Experimental study on modulated structure in Alnico alloys under high magnetic field and comparison with phase-field simulation

A series of magnetic isothermal heat treatment of Alnico alloys (Alnico5 and Alnico8) in a 10 T magnetic field were performed. It was found that the high magnetic field strongly influences the modulated microstructure. Our observation shows that high magnetic field can enhances the nucleation rate of spinodal decomposition in Alnico5 alloy, leads the decomposed particles finer, and also increases the volume fraction of ferromagnetic particles. The external magnetic field (H_ext) can also accelerate the atom diffusion and turn the diffusion direction to itself. The effect of both the E_ext (the external magnetic field energy) and the E_elast (the elastic energy) on modulated structure in a hypothetical A-B system was simulated by phase field method. The littler the E_elast is, the bigger the E_ext is, the decomposed ferromagnetic particles become smaller, and parallel along the direction of the external magnetic field.