Universal Electromotive Force Induced by Domain Wall Motion

The electromotive force induced by a moving magnetic domain wall in a nanostrip has been calculated theoretically and detected experimentally. It is found that the emf depends only on the domain wall transformation frequency through a universal Josephson type relation, which is closely related to the topological nature of the domain wall. Our experimental measurements confirm the theoretical prediction.

Figure 1

Experiment schematic. (a) Drive, modulation, and bias field configuration with respect to sample. (b) Scanning electron micrograph of nanowire device. (c),(d) Total field waveform for two bias field levels. Injection field $H_{\mathrm{inj}}$ indicated by horizontal lines. Black solid lines indicate field waveform; blue indicates voltage signal expected from DW moving along nanowire. (e) Detail of several drive-field cycles immediately before and after a step in the modulation field. Before the step, the nanowire is saturated and no DWs travel along it. After the step, each drive-field half-cycle (duration $T_{1/2}$) injects a DW that moves along the wire, generating a voltage until it reaches the end of the wire after a time ${\tau }_{\mathrm{DW}}$.

Figure 2

(a) Lock-in voltage versus $H_{\mathrm{dc}}$ for the drive-field waveforms with $H_d=20\mathrm{Oe}$ with/and without injection pulse. (b) Odd components of the curves in (a).

Figure 3

Odd-symmetry component of lock-in voltage at $H_{\mathrm{dc}}=H_m$ for drive-field waveforms of varying half-period $T_{1/2}$ (half-cycles shown in inset). Solid line is fit to $1/T_{1/2}$.

Figure 4

Measured wall velocity (open symbols) and wall-induced voltage (solid symbols) versus drive-field. Solid line is fit with slope $10\mathrm{nV}/\mathrm{Oe}$.