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arXiv · 2007.06561

Noncollinear antiferromagnetic order in the buckled honeycomb lattice of magnetoelectric Co4Ta2O9 determined by single-crystal neutron diffraction

Sungkyun Choi·Dong Gun Oh·Matthias J. Gutmann·Shangke Pan·Gideok Kim·Kwanghyo Son·Jaewook Kim·Nara Lee·Sang-Wook Cheong·Young Jai Choi·Valery Kiryukhin
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Abstract

Co4Ta2O9 exhibits a three-dimensional magnetic lattice based on the buckled honeycomb motif. It shows unusual magnetoelectric effects, including the sign change and non-linearity. These effects cannot be understood without the detailed knowledge of the magnetic structure. Herein, we report neutron diffraction and direction-dependent magnetic susceptibility measurements on Co4Ta2O9 single crystals. Below 20.3 K, we find a long-range antiferromagnetic order in the alternating buckled and flat honeycomb layers of Co2+ ions stacked along the c axis. Within experimental accuracy, the magnetic moments lie in the ab plane. They form a canted antiferromagnetic structure with a tilt angle of ~ 14 degrees at 15 K in the buckled layers, while the magnetic moments in each flat layer are collinear. This is directly evidenced by a finite (0, 0, 3) magnetic Bragg peak intensity, which would be absent in the collinear magnetic order. The magnetic space group is C2'/c. It is different from the previously reported C2/c' group, also found in the isostructural Co4Nb2O9. The revised magnetic structure successfully explains the major features of the magnetoelectric tensor of Co4Ta2O9 within the framework of the spin-flop model.

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Sungkyun Choi, Dong Gun Oh, Matthias J. Gutmann, Shangke Pan, Gideok Kim, Kwanghyo Son, Jaewook Kim, Nara Lee, Sang-Wook Cheong, Young Jai Choi, Valery Kiryukhin. 2021-01-13. Noncollinear antiferromagnetic order in the buckled honeycomb lattice of magnetoelectric Co4Ta2O9 determined by single-crystal neutron diffraction. https://doi.org/10.1103/physrevb.102.214404

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