The Pulsed Field Magnetometer - a tool for characterizing Permanent Magnets.

R. Gössinger*), M. Küpferling*), A. Wimmer*), M. Taraba*), W. Scholz*), J. Dudding**), P. Lethuillier***), B. Enzberg-Mahlke****), W. Fernengel*****), G. Reyne******)

Proceedings of the Sixteenth International Workshop on Rare-Earth Magnets and Their Applications, Ed. H. Kaneko, M. Homma, M. Okada, The Japan Institute of Metals, 2000, pp. 1129-1138.

A large bore pulsed field hysteresograph working at room temperature is described. The system shall be used for a fast quality control of industrial permanent magnets. It consists of a pulse magnet which is driven by a 24 mF condenser battery (U = 2500 V) with a bore of 70 mm inner diameter and a maximum field of 10T. Hirst constructed a second system working with a smaller battery but also with two different pulse durations. The Hirst system can be charged up to 3 kV - the whole charging and measuring cycles is surveyed by a PC. Applying two different pulse duration can be used to make eddy current corrections for the true shape of the loop. The magnetization is calibrated with pure Fe and Ni within 1%. For the field calibration a hall probe can be used as well as a critical field of a sample. The effect of eddy currents is careful studied measuring the ``eddy current - magnetization'' in spheres and cylinders of Al and Cu. The magnetization scales linear with dH/dt - the slope is proportional to the resistivity. The experimental results are compared with analytical, as well as finite element calculations. The hysteresis of technical permanent magnets (barium ferrite, Nd-Fe-B) as obtained in a static magnetometer is compared with that measured in the pulsed field system. The loop agrees for barium ferrite within 1%. The loop is measured with different types of pick-up systems (axial N/N (TU PFM) but also coaxial (Hirst PFM) with extended homogeneity).

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Feb. 13, 2001