ИСТИНА

Class of hard magnetic ferrites is not numerous, but it attracts much interest for industrial ap-plications due to their broad availability, appropriate magnetic properties and low cost. Epsilon iron oxide (ε-Fe2O3) is only rare-earth-free nanosized material possessing a giant coercivity (i.e. > 20 kOe) at room temperature, which makes it gripping for durable magnetic recording media and hard magnetic tips for magnetic force microscopy. Furthermore, due to its natural ferromagnetic resonance absorption in sub-terahertz (100 – 222 GHz) range and room temperature multiferroic properties ε-Fe2O3 is of great interest for high-frequency and spintronics applications. As a pure material epsilon iron oxide can be obtained only in a kind of nanoparticles stabilized within silica matrix and thin films stabilized by a substrate. However, most of applications require a monolithic bulk material such as ceramics. A ceramics fabrication process includes a heat treatment to sinter the initial powder, which usually leads to particle growth due to the Ostwald ripening. Because of metastable thermodynamic nature of ε-Fe2O3 with an increase of its particle size the ε-phase easily transforms to more stable hematite α-Fe2O3. As a result, there is a challenge to obtain ceramics based on pure ε-Fe2O3. In this study epsilon-iron oxide samples were obtained via an economical surfactant - and alka-line-free sol-gel method using a rapid hydrolysis of TEOS in an aqueous alcohol solution of iron (III) nitrate. Obtained nanopowders of pure ε-Fe2O3 phase were pressed in tablets and sintered at 500-1000°С for 30 min. At 800°С and higher sintering temperatures, α-Fe2O3 emerges. The nanoceramics sintered at 700 °C reveals the coercivity of 20 kOe and the natural ferromagnetic resonance frequency of 176 GHz at a specific density of 60%, which corresponds to pure ε-Fe2O3 phase. Since the devel-oped synthetic technique is fast and effective, it is advantageous for industrial applications to produce materials for high-density magnetic recording and as well as for terahertz technologies. Support by RSF Grant 21-79-10184 is acknowledged.