Spin dynamics in the geometrically frustrated multiferroicCuCrO2

Abstract

The spin dynamics of the geometrically frustrated triangular antiferromagnet multiferroic CuCrO 2 have been mapped out using inelastic neutron scattering. The relevant spin Hamiltonian parameters modelling the incommensurate modulated helicoid have been determined, and correspond to antiferromagnetic nearest and next-nearest neighbour interactions in the ab plane, with a strong planar anisotropy. The weakly dispersive excitation along c reflects the essentially two-dimensional character of the magnetic interactions and according to classical energy calculations it is weakly ferromagnetic. Our results clearly point out the relevance of the balance between a ferromagnetic coupling between adjacent planes and a weakly antiferromagnetic next-nearest neighbour interaction in stabilising the threedimensional ferroelectric magnetic order in CuCrO 2 . This novel insight on the interplay between magnetic interactions in CuCrO 2 should provide a useful basis in the design of new delafossite-based multiferroic materials.2

Lattice dynamics and thermal transport in multiferroicCuCrO2

“…Figure 3-(d-i) shows χ ′′ (Q, E) at low Q zooming on magnetic excitations (12 meV data). As one can observe, the magnetic intensity extends from 0 to 15 meV for Q < 5Å −1 , and remains visible up to 300 K, far above T N ≃ 24 K. Even the 55 meV data measured at 530 K show some remnant magnetic intensity at low Q , see Figure 3-f. A similar observation was also reported by Poienar et al [9], but their measurements were limited to low temperatures (T ⩽ 40 K). We show the temperature dependence of magnetic intensity between 2.25 ⩽ E ⩽ 11 meV in Fig 8-d.…”

“…Thus, it presents an opportunity to study the direct coupling between the magnetic and ferroelectric order parameters [3,4]. A number of studies have investigated the crystal structure, magnetic excitations, magnetization, and electric polarization in CuCrO 2 [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], but little is known about the phonons and their coupling or response to the magnetic/ferroelectric ordering.…”

Magnetic structure of CuCrO2: a single crystal neutron diffraction study

“…The cause of the incommensurability of the propagation vector has been discussed earlier, and two different explanations have been proposed: either an inplane lattice distortion [4,5] or interlayer exchange interaction [20][21][22][23]. The latter is in better agreement with the occurrence of 3-dimensional order, although it had been shown that an interlayer exchange has to be relatively small (<0.2meV) [24]. The maximum ordered moment in our model is 2.8(2) µ B which is close to the expected 3 µ B for the Cr 3+ ion and the reported values from the powder measurements [10,11].…”

Hierarchy of Exchange Interactions in the Triangular-Lattice Spin Liquid YbMgGaO4

“…However, precise numerical calculations for the spin-1=2 TLHAF, which take into account nearest-neighbor interactions only [24][25][26], indicate that quantum fluctuations are not enough to suppress magnetic ordering and the actual ground state is a noncollinear long-range ordered spin structure. Experiments on various spin-S triangular-lattice antiferromagnets have overwhelmingly confirmed this picture [27][28][29][30], with a few noteworthy exceptions [31][32][33]. Several perturbations from the pure TLHAF have been proposed to enhance quantum fluctuations: next-nearest neighbor (NNN) interactions [34][35][36][37][38], ring-exchange terms [39,40], and anisotropic exchange [41][42][43][44], although it remains theoretically unclear if the latter mechanism alone can stabilize a QSL [45][46][47][48].…”