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M: Metallphysik

M 3: Nanoskalige Materialien I

M 3.4: Fachvortrag

Montag, 11. März 2002, 11:45–12:00, H6

Structural Evolution of Nanocrystalline Pr₂Fe₁₄B and Nd₂Fe₁₄B Studied by Positron Annihilation Spectroscopy — •Y.C. Wu^1,2, W. Sprengel², K. Reimann², K.J. Reichle², R. Würschum³, and H.-E. Schaefer² — ¹Faculty of Materials Science and Engineering, Hefei University of Technology, 230009 Hefei, P. R. China — ²Insitut für Theoretische und Angewandte Physik, Universität Stuttgart, 70550 Stuttgart, Germany — ³Institut für Technische Physik, Universität Graz, 8010 Graz, Austria

Nanocrystalline hard magnetic Pr₂Fe₁₄B was prepared by crystallization of the melt-spun amorphous material. The evolution of the grain size as determined from x-ray diffraction was studied together with positron lifetime measurements. An observed increase of the mean positron lifetime at the onset of crystallization might be attributed to positron trapping in newly formed interfaces. Upon further annealing the mean lifetime decreases as the grain size increases. For nanocrystalline Nd₂Fe₁₄B prepared by sintering coincident measurements of the Doppler broadening of the positron electron annihilation photon are in progress to determine the local chemical enviroment of the free volumes in the interfaces.