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In this work, we study magnetic properties and magnetic structure of the frustrated one-dimensional antiferromagnet SrCuTe2O6. Noncentrosymmetric SrCuTe2O6 crystallizes in the chiral cubic space group P4132 with lattice parameter a = 12.473(1) Å. The crystal structure consists of CuO4 square plates, units of TeO3, and oxygen octahedra surrounding strontium (Sr) atoms. The Cu2+ ions in the CuO4 plaquettes carry spin 1/2 and give rise to the magnetic properties of this system. The spin network for S=1/2 Cu2+ spins consists of three types of intertwined networks connected by the nearest-, second-nearest-, and third-nearest-neighbor exchange interactions J1 , J2 , and J3, respectively. The spins connected by J1 form an isolated triangle with Cu-O-Sr- O-Cu superexchange pathways. The second-nearest-neighbor network formed by J2 via Cu-O-Te-O-Cu pathways connect the spins to form a hyper-kagome network. J3 links the spins to form spin chains along the cubic crystallographic axes. First principle calculations performed to estimate the strength of these exchange interactions showed that, J3 is the most dominant with J2 about 10% of J3 and J1 about 1% of J3, and established that SrCuTe2O6 is a spin-chain system with relatively weak and intricate frustrated interchain couplings.

Our magnetization measurements on single-crystal SrCuTe2O6 reveal highly isotropic magnetic susceptibility along the three inequivalent directions [100], [110], and [111] in this cubic system. The value of the leading exchange interaction (J3/kB) estimated using a quantum Monte Carlo simulation on the 1D spin-chain model is between 50.1 and 52.5 K. The order parameter measured by neutron scattering confirms that the system magnetically orders below TN1 = 5.25(5) K. However, from our zero-field neutron diffraction measurements, we are unable to confirm the field-dependent second transition at lower TN2, which was previously observed in magnetization and heat capacity measurements. Further in-field neutron scattering measurements are required to investigate this second transition. Based on the neutron diffraction data on the powder and single-crystal samples, the magnetic structure in the Shubnikov space group P4132, where the Cu2+ S = 1/2 spins antiferromagnetically align along the direction perpendicular to the spin chain, is proposed with the ordered magnetic moment of 0.52(6)μB. This work suggests the dominance of the intrachain interaction J3 over the frustrated J1 and J2 bonds, and sheds light on the difference in magnetic ground states between SrCuTe2O6 and PbCuTe2O6. The 48% reduction of the ordered moment in SrCuTe2O6 points to the residual effect of frustration, which could have nontrivial influence on spin dynamics in this magnetically ordered system.

Reference

P. Saeaun , Y. Zhao, P. Piyawongwatthana, T. J. Sato, F. C. Chou, M. Avdeev, G. Gitgeatpong, and K. Matan, Physical Review B 102, 134407 (2020). [link] [arXiv:2007.03268]