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

Abstract

Exchange coupled nanocrystalline Ni_0.8Zn_0.2Fe₂O₄ (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 °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 °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 °C. However, as further increasing the annealing temperature to 1100 °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.