Persistent Photocontrolled Magnetism in Core-Shell Prussian Blue Analogues

Cubic heterostructured (\textbf{BA}) particles of Prussian blue analogues, composed of shells of ferromagnetic K$_j$Ni$_k$[Cr(CN)$_6$]$_l\cdot n$H$_2$O (\textbf{A}), \mbox{$T_c\sim70$~K}, surrounding bulk cores ($\sim350$~nm) of photoactive ferrimagnetic Rb$_a$Co$_b$[Fe(CN)$_6$]$_c\cdot m$H$_2$O (\textbf{B}), $T_c\sim20$~K, have been studied. \mbox{Below} $T_c\sim 70$~K, these samples exhibit a persistent photoinduced decrease in low-field magnetization, resembling results from previous core-shell particles\footnote{M.F. Dumont \emph{et al.}, Inorg. Chem. \textbf{50} (2011) 4295.} and analogous \textbf{ABA} films.\footnote{D.M. Pajerowski \emph{et al.}, J. Am. Chem. Soc. \textbf{132} (2010) 4058.} This net decrease suggests that the photoinduced lattice expansion in the \textbf{B} layer generates a strain-induced decrease in the magnetization of the \textbf{A} layer, similar to a pressure-induced decrease observed by others in a pure \textbf{A} material\footnote{M. Zentkov\'a \emph{et al.}, J. Phys.: Condens. Matter \textbf{19} (2007) 266217.} and by us in the \textbf{BA} cubes. To quantify the length scale over which the photoinduced strain dissipates into the \textbf{A} layer, a series of \textbf{B} and \textbf{BA} cubes of varying shell thickness have been characterized.