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Report No.

Magnetoelectric coupling in the honeycomb antiferromagnet Co$$_{4}$$Nb$$_{2}$$O$$_{9}$$

Khanh, N. D.*; Abe, Nobuyuki*; Sagayama, Hajime*; Nakao, Akiko*; Hanashima, Takayasu*; Kiyanagi, Ryoji ; Tokunaga, Yusuke*; Arima, Takahisa*

The magnetic structure and magnetoelectric effect have been investigated for single crystals of the antiferromagnet Co$$_{4}$$Nb$$_{2}$$O$$_{9}$$. Single-crystal neutron diffraction and magnetic susceptibility measurement have revealed that the magnetic structure is different from a collinear arrangement with spin parallel to the trigonal axis as proposed previously. Co$$^{2+}$$ magnetic moments are found to be almost lying in the basal plane, which lowers the magnetic symmetry to $$C2/c'$$ with the propagation vector $$k$$ = 0. Associated with the magnetic phase transition, a sharp anomaly in the dielectric constant and displacement current indicate the appearance of the magnetoelectric below Neel temperature TN with a large coupling constant up to 30 ps/m. The existence of off-diagonal components in a magnetoelectric tensor indicate the formation of ferrotoroidic order in Co$$_{4}$$Nb$$_{2}$$O$$_{9}$$. Such a magnetoelectric effect can be ascribed to the reduction of symmetry caused by simple antiferromagnetic order in a honeycomb network.



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Category:Materials Science, Multidisciplinary



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