Improved performance of SrFe12O19 bulk magnets through bottom-up nanostructuring†
The influence of synthesis and compaction parameters is investigated with regards to formation of high performance SrFe12O19 bulk magnets. The produced magnets consist of highly aligned, single-magnetic domain nanoplatelets of SrFe12O19. The relationship between the magnetic performance of the samples and their structural features is established through systematic characterization by Vibrating Sample Magnetometry (VSM) and Rietveld refinement of powder X-ray diffraction data (PXRD). The analysis is supported by complementary techniques including Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and X-ray pole figure measurements. SrFe12O19 hexagonal nanoplatelets with various sizes are synthesized by a supercritical hydrothermal flow method. The crystallite sizes are tuned by varying the Fe/Sr ratio in the precursor solution. Compaction of SrFe12O19 nanoplatelets into bulk magnets is performed by Spark Plasma Sintering (SPS). Rietveld refinement of the pressed pellets and texture analysis of pole figure measurements reveal that SPS pressing produces a high degree of alignment of the nanoplatelets, achieved without applying any magnetic field prior or during compaction. The highly aligned nanocrystallites combined with crystal growth during SPS give rise to an enormous enhancement of the magnetic properties compared to the as-synthesized powders, leading to high performance bulk magnets with energy products of 26 kJ m−3.