Anisotropic neodymium-iron-boron powder with high coercivity and method for forming same

A method for forming magnetically anisotropic particles of a composition that has as its magnetic constituent the tetragonal crystal phase RE.sub.2 TM.sub.14 B, wherein the particles have an intrinsic coercivity at room temperature of at least 5,000 Oersteds, comprising the steps of:

• rapidly solidifying a melt of a composition comprising, on an atomic percent basis, about 40 to 90 percent transition metal (TM) taken from the group consisting of iron and mixtures of iron and cobalt wherein iron makes up at least 40 percent of the total composition, about 10 to 40 percent rare earth metal (RE) wherein at least about 6 percent of the total composition is neodymium and/or praseodymium, and at least about 0.5 percent boron, and forming a particulate solid material thereof in which crystalline material, if present, has a grain size no larger than about 500 nanometers;
• hot pressing said particles into a body and thereafter hot working said body to plastically deform the original particulate constituents so as to thereby produce in said body aligned platelet-shaped grains of said magnetic phase wherein the largest average dimension is no greater than about 500 nanometers;
• and
• comminuting said body to form a powder, the individual particles of said powder each comprise a multitude of said aligned grains, said particles thereby being magnetically anisotropic and having a first intrinsic magnetic coercivity,
• wherein the improvement comprises the further step of:
• heating the individual particles of said powder at a temperature and for a duration sufficient to effect a second intrinsic magnetic coercivity within said particles which is greater than about 5,000 Oersteds and greater than said first magnetic coercivity.