Effects of Hydrostatic Pressure and Uniaxial Strain on Spin-Peierls Transition in an Organic Radical Magnet, BBDTA·InCl₄

Abstract

We investigated the effects of hydrostatic pressure and uniaxial strain on the spin-Peierls (SP) transition of an organic radical magnet, benzo[1,2-d:4,5-d′]bis[1,3,2]dithiazole(BBDTA)·InCl₄. It has a one-dimensional coordination polymer structure along its c-axis and its SP transition occurs at 108 K. The SP transition temperature T_SP decreased to 99 K at a hydrostatic pressure of 10 kbar, while it increased to 132 K at a uniaxial strain along the c-axis of 8 kbar. The pressure dependences of T_SP under these two conditions were discussed by evaluating two parameters, namely, the intrachain interaction 2J⁄k_B and the effective spin–lattice coupling parameter η, that are related to T_SP by the equation T_SP=1.6ηJ⁄k_B. Under ambient pressure, the a- and c-axes of this material shortened monotonically with decreasing temperature, while the b-axis elongated below T_SP. In this study, we found the correlation between η and the change in the lattice constant b. 2J⁄k_B increased with increasing hydrostatic pressure and uniaxial strain, suggesting that the contraction along the c-axis does not depend on the manner of pressurization. From the evaluation of η, the observed variation in T_SP is explained by the difference between the changes in b under the two pressurization conditions.