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 rectangle, 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 planar Hall effect (PHE) signal was affected by adding a transverse field Hy along the easy-axis direction of the sample. It was found that in a certain range of Hy, the PHE sensitivity S might become inoperative, i.e., S changed linearly as a function of Hy from −Smax to +Smax (or vice versa), where Smax was the maximum sensitivity. This phenomenon is explained by considering the Zeeman-energy and the single-domain-rotation effects. In particular, for the square sample, the following data exist: (1) Smax is as high as 310 Ω/T at the film thickness t=500 A, and (2) the inoperative range for Hy is the narrowest among all the samples. From this study, we conclude that the field of the Earth He—as long as its horizontal component is larger than 0.25 Oe—can be employed to stabilize the magn...