Increase in the Magnetic Ordering Temperature (Tc) as a Function of the Applied Pressure for A2Mn[Mn(CN)6] (A = K, Rb, Cs) Prussian Blue Analogues

Magnetization measurements under pressure reveal that the external hydrostatic pressure significantly increases in the ferrimagnetic transition temperature, T-c, for A(2)Mn[Mn(CN)(6)] (A = K, Rb, Cs). In the case of monoclinic A = K and Rb, dT(c)/dp values are 21.2 and 14.6 K GPa(-1), respectively, and T-c increases by 53 and 39%, respectively, from ambient pressure to 1.0 GPa. The cubic A = Cs compound also shows a monotonous increase with an initial rate of 4.22 K GPa(-1) and about 11.4 K GPa(-1) above 0.6 GPa, and an overall T-c increase by 26% at 1.0 GPa. The increase in T-c is attributed to deformation of the structure such that the Mn-II-N equivalent to C angle decreases with increasing pressure. The smaller the alkali cation, the greater the decrease in the Mn-II-N equivalent to C angle induced by pressure and the larger the increase of dT(c)/dp. This is in accordance with the ambient-pressure structures for A(2)Mn[Mn(CN)(6)] (A = K, Rb, Cs), which have decreasing Mn-II-N equivalent to C angles that correlate to the observed increasing T(c)s as K > Rb > Cs. The large increase in T-c for the A = K compound is the highest class among several cyano-bridged metal complexes. The tuning of the transition temperature by such a weak pressure may lead to additional applications such as switching devices.