Observation of a bias-dependent constrained magnetic wall in a Ni point contact

Quantized electron transport in a Ni point contact exhibits nonlinear bias dependence without an external magnetic-field application. The nonlinear features are categorized into two distinctive types dependent on the shapes, which are confirmed based on our measurements on hundreds of break junctions. Such nonlinear characteristics are unique to a magnetic point contact, showing the contribution of spin-dependent transport within a microscopic magnetic structure. Ab initio calculations on atomic wire model demonstrate that the magnetic point contact is comprised of an abrupt change in magnetic moments at the contact region, drastically modifying only the flow of a spin-down current. The calculations reproduce the nonlinear features observed experimentally. Our results therefore offer a method to analyze the spin transport in a magnetic point contact without a magnetic-field application, which can minimize the ambiguity in the origin of ballistic magnetoresistance.