T.Y. Chen

Study of domain wall magnetoresistance by submicron patterned magnetic structure

Through the proper design of submicron permalloy (Ni80Fe20) wires, domain wall magnetoresistance is investigated. A positive contribution to magnetoresistance (MR) was found for domain walls in these wires after extracting the anisotropic MR effect. Some theoretical models are used to discuss our results.

Current driven domain wall motion in magnetic U-pattern

We have studied the current induced domain wall motion by using patterned U geometry. The observation of two magnetic states of the U-pattern was evidenced. One is the vortex domain wall at the center of semicircular arc in U-pattern and the other is the continuous magnetic state without wall. We investigated the influence of the positive and negative dc current injection on domain wall motion before switching field with density on the order of ∼107A∕cm2. The critical current varied dramatically as the bias field is close to the switching field and only gradually as the field is far away from the switching field.

Magnetoresistance study in NiFe semicircle-ring patterned wires

Micron size NiFe wire having a patterned shape of semicircle in series was fabricated. Magnetoresistance of the wire has been studied from 10 to 300 K. Domain wall resistivity is nearly independent of the temperature; however, the domain wall switching field decreases relatively rapidly with increasing temperature. We have observed experimentally two distinct domain structures at the corners of the NiFe semicircle-ring patterned wire at remanence after longitudinal and transverse saturation fields. We can explain successfully the magnetization reversal process on the magnetoresistance loops by the contribution from anisotropic magnetoresistance and magnetic domain configuration.

Magnetoresistance and magnetic force microscopy studies in Ni80Fe20 disk- and ring-patterned wires

We have investigated the magnetization reversal process of the disk-, ring-, and center dot ring-patterned Ni80Fe20 wires. For the fields applied perpendicular to the wire direction, interesting shape dependent magnetoresistance (MR) ratios were found. The MR ratios were varied from 0.8%, 0.65%, and 0.4% at room temperature and 1.7%, 1.5%, and 1.1% at 10 K for the disk-, ring-, and center dot ring-patterned wires. For the same wires, the switching field is reduced from −170, −110, and −90 Oe at room temperature to −140, −70, and −20 Oe at 10 K. These results were due to the shape anisotropy and domain-wall motion. The anisotropy MR (AMR) ratios measured at 10 K of the disk-, ring-, and center dot ring-patterned wires were 1.9±0.1%, 1.7±0.1%, and 1.3±0.1%, respectively, it is almost even the same (1.1±0.1%) at room temperature. We have observed that the center dot reduces the MR ratio and increases magnetic saturation field of the nanosize Ni80Fe20 wires.

Current-induced domain-wall motion in U-shaped permalloy wire

The current-induced domain-wall motion has been observed by using a U-shaped permalloy wire. We observed two magnetic states in a U-shaped pattern. One is the vortex domain wall at the center of semicircular arc region of the U-shaped pattern, and the other is the continuous magnetic state without the domain wall in between. In general, the current density of the order of /spl sim/10/sup 7/ A/cm/sup 2/ is needed to drive a magnetic domain wall. In this paper, the critical current for domain-wall motion increases as the bias field increases. The bias field means the field deviated from the switching field of the wire.