Alexander V. Vasiliev

Rotational dynamics of colloidal hexaferrite nanoplates

Here, we report an experimental study on the rotational dynamics of hard magnetic hexaferrite nanoparticles in water. A stable aqueous colloid of SrFe12O19 was synthesized by the borate glass-ceramic dissolution technique and studied by TEM, small-angle X-ray scattering (SAXS), magnetometry, and optical transmission methods in applied DC and AC magnetic fields. The particles represent nanoplates with a mean diameter of 50 nm and a mean thickness of 5 nm having a coercive force of 4700 Oe and a saturation magnetization of 51.5 emu/g. According to magnetic field dependent SAXS data, a probability orientation function was suggested considering the colloidal particle rotation in the applied field as an activation-free process. The magnetization dynamics of the colloidal rotators was described by an interplay of magnetic torque and drag force in the frame of a non-interacting particle model. At frequencies below 100 Hz, the particles are able to fully rotate after the magnetic field. At higher frequencies, the complete following becomes impossible due to the energy dissipation and the particle movement changes to oscillations around randomly oriented axes. These vibrational axes can be aligned by a strong external permanent magnetic field, causing the coherent particle oscillations and correspondingly the rise of the high-frequency response of the colloid optical transmission. As a result, the efficient magneto-optical light modulation has been achieved at frequencies exceeding 5 kHz, revealing the fastest response rates among known colloidal magneto-optical media.Here, we report an experimental study on the rotational dynamics of hard magnetic hexaferrite nanoparticles in water. A stable aqueous colloid of SrFe12O19 was synthesized by the borate glass-ceramic dissolution technique and studied by TEM, small-angle X-ray scattering (SAXS), magnetometry, and optical transmission methods in applied DC and AC magnetic fields. The particles represent nanoplates with a mean diameter of 50 nm and a mean thickness of 5 nm having a coercive force of 4700 Oe and a saturation magnetization of 51.5 emu/g. According to magnetic field dependent SAXS data, a probability orientation function was suggested considering the colloidal particle rotation in the applied field as an activation-free process. The magnetization dynamics of the colloidal rotators was described by an interplay of magnetic torque and drag force in the frame of a non-interacting particle model. At frequencies below 100 Hz, the particles are able to fully rotate after the magnetic field. At higher frequencies, the...

Synthesis and Properties of Magnetoresistive (La,Sr)MnO3-Based Glass-Ceramic Borate-Matrix Composites

Magnetic glass-ceramic borate-matrix composites containing micron-sized lanthanum strontium manganite grains have been prepared by ceramming amorphous La2O3-SrO-MnOx-B2O3 materials at 800 and 900°C. The glass-ceramics had a magnetization of up to 48.7 A m2/kg in a magnetic field of 400 kA/m. Their relative magnetoresistance reached 6.2% at 290 K in a magnetic field of 80 kA/m and 16% at 77 K in a field of 160 kA/m.