Diffusion in nanocrystalline magnetic materials

In this work the diffusion in dense and structurally stable nanocrystalline samples was studied without any influence of porosity, relaxation and migration of the grain boundaries. Soft and hard magnetic materials are used as a model system, because in these materials the self diffusion is important for the generation of the magnetic anisotropy. In the soft-magnetic nanocrystalline alloys Fe73.5Si13.5B9Nb3Cu1 and Fe90Zr7B3, the interfacial diffusion characteristics is determined by intergranular amorphous phases with strongly reduced diffusivities compared to grain boundaries in metals. Indication for a second fast interfacial diffusion path is found for nanocrystalline Fe90Zr7B3. In Fe73.5Si13.5B9Nb3Cu1 the Ge diffusion is much slower than the Fe-diffusion due to Fe3Si nanocrystallites with D03-ordering. The permanent magnetic material Nd2Fe14B exhibits an intergranular melting transition which is used for inducing a magnetic texture by hot deformation. Below this intergranular melting transition the product δDB of interface diffusion coefficient DB and interface thickness δ is similar to that in grain boundaries of coarse grained α-Fe. A strong increase of δDB above the intergranular melting transition is observed. (orig.)