Experimental determination of an effective demagnetization factor for nonellipsoidal geometries

Abstract

For a nonellipsoidal magnetic sample, the internal magnetic field H_int(r) is inhomogeneous even when a uniform external magnetic field H_app is applied to it. In such a case the elements of the demagnetizing tensor become position‐dependent, N=N(r). The knowledge of the local demagnetization tensor is important for the analysis and design of devices using finite size and shape magnetic elements. The demagnetizing tensor elements can be calculated analytically and/or numerically, however, often a quick check of the extent of the inhomogeneity of the magnetization distribution of a sample, or a single approximate value of the demagnetizing factor for the given non‐ellipsoidal geometry, would be satisfactory. Therefore a method to define and measure an effective demagnetizing tensor element N_eff for rectangular and circular shapes has been developed. Experiments, performed on 2×4 mm² yttrium iron garnet samples up to 220 μm thickness, show that the analytical approximation can be used to define an N_eff. But even for a length/thickness ratio of 200, the thin film approximation still is in an error of 3.7%.