]3/Pt(3 nm)/Fe(3 nm) multilayers to reduce the ordering temperature. Pt(3 nm)/Fe(3 nm) layer beneath the [Pt(1 nm)/Fe(1 nm)]3 multilayer played a role as a seed layer to attain perpendicular magnetic anisotropy. These films, after being annealed at 500 °C under hydrogen atmosphere, exhibited better growth characters of FePt(001) oriented crystallites than those of FePt prepared from [Pt(1 nm)/Fe(1 nm)]6. Additionally, [Pt(1 nm)/Fe(1 nm)]3/Pt(3 nm)/Fe(3 nm) multilayers, after being annealed at 500 °C, showed high value of saturation magnetization around 12 kG.

Comparison of Playback Performance of Facing Targets Sputtered Perpendicular and Longitudinal Tape Media

Playback performances of sputtered perpendicular recording tape media were investigated in comparison with longitudinal media. Perpendicular (Media P, out-of-plane coercivity of 318.3 kA/m) and longitudinal (Media L, inplane coercivity of 279.3 kA/m) recording tape media were deposited by facing targets sputtering from the same target of Co74Pt16Cr10-SiO2 for the recording layer at room temperature. For Media P, a soft magnetic FeCoB(50 nm) layer and a Ru(5 nm) seed layer were formed between the recording layer and an Aramid substrate. On the playback test by a drum tester with a ring writer/GMR reader, the waveform of all-ones signal at 5 kfci indicates that Media P has a dipulse response and the shorter PW50 value than Media L. Measured values of D50 were 233 kfci for Media P and 216 kfci for Media L, respectively. Saturation curves show that Media P has good writability. The signal-to-noise ratio (SNR) value of Media P is higher by 2.4 dB at 337 kfci than Media L. These high-resolution and high SNR properties indicate that sputtered perpendicular tape media are suitable for extremely high-density recording.

Ru/FeCoB double layered film with high in-plane magnetic anisotropy field of 500 Oe

FeCoB layers prepared on Ru underlayer possess a high saturation magnetization Ms and a high in-plane magnetic anisotropy filed Hk. Effects of preparation conditions were investigated. Low Ar gas pressure condition and thicker film thickness were effective to attain distortion of FeCo crystallite. As the crystallinity of Ru underlayer became higher, higher Hk was induced. The accumulation of anisotropic stress in the film caused by the oblique incidences of depositing atoms with high energy seems to be one of the important effects to attain high anisotropy field. It was succeeded to prepare the Ru/FeCoB film with high Hk of 500 Oe.

FePt films 2 nanometers thick with (001) preferential orientation on a MgO underlayer

A MgO underlayer with (100) preferential orientation formed on a thin Fe seed layer is used to attain L10 ordered phase 2 nm-thick FePt films with (001) orientation. The Fe[1 nm]/Pt[1 nm] bilayer can be grown epitaxially on the MgO underlayer with (100) aligned texture and the bilayer transformed into (001)-textured L10-FePt films after annealing at 600 °C. FePt films 2 nm thick with (001) preferential orientations can be prepared on a thick MgO underlayer with (100) orientation. Since the thinness of Fe and Pt layers enhances an inter-diffusion process between the layers, the crystallization and ordering temperature of FePt decreases from 550 °C to 500 °C.

Direct observation of an anisotropic in-plane residual stress induced by B addition as an origin of high magnetic anisotropy field of Ru/FeCoB film

Although boron-free FeCo films prepared on a Ru underlayer exhibits isotropic in-plane magnetic property, boron added FeCoB films prepared on Ru underlayer revealed large in-plane magnetic anisotropy with a high anisotropy field of 500 Oe. The effect of boron addition on the in-plane anisotropic residual stress in FeCoB film was investigated using sin2 ψ method of x-ray diffraction analysis. Large isotropic compressive stress was observed in Ru/FeCo film. In contrast, anisotropic in-plane residual stress was observed in Ru/FeCoB film. The compressive stress along the easy axis of Ru/FeCoB film is released more than that along the hard axis. Such anisotropic residual stress is regarded as an origin of the in-plane magnetic anisotropy through inverse magnetostriction effect. Owing to the configuration of the facing targets sputtering system, boron atoms are sputtered and deposited anisotropically, and so they penetrate FeCo crystals and release the compressive stress along the incidence direction.

Highly (100) oriented MgO growth on thin Mg layer in MTJ structure

In order to apply Stress Assisted Magnetization Reversal (SAMR) method to perpendicular magnetoresistive random access memory (p-MRAM) with magnetic tunnel junction (MTJ) using MgO (001) oriented barrier layer, multilayer of Ta/ Terfenol-D/ Mg/ MgO and Ta/ Terfenol-D/ MgO were prepared. While the MgO layer, deposited directly on the Terfenol-D layer, did not show (100) orientatin, very thin metallic Mg layer, deposited prior to the MgO deposition, was effective to attain MgO (100) orientation. The crystalline orientation was very weak without Mg, however, the multilayer with Mg showed very strong MgO(100) peak and the MgO orientation was shifted depending on the Mg thickness.

Evaluation of Magnetization Interaction at the Interface between FeCo and TbFeCo for p-MTJ

Magnetic interaction at the interface between FeCo and TbFeCo were investigated to improve perpendicular magnetic tunnel junction. Magnetic properties of TbFeCo/thin and thick FeCo were observed by anomalous Hall effect (AHE). A perpendicular component of magnetization of thin FeCo layer adjacent to TbFeCo layer was larger than that of thick FeCo one. Kerr hysteresis observation clarified the magnetization behavior of the region of the TbFeCo layer adjacent to FeCo layer using the characteristic of a penetration depth of the probe light. The TbFeCo layer attached with thinner FeCo layer was saturated at lower applied field than that with thicker one. This suggested that the magnetization of FeCo layer affected the TbFeCo magnetization and the thicker FeCo layer tilts the TbFeCo magnetization more greatly than thinner one.

Enhancement of bcc-FeCo(100) Crystalline Orientation by Introducing Oxygen

The introduction of oxygen at the surface of a-TbFeCo layer is effective to attain (100) orientation of bcc-FeCo layers deposited on it. The oxygen introducing time required to exhibit FeCo(100) orientation decreased as increasing oxygen flow rate. The product of oxygen flow rate and the introducing time to attain (100) orientation of FeCo was almost constant regardless of the flow rate. This may indicate that the total amount of oxygen needed to attain (100) orientation of FeCo was almost constant. Depth profiles of constituents and chemical-bonding states were observed in order to clarify the mechanism of (100) crystalline orientation of FeCo deposited on the a -TbFeCo layer with oxidized surface. It was found that oxygen atoms existed at the interface between TbFeCo and FeCo layers in the specimen that exhibited (100) orientation of FeCo. It was also confirmed that the Tb was selectively oxidized to form Tb2O3 at the surface of the a -TbFeCo layer. This may indicate that the interaction between FeCo and this oxide leads to (100) orientation of FeCo.