nanocrystalline grains are a key factor in material properties. The existence of nanocrystalline phase makes the magnetocrystalline anisotropy of the material decrease effectively. For example, in a typical Fe-Si-B-Cu-Nb nanocrystalline soft magnetic alloy, the size of the nanocrystalline grains can be controlled by adjusting the alloy composition and heat treatment process. When the grain size is reduced to the nanometer scale, the exchange coupling of electron spins is enhanced, which helps to reduce the resistance of the magnetic domain wall motion, thereby improving the soft magnetic properties.