High-performance hexaferrite magnets tailored through alignment of shape-controlled nanocomposites.

Nanoparticles of strontium hexaferrite, SrFeO, were prepared by two different synthesis methods: hydrothermal (autoclave) and sol-gel autocombustion (solid-salt-matrix). The two synthesis pathways yield nanoparticles with different morphologies and correspondingly different magnetic characteristics. The autoclave synthesis results in large plate-like crystallites, which spontaneously align with a preferred crystallographic orientation when applying a uniaxial pressure, but exhibit a relatively poor coercivity.

Elucidating the relationship between nanoparticle morphology, nuclear/magnetic texture and magnetic performance of sintered SrFeO magnets.

Several M-type SrFe12O19 nanoparticle samples with different morphologies have been synthesized by different hydrothermal and sol-gel synthesis methods. Combined Rietveld refinements of neutron and X-ray powder diffraction data with a constrained structural model reveal a clear correlation between crystallite size and long-range magnetic order, which influences the macroscopic magnetic properties of the sample. The tailor-made powder samples were compacted into dense bulk magnets (>90% of the theoretical density) by spark plasma sintering (SPS).

Optimization of magnetic properties in fast consolidated SrFeO nanocrystallites.

The magnetic properties of SrFeO nanocrystallites produced by hydrothermal synthesis and consolidated by Spark Plasma Sintering (SPS) were optimized by varying the compaction parameters: sintering time, sintering temperature, uniaxial pressure or pre-compaction in a magnetic field. Highly textured compacts with a high degree of crystallite alignment were produced. Qualitative and quantitative textural information was obtained based on X-ray diffraction pole figure measurements.

Enhancement of magnetic properties through morphology control of SrFeO nanocrystallites.

Nanocrystallites of the permanent magnetic material SrFeO were synthesised using a conventional sol-gel (CSG) and a modified sol-gel (MSG) synthesis route. In the MSG synthesis, crystallite growth takes place in a solid NaCl matrix, resulting in freestanding nanocrystallites, as opposed to the CSG synthesis, where the produced nanocrystals are strongly intergrown. The resulting nanocrystallites from both methods exhibit similar intrinsic magnetic properties, but significantly different morphology and degree of aggregation.