Magnetic microstructure of YFe11Ti aggregates

The microstructure and magnetic domain configuration of splat-quenched YFe11Ti aggregates have been investigated by transmission electron microscopy, Lorentz microscopy and magnetic force microscopy. The splat-quenched material adopted essentially the ThMn12-type structure and displayed an equiaxed polycrystalline microstructure with a scattered presence of α-Fe(Ti). Lorentz microscopy and magnetic force microscopy showed that the critical size for single-domain behaviour in the splat-quenched aggregates is close to 100 nm. Annealing induced a decrease in coercivity justified by overall grain coarsening and additional α-Fe(Ti) formation. Lorentz microscopy evidenced stripe/maze patterns in coarse YFe11Ti grains; while coarse α-Fe(Ti) grains exhibited vortex configurations resulting from accommodation to the demagnetizing fields of adjacent YFe11Ti grains. Planar defects with twin appearance and thermal antiphase boundaries have been observed in YFe11Ti grains but showed no interaction with domain walls. On the other hand, grain boundaries and in particular grain-boundary triple joints exhibited a moderate pinning effect.