Abstract: There is disclosed a process for optimizing the magnetic properties of a multiphase product of composition rare earth/iron/boron endowed with permanent magnet properties at ambient temperature. This composition serves as a precursor, which is first subjected to a decrepitation treatment by hydrogenation under low pressure at low temperature to obtain an intermediate hydride in pulverulent form. The pulverulent intermediate hydride is subsequently subjected to a first heat treatment under vacuum for partial dehydrogenation at a temperature below its element separation temperature. The non-separated product thereby obtained is subjected to a second heat post-treatment under an initial primary vacuum and extensively dehydrogenated until the primary vacuum is reestablished at a temperature close to 600.degree. C. The precursor can be an isotropic material obtained by fast quenching, such as wheel quenching or hot welding with a forging ratio of at least 10.

Abstract: New magnetic hydride Nd.sub.2 Fe.sub.14 BH.sub.x (0<x<5) and family corresponding to other rare earths and yttrium. Possible substitution of Fe by Co. Preparation from Nd.sub.2 Fe.sub.14 B by hydrogenation (ambient temperature; pH.sub.2 >20 bar), which can be reversed to give powdered Nd.sub.2 Fe.sub.14 B. Remarkable magnetic properties.