Infrared phonon anomaly and magnetic excitations in single-crystal Cu3Bi(SeO3)2O

Kevin H. Miller

¹

,

Peter W. Stephens

²

,

C. Martin

³

et al.

Abstract

Infrared reflection and transmission as a function of temperature have been measured on single crystals of Cu3Bi(SeO3)2O2Cl. The complex dielectric function and optical properties along all three principal axes of the orthorhombic cell were obtained via Kramers-Kronig analysis and by fits to a Drude-Lorentz model. Below 115 K, 16 additional modes (8(E â)+6(E b )+2(E ĉ)) appear in the phonon spectra; however, powder x-ray diffraction measurements do not detect a new structure at 85 K. Potential explanations for the new phonon modes are discussed. Transmission in the far infrared as a function of temperature has revealed magnetic excitations originating below the magnetic ordering temperature (Tc ∼24 K). The origin of the excitations in the magnetically ordered state will be discussed in terms of their response to different polarizations of incident light, behavior in externally-applied magnetic fields, and the anisotropic magnetic properties of Cu3Bi(SeO3)2O2Cl as determined by d.c. susceptibility measurements.2

Lattice and magnetic instabilities in Cu3Bi(SeO3)2OGnezdilov1, Pashkevich2, Lemmens3 et al. 2017Phys. Rev. B235190View full textAdd to dashboardCite

“…In general, the observed behaviour in the temperature regime T N < T < T* is consistent with the temperature behaviour of the a and b lattice parameters reported in Ref. 6. At T N we observed a jump of the frequency which is associated with the onset of magnetic ordering.…”

“…This anomaly is not observed in the magnetization and can be ascribed to the structural phase transition, as found in infrared (IR) spectroscopy 6 and birefringence measurements. Freshly cleaved plate-like samples with size of about 3 × 3 × 1 mm 3 were used for the Raman scattering investigations.…”

“…Note that a magnon excitation with the same energy was observed in an IR study of Cu 3 Bi(SeO 3 ) 2 O 2 Cl. 6 The spectral lineshape of this magnetic mode is asymmetric which we take as evidence of strong coupling with the neighbouring phonon mode. TO modes may appear in the Raman spectra at our experimental conditions.…”

“…Earlier experimental investigations revealed: (i) almost identical magnetic properties for the bromide and chloride compounds with the magnetic ordering temperatures 27.4 and 24 K, respectively, 3,4,5,6 (ii) two magnetic modes at low temperatures at 1.23 meV (9.92 cm -1 ) and 1.28 meV (10.32 cm -1 ) in X = Br 5 and two modes at 1.18 meV (9.5 cm -1 ) and 4.1 meV (33.1 cm -1 ) in X = Cl 6 , and (iii) the existence of a structural phase transition with symmetry lowering at T ≈ 115 K in X = Cl. 6 The magnetic structure has already been discussed in Refs.…”

“…In particular, Raman scattering provides a way to distinguish possible ground states. 7 , 8 Recently, this technique has been successfully applied to characterize the excitation spectrum of the spin liquid state in a Heisenberg S = 1/2 antiferromagnet on a perfect kagome lattice -herbertsmithite ZnCu 3 (OH) 6 2 ) with slightly distorted, kagome planes demonstrate that even small modifications of the crystal structure may have a huge effect on its properties. 10 Here, we report on a detailed study of the temperature dependence of the vibrational and magnetic excitations in Cu 3 Bi(SeO 3 ) 2 O 2 X (X = Cl, Br).…”