Regensburg 2000 – scientific programme

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AM: Magnetismus

AM 7: Dauermagnete, nanokristalline hart- und weichmagnetische Werkstoffe

AM 7.5: Talk

Monday, March 27, 2000, 16:30–16:45, H10

Hydrogen disproportionation by reactive milling and recombination of Nd₂(Fe,Co)₁₄B alloys — •A. Bollero, O. Gutfleisch, M. Kubis, K.-H. Müller, and L. Schultz — IFW Dresden, Postfach 270016, D-01171 Dresden

Using a reactive milling procedure it has been demonstrated that Nd₂Fe₁₄B and also thermodynamically much more stable Nd₂Co₁₄B stoichiometric alloys can be disproportionated into NdH₂ and bcc-Fe, or NdH₂ and fcc-Co, respectively, when milling in 5bar hydrogen and 350^∘C for 20 — 40h. Thus, the grain refinement via the hydrogenation disproportionation desorption and recombination (HDDR) process is now applicable to Nd₂Co₁₄B-type alloys using this modified technique. Grain sizes of disproportionated and recombined materials were found to be < 10nm and 40 — 50nm, respectively, - approximately an order of magnitude smaller than those of conventional-HDDR processed alloys. The desorption / recombination temperature was shifted to significantly lower temperatures for the Nd₂Co₁₄B alloy which is consistent with the thermodynamic expectations. The magnetic properties of the recombined powders have been studied and a more effective exchange coupling leading to enhanced remanences, possibly due to the slightly smaller grain size, has been observed for the Nd₂Co₁₄B alloy.