Experimental determination of an effective demagnetization factor for nonellipsoidal geometries

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 2x4 mm(2) yttrium iron garnet samples up to 220 mu m 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%. (C) 1996 American Institute of Physics.