Speaker
Description
Thin magnetic cylindrical wires attract considerable attention due to interesting features of a domain wall motion like absence of the Walker breakdown that prevents fast domain wall dynamics [1]. Amorphous glass-coated microwires are composite material, in which very high domain wall velocities have been observed [2]. Owing to the amorphous state of wires, the magneto crystalline anisotropy vanishes. Recently, it was shown that the axial magnetic anisotropy resulting from rapid quenching has comparable strength, leading to a tilted domain wall orientation [3]. It is an open question of how the tilted domain wall in cylindrical wires moves with application of mechanical torsion stresses.
Magneto-optical Kerr effect is used to visualize a surface magnetization dynamics in microwires. The domain wall is stabilized by two opposite magnetic fields, resulting in effective one-dimensional potential well. Periodic back-and-forth motion of the well is used to synchronize the domain wall position with MOKE imaging and direct time-resolved images of a surface magnetism are performed. In contrast to previous measurements, mechanical torsion is applied to the microwire. Our spatial imaging of a surface domain wall shape reveals two typical types of a DW distortions. In highly magnetostrictive alloy (e.g. FeSiB), the mechanical torsion stress results in a screw-like distortions of a DW (Fig. 1). On the other side, microwires with reduced magnetostriction exhibits almost zero distortion of a domain wall shape. In both cases, the magnetostriction plays an essential role because the mechanical distortion is always smaller than the distortion of a DW. Time-resolved observation of a magnetization dynamics allows optimization of the giant-magnetoimpedance effect (GMI) in highly sensitive sensors.
Fig.1 Snapshots of domain wall profiles for specific angles of torsion in FeSiB microwire.
References
[1] M. Yan, A. Kákay, S. Gliga, and R. Hertel, “Beating the Walker Limit with Massless Domain Walls in Cylindrical Nanowires,” Physical Review Letters, vol. 104, no. 5. American Physical Society (APS), Feb. 01, 2010. doi: 10.1103/physrevlett.104.057201.
[2] P. Klein, R. Varga, G. A. B. Confalonieri, and M. Vazquez, “Domain Wall Dynamics in Amorphous and Nanocrystalline FeCoMoB Microwires,” Journal of Nanoscience and Nanotechnology, vol. 12, no. 9. American Scientific Publishers, pp. 7464–7467, Sep. 01, 2012. doi: 10.1166/jnn.2012.6526.
[3] O. Vahovsky, R. Varga, and K. Richter, “Experimental method for surface domain wall shape studies in thin magnetic cylinders,” Journal of Magnetism and Magnetic Materials, vol. 483. Elsevier BV, pp. 266–271, Aug. 2019. doi: 10.1016/j.jmmm.2019.03.015.
