EXPERIMENTAL-DETERMINATION OF AN EFFECTIVE DEMAGNETIZATION FACTOR FORNONELLIPSOIDAL GEOMETRIES

For a nonellipsoidal magnetic sample, the internal magnetic field H-in t(r) is inhomogeneous even when a uniform external magnetic field H-ap p is applied to it. In such a case the elements of the demagnetizing t ensor become position-dependent, N=N(r). The knowledge of the local de magnetization tensor is important for the analysis and design of devic es using finite size and shape magnetic elements. The demagnetizing te nsor elements can be calculated analytically and/or numerically, howev er, often a quick check of the extent of the inhomogeneity of the magn etization distribution of a sample, or a single approximate value of t he 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 shape s has been developed. Experiments, performed on 2x4 mm(2) yttrium iron garnet samples up to 220 mu m thickness, show that the analytical app roximation can be used to define an N-eff. But even for a length/thick ness ratio of 200, the thin film approximation still is in an error of 3.7%. (C) 1996 American Institute of Physics.