Transverse field dependence of the planar Hall effect sensitivity in Permalloy films

A series of Permalloy films, of various shapes such as a square, a rectangl e, a circle, and a rhombus, was made. The sample length to width ratio L/w varied from 1 (i.e., square) to 29 (i.e., rectangle). We studied how the pl anar Hall effect (PHE) signal was affected by adding a transverse field H-y along the easy-axis direction of the sample. It was found that in a certai n range of H-y, the PHE sensitivity S might become inoperative, i.e., S cha nged linearly as a function of H-y from -S-max to +S-max (or vice versa), w here S-max was the maximum sensitivity. This phenomenon is explained by con sidering the Zeeman-energy and the single-domain-rotation effects. In parti cular, for the square sample, the following data exist: (1) S-max is as hig h as 310 Omega /T at the film thickness t=500 Angstrom, and (2) the inopera tive range for H-y is the narrowest among all the samples. From this study, we conclude that the field of the Earth H-e-as long as its horizontal comp onent is larger than 0.25 Oe-can be employed to stabilize the magnetic stru cture of a Permalloy element and to achieve the best PHE performance with S -max. (C) 2001 American Institute of Physics.