Sprayed Nanometer-Thick Hard Magnetic Coatings with Strong Perpendicular Anisotropy for Data-Storage Applications

by Andrei Chumakov (FS-PETRA-D (FS-PET-D Fachgruppe P03))




The rapid growth of digital information in the world necessitates a big leap in improving the existing technologies for magnetic recording. For the best modern perpendicular recording, the highest coercivity materials with minimal volume are required. We present a study of a facile technology for establishing mono- and multi-layer surfaces from various single-domain flat magnetic nanoparticles that exhibit a strong perpendicular-oriented magnetic moment on solid and flexible substrates. Surfactant-free, hard ferromagnetic and single-domain anisotropic strontium hexaferrite SrFe12O19 nanoparticles with perpendicular magnetic moment orientation and two different aspect ratios are self-ordered into magnetic thin nanofilms exploiting the templating effect of cellulose nanofibrils and magnetic fields. Uniform magnetic coatings obtained by scalable layer-by-layer spray deposition from a monolayer coverage up to thicknesses of a few tens of nanometers show preferred in-plane orientation of the hard-magnetic nanoparticles. High coercivities of the films of up to 5 kOe and high perpendicular anisotropy of MR┴/MS>80% are found. Application of the magnetic field during film deposition ensures additional improvement in perpendicular magnetic anisotropy and the appearance of residual magnetization in the film of up to 0,6MS. For low aspect ratio nanoparticles stacked in periodic planar structures, the signs of the photonic bandgap are revealed. The ability to create scalable, thin magnetic structures based on nanosized particles/building blocks opens great opportunities for their application in a wide variety of optoelectronic and magnetic storage devices.