Magnetic Fields of Square-Loop Thin Films of Oblate Spheroidal Geometry

Thin films of Ni-Fe alloy may be prepared to be anisotropic and exhibit square-loop M-H characteristics. In films that are single-domained with flux changes involving only rotation of intrinsic magnetization controlled by cross-magnetization fields, very fast switching action can be obtained for storage and logic functions. Problems of coupling to the flux changes and interaction in an array of such films require study of the magnetic-field distribution. In the treatment given, a circular, single-domain, thin film is represented by a very flat oblate spheroid. The field distribution outside the spheroid is found by assuming that the magnetic properties are characterized by an intrinsic magnetization M constant in magnitude, but varies in direction depending on field and energy considerations. Calculation of the field distribution is given for a typical film with diameter to thickness ratio of 105. From the regions over which field changes are most significant, conclusions are drawn as to the proper size of sensing loops and spacing to avoid interaction during switching in film arrays.