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 e ffect (PHE) hysteresis loops were simultaneously measured with a slowl y 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 mag netization or demagnetization process. Besides the usual AMR and PHE b ehaviors, we have observed the forms of a voltage ''mountain,'' like D elta V-mr and Delta V-ph, superimposed on the normal curves at the swi tching 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 t he Delta V-ph data observed experimentally. In addition, from the angu lar dependence of Delta V-ph, we not only check the direction of the m ean easy axis consistently, but also tell the degree of easy-axis disp ersion 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. [S0 021-8979(98)05314-6].