Anisotropic Photoinduced Magnetism in Thin Films of the Prussian Blue Analogue A_jCo_k[Fe(CN)₆]_l·nH₂O

The photoinduced magnetism in thin films of the Prussian blue analogue AjCok[Fe(CN)6]l·nH2O 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 (TC) of 17 K, and in applied fields of less than ∼1.5 kG. The thin films with formulas Rb0.7Co4[Fe(CN)6]3.0, Rb2.3Co4[Fe(CN)6]3.1, and K0.5Co4[Fe(CN)6]3.2 were generated using sequential adsorption methods, alternately immersing the Melinex solid support in solutions of the constituent Co2+ 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.