Magnetically exchange coupled SrFe12O19/Fe-Co composites with different mass percentage of Fe-Co were synthesized through an ex situ process. The morphology, magnetic properties, and crystallization of SrFe12O19/Fe-Co composites were investigated. Lower mass percentage of Fe-Co presented an even distribution of Fe-Co nanoparticles on the surface of SrFe12O19, and effective magnetic exchange coupling between Fe-Co and SrFe12O19. Higher mass percentage of Fe-Co leads to an agglomeration of Fe-Co nanoparticles on SrFe12O19 surface, and a weak magnetic exchange coupling between Fe-Co and SrFe12O19. This ex situ process proposed a new method to synthesize magnetically exchange coupled SrFe12O19/Fe-Co core/shell composites with precise control of the magnetic properties. This method can also be potentially used for other hard/soft magnetic composite synthesis.

We have calculated the electronic structure of MnB using first-principles calculations based on the density functional theory within the local-spin-density approximation. The temperature dependence of saturation magnetization [Ms(T)] was calculated by mean field approximation. The calculated density of states (DOS) shows that the energy region near the Fermi energy (EF) is mostly attributed to the d bands of Mn. The saturation magnetizations (Ms) of MnB were calculated to be 964.5 emu/cm3 (1.21 T) at 0 K and 859.3 emu/cm3 (1.08 T) at 300 K. The calculated Ms at 300 K is in good agreement with experimental Ms of 851.5 emu/cm3.

We have calculated electronic structures of nanocrystalline Fe90−xCuxSi10−yBy using first principles calculations based on density functional theory (DFT) to obtain saturation magnetic flux density (Bs). The Bs of crystalline (Fe3Si) and amorphous (Fe-B) phases in Fe90−xCuxSi10−yBy were separately calculated, and the total Bs of Fe90−xCuxSi10−yBy was derived by the summation of the Bs for the Fe3Si and Fe-B phases. The calculated Bs of Fe3Si is 1.35 T, and that of Fe-B varies from 2.08 to 2.22 T based on Fe to B ratios. Therefore, a total Bs higher than 1.80 T can be obtained with y ≥ 4 for both x = 1 and 2 in Fe90−xCuxSi10−yBy.