Yuichi Ohsawa

Soft magnetic properties of Co-Fe-Al-N films

This article reports on the relations between the magnetic properties and crystal structure of Co‐Fe‐Al‐N films prepared by rf magnetron sputtering in a mixed Ar and N2 gas atmosphere. Slightly substrate‐biased 4 at. % Al films showed a low coercivity of less than 80 A/m, a low magnetostriction of less than 1×10 −6, and a high saturation magnetic flux density of 1.7 T. These features were maintained after annealing at up to more than 500 °C. The low Hc was related to the crystal structure of a face‐centered‐cubic phase with an about 10‐nm grain size. No detectable AlN was observed by an x‐ray diffractometry even after annealing. However, the lattice constant after annealing was nearly equal to that of a Co‐Fe alloy and the Al content increased with the increase in sputtering N2‐gas content, suggesting the binding of Al and N atoms.

Magnetoresistance and Current-driven Resistance Change Measurements in NiFe films with a Nanoconstriction

Ballistic magnetoresistance (MR) measurements with large magnetic field were performed using sputtered NiFe film as the MR layer. The origin of MR is deduced from current-driven resistance change measurements. The nanoscale point contact (PC) was formed at the junction of the pinned area, which is covered with a CoPt hard magnetic film, and the free area. Results show that the resistance increased (decreased) with positive (negative) sense current. This asymmetry might be due to the domain wall (DW) state, which was pinned at or depinned from the PC by a spin transfer effect.

Voltage-control spintronics memory (VoCSM) having potentials of ultra-low energy-consumption and high-density

We propose a new spintronics-based memory employing the voltage-control-magnetic-anisotropy effect as a bit selecting principle and the spin-orbit-torque effect as a writing principle. We have fabricated the prototype structure, and successfully demonstrated the writing scheme specific to this memory architecture.

Writing Performance of a Planar Single-Pole Head With a Main Pole Fabricated by Ion-Beam Milling

Writing performance of a shielded planar head with an ion-beam-fabricated main pole was estimated. Magnetic field simulation based on an ion-beam-etched Fe-Co film profile revealed that the two- or three-step-tapered main pole structure, which is one of characteristic configurations of the ion-beam process, has high writing and fabricating potential compared with that of the silicon template process. Especially, the three-step-tapered main pole shows not only high field strength (15 kOe) and field gradient (500 Oe/nm) but also well- suppressed fringing field. The shielded planar head with the ion-beam-milling-processed main pole is one of the leading candidates for application as a writer in the era of Tbpsi recording.

In situ magnetoresistance measurements of ion-beam-etched Fe-Co thin films

The effect of ion-beam (IB) irradiation on magnetic softness in Fe-Co thin films was evaluated by means of in situ magnetoresistance (MR) measurements. A 25 nm Fe70Co30 film was etched by Ar IB, and successive MR measurements were performed in the same IB etching chamber. Since the IB etching and MR measurements were performed alternately in vacuum, it was possible to evaluate the etching effect on magnetic softness of the single sample without any capping layer interaction. We name the thickness below which the magnetic softness of the etched film starts to decrease as the critical thickness (Tcr). The Tcr was found to be affected by IB energy: 150 and 250 V IB, respectively, showed 7.5 and 10 nm smaller Tcr than that of 600 V IB. Structural analysis revealed the 600 V IB introduced a larger deterioration in the film crystallinity than with the 250 V IB.

Pole design optimization of shielded planar writer for 2 Tbit/in2 recording

A shielded planar head with a multi-step-tapered main pole assuming ion-beam milling fabrication was studied to obtain a large recording field along with suppressed fringing field. The head main pole with a three-step-tapered structure was optimized in terms of the top, main, and bottom slope angles. The optimized head showed a remarkably suppressed fringing field compared with a conventional single-step-tapered pole head. The recording simulation suggests that the head has the potential for 2 Tbit/in2 recording in combination with a bit patterned medium.

Effect of ion-beam etching damage in Fe-Co tapered main pole

Effect of ion-beam etching damage in Fe–Co films was estimated and magnetic calculation of the planar head using tapered main pole (MP) including the etching damage was performed. The etching test on the Fe–Co films, whose thickness corresponds to half of the trackwidth for several Tbits/in.2, showed decrease in saturation magnetic flux density (Bs) and increase in coercivity with a 250 eV ion beam. The magnetic calculation showed relatively large decrease in head field and head field gradient as Bs of the damaged region decreases from 2.4 T. Damage control in the MP fabrication is one of the important issues for Tbits/in.2-era write heads.

Magnetoresistance Characterization of NiFe Films With a Planar Point Contact

Magnetoresistance (MR) characterization of NiFe films was performed with a point-contact (PC) whose size was varied from several hundreds to around ten nm2 by the ion milling process. Two kinds of MR origin, which were estimated to be domain wall MR (DWMR) and anisotropic MR (AMR), were observed by analytical decomposition of the R-H curves. The MRs showed contrastive dependence on the PC conductance due to difference of area in which they occurred. The DWMR in the PC increased as the PC size decreased and reached to a maximum of about 12.5%. The DWMR dependence on the NiFe-PC size coincided with that of fitting approximation based on some previous reports

Precise Damage Observation in Ion-Beam Etched MTJ

Patterning damage at the sidewall in a magnetic tunnel junction (MTJ) was observed precisely using a rectangular MTJ where deterioration in crystallinity is easier to identify than in the case of a dot-shaped conventional MTJ. A 200-500 nm-square rectangular MTJ was patterned by a 200 eV ion beam (IB). Cross-sectional transmission electron microscopy was used for damage observation. A bright-field image showed that crystallinity deteriorated to a depth of

Irradiation Damage in Fe-Co Thin Films With Low-Energy Ion Beam

\sim 1.3