Preisach analysis of Nd2Fe14B

The moment and remanence of a thermally demagnetized sample of sintered, aligned Nd2Fe14B have been measured along the initial magnetizing curve and along the descending branch of the major loop, over an applied field range -12 kOe less than or equal to h(a) less than or equal to + 12 kOe, and over a wide range of temperatures 25 degrees C less than or equal to T less than or equal to 220 degrees C. Changes in temperature have only a weak influence on the magnetizing process, but have a profound effect on the demagnetizing branch and on the curvature of the Henkel plots, which varies from strongly magnetizing-like at room temperature to strongly demagnetizing-like above 140 degrees C. We present numerical calculations based on a modified version of the scalar Preisach model, which assumes that moment reversal along the demagnetizing branch is characterized by two distinct sets of energy barriers which must be activated sequentially, so that the availability of one set is conditional upon the activation of the other. The model is able to replicate all of the experimental systematics, and shows that long range, mean field interactions, positive or negative, are absent from this system. (C) 1999 American Institute of Physics. [S0021-8979(99)17408-5].