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

Different magnetic phases have been identified in nanosized core/shell Prussian blue analogue (PBA) cubes, with a 250 nm Rb-Co-Fe phase (Rb_0.48Co[Fe(CN)₆]_0.75[(H₂O)₆]_0.25·0.34H₂O) in the core coated by a 45 nm K-Ni-Cr phase (K_0.36Ni[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.