The effect of hydrogen on the magnetic properties of the Nd-Fe-B-H compound

We present a comprehensive study of the effect of hydrogen on the magnetic properties of Nd-Fe-B magnets. The research has been done on powder, bulk s amples and plates of thickness 200-800 mu m. It includes the determination of the concentration of hydrogen by total combustion and by precision weigh t balance, X-ray studies, thermal desorption of hydrogen in high vacuum, in sertion of hydrogen and deuterium by electrolysis, and SQUID measurements o f magnetization and magnetic relaxation. The extraction of hydrogen towards concentrations below 0.3 at% results in the decrease of the maximal BH pro duct as large as 30%. Methods have been proposed that allow to catalyze the absorption of hydrogen with the help of palladium and to measure concentra tion of hydrogen by substituting it with deuterium. We report dramatic effe cts caused by the Pd coating and argue that the coercivity of sintered Nd-F e-B magnets is determined by the pinning of domain walls in the intergranul ar regions. (C) 1999 Elsevier Science B.V. All rights reserved.