Optically switchable magnetic materials are becoming increasingly important in the field of high-density information storage media. [1][2][3] We have been trying to prepare new types of magnets in which the magnetic properties can be controlled by photo-illumination. Our previous work has shown that cobalt-iron cyanide exhibits photoinduced magnetization effects due to an internal electron transfer.[4] However, practical examples of such photo-magnetic systems are limited in number [5] because the strategies that are necessary to achieve photoinduced switching in the solid state are yet to be clarified.The use of organized organic assemblies to direct the formation of mesoscopic inorganic structures under mild conditions and the attempts to intercalate inorganic materials into functional organic molecules are also of topical interest. [6] We have focused our attention on composite materials as a novel strategy for realizing such photo-functional magnetic systems. These include the incorporation of organic photochromes into magnetic systems, for example, photo-controllable magnetic vesicles and Langmuir-Blodgett films containing Prussian blue (a ferromagnet at low temperature) and azobenzene. [7] Although the examples described above show interesting photo-responsive phenomena, the results were only achieved at low temperature. It is evident that the temperature at which photo-switching occurs needs to be increased to room temperature in order to realize devices for practical applications. In the present work we have focused on iron oxide

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Optically switchable magnetic materials are becoming increasingly important in the field of high-density information storage media. [1][2][3] We have been trying to prepare new types of magnets in which the magnetic properties can be controlled by photo-illumination. Our previous work has shown that cobalt-iron cyanide exhibits photoinduced magnetization effects due to an internal electron transfer.[4] However, practical examples of such photo-magnetic systems are limited in number [5] because the strategies that are necessary to achieve photoinduced switching in the solid state are yet to be clarified.The use of organized organic assemblies to direct the formation of mesoscopic inorganic structures under mild conditions and the attempts to intercalate inorganic materials into functional organic molecules are also of topical interest. [6] We have focused our attention on composite materials as a novel strategy for realizing such photo-functional magnetic systems. These include the incorporation of organic photochromes into magnetic systems, for example, photo-controllable magnetic vesicles and Langmuir-Blodgett films containing Prussian blue (a ferromagnet at low temperature) and azobenzene. [7] Although the examples described above show interesting photo-responsive phenomena, the results were only achieved at low temperature. It is evident that the temperature at which photo-switching occurs needs to be increased to room temperature in order to realize devices for practical applications. In the present work we have focused on iron oxide