A comparative study of melt-spun ribbons of Nd₁₂Fe₈₂B₆ and Nd₁₅Fe₇₇B₈

This work has shown that isotropic single-phase materials can exhibit remanence enhancement due to exchange coupling between spins in grain boundary areas. Magnetic materials with remanence enhancement are required to have nanocrystalline structures with grain sizes comparable to the domain-wall thickness. The presence of non-magnetic phases may result in de-coupling of magnetic grains, therefore leading to an increase in coercivity but a decrease in remanence. The demagnetization processes of single-phase materials with enhanced remanence are different from those of nanocomposites consisting of hard and soft phases, in that no exchange-spring magnet behaviour was observed for single-phase ribbons of Nd₂Fe₁₄B with a nanocrystalline structure. A negative deviation of the demagnetization remanence from the Wohlfarth model [15] was observed due to exchange coupling.