Novel photoactive magnetic semiconductor nanocomposites with potential magneto-optical properties

A novel magnetic semiconductor nanocomposite based on functionalized magnetite nanoparticles (MNPs) embedded in a matrix of bismuth ferrate compound (BFO) was obtained in a single step for the first time using the microwave-assisted hydrothermal synthesis. The synthesis method allows obtaining multiferroic BFO small particles and MNPs-BFO nanocomposites with optical activity in the near-infrared region (1.6 eV) due to d-d charge transfer transitions on Fe(III) ion orbitals. The functionalized MNPs exhibit strong superparamagnetic behavior with blocking temperature T-B near room temperature and high saturation magnetization of M-S = 59 emu/g, attributed to ferrimagnetic nano-monodomains with critical size. Meanwhile, the synthesized BFO shows an unusual superparamagnetic behavior with T-B = 20 K and an interesting magnetic transition from the blocked superparamagnetic state to quantum superparamagnetic state at a critical temperature T-c = 11 K, attributed to ferromagnetic very small, critical size nano-monodomains. As result, the MNPs-BFO nanocomposite shows a superparamagnetic behavior at room temperature which, in close connection with its optical properties, makes it an excellent candidate for infrared magneto-optical applications.