Treating agent for forming a fluoride coating and method for forming a fluoride coating

A fluoride coating film formed with a fluoride-containing solution wherein a rare earth fluoride or an alkaline earth metal fluoride, in particular, fluoride of Pr, Nd, Dy, Tb and Ho, is swollen in a solvent comprising a major amount of an alcohol, and the solution is a colloidal solution in which the rare earth fluoride or the alkaline earth metal fluoride is dispersed homogeneously in the solvent comprising a major amount of an alcohol improves magnetic properties of NdFeB rare earth magnets including not only sintered magnets but also bonded magnets.