Magnetoresistance of single-domain ferromagnetic particles

The magnetoresistance on single-domain, submicron elliptical ferromagnetic Ni particles is measured using nonmagnetic probes in a four-probe geometry at liquid-helium temperatures. The magnetic resistance shows sharp jumps on the smallest particles which are associated with the switching of individual domains. The normalized magnetization hysteresis loops can be reconstructed using an anisotropic magnetoresistance model. The remanent magnetization in zero applied magnetic field is less than the saturation magnetization and this relaxation may be due to surface effects or crystal grain structure in the particles.