Magnetically tunable colloidal photonic structures in alkanol solutions

The development of magnetically responsive and tunable photonic structures in alkanol solutions that can operate in nonaqueous solutions was reported. The procedure was found to produce Fe₃O₄ colloidal nanocrystal clusters (CNC) with sizes only up to 200 nm, which limit the maximum diffraction wavelength to below ca. 800 nm. The reflection spectra shows that under a steadily rising magnetic field, the Fe₃O₄ aqueous system starts to form ordered structures at 130 nm and the diffraction intensity reaches its maximum. The diffraction spectra of the Fe₃O ₄@SiO₂ colloids can be modified by changing the thickness of the silica shell. For strong hydrogen-bonding solvents such as methanol, ethanol, and ethylene glycol, solvation layers are relatively thick such that the colloids diffract light at longer wavelengths under a magnetic field.