Submicron size particles of Fe/Co multilayers: Effects of tunable anisotropy

Paper in proceeding, 2002

Particle arrays prepared by electron beam lithography and ion beam milling of magnetic films can be designed to yield a wide range of magnetic properties. The shape and size of the particles as well as the distance between them may be varied independently of each other. Furthermore, by choosing multilayers as starting materials the intrinsic magnetic properties, e.g. the crystalline anisotropy may be tuned. In the present work we have extended our earlier studies of fcc Co and Fe submicron structures, with an investigation of arrays of elliptical particles (150 nm x 450 nm x 20 nm) prepared of Fe/Co multilayers. In these the crystalline anisotropy varies between those of Co and Fe. The zero-field state of the magnetic particles, the strength of the dipolar interactions, as well as the processes of magnetization reversal vary significantly with the composition of the starting film. An example is shown in the magnetic force microscopy (MFM) images of 20 nm thick particles of elliptical shape made of pure Co with 100% single domains (See figure la), Fe2ML/Co6ML with 75% single domains and pure Fe with no single domains. The images represent the zero-field state after demagnetization. We conclude that the critical size at which the particles will form a stable single domain state in zero field varies in a way that can be explained by the magnetocrystalline anisotropy decreasing when going from Co to Fe/Co to Fe.