Energy product enhancement in sufficiently exchange-coupled nanocomposite ferrites

Ferrite based hard-soft magnetic nanocomposites with the composition of (100 − x) SrFe₁₀Al₂O₁₉/(x) Co_0.8Ni_0.2Fe₂O₄, where x = 10, 15, 20 and 30 wt%, were prepared by one-pot sol-gel auto-combustion method. The nanocomposites prepared by this method showed crystallographically two phase behavior, but magnetically a good single phase exchange spring-coupled behavior with high saturation as well as high coercivity. The nature of magnetic interactions in these nanocomposites and their magnetic properties were evaluated in detail using various characteristic methods including vibrating sample magnetometer measurements, Henkel plots measurements, magnetic force microscopy and magneto-optical Kerr effect microscopy. Microstructural evolution showed formation of soft phase below the critical size of exchange length in the vicinity of hard phase. The nanocomposite with 15 wt% of soft phase showed a 10.5% increase in the maximum energy product compared to pure hard phase and reaches as high as 29.5 kJ/m³ that is a high value of (BH)_max for this type of materials.