Investigation of interaction effects in a nanocrystalline Nd2Fe14B+αFe composite system

The interactions responsible for the observed properties in a two-phase Nd2Fe14 B + alpha Fe composite are investigated. These interactions are demonstrated by irreversible magnetization curves strongly dependent on the magnetic configuration of the system. Their effects are analyzed by a) considering the changes in the effective distribution of critical fields for reversion of the magnetization in different configurations and b) assuming that they are described by a uniform mean interaction field superimposed to the applied field. Both descriptions lead to confirm the results of micromagnetic calculations in the sense that the magnetic behavior of these fine grained composites is governed by exchange interactions. As the grain size decreases, two competitive effects are found to determine the grain size dependence of coercivity: the exchange hardening of the soft phase and the exchange weakening of the hard phase.