Structure and magnetism in the Zn–Mn–O system: A candidate for room temperature ferromagnetic semiconductor

The reactivity of the Zn–Mn–O system, prepared by conventional ceramic routes using ZnO and MnO2 as starting materials are described and correlated with the magnetic response. X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy techniques have been used for the structural analysis. The ferromagnetic response is unambiguously determined to be due to the simultaneous presence of Mn+3 and Mn+4 ions at the Zn diffusion front into the manganese oxide grain. Thus, it is demonstrated that Mn does not incorporate into the ZnO lattice substitutionally, but it is the Zn that diffuses into the manganese oxide grains, acting as a retardant of the manganese reduction, Mn+4 → Mn+3. At the diffusion front, both ions coexist and their spins couple ferromagnetically through a double exchange mechanism. This mechanism explains the origin of the room temperature ferromagnetism recently discovered in Zn–Mn–O system as a promising material for spintronic devices.