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 TB near room temperature and high saturation magnetization of MS = 59 emu/g, attributed to ferrimagnetic nano-monodomains with critical size. Meanwhile, the synthesized BFO shows an unusual superparamagnetic behavior with TB = 20 K and an interesting magnetic transition from the blocked superparamagnetic state to quantum superparamagnetic state at a critical temperature Tc = 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.