Pressure Dependence of the Magnetic Ordering Temperature (Tc) for the Na2Mn[Mn(CN)6] Noncubic Prussian Blue Analogue

Abstract

The pressure dependence of the magnetic properties of rhombohedral Na₂Mn[Mn(CN)₆] up to 10 kbar has been studied. The magnetic ordering temperature, T_c, for Na₂Mn[Mn(CN)₆] reversibly increases with increasing applied hydrostatic pressure, P, by 9.0 K (15.2%) to 68 K at 10 kbar with an average rate of increase, dT_c/dP, of 0.86 K/kbar. The magnetization at 50 kOe and remanent magnetization, M_r(H), remain constant with an average value of 13,100 ± 200 and 8500 ± 200 emuOe/mol. The coercive field H_cr increases by 12% from 13,400 to 15,000 Oe. The increase and rate of increase of T_c for rhombohedral Na₂Mn[Mn(CN)₆] are reduced with respect to monoclinic A₂Mn[Mn(CN)₆] (A = K and Rb), but they are still greater than those of cubic Cs₂Mn[Mn(CN)₆]. This is attributed to the compression of the MnNC framework bonding without decreasing ∠Mn^II-N≡C, maintaining the unit cell in accord with cubic A = Cs at lower applied pressures, and not due to reduction in ∠Mn^II-N≡C, which correlates with increasing T_c that is reported for A = K and Rb as well as Cs at higher applied pressures.