Structural and Magnetic Studies of Metal-Insulator Transition in Thiospinel CuIr₂S₄

Structural and Transport Properties of CuIr2(S,Se)4 under High Pressure.

“…Because of the broad transition in the resistivity, it is difficult to estimate the pressure coefficient dTM.I/dP correctly, but roughly it was obtained to be 0.2-0.3K/GPa. These results are in agreement with the previous works [2,7]. The insulating phase is stable up to 10 GPa , that is the maximum pressure in the present work .…”

“…The metallic phase appears in higher temperature region and the resistivity shows a discontinuous change at the metal-insulator (M-I) transition. An activation energy of 47 meV was obtained in the temperature range from 140K to 200 K. Accompanied with the transition, a structural transition from the cubic to the tetragonal lattice was also observed [2]. The volume of the metallic cubic phase at higher temperature becomes smaller by 0.7% at the transition to the insulating tetragonal phase.…”

“…Therefore, the diamagnetic property in the insulating phase indicated from the magnetic susceptibility [2] is interpreted as the formation of Ir4+ dimers. This might be consistent with the observation of some superstructure spots in the X-ray diffraction for the insulating phase.…”

“…It seems to indicate the existence of some superstructure originated from small atomic displacements. In addition, it was found that a magnetic transition occurs from paramagnetic in the metallic phase to diamagnetic in the insulating phase [2,3].…”

NMR Study of the Dimerized State in CuIr2S4

“…This 1vHT is accompanied by a structural transition from cubic to tetragonal (trielinic) H)'IIlInetry vvith volume contraction of 0.7%. [4] Recently, a precit-ie X-ray measurement [5] has shmvn that a charge ordering of 11'3+ and Ir1+ and spin dimerization of Ir1+ ions occurs simultaneously belmv 'l',H T. The Ir su blattice consists of two type of Ir bicapped hexagonal rings \vhich described &'3 11':3+ and 1r 4 + octamert-i. In order to elucidate the origin of the 1HT in the Cu-t-ipineIH, it it-i important to accuIIllllate the information about the valence state and magnetic properties in the insulating state from a microscopic point of vie\v.…”