Coercive properties of Nd2Fe14B+aFe nanocrystalline composites exhibiting wide distributions of switching fields in the frame of the Global Nucleation Model

O. V. BILLONI, S. E. URRETA, L. M. FABIETTI, H. R. BERTORELLO

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS

Año: 2002 p. 179 - 189

0304-8853

The demagnetization processes in Nd2F14B+aFe nanocrystalline composites exhibiting square and two-step hysteresis loops are investigated. In all these microstructures, an expanding nucleus model (Global Model) reasonably describes the experimental results in the entire range of the demagnetization loop, provided different sites acting as inverse nucleus are considered. Nucleation is found to take place in both phases and under different coupling conditionsexhibiting, in each case, a different reversion regime. Each regime has associated definite values of specific nucleus surface energy and effective local demagnetizing factor, which are similar in all the specimens, in spite of their different microstructures and compositions. These specific surface energy values are close to those expected for domain wall-like configurations resulting from competing interactions in the particular nucleation site, not always related to the intrinsic properties of the phase itself but largely determined by inter-grain interactions.