Spin Injection and Transport in Organic Materials

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.

Simulation and Theory of Classical Spin Hopping on a Lattice

The behavior of spin for incoherently hopping carriers is critical to understand in a variety of systems such as organic semiconductors, amorphous semiconductors, and muon-implanted materials. This work specifically examined the spin relaxation of hopping spin/charge carriers through a cubic lattice in the presence of varying degrees of energy disorder when the carrier spin is treated classically and random spin rotations are suffered during the hopping process (to mimic spin–orbit coupling effects) instead of during the wait time period (which would be more appropriate for hyperfine coupling). The problem was studied under a variety of different assumptions regarding the hopping rates and the random local fields. In some cases, analytic solutions for the spin relaxation rate were obtained. In all the models, we found that exponentially distributed energy disorder led to a drastic reduction in spin polarization losses that fell nonexponentially.