Heterostructures having both magnetism and topology are promising materials for the realization of exotic topological quantum states while challenging in synthesis and engineering. Here, we report natural magnetic van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n that exhibit controllable magnetic properties while maintaining their topological surface states. The interlayer antiferromagnetic exchange coupling is gradually weakened as the separation of magnetic layers increases, and an anomalous Hall effect that is well coupled with magnetization and shows ferromagnetic hysteresis was observed below 5 K. The obtained homogeneous heterostructure with atomically sharp interface and intrinsic magnetic properties will be an ideal platform for studying the quantum anomalous Hall effect, axion insulator states, and the topological magnetoelectric effect.

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We measure voltage noise spectra S V ͑f͒ generated by current-driven vortices at various fields B including the peak-effect regime for amorphous Mo x Ge 1−x films with Corbino-disk and striplike contact geometries. Field dependences of the critical current I c and S V ͑f͒ are nearly independent of contact geometries, indicating that edge effects are not important on static or dynamic vortex properties. This is in contrast to the result reported for NbSe 2 crystals with much larger thickness. S V ͑f͒ at low frequency f exhibits a sharp peak just below the peak field B p of I c , where the characteristic time of vortex motion increases significantly. The results suggest the existence of the order-disorder transition and vortex instabilities due to coexisting vortex phases at around B p .

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We present measurements of ac complex resistivity, as well as dc resistivity, for a thick amorphous MoxSi1-x film at low temperatures ( T>0.04 K) in various constant fields B. We find that the vortex glass transition (VGT) persists down to T approximately 0.04Tc0 up to B approximately 0.9Bc2(0), where Tc0 and Bc2(0) are the mean-field transition temperature and upper critical field at T = 0, respectively. In the limit T-->0, the VGT line Bg(T) extrapolates to a field below Bc2(0), while the dc resistivity rho(T) tends to the finite nonzero value in fields just above Bg(0). These results indicate the presence of a metallic quantum vortex liquid at T = 0 in the regime Bg(0)