Magnetic epitaxial films: Applications and potential

Abstract

Magnetic films in amorphous, polycrystalline and single-crystal form have shown promise for many years as a method for miniaturizing magnetic components in the design of electronic devices. With the exception of a few specialized applications, e.g. thin film Permalloy memory elements and magnetic tape heads, widespread use of these films has not yet been realized. Recent advances in the preparation of high quality non-metallic single-crystal garnet films have brought a number of important components much closer to reality. The most immediate widespread use of the single-crystal magnetic film is bubble memory devices. These devices exploit recent advances in the magnetic garnet technology and achieve an extremely high data storage density. They are expected to supplant mechanical tape and disc recorders in some applications soon. Another class of single-crystal magnetic film devices with great potential but not as well developed as the bubble devices are the planar yttrium iron garnet microwave devices. Included in this category are limiters, filters and magnetically tunable oscillators, which are compatible with conventional microwave integrated circuits. Magnetostatic surface wave devices represent another class of devices which rely upon high quality single-crystal magnetic films. These devices are capable of carrying out signal processing functions such as fixed, variable and tapped delay, convolution and pulse compression directly at microwave frequencies. This paper concentrates on the material parameters which are most important in the bubble, filter and magnetostatic surface wave applications, on how the parameters can be optimized and on the fundamental limits they place upon device performance.