Imaging the motion of individual domain walls in the magnetic Weyl semimetal Co₃Sn₂S₂

The recently discovered magnetic Weyl semimetal Co₃Sn₂S₂ is a uniaxial ferromagnet with a large c-axis anisotropy and a T_c of 175 K. Previous measurements of the temperature dependence of magnetization and ac susceptibility have revealed anomalous changes in slope near 130 K. Here we use scanning magneto-optic Kerr microscopy to measure the motion of individual domain walls in response to oscillating magnetic fields in the frequency range from 10 Hz to 10 kHz. As the temperature reaches 130 K from below, the amplitude of domain wall motion abruptly decreases by an order of magnitude, indicating that the effective magnetic torque exerted on the wall is significantly reduced. As the temperature is further increased toward the Curie temperature, the magnitude of wall motion becomes larger again and the magnetic domains shrink in size. We comment on how various scenarios of magnetic ordering can generate striking anomalies in the amplitude of domain wall motion vs. temperature.