Shape Anisotropy and Magnetic Texture Determination in Anisotropic and Isotropic Alnico Magnets

Hysteresis curves of commercial Alnico 5 and Alnico 2 magnets were evaluated with the anisotropic Stoner-Wohlfarth model. Alnico 2 is an isotropic magnet, whereas Alnico 5 is an anisotropic magnet. These magnets have five main alloying elements: Al, Fe, Ni, Co and Cu. The described method allows a direct estimate of the shape anisotropy in any commercial Alnico magnet, avoiding laborious production of single crystals. Besides, the magnetic anisotropy of any sample with fiber texture can be determined. Parameters related to magnetic shape anisotropy can be directly extracted from the hysteresis of either isotropic or anisotropic Alnico magnets. A shape anisotropy of 1.4 kOe was estimated for the isotropic Alnico 2. The shape anisotropy of the anisotropic Alnico 5 was estimated at 2.2 kOe. The magnetic texture of the Alnico 5 sample can be well described by a Gaussian distribution and remanence to saturation ratio, Mr/Ms, of 0.931. A spring effect is observed in the hysteresis of the Alnico 2 and Alnico 5 magnets, confirming that the ferromagnetic phase is single domain size and that the mechanism of reversal is coherent rotation.