Magnetic phases of the quasi-two-dimensional antiferromagnetCuCrO2on a triangular lattice

Abstract

We have carried out 63,65 Cu NMR spectra measurements in magnetic field up to about 45 T on single crystal of a multiferroic triangular antiferromagnet CuCrO2. The measurements were performed for magnetic fields aligned along the crystal c-axis. Field and temperature evolution of the spectral shape demonstrates a number of phase transitions. It was found that the 3D magnetic ordering takes place in the low field range (H 15 T). At higher fields magnetic structures form within individual triangular planes whereas the spin directions of the magnetic ions from neighboring planes are not correlated. It is established that the 2D-3D transition is hysteretic in field and temperature. Lineshape analysis reveals several possible magnetic structures existing within individual planes for different phases of CuCrO2. Within certain regions on the magnetic H-T phase diagram of CuCrO2 a 3D magnetic ordering with tensor order parameter is expected.

Search for a nematic phase in the quasi-two-dimensional antiferromagnet CuCrO2 by NMR in an electric field

“…We emphasize that the high-field helmet shaped spectra persists up to 45 T (Ref. [4]). Similar measurements carried out at different temperatures allow us to determine the upper boundary of the first-order phase transition from the 3D spiral to the 3D phase with tensor order parameter.…”

“…Two regions, identified as C and PM, demonstrate single peaked NMR spectra and can be attributed to a collinear up-up-down (UUD) and paramagnetic structures, respectively. 4 The electric field does not appreciably change the shape of the spectra in Fig.2. Nevertheless note that near the transition (15.933 T ≤ µ 0 H 0 ≤ 19.975 T) there is a difference between the E = 0 spectra (A) and the E = 0 spectra (B): The intensity of the central peak as compared to the left and right ones is bigger for the spectra (B).…”

“…As elaborated in Refs. [3,4] the "double-horn" and "helmet" shaped NMR spectra in CuCrO 2 are specific for incommensurate magnetic structures within triangular planes with inter-plane order and disorder, respectively. We emphasize that the high-field helmet shaped spectra persists up to 45 T (Ref.…”

“…The rest of the points are taken from Ref. [4]. There are two regions, marked as '3D-spiral phase' and 'Polar nematic phase', that are identified with either double-horn or helmet-shaped spectra.…”

“…1,2 The transition observed at ≈ 15 T was interpreted in Ref. [4] as a transition to 3D ordered phase with tensor order parameter. The main properties of magnetic structure realized in CuCrO 2 at low magnetic fields such as incommensurability, the peculiarities of magnetic anisotropy, electrical polarization and weak elastic distortions of the lattice can be naturally explained in the frame of Dzyaloshinskii-Landau theory of magnetic phase transitions given in Ref.…”