Magnetic-field effects on the reentrance transition of the alloy of pristine and fully deuterated (DMeDCNQI)/sub 2/Cu

Summary form only given. The title compound undergoes a metal-insulator-metal reentrance transition with decreasing temperature. The metal-insulator transition occurring at the higher transition temperature has been ascribed to the combination of a Peierls instability in the /spl pi/ -like band of DCNQI molecular stacks and the so-called 4K/sub F/ instability of d-like band of copper ions. We investigate possible origins of ´the reentrance transition to the metallic state with decreasing temperature. The electrical resistance of the title compound is measured in the metal-insulator-metal reentrance transition regime as functions of temperature and magnetic field under pressure up to 12 MPa (120 bar). Its heat capacity is measured in vacuum in the range of 0.1 K to evaluate the electronic density-of-states. Also the lattice parameter was measured at ambient pressure as functions of temperature. We found resistance enhancement by the application of magnetic fields in the vicinity of the insulating state. We propose that this transition is ascribed to the stabilization of Cu/sup 2+/ ionic state having paramagnetic spins. The idea is consistent with the lattice parameter change accompanying the reentrance transition. We found, in addition, the density-of-states is not anomalously large as an organic conductor. This suggests the reentrance transition is hardly explained in terms of the heavy electron model. We will discuss alternative models for the reentrance transition.