Method of increasing the coercivity of a sintered nd-fe-b permanent magnet

A method of increasing coercivity of a sintered Nd—Fe—B permanent magnet, the method including the steps of:

• a) providing a sintered Nd—Fe—B magnet block having a pair of block surfaces, opposite and spaced from one another, extending perpendicular to a magnetization direction;
• b) depositing an organic adhesive layer, has a predetermined thickness of between 3 μm and 30 μm, on one of the block surfaces of the sintered Nd—Fe—B magnet block with the organic adhesive layer being a pressure-sensitive adhesive or a double-sided tape;
• c) depositing a powder containing at least one heavy rare earth element on the organic adhesive layer under an inert gas environment, the least one heavy rare earth element being selected from a group consisting of Tb, Dy, a chemical compound containing Tb or Dy, or an alloy containing Tb or Dy, and the powder having a particle size of between 100 mesh and 500 mesh;
• d) pressing the sintered Nd—Fe—B magnet block containing the powder to adhere the powder to the organic adhesive layer;
• e) removing excess powder from the sintered Nd—Fe—B magnet block to form a uniform film on the Nd—Fe—B magnet block;
• f) rotating the sintered Nd—Fe—B magnet block including the uniform film 180° along an axis orthogonal to the magnetization direction exposing another one of the block surfaces of the sintered Nd—Fe—B magnet block;
• g) repeating steps b)-e) on the another one of the block surfaces of the sintered Nd—Fe—B magnet block
• h) diffusing the powder into the sintered Nd—Fe—B magnet block under a vacuum environment or an inert gas environment to produce a diffused magnet block;
• i) cooling the diffused magnet block;
• j) aging the diffused magnet block under the vacuum environment or the inert gas environment.