Nanocrystalline Ni0.8Zn0.2Fe2O4/SrFe12O19 composite fibers with enhanced exchange coupling behavior

Exchange coupled nanocrystalline Ni0.8Zn0.2Fe2O4 (NZFO)/SrFe12O19 (SFO) composite fibers were successfully fabricated using the sol-gel spinning technique followed by annealing. Pure phase nanocrystalline composite fibers, consisting of magnetically soft NZFO and hard SFO phases, were obtained at 900 degrees C for 2 h in air. The results showed that the magnetic properties of the NZFO/SFO composite fibers strongly depended on annealing temperature. At the annealing temperature of 900 degrees C, the hysteresis loop of the NZFO/SFO composite fiber showed a single-phase-like magnetic characteristic, indicating the existence of effective exchange coupling between the NZFO phase and the SFO phase. The saturation magnetization (M-s), coercive force (H-c) and remanence (M-r) increased initially, reaching their maximum values at 1000 degrees C. However, as further increasing the annealing temperature to 1100 degrees C, a constrictive hysteresis loop appeared which implied the reduction of exchange coupling interactions and therefore decreased the magnetic properties of NZFO/SFO composite fibers.