The angular dependence of the planar Hall effect in Co-Ni films

Co100-xNix (x = 70, 75, 80, 90 at. % Ni) alloy films were made by the vapor deposition method. An easy axis could be defined by a deposition field parallel to either the length (L film) or width (T film) of the sample. The anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) hysteresis loops were simultaneously measured with a slowly sweeping field H. The angle theta between the hard axis and H could be varied. Domain patterns were also recorded at each stage of the magnetization or demagnetization process. Besides the usual AMR and PHE behaviors, we have observed the forms of a voltage "mountain," like Delta V-mr and Delta V-ph, superimposed on the normal curves at the switching field H-sw. Delta V-mr is an even function of theta and Delta V-ph is an odd function. The well known magneto-transport theory based on the single-domain model is modified to adopt the real situation of the multidomain structure. We have been successful in explaining all the Delta V-ph data observed experimentally. In addition, from the angular dependence of Delta V-ph, we not only check the direction of the mean easy axis consistently, but also tell the degree of easy-axis dispersion in the film. It is found that the Co30Ni70 T film has the least dispersion and a sizable AMR ratio Delta rho/rho(perpendicular to), = 3.6% at room temperature. (C) 1998 American Institute of Physics. [S0021-8979(98)05314-6].