The depinning of magnetic domain walls and the magnetization anomaly within the ferromagnetic phase of the Weyl semimetal Co3Sn2S2

We report bulk magnetization measurements and spatially resolved measurements of magnetic domains in Co3SnS2 single crystals. The results indicate that a previously reported magnetic anomaly at 130K is due to domain wall pinning. Our measurements also reveal a hysteresis between field-cooled-cooling (FCC) and field-cooled-warming (FCW) magnetization curves acquired under a constant magnetic field below 300Oe. The observation rules out the possibility that the anomaly stems from a second-order AFM-FM phase transition. Our results further suggest that changes in the shape of hysteresis loops from 5K to 170K is caused by an unusual temperature-dependent domain nucleation field that changes the sign at around 130K. The Kerr rotation images of the magnetic domains obtained between 120K and 140K support the notion that a domain wall pinning effect exists near 130K.