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

• High magnetic field changes the thermodynamics and kinetics of spinodal decomposition in Alnico alloys.
• High magnetic field increases the nucleation rate of spinodal decomposition in the Alnico5 alloy.
• High magnetic field makes the decomposed particles finer, and increases the volume fraction of them.

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 (Hext) can also accelerate the atom diffusion and turn the diffusion direction to itself. The effect of both the Eext (the external magnetic field energy) and the Eelast (the elastic energy) on modulated structure in a hypothetical A–B system was simulated by phase field method. The littler the Eelast is, the bigger the Eext is, the decomposed ferromagnetic particles become smaller, and parallel along the direction of the external magnetic field.

TEM and HADDF images shown the morphology of decomposed particles in Alnico5 alloy treated at 830oC for 10 min under different external magnetic field intensities.Figure optionsDownload as PowerPoint slide