Influence of vortex domain walls on magnetoresistance signals in Permalloy rings

Abstract

The magnetization reversal and the corresponding magnetoresistance of Permalloy rings are investigated here both numerically and experimentally. Micromagnetic simulations reveal that during the reversal process there exist three intermediate metastable states which lead to an unconventional triple-switching characteristic. Size effects are studied as well. The simulation results are in good agreement with our magnetoresistance measurements. Significant differences in the magnetoresistance at two orthogonal directions of the magnetic fields are observed and explained. An important contribution to the magnetoresistance due to the relative position of the domains and the current leads is also investigated.

Short-circuiting effect on the magnetoresistance of microstructured permalloy rings

“…3. The external fields corresponding to the aforementioned magnetization configurations have a good agreement with those measured for the MR curves based on the AMR effect, as argued in our previous paper [4]. In comparison to the resistance drop due to vortex pair formation, as shown in Fig.…”

“…The nonmagnetic gold leads shunt the segment of the permalloy ring underneath. These phenomena were indeed further identified with the transverse MR measurements, where vortex domain wall structures formed in the opposite ends encounter no gold leads, thus giving rise to no resistance drops at the transition fields, as shown elsewhere [4].…”

“…However, among the magnetoresistance measurements reported in the past no concern has been paid to the effect associated with the nonmagnetic current/voltage leads. In our previous paper [4], an electrical shorting behavior resulted from the gold current/voltage leads was for the first time reported. Herein, we present a systematic study on the influence of the nonmagnetic leads by varying the patching areas, from which the degree of shorting effect can be seen from the MR curves and furthermore one may be able to estimate the size of the vortex.…”

“…It has been known that the magnetoresistance of permalloy thin film depends on the angle between current and magnetization direction, which is called anisotropic magnetoresistance (AMR) effect. In our previous finding [4], it was shown that the magnetization of ring devices evolved from onion state at the saturation field to vortex pair state at the near zero field. Consequently, the formation of the vortex domain wall gives rise to the ring resistance change in low field, provided that the patching area is smaller than the size of vortex.…”

Strain-induced magnetization reorientation in epitaxial Cu/Ni/Cu rings

“…The initiation of the reversal of M appeared to take place by the generation of domains in some sections of the ring and not by the depinning and movement of the DWs, as was observed in rings with circumferential magnetization that exhibit onion and vortex states. [11][12][13] For H = 16.7 kA/m, the domains parallel to the field were enlarged by movement of domain walls and, at 32 kA/m, the inversion of the polarity of M was nearly complete. The fact that the polarity of the contrast of the ring followed the field direction suggests that the tip magnetization was maintained perpendicular to H and was not demagnetized during the measurements.…”