Rotating Field Magnetometer for Measurement of Anisotropic Magnetic Materials

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Abstract
A new technique is discussed for the measurement of the properties of anisotropic magnetic materials. The basis of the technique is the harmonic analysis of the signal induced in a pick‐up loop when the anisotropic material is immersed in a spatially rotating magnetic field. It is shown that the harmonics which are generated are related in a simple way to the Fourier coefficients of the anisotropy energy. High sensitivity is achieved through use of a lock‐in detector for the harmonic analysis. Apparatus is described in which the magnetic field rotates at 500 Hz with an amplitude up to 50 Oe. This apparatus can detect a magnetic moment of 10−7 emu and equivalent torque of 10−6 dyne·cm. Illustrative data obtained from a thin Permalloy film (moment of 5×10−3 emu) are given, in which the first three Fourier coefficients of the anisotropy energy are 817, 3. The absolute accuracy of the first coefficient is about 2%, while the reproducibility of this measurement is better than ½%.

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