Transverse barrier formation by electrical triggering of a metal-to-insulator transition

Application of an electric stimulus to a material with a metal-insulator transition can trigger a large resistance change. Resistive switching from an insulating into a metallic phase, which typically occurs by the formation of a conducting filament parallel to the current flow, is a highly active research topic. Using the magneto-optical Kerr imaging, we found that the opposite type of resistive switching, from a metal into an insulator, occurs in a reciprocal characteristic spatial pattern: the formation of an insulating barrier perpendicular to the driving current. This barrier formation leads to an unusual N-type negative differential resistance in the current-voltage characteristics. We further demonstrate that electrically inducing a transverse barrier enables a unique approach to voltage-controlled magnetism. By triggering the metal-to-insulator resistive switching in a magnetic material, local on/off control of ferromagnetism is achieved using a global voltage bias applied to the whole device.

Magnetic Domain Structure in Ferromagnetic Kagome Metal DyMn6Sn6

Two types of magnetic domains, that is, type-I domain belt domain and type-II new stripe domain, are observed in a kagome metal DyMn6Sn6 by microscopic magneto-optic Kerr imaging technique. From 255 to 235 K, the spin reorientation is observed directly in DyMn6Sn6. We analyze the structure of two types of domains through brightness distribution of the images. The type-II domain exists from 235 to 160 K by zero-field cooling (ZFC). At the same time, type-I domain and type-II domain coexist and transform into each other with variation of temperature. Type-II domains can easily transform into type-I domains when the temperature and magnetic field changes, and this process is irreversible. These results demonstrate that the type-I domain is more stable than the type-II domain. The phase diagram of magnetic domains in DyMn6Sn6 is obtained.

ELECTRON SPIN IMAGING IN QUANTUM HALL DEVICES BY KERR ROTATION MEASUREMENT

The electron spin polarization images in a single layer GaAs / AlGaAs quantum well in the quantum Hall effect (QHE) regime have been observed by using an optical fiber-based high sensitive Kerr rotation microscope. The observed Kerr signal image at the Landau level filling factor ν = 1 reveals the small electron density fluctuation less than 1% through the degree of electron spin polarization. We have also observed the Kerr rotation images in the current flowing QHE devices. At ν = 1 QHE plateau, the winding strip of just ν = 1 incompressible state, which contributes the dissipationless electron transport, has been clearly observed in the bulk region of the devices. The highly current dependent Kerr images have valuable information for studying current density distribution and the distribution of spin polarization in the QHE regime. The experimental results and techniques of the Kerr imaging in the QHE regime have been reported in detail.