Enhancement of magnetic properties by spark plasma sintering of hydrothermally synthesised SrFe12O19

Abstract

Platelet-shaped nano-crystallites of SrFe₁₂O₁₉ were hydrothermally synthesised and compacted into bulk magnets using Spark Plasma Sintering (SPS). Pellets were obtained with densities >90% of the theoretical crystallographic density. Compaction of the as-synthesised powders at 950 °C for 2 minutes causes improved alignment of the crystallites within the pellet, compared with room-temperature compaction. Applying an external magnetic field prior to the SPS compaction further increases the degree of alignment leading to an enhanced magnetic saturation and remanence, resulting in a 25% improvement of the energy product (BH_max), from 21.5 kJ m⁻³ obtained without magnetic alignment to 27.0 kJ m⁻³ with the applied magnetic field. Post-annealing of the SPS-pressed pellets improves the magnetic saturation even further leading to an increase of the energy product to 30.4 kJ m⁻³. Ball milling, on the other hand, diminishes the magnetic remanence, causing a reduction of the energy product.