ABSTRACT
The pressure dependence of the magnetic properties of ferrimagnetic Mn(II)(TCNE)I(OH2) up to 14.05 kbar and Mn(II)(TCNE)(3/2)(I3)(1/2)·zTHF up to 14.32 kbar were studied. For Mn(II)(TCNE)I(OH2), two distinct pressure regions separated at â¼1 kbar were evident in both the temperature and the field-dependent magnetic measurements. No increase of the magnetic properties was observed in the low-pressure region, while significant increases to the magnetic ordering temperature, T(c), bifurcation temperature, T(b), coercive field, H(cr), and remnant magnetization, M(r), were evident in the high-pressure region. The T(c), T(b), H(cr), M(r), and M(5 T) reversibly increased from ambient pressure values of 169 K, 169 K, 690 Oe, 620 emuOe/mol, and 13,800 emuOe/mol to 257 K, 261 K, 1460 Oe, 2300 emuOe/mol, and 17,100 emuOe/mol at 14.05 kbar, respectively. For Mn(II)(TCNE)(3/2)(I3)(1/2)·zTHF, the T(c) and T(b) were nearly coincident and increased linearly from 173 and 173 K, respectively, at ambient pressure to 273 and 272 K, respectively, at 14.32 kbar. Thus, the T(c) increased at an average rate of 6.25 and 7.18 K/kbar for Mn(II)(TCNE)I(OH2) and Mn(II)(TCNE)(3/2)(I3)(1/2)·zTHF, respectively. For Mn(TCNE)(1/2)(I3)(1/2)·zTHF remnant magnetization and saturation magnetization did not significantly change with applied pressure. The H(cr) exhibited a linear increase from ambient pressure to 5.00 kbar, reaching 860 Oe, but only achieving 880 Oe at 14.32 kbar.
ABSTRACT
Mn(II)(TCNE)[C(4)(CN)(8)](1/2) (TCNE = tetracyanoethylene) exhibits a reversible pressure-induced piezomagnetic transition from a low magnetization antiferromagnetic state to a high magnetization ferrimagnetic state above 0.50 ± 0.15 kbar. In the ferrimagnetic state, the critical temperature, T(c), increases with increasing hydrostatic pressure and is ~97 K at 12.6 kbar, the magnetization increases by 3 orders of magnitude (1000-fold), and the material becomes a hard magnet with a significant remnant magnetization.
ABSTRACT
Mn(II)(TCNE)I(OH(2)) was isolated from the reaction of tetracyanoethylene (TCNE) and MnI(2)(THF)(3), and has a 2-D structure possessing an unusual, asymmetric bonded µ(4)-[TCNE]Ë(-). Direct antiferromagnetic coupling between the S = 5/2 Mn(II) and S = 1/2 [TCNE]Ë(-) leads to magnetic ordering as a canted antiferrimagnet at a T(c) of 171 K.
