Synthesis of magnetically exchange coupled SrFe₁₂O₁₉/FeCo composites through cryogenic ball milling

SrFe₁₂O₁₉/FeCo composite particles with different mass ratios of SrFe₁₂O₁₉ to FeCo were synthesized through a cryogenic ball milling process. The corresponding products were characterized with scanning electron microscopy (SED), transmission electron microscopy (TEM), x-ray diffraction (XRD) and vibrating sample magnetometer (VSM) for crystal morphology, elemental distribution, crystal phases, and magnetic properties. The results showed that when the mass percentage of FeCo was less than 15%, smooth magnetic hysteresis loops could be obtained from SrFe₁₂O₁₉/FeCo composite particles, indicating effective magnetic exchange coupling between the SrFe₁₂O₁₉ and FeCo particles. A further FeCo mass increase resulted in kinks in the magnetic hysteresis loop and destroyed the magnetic exchange coupling. As a comparison, room temperature ball milling of SrFe₁₂O₁₉/FeCo (95/5 wt%) cannot achieve magnetic exchange coupling between SrFe₁₂O₁₉ and FeCo due to FeCo nanoparticle agglomeration. (paper)