Heterostructured thin films consisting of distinct layers of the Prussian blue analogues Rb a Co b [Fe(CN)6] c ·mH2O (CoFe PBA) and Rb j M k [Cr(CN)6] l ·nH2O (MCr PBA, where M = Ni or Co) have been fabricated, and their photomagnetic properties have been investigated. The CoFe PBA is known to be photoactive, with light induced changes in the unit cell size and the spin states below ∼150 K and magnetic order below ∼20 K. The NiCr and CoCr PBAs do not have native photoeffects, but are known to have higher magnetic ordering temperatures (T C NiCr ∼ 70 K, T C CoCr ∼ 30 K), and a pressure dependence of the magnetization. The layered heterostructures are synthesized using aqueous chemistry and sequential adsorption techniques that allow for fine control of layer thickness. Some of the heterostructured films show photoinduced magnetization changes up to the ordering temperatures of the MCr PBA component, behavior that is not seen when the individual materials are measured separately. A variety of different layer arrangements and thicknesses has been investigated with the goal of identifying structures that optimize the photocontrol of the magnetic response in the MCr PBA lattices, which are in intimate contact with the photoactive CoFe PBA lattices. The new behavior is optimized when the constituent layers have thicknesses on the order of hundreds of nanometers. When layers are too thin, it is shown that mixing of ions at the interface between PBA components leads to mixed-metal phases. The concurrence of the maximum temperature of the large photomagnetic effect with the native ordering temperature of the MCr PBA lattice, as well as its magnetic field dependence, supports the interpretation that the photocontrol is the result of photoinduced structural changes in the CoFe PBA lattice coupling to the MCr PBA component of the heterostructure, inducing random magnetic anisotropy.

Nanoparticles of rubidium cobalt hexacyanoferrate (Rb j Co k [Fe(CN) 6 ] l · nH 2 O) were synthesized using different concentrations of polyvinylpyrrolidone (PVP) to produce four different batches of particles with characteristic diameters ranging from 3 to 13 nm. Upon illumination with white light at 5 K, the magnetization of these particles increases. The long-range ferrimagnetic ordering temperatures and the coercive fields evolve with nanoparticle size. At 2 K, particles with diameters less than approximately 10 nm provide a Curie-like magnetic signal.

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A magneto-optically active thin film of Rb j Co k [Fe(CN) 6 ] l ·nH 2 O has been prepared using a sequential assembly method. Upon irradiation with light and at 5 K, the net magnetization of the film increased when the surface of the film was oriented parallel to the external magnetic field of 0.1 T. However, when the surface of the film was perpendicular to the field, the net magnetization decreased upon irradiation. The presence of dipolar fields and the low-dimensional nature of the system are used to describe the orientation dependence of the photoinduced magnetization.The ability to increase or decrease the photoinduced magnetization by changing the orientation of the system with respect to the field is a new phenomenon that may be useful in future device applications.

The photoinduced magnetism in thin films of the Prussian blue analogue A j Co k [Fe(CN) 6 ] l · nH 2 O deposited on Melinex solid supports is anisotropic, exhibiting a photoinduced increase when oriented parallel to the external magnetic field and a decrease when oriented perpendicular. The anisotropic behavior is observed for films less than ∼200 nm thick below nominally 10 K, which is less than the ferrimagnetic ordering temperature (T C ) of 17 K, and in applied fields of less than ∼1.5 kG. The thin films with formulas Rb 0.7 Co 4 [Fe(CN) 6 ] 3.0 , Rb 2.3 Co 4 [Fe(CN) 6 ] 3.1 , and K 0.5 Co 4 [Fe(CN) 6 ] 3.2 were generated using sequential adsorption methods, alternately immersing the Melinex solid support in solutions of the constituent Co 2+ and [Fe(CN) 6 ] 3-ions. Film thickness is controlled by the number of deposition cycles and by variations in the deposition protocols. Measurements on films with different alkali ions and with different stoichiometry indicate that the microscopic mechanism for the photoinduced magnetization is the same in the films as in the bulk material. The unique anisotropy is qualitatively associated with the interface between the magnetic film and the solid support. Detailed studies of the influence of film thickness, applied field strength, and temperature support this description.