Evidence of a quantitative relationship between the degree of hydrogen intercalation and the coercivity of the two permanent magnet alloys Nd2Fe14B and Nd2Fe11Co3B

Nd₂Fe₁₄BH_x micron-size loose particles are synthesized by the oxide reduction-diffusion technique. When excess Ca is used as a reducing agent, an exothermic reaction is observed by washing under water, with production of native hydrogen that diffuses in the interstitial sites of the alloy. Depending on the experimental conditions, different contents of hydrogen intercalation are observed, with x ranging from x~0 to x~4-5. Cell parameters are observed to quickly increase with hydrogen uptake, resulting in a drastic and regular decrease of the coercivity. In order to understand the relation between the coercivity and the content of hydrogen uptake, 2 to 4 μm size powders of a highly coercive Nd₂Fe₁₄B industrial alloy are submitted to a native hydrogen environment obtained through different chemical conditions. A very reliable relationship is established between the cell parameters (and thus the content of interstitial hydrogen) and the coercivity of the alloy particles