Creation of New memory devices with functional harmonized artificial lattices and elucidation of phase transition

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Photo induced ferromagnetism in Spinel-Ferrite (Natural superlattice with "Kagome Lattice")The spin-glass system consists of various metastable states depending on the degree of 'spin freezing '. Accordingly, applying appropriate external fields such as light perturbation to the spin-glass state is able to cause a 'melt' of the frozen spins and accelerate the magnetic relaxation, giving rise to an increase of the magnetization up to a new steady state value. We have demonstrated the high temperature spin glass and photo-induced magnetization in the spinel-type ferrite films.Room temperature spin-glass states have been found in (Mg,Fe) {Mg,Fe,Ti}_2O_4, (Co, Zn)FeO_4 and (Ru. Al) FeO_4 spinel ferrite thin films. Here we have reported that room temperature spin-glass has been achieved by the fine-tuning of spin states through the control of composition, random oxygen deficiencies and the stress induced by the film/substrate lattice mismatch in hetero-epitaxial films. All of which give rise to effects that enhance the exchange interaction of spins in the ferrite films. We have demonstrated the change of magnetic state by means of light-irradiation from spin-glass to a ferri-magnet over a wide range of temperatures up to 300 K. The direct photo-excitation of spins with photon energy around 2.0 eV, which corresponds to the spin excitation energy for Fe ions, is the most effective for realizing photo-induced magnetization. Therefore, we can demonstrate that the photo induced ferromagnetism in Spinel-Ferrite (Natural superlattice with "Kagome Lattice").