Synthesis and magnetic properties of 4:1 hard-soft SrFe12O19-La1-xSrxMnO3 nanocomposite prepared by auto-combustion method

Magnetic nanocomposite (hard) SrFe12O19-(soft) La(1-x) SrxMnO3 powders in 4:1 weight ratio was synthesized via a one-pot auto-combustion technique using nitrate salts followed by heat treatment in air at 950°C. Structural and morphological characterizations were performed via x-ray diffraction (XRD) and transmission electron microscopy (TEM). Vibrating sample magnetometer (VSM) was used to study the magnetic properties of the samples. XRD analysis shows presence of pure phase components in the nanocomposite. TEM images show presence of needle shape Sr-Ferrite particles. The room temperature hysteresis loops of the samples showed the presence of exchange-coupling between the hard and soft phases of the composite. The room temperature magnetic measurements revealed the higher Mr/Ms ratio for the nanocomposite than that for the single phase SrFe12O19 which proves the existence of the inter-grain exchange coupling between hard and soft magnetic phases with the exchange spring behavior. The highest Mr/Ms ratio of 0.58 was obtained in SrFe12O19- La0.25Sr0.75MnO3 composite which exhibited 82% increase in the coercivity (Hc∼6.26 kOe) as compared to pure SrFe12O19 (Hc∼3.63kOe). Synthesis of hard-soft exchange couple nanocomposite by controlling the “magnetic softness” of a soft phase instead of more traditional approach of varying concentration of the soft phase could be the promising way to use them in many magnetic applications.