Hall Effect Spintronics

Abstract

Abstract : The grant research covered a wide variety of Hall effect topics. First, a non-switching van der Pauw technique was developed using two electrically isolated AC sources with two frequencies and averaging two sets of simultaneous data, which reduces the effect of parasitic offset voltage for more accurate measurements of the Hall effect. Second, investigation of asymmetric in-field magnetoresistance was investigated in seeming violation of Onsager s reciprocity relations, with the conclusion that variations in thickness, Hall coefficient, and nonuniform magnetization reversal can explain the phenomena. Third, thin Co/Pd multilayers with room temperature perpendicular anisotropy and enhanced surface scattering were examined for possible use in extraordinary Hall effect (EHE)-based memory devices, and several parameters important for EHE-based devices were found promising. Fourth, a novel technique was developed to monitor magnetization reversal and perpendicular anisotropy using the extraordinary Hall effect and anisotropic magnetoresistance, finding that canted fields at certain angles can significantly improve measurements of anisotropy. Fifth, the response of magnetization to an unpolarized current is examined, proposing a mechanism which acts in the bulk of the ferromagnet rather than the interface between normal and ferromagnetic layers, and a study was performed on the effects of temperature and current density on magnetization reversal of thin Ni films, showing evidence of destabilization of magnetization by unpolarized electric current. Sixth, a method was developed for realizing two-bit- per-ferromagnetic-dot magnetic random access memory using magnetic vortex states, in which two states are contributed by clockwise and counter-clockwise chirality and two by up/down core polarity.