Pressure Induced Crossover between a Ferromagnetic and a Canted Antiferromagnetic State for [Bis(pentamethylcyclopentadienyl)-iron(III)][Tetracyanoethenide], [FeCp2*][TCNE]

Pressure and temperature dependences of the canting angle and increase in the magnetic ordering temperature, Tc(P), for the weak ferromagnet Li+[TCNE]˙- (TCNE = tetracyanoethylene)

The hydrostatic pressure dependence of the magnetic ordering temperature, T_c(P), for the interpenetrating, diamondoid lattice-structured, weak ferromagnet (= canted antiferromagnet) Li⁺[TCNE]˙^- (TCNE = tetracyanoethylene) reversibly increases from 20.9 to 23.4 K at 9.73 kbar, an increase of 12% with a rate of increase, dT_c/dP, of 0.27 K kbar^-1. The 5 T magnetization increased by 672% from 186 emu Oe mol^-1 at ambient pressure to an average of 1440 emuOe mol^-1 upon application of pressure. The remanent magnetization initially increases 30% from 10.8 to 14.0 emuOe mol^-1 from ambient to 0.06 kbar, and increases further by 6% to a maximum of 14.8 emuOe mol^-1 at 0.56 kbar before declining by 22% to 11.5 emuOe mol^-1 at 9.73 kbar. The pressure-dependent coercive field, H_cr(P), initially decreases by 42% from 31.1 Oe at ambient pressure to 18 Oe at 0.06 kbar, then increases to 52 Oe at 9.73 kbar. The canting angle, α, increases by 28% from 0.52° to 0.66° at 0.06 kbar, then decreases by 23% to 0.51° at 9.73 kbar, as well as increases by 2% from 0.536° to 0.548° from 1.8 to 2.5 K, before decreasing by 79% to 0.117° at 19 K. The interlattice interactions are attributed to be the primary exchange mechanism. Thus, α(T) and α(P) have similar dependencies that are attributed to a competition between an increase and a decrease in the intra- and interlayer C⋯N interlattice separations as the temperature and pressure increases.

Local Lattice Distortions in Mn[N(CN)2]2 under Pressure

We combined synchrotron-based infrared spectroscopy, Raman scattering, and diamond anvil cell techniques with complementary lattice dynamics calculations to reveal local lattice distortions in Mn[N(CN)2]2 under compression. Strikingly, we found a series of transitions involving octahedral counter-rotations, changes in the local Mn environment, and deformations of the superexchange pathway. In addition to reinforcing magnetic property trends, these pressure-induced local lattice distortions may provide an avenue for the development of new functionalities.