Hideki Fujimoto

Study on the magnetization reversal process in a magnetic nanowire and a magnetic dot observed by magnetic field sweeping magnetic force microscopy measurements (invited)

We have studied the details of the magnetization reversal process in Ni–Fe nanowires and dots using magnetic field sweeping (MFS)-magnetic force microscopy (MFM). All the points within the nanowire and the dot show important changes in phase (changes in stray field) including a hysteresis loop, a decrease and an increase in phase, as the magnetic field is varied. From these results, it is demonstrated that domain wall motion dominates the magnetization reversal process of a 10-nm-thick Ni–Fe nanowire with widths between 100 and 1000nm. It is also demonstrated that the nucleation, the movement, and the annihilation of the vortex core can be directly observed in the magnetization reversal process of a 40-nm-thick Ni–Fe circular dot with diameters between 200 and 800nm. Furthermore, it is found that, in the magnetization reversal process of a 10-nm-thick Ni–Fe elliptical dot with several major axial distances between adjacent dots, the magnetization between the adjacent dots magnetostatically couples as the ...

Effect of the Dot Separation on the Switching Behavior of Ni-Fe Elliptical Dot Arrays

We have studied the effect of the dot separation on the switching behavior of Ni-Fe elliptical dot arrays with major axial distances between the adjacent dots. The magnetization process and the magnetic configuration in the dot arrays apparently differ according to the distance between the adjacent dots. These differences are due to the fact that the dipole-dipole interaction becomes stronger while decreasing the major axial distance between the adjacent dots. From these results, it is evident that the optimal distance at which the magnetization between the adjacent dots couples by the dipole-dipole interaction is below 30 nm.

Observation of Magnetization Reversal Process in Ni-Fe Nanowire Using Magnetic Field Sweeping-Magnetic Force Microscopy

The details of the magnetization reversal process of Ni–Fe nanowires, which were 10, 30, and 50-nm thick, were successfully observed using our newly proposed magnetization measurement method, namely, magnetic field sweeping (MFS)-magnetic force microscopy (MFM). All the points within the nanowire show marked phase changes (stray fields change) as the magnetic field is varied. In particular, each nanowire edge displays a hysteresis loop, while the center shows a sharp jump or a plateau area. These results demonstrate that domain wall motion is dominant in the magnetization reversal process of a 10-nm-thick Ni–Fe nanowire and that domain wall motion along with domain wall pinning play important roles in the magnetization reversal process in both 30- and 50-nm-thick Ni–Fe nanowires.

Reactive Ion Etching of Al Alloy Films in a Rotating Magnetic Field

Excellent etching characteristics of Al-1%Si-0.5%Cu/TiN film were obtained at low pressure of 0.9 Pa using a magnetically enhanced reactive ion etching system with a rotational permanent magnet. A 2-step resist stripping process was also developed in order to avoid after-corrosion and resist residue. Negative and positive flatband voltage (Vfb) shifts of Al/Si3N4/SiO2/Si capacitor were observed using a static magnetic field, and the Vfb distribution is uniformalized using the rotational magnetic field. We simulated the drift motion of secondary electrons in the cathode sheath in order to clarify the origin of the Vfb distribution. The simulation results showed that the E×B drift motion of the electrons caused the nonuniform distribution of electron density on the wafer, and that this nonuniform distribution of the electrons corresponded to the Vfb distribution.

Local Probing of Magnetization Reversal in Ni–Fe Elliptical Dots With Variable Geometry

We have investigated the detailed magnetization reversal in 10-nm-thick Ni-Fe elliptical dots with several dot sizes using magnetic field sweeping (MFS)-magnetic force microscopy (MFM). At the dot edges, the shape of the phase (the stray field) curve versus magnetic field changes from a stepped hysteresis loop to a almost nonstepped hysteresis loop with increasing dot size. On the other hand, at the center within the dot, sharp or weak decreases in phase are observed as the magnetic field is varied. From these results, it is found that, in the magnetization reversal of a 10-nm-thick Ni-Fe elliptical dot with several dot sizes, the dominant factor changes from the change in the magnetic domain configuration to the domain wall motion as the length of major axis increases.

Reactive ion etching of Al alloy and silicon dioxide films in a rotating magnetic field

A diode type magnetically enhanced reactive ion etching system was used for Al alloy films and a triode type magnetically enhanced reactive ion etching system was used for SiO2 films. A same rotational permanent magnet was used for the diode and triode reactors. Excellent etching characteristics of TiN/Al-1%Si-0.5%Cu/TiN and SiO2 films were obtained at low pressure of about 1Pa. Simulations were also performed for drift motions of secondary electrons in the cathode sheath.