ИСТИНА

M-type hexaferrites are promising magnetic materials with high magnetic anisotropy, high saturation magnetization, good chemical stability and inexpensive raw materials. The hard-magnetic particles of SrFe12O19 are typically plate-like. High magnetocrystalline anisotropy of strontium hexaferrite allows plate-like particles to have a magnetic moment perpendicular to the largest face of the crystallite. Such particles have properties of microscopic permanent magnets, so that under an applied magnetic field such particles in the colloid solution will orient themselves and the optical density of the solution will change. At the same time, synthesis of colloid solutions of hard-magnetic hexaferrite particles is rather problematic, because of thermodynamic instability of such solutions however, decreased concentrations of particles could extend coagulation time and make a life-time of magnetic colloids longer. The new method was developed for generation of the colloidal solutions of plate-like SrFe12O19 particles based on the glass crystallization technique and on the hydrothermal method. It’s seem very attractive possibility to use thin-film materials based on single-domain hexaferrite particles in microwave technology as shields, waveguides, filter elements and generators. This is due to the fact that strontium hexaferrite has a ferromagnetic resonance frequency around 60 GHz. Hexaferrite film should be well-textured and magnetized for efficient operation of active microwave components. However, there remains the problem of obtaining simultaneously high-textured and high-coercivity hexaferrite films because the texturing leads to coalescence of grains and a sharp drop in the coercive force. To solve this problem, we used pre-synthesized particles and deposit it onto substrates. Substrates were kept in colloidal solutions in magnetic field (different value and orientation). At the same time adsorption of positively charged nanoparticles take place on a negatively charged surface of the substrate. The aim of the present work – is to investigate self-organization processes of hard-magnetic plate-like nanoparticles in colloidal solutions and on solid surfaces under magnetic field and determine anisotropy of magnetic and magnetooptical properties of formed structures. Obtained plate-like strontium hexaferrite nanoparticles have coercive force >800 Oe, saturation magnetization >20 e.m.u/g, mean diameter between 30 and 220 nm, aspect ratio up to 15. Coercive force of the colloidal solutions is very close to zero. In the solution particles behaved as molecules of paramagnetic gas and showed self-aligning under the applied magnetic field. Dynamic light-scattering data of obtained magnetic fluids indicate the absence of large aggregates. The magnetic properties of the colloidal solutions show that the magnetic field of 100 Oe is enough for complete rotation of the particles in one direction (magnetic field perpendicular to the plane of the particle). Obtained magnetic fluids of SrFe12O19 nanoparticles show significant linear dichroism under the applied magnetic field related to the shape anisotropy of the particles (ratio of optical densities achieved 3.8 for the wavelength 550 nm). Mono-layers of c-oriented nanoparticles were obtained on glass and ITO substrates. We studied the effect of the magnetic field and exposure time on the structure of the resulting planar structures. This work was supported by RFBR, grants 11-08-01256-a and 10-03-00694-а.