Photo-Enhanced Ferromagnetism in High K+-Containing K-Ni-Cr Prussian Blue Analogues Coated on Rb-Co-Fe Nanocubes

Many fascinating magnetic behaviors have been identified in Prussian blue analogues (PBAs) with a general chemical formula of A
_x
M[M'(CN)
₆
]
_y
·nH
₂
O (denoted as A-M-M'), where M and M' can be divalent or trivalent transition metal ions and A is a monovalent alkali ion that is accommodated in the voids enclosed by the MN
₆
and M'C
₆
octahedra. Their magnetic characteristics depend not only on the intrinsic nature of the complexes, but can also be greatly altered by extrinsic stimulations, such as the applied pressure or light irradiation. [1]-[3] In particular, one very promising characteristics is the photo-induced magnetism found in A-Co-Fe (with A = K, Na, Rb, Cs), which has been demonstrated to be sensitive to the type and the amount of A+ ion that has been incorporated into the compound. [1]-[3] This behavior is believed to originate from the electron transfer that occurs between the MN
₆
and M'C
₆
octahedra, known as the charge transfer induced spin transition (CTIST).[4] In addition, the photo-magnetic responses in nano-sized core/shell heterostructures have recently been found to be sensitive to the shell thickness. [5]-[7] No photo-induced magnetism has been identified in isolated K-Ni-Cr, but noticeable reductions (~8%) of the magnetization by light irradiation appear when this material is coated on a Rb-Co-Fe nano-cube.[5]