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Description
A new experiment (Fig. 1) is presented for studying the dynamics of a single domain wall (DW) driven by an alternating magnetic field. The bistable cylindrical glass-coated microwire is placed in a system of four coaxial coils. One pair of coils in Helmholtz geometry (HC) in parallel combination allows the whole wire to be axially magnetized. This pair of coils in antiparallel combination provides the possibility of creating a single DW in the place of the local zero field. As long as this magnetic field remains active, the created DW is located in an artificial potential well. The alternating sinusoidal magnetic (AC) field with angular frequency $\Omega$ generated by the magnetizing coil (MC) causes DW to start oscillating. The voltage induced due to the wall oscillation is measured through the pick-up coil (PuC) connected to the lock-in amplifier (LI). The parameters of the entire system of coils were optimized in order to prevent the possible influence of resonance effects in the range of measured frequencies. Using this experimental set-up, two types of measurement of the induced voltage can be performed: firstly as a function of the angular frequency (in the frequency range from 30 kHz to 600 kHz), and secondly as a function of the amplitude of the alternating field. These measurements were carried out without the wire and with the wire in the coil system in two cases, first without a DW and then with a single DW in the wire. The dependences without wire and with wire but without DW were identical, which made it possible to obtain a signal from the DW oscillation alone.
Analysis of the measured dependences of the induced voltage versus AC magnetic field amplitude revealed the amplitudes of the critical current when the DW left the region inside the pick-up coil for various frequencies. We then performed measurements without an artificial potential well in order to verify the validity of the DW oscillation model in a local potential well. Based on the measured results, it seems that this model does not describe the observed behaviour correctly. This is probably due to excessive DW axial length.
Fig. 1 Experimental set-up.
Acknowledgement
This research was supported by VEGA Grant No. 1/0350/24 from the Scientific Grant Agency of the Ministry for Education of the Slovak Republic, and project No. 019/2019/1.1.3/OPVaI/DP (ITMS code 313011T557).
