Synthesis of colloidal solutions of SrFe12O19 plate-like nanoparticles featuring extraordinary magnetic-field-dependent optical transmission

Abstract

Hard-magnetic plate-like nanoparticles of SrFe 12 O 19 were synthesised hydrothermally. The particles, fixed in a polymer, exhibited a coercivity in the range 0.9-1.8 kOe, and the saturation magnetization values reached 64 emu g À1 . Electrostatically stabilized aqueous colloidal solutions of the plate-like particles with average thickness of 5-8 nm and average diameter of 30-80 nm were prepared. The nanoparticles readily oriented when applying a weak magnetic field as low as a few Oe, and due to the linear dichroism phenomena a strong change in the optical transmittance of the solution took place. The extinction coefficient ratio for the perpendicular and the parallel light's electric field vector relative to the magnetic field direction was found to be up to 4.5. The experimental results were compared with a theoretical model, in which the optical absorption of the nanoparticles was calculated from the polarizability of oblate ellipsoids.

Width-controlled M-type hexagonal strontium ferrite (SrFe12O19) nanoribbons with high saturation magnetization and superior coercivity synthesized by electrospinning

“…Of which, the highest M s of 67.9 emu·g −1 or 346.29 emu·cm −3 ( ρ ≈ 5.1 g·cm −3 ) and H c of 7.31 kOe for S3 are slightly smaller than the values of 74.3 emu·g −1 and 7.4 kOe for theoretical limits predicted by Stoner–Wohlfarth 5 , respectively. Moreover, they are larger than the corresponding reported values of all 1D 2 21 22 23 , several typical 0D 7 47 48 49 50 51 and 2D 9 10 52 53 nanostructures of pure SrFe 12 O 19 in recent years ( Table 2 ). Their remanence ratios ( M r / M s ) are basically equivalent and approximately equal to 0.55.…”

“…Nevertheless, a further improvement of its permanent magnetic performance is still of great significance 2 6 . Plenty of work has indicated theoretically and experimentally that magnetic properties of nanomaterials are highly relevant with their microstructures, dimensions, components and preparation methods 2 5 7 8 9 10 .…”

Rapid Formation of a Monolayer of Oriented Hard‐Magnetic Strontium Hexaferrite Nanoparticles on a Solid Substrate

“…This behavior is drastically differs from hard magnetic properties of fixed strontium hexaferrite nanoparticles due to free rotation of the nanoparticles under external magnetic field. Fitting of the M(H) curve according to the model described in [10] gives an average particle volume of 3 Â 10 4 nm 3 which roughly equal to that found by TEM (2.3 Â 10 4 nm 3 ). These findings testify that such colloidal solutions contain mostly separate nanocrystals of strontium hexaferrite.…”

“…The resulting glass-ceramic samples were treated with acetic acid solution and subsequently with water to dissolve matrix strontium borate phases and to extract the hexaferrite nanoparticles to the colloidal solution by a procedure described in ref. [10]. This way three different colloidal solutions were prepared: A (T an ¼ 630°C, t ¼ 120 min), B (T an ¼ 680°C, t ¼ 100 min), and C (T an ¼ 680°C, t ¼ 0 min).…”

“…A silicate glass was chosen as a substrate material, since during our preliminary experiments we observed irreversible adsorption of the strontium hexaferrite nanoparticles from the colloidal solution on the walls of glass containers. [10] …”