Magnetic field induced transition in the charge-glass former theta-(BEDT-TTF)2CsCo(SCN)4

We perform thermodynamic and transport measurements on a magnetic charge-glass former, theta-(BEDT-TTF)2CsCo(SCN)4, to discuss the pi-d interaction occurring in the interlayer direction. An anomalous temperature dependence and sharp peak structure of the heat capacity are observed in magnetic fields, indi-cating a field-induced transition in this compound. Furthermore, a sharp peak of the thermoelectric power is also observed in magnetic fields, supporting the presence of the field-induced transition. Comparison with a nonmagnetic analog compound indicates that the introduction of magnetic Co2+ ions (S = 3/2) triggers this transition. This strongly suggests that the pi-d interaction effectively works in this compound and affects the physical properties. To explain the field-induced phenomenon in this compound, we propose a speculative scenario in which the pi-d interaction between the pi spins in the insulating domains and the d spin of Co2+ induces the reconstruction of the domain structure in the CG state.