Increase in the Magnetic Ordering Temperature (T) as a Function of the Applied Pressure for AMn[Mn(CN)] (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, for AMn[Mn(CN)] (A = K, Rb, Cs). In the case of monoclinic A = K and Rb, dT/dp values are 21.2 and 14.6 K GPa, respectively, and T 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 and about 11.4 K GPa above 0.6 GPa, and an overall T increase by 26% at 1.0 GPa. The increase in T is attributed to deformation of the structure such that the Mn-N≡C angle decreases with increasing pressure. The smaller the alkali cation, the greater the decrease in the Mn-N≡C angle induced by pressure and the larger the increase of dT/dp. This is in accordance with the ambient-pressure structures for AMn[Mn(CN)] (A = K, Rb, Cs), which have decreasing Mn-N≡C angles that correlate to the observed increasing Ts as K > Rb > Cs. The large increase in T 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.