Nonanaliticity of the Magnetization Curve: Application to the Measurement of Anisotropy in Polycrystalline Samples

We studied the second derivative of the magnetization with respect to the magnetic field, $\frac{d^{2}M}{d{H}^2}$, for polycrystalline materials having uniaxial anisotropy. Evidence is given of a singular point located at $H=H_A$, the anisotropy field. The observed sharp peak is associated with the infinity at $H=H_A$ of the $\frac{d^{2}M}{d{H}^2}$ curve for the single crystal in the hard direction. The detection of singularities is proposed as a new, and sometimes unique, method of measuring magnetic anisotropy using polycrystalline samples.