Structure and thermodynamic properties of a weakly-coupled antiferromagnetic spin-1/2 chain compound (C5H12N)CuBr3
Abstract
Single crystals of a metal organic complex (C5H12N)CuBr3 (C5H12N = piperidinium, pipH for short) have been synthesized and the structure was determined by single-crystal X-ray diffraction. (pipH)CuBr3 crystallizes in the monoclinic group C2/c. Edging-sharing CuBr5 units link to form zigzag chains along the c axis and the neighboring Cu(II) ions with spin-1/2 are bridged by bi-bromide ions. Magnetic susceptibility data down to 1.8 K can be well fitted by the Bonner-Fisher formula for antiferromagnetic spin-1/2 chain, giving the intrachain magnetic coupling constant J 17 K. At zero field, (pipH)CuBr3 shows three-dimensional (3D) order below TN = 1.68 K. Calculated by the mean-field theory, the interchain coupling constant J' = 0.65 K is obtained and the ordered magnetic moment m0 is about 0.20 μB. This value of m0 makes (pipH)CuBr3 a rare compound suitable to study the dimensional crossover problem in magnetism, since both 3D order and one-dimensional (1D) quantum fluctuations are prominent. In addition, specific heat measurements reveal two successive magnetic transitions with lowering temperature when external field H ≥ 3 T is applied along the a' axis. The H - T phase diagram of (pipH)CuBr3 is roughly constructed. The interplay between exchange interactions, dimensionality, Zeeman energy and possible Dzyaloshinkii-Moriya interaction should be the driving force for the multiple phase transitions.
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