UNUSUAL MAGNETIC-BEHAVIOR IN ND-FE-B ALLOY POWDER COMPACTS

We report an unusual magnetic behavior in powders prepared by spark-er oding (in liquid Ar) alloy electrodes containing approximately equal w eights of Fe and Nd2Fe14B in an effort to prepare composite permanent magnets. Magnetization exhibits reproducible thermal hysteresis, peaki ng in all applied fields near 520 degrees C when warming, but increasi ng monotonically when cooling to room temperature from 700 degrees C a nd above. Mossbauer spectroscopy was used to show that the behavior is due to the metastability of Fe1-xO produced in the powders by partial oxidation in Ar gas flow. This compound, paramagnetic at room tempera ture, decomposes only slowly below 570 degrees C into ferromagnetic Fe and ferrimagnetic Fe3O4. The reverse reaction occurs readily at highe r temperatures. (C) 1996 American Institute of Physics.