Temperature- and photo-induced phase transition in rubidium manganese hexacyanoferrate

This article describes a temperature- and photo-induced phase transition in rubidium manganese hexacyanoferrate, RbMn[Fe(CN)(6)]. This compound displays a drop in the magnetic susceptibility at 225 K (=T-1/2 down arrow) and an abrupt increase in the magnetic susceptibility at 300K (=T-1/2 up arrow) in the cooling and warming processes, respectively. This phase transition is accompanied by a structural change from cubic (F43m) to tetragonal (14m2). The high-temperature (HT) and low-temperature (LT) phases are composed of Mn-II(S=2/5)-NC-Fe-III(S=1/2) and Mn-III(S = 2)-NC-Fe-II(S = 0), respectively. A metal-to-metal charge transfer from Mn-II to Fe-III and a Jahn-Teller distortion of the produced Mn-III ion cause this phenomenon. The magnetic transition entropy and enthalpy of the LT phase indicate that this phase shows a three-dimensional Heisenberg-type ferromagnetic lattice for the Mn-III sites with a T-c of 11.0 K, which is due to a valence delocalization mechanism. Ferromagnetic magnetization of LT phase in Rb-0.91 Mn-1.05 [Fe(CN)(6)]0.6H(2)O is reduced by irradiation with only one-shot of laser pulse and the quantum yield is above one and reaches 4.5. This photomagnetic effect is caused by a photo-induced phase transition from the LT phase to the HT phase. (c) 2004 Elsevier B.V All rights reserved.