Complex Magnetic Phases in Nanosized Core@Shell Prussian Blue Analogue Cubes: Rb_0.48Co[Fe(CN)₆]_0.75[(H₂O)₆]_0.25·0.34H₂O@K_0.36Ni[Cr(CN)₆]_0.74[(H₂O)₆]_0.26·0.11H₂O

Abstract

Different magnetic phases have been identified in nanosized core/shell Prussian blue analogue (PBA) cubes, with a 250 nm Rb–Co–Fe phase (Rb0.48Co[Fe(CN)6]0.75[(H2O)6]0.25·0.34H2O) in the core coated by a 45 nm K–Ni–Cr phase (K0.36Ni[Cr(CN)6]0.74[(H2O)6]0.26·0.11H2O) on the shell. Three separate characteristic temperatures at 86, 69, and 67 K are associated with magnetic phases in the K–Ni–Cr shell. Two magnetic exchange paths are identified. One propagates along the three crystallographic axis directions. The other propagates along the [110] crystallographic direction for the associated Ni–Ni interactions, but not for Cr–Cr interactions. The severe Cr deficiency and the appearance of direct Ni–Ni exchange are used to understand the appearance of two separate transitions associated with magnetic ordering. A weak moment develops in the core at low temperature, corresponding to separate ordering of the Co–Fe PBA network.