Pressure Dependence of the Magnetic Ordering Temperature (T_c) 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 ∠MnIINC, maintaining the unit cell in accord with cubic A = Cs at lower applied pressures, and not due to reduction in ∠MnIINC, which correlates with increasing T c that is reported for A = K and Rb as well as Cs at higher applied pressures.

Optical Phenomena in Molecule-Based Magnetic Materials

“…1088−1091 Simultaneously, the pressure-induced structural changes in molecular materials were found to be a tool for switching a broad range of magnetic phenomena from spin transitions, through magnetic ordering to SMM characteristics. 110,268,1092,1093 Concerning the potential switching of both magnetic and optical effects in molecule-based materials, the spin transition systems were reported to be the most promising. As most iron(II) complexes showing the spin-crossover behavior reveal the impact of pressure upon the temperature and cooperativity of the related magnetic transition which usually leads to optical absorption modulation (see section 2), such magnetic molecular systems appear to be suitable for the construction of dual output pressure switches or sensors employing also optical absorption features.…”

“…The pressure and mechanical force were widely recognized as efficient external stimuli for switching light absorption, emission, and other optical effects. − Simultaneously, the pressure-induced structural changes in molecular materials were found to be a tool for switching a broad range of magnetic phenomena from spin transitions, through magnetic ordering to SMM characteristics. ,,, Concerning the potential switching of both magnetic and optical effects in molecule-based materials, the spin transition systems were reported to be the most promising. As most iron­(II) complexes showing the spin-crossover behavior reveal the impact of pressure upon the temperature and cooperativity of the related magnetic transition which usually leads to optical absorption modulation (see section ), such magnetic molecular systems appear to be suitable for the construction of dual output pressure switches or sensors employing also optical absorption features. ,, It is well known and already presented in section that the low-spin Fe II octahedral complexes are usually strongly colored due to their spin-allowed inter-configurational electronic transitions between the fully occupied t 2g end empty e g states.…”

Cation Adaptive Structures Based on Manganese Cyanide Prussian Blue Analogues: Application of Powder Diffraction Data to Solve Complex, Unprecedented Stoichiometries and New Structure Types

“…The 4‐K magnetic structure of monoclinic K 2 Mn[Mn(CN) 6 ] was determined from neutron diffraction and the average ∠Mn−N≡C angle is reduced from 148.8° at 293 K to 144.0° [48] . The high‐spin, S =5/2 N‐bonded Mn II ion has a magnetic moment of 4.4 μ B while the low‐spin, S =1/2 C‐bonded Mn II ion has a moment of −1.0 μ B ; hence, K 2 Mn[Mn(CN) 6 ] has non‐compensated, collinear, antiparallel magnetic moments oriented along the crystallographic b axis, consistent with it being a ferrimagnet, Figure 6, and are in accord with the DFT‐computed values of 4.50 and −1.02 μ B for the high and low‐spin Mn II ions, respectively [48] . Both high‐ and low‐spin Mn II ion are strongly spin polarized and the spin electron density is localized.…”

“…Figure 6. Perspective polyhedral view of the non-compensated, collinear ferrimagnetic structure observed for K 2 Mn[Mn(CN) 6 ] [high-spin Mn(II) is pink/ up arrow (spin up), low-spin Mn(II) is orange/down arrow (spin down), C is black, N is light blue, and K is purple] [48]. …”