Sintered neodymium-iron-boron magnet containing grain boundary diffusion composite film and preparation method thereof, and modified sintered neodymium-iron-boron magnet and preparation method thereof

The invention provides a sintered NdFeB magnet containing a grain boundary diffusion composite film, a preparation method of the sintered NdFeB magnet, a modified sintered NdFeB magnet and a preparation method of the modified sintered NdFeB magnet. The sintered neodymium-iron-boron magnet containing the grain boundary diffusion composite film comprises a sintered neodymium-iron-boron magnet body and the grain boundary diffusion composite film wrapping at least one surface of the sintered neodymium-iron-boron magnet body. The grain boundary diffusion composite film comprises a Dy film and a Tb film which are alternately stacked, and the Tb film is in contact with the surface of the sintered neodymium-iron-boron magnet. The Tb element and the Dy element can permeate into the magnet, and the coercive force of the magnet is improved. And due to the limitation of the diffusion rate and depth, the heavy rare earth on the outermost layer of the sintered neodymium-iron-boron magnet is difficult to permeate into the s