A study of the transferred hyperfine field and spin–lattice relaxation time of [N(CH3)4]2CuCl4[N(CH3)4]2CuCl4 single crystals

The molecular susceptibility and paramagnetic shift of [N(CH3)4]2CuCl4[N(CH3)4]2CuCl4 single crystals were measured, and from these experimental results we obtained the transferred hyperfine interaction, HhfHhf, due to the spin transfer from Cu2+Cu2+ ions to [N(CH3)4]+[N(CH3)4]+ ions. We conclude that the decrease in HhfHhf with increasing temperature is not sufficient to allow the spin transfer between Cu2+Cu2+ ions and the nuclear spins of the nonmagnetic [N(CH3)4]+[N(CH3)4]+ ions in the lattice. In addition, the proton spin–lattice relaxation time, T1T1, of [N(CH3)4]2CuCl4[N(CH3)4]2CuCl4 single crystals was determined as a function of temperature; the variation in T1T1 with temperature exhibited discontinuities near 263 and 200 K, confirming previous reports of phase transitions at these temperatures. Comparison of the T1T1 and HhfHhf results revealed that T1T1 decreases with increasing HhfHhf, which is the opposite of the trend reported for [N(CH3)4]2CoCl4[N(CH3)4]2CoCl4. This difference may be due to differences in the electronic structures of Co and Cu ions: Cu2+Cu2+ has one s electron outside closed d   shells whereas Co2+Co2+ has unpaired dd electrons, which screen the nuclear charge from the motion of the outer electrons.