Dislocation nucleation: Diffusive origins.

observed by Meiklejohn and Bean1 (cobalt particles in shells of antiferromagnetic cobalt oxide); both are inhomogeneous and the coexistence of a ferromagnetic and an antiferromagnetic phase gives rise to large exchange bias. This demonstration of tuning the composition of certain Heusler alloys to attain exceptionally high exchange bias fields indicates a route for designing rare-earth-free hard magnets, built of two hard magnetic phases in contrast to exchange spring magnets where a soft magnetic phase is exchange coupled to a hard magnetic phase. A second step towards exchange-biased hard magnets would be realized if the fraction of nonpercolating ferromagnetic phase could be increased, thus achieving much higher magnetization, while possibly maintaining high values of the exchange bias and the coercive field. This would provide high enough remnant magnetization for an applicable permanent magnet. The remaining big challenge is to find the material combination where these favourable hard magnetic properties are preserved well above room temperature. ❐