Magnetic structure and Dzyaloshinskii-Moriya interaction in theS=12helical-honeycomb antiferromagnetα−Cu2V2

Abstract

Magnetic properties of the S = 1/2 antiferromagnet α-Cu2V2O7 have been studied using magnetization, Quantum Monte Carlo (QMC) simulations, and neutron diffraction. Magnetic susceptibility shows a broad peak at ∼ 50 K followed by an abrupt increase indicative of a phase transition to a magnetically ordered state at TN = 33.4(1) K. Above TN , a fit to the Curie-Weiss law gives a Curie-Weiss temperature of Θ = −73(1) K suggesting the dominant antiferromagnetic coupling. The result of the QMC calculations on the helical-honeycomb spin network with two antiferromagnetic exchange interactions J1 and J2 provides a better fit to the susceptibility than the previously proposed spin-chain model. Two sets of the coupling parameters J1 : J2 = 1 : 0.45 with J1 = 5.79(1) meV and 0.65 : 1 with J2 = 6.31(1) meV yield equally good fits down to ∼ TN . Below TN , weak ferromagnetism due to spin canting is observed. The canting is caused by the Dzyaloshinskii-Moriya interaction with an estimated bc-plane component |Dp| 0.14J1. Neutron diffraction reveals that the S = 1/2 Cu 2+ spins antiferromagnetically align in the F d d 2 magnetic space group. The ordered moment of 0.93(9) µB is predominantly along the crystallographic a-axis.

Nonreciprocal spin Seebeck effect in antiferromagnets

“…Below T N = 33.4 K, α-Cu 2 V 2 O 7 shows an antiferromagnetic order, where Cu 2+ spins (S = 1/2) align antiparallel along [100] [ Fig. 2(a)] with a small canting along [001] [9,[21][22][23]. The magnon bands obtained by a recent neutron scattering experiment indicate the presence of the strong uniform DM interaction [9] similar to the polar AFMs discussed above.…”

Bound spinon excitations in the spin- 12 anisotropic triangular antiferromagnet Ca3ReO5Cl2

“…In particular, an incommensurate spiral order often induces a wave-vector shift of the magnons, as we have discussed so far. Another example is α-Cu 2 V 2 O 7 , which exhibits a commensurate collinear antiferromagnetic order [68]. The uniform DM component parallel to the magnetic moment shifts the minimum of the magnon branches to the incommensurate wave-vector position [69].…”

Nonreciprocal Magnons and Symmetry-Breaking in the Noncentrosymmetric Antiferromagnet

“…In particular, the absence of spatial inversion symmetry in magnetic systems causes the relativistic spin-orbit coupling, which gives rise to many intriguing phenomena such as the spin Hall effect [7], topological insulators [8], multiferroics [9], and noncentrosymmetric superconductors [10], to acquire antisymmetric Dzyaloshinskii-Moriya (DM) interactions [5,6]. For noncentrosymmetric α-Cu 2 V 2 O 7 , the crystal structure breaks spatial inversion symmetry [11,12], and the antiferromagnetic ordering below T N = 33.4 K [13,14] breaks time reversal symmetry. The simultaneous breaking of both symmetries sets the stage for the intertwining electric and magnetic properties [14,15] and for the existence of toroidal moments [16][17][18].…”