Satoshi Shirotori

All-metallic nonlocal spin valves using polycrystalline Co2(FeMn)Si Heusler alloy with large output

A large output voltage of 0.7 mV at 1 mA charge current is demonstrated for all-metallic nonlocal spin valves using Co2(FeMn)Si Heusler alloy and Cu with a junction area of about 50 nm2. The output is attributed to the junction size reduction as well as to the high spin polarization in the Heusler alloy. An analysis using a one-dimensional model reveals that the spin diffusion length in the Cu layer shows no clear degradation even in the case of a 50 nm2 junction. When the junction is reduced further to 10 nm2, an output voltage of about 10 mV is expected.

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.

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

Improved read disturb and write error rates in voltage-control spintronics memory (VoCSM) by controlling energy barrier height

\sim 1.3

High-Speed Voltage-Control Spintronics Memory (High-Speed VoCSM)

nm in the MgO-barrier layer. A Fourier transform mapping image and a dark-field transmission electron microscopy image indicated the existence of an amorphous region at the patterning edge in the MgO layer. IB etching is one of the strong candidates for magnetic random access memory (MRAM) fabrication. However, a typical IB etching energy, e.g., 200 eV, introduces a damage depth of several monolayers at the patterned surface. Since nearly damage-free-patterned surface would be needed for high-density MRAM with nanoscale MTJs of

High-output tri-magnetic terminal-based non-local spin valves

\sim 10

Magnetic recording medium and magnetic storage device

nm in diameter, IB etching with much lower energy would be necessary for fabrication.

Method for producing magnetic recording medium

A hybrid writing scheme that combines the spin Hall effect and voltage-controlled magnetic-anisotropy effect is investigated in Ta/CoFeB/MgO/CoFeB/Ru/CoFe/IrMn junctions. The write current and control voltage are applied to Ta and CoFeB/MgO/CoFeB junctions, respectively. The critical current density required for switching the magnetization in CoFeB was modulated 3.6-fold by changing the control voltage from −1.0 V to +1.0 V. This modulation of the write current density is explained by the change in the surface anisotropy of the free layer from 1.7 mJ/m2 to 1.6 mJ/m2, which is caused by the electric field applied to the junction. The read disturb rate and write error rate, which are important performance parameters for memory applications, are drastically improved, and no error was detected in 5 × 108 cycles by controlling read and write sequences.

Patterned media and method of manufacturing the same, and magnetic recording apparatus

We propose a new spintronics-based memory architecture with 2 MTJs and 4 transistors as a unit cell for high-speed application. The architecture employs spin-Hall effect as a writing principle and voltage-control-magnetic-anisotropy (VCMA) effect as a write speed acceleration. We successfully demonstrated the unique complementary flash-writing scheme and proved a potential of ultrahigh speed writing with the prototype unit-cell and the test-element.

Discrete track media and method of manufacturing the same

We propose tri-magnetic terminal-based non-local spin valves (TM-NLSVs) for lateral structures. A lateral structure has dual spin injector terminals with an anti-parallel spin configuration. The accumulated spin is detected as the voltage between the free layer and one side of the spin injector. Numerical investigation revealed that the output voltage of the TM-NLSV is 2.4-fold higher than that of the conventional four-terminal structure. A further 3.7-fold increase is expected by increasing the injector area by a factor of 9. These results indicate the possibility of obtaining an output voltage that is almost the same as that of conventional (non-lateral) spin valves.