Are you an EPFL student looking for a semester project?
Work with us on data science and visualisation projects, and deploy your project as an app on top of Graph Search.
VOCI develops magnetic order below T-N=80.3(3) K. Employing single-crystal x-ray diffraction and powder neutron diffraction it is shown that the magnetic phase transition is accompanied by a small, temperature-dependent monoclinic lattice distortion with gamma=90.212(2)degrees at T=3.2 K. The phase transition presumably is of second order with a critical exponent beta=0.099(12)degrees. The monoclinic distortion lifts the frustration of interchain interactions along 1/2a +/- 1/2b of the orthorhombic room-temperature structure with the result that chains of antiferromagnetic order exist along 1/2a +/- 1/2b while ferromagnetic chains exist along 1/2a +/- 1/2b. Both antiferromagnetic interchain coupling (if stronger along 1/2a +/- 1/2b than along 1/2a +/- 1/2b) and ferromagnetic interchain coupling (if stronger along 1/2a +/- 1/2b than along 1/2a +/- 1/2b) can explain the observed magnetic superstructure with magnetic space group F2'/d' on the 2a X 2b X 2c supercell (standard setting C2'/c') and with magnetic moments parallel to a. Remarkably, the lattice distortion is not accompanied by a structural distortion so that the driving force for the lattice distortion is completely governed by the magnetic interactions.
Bruce Normand, Ying Chen, Sheng Xu, Shuo Li, Xiaoyu Xu, Zeyu Wang, Weiqiang Yu