_{4})

_{2}crystal

^{1,a)}, V. I. Fomin

^{1}and A. V. Yeremenko

^{1}

### Abstract

Raman scattering of light in the KTb(WO_{4})_{2}single crystal is investigated in the frequency range of 3–950 cm^{−1} at 5 K. The ground multiplet ^{7} *F* _{6} of Tb^{3+} ion is split by the crystal field with symmetry *C* _{2}, and all the multiplet components are detected. It is found that the first excited electronic quasidoublet consists of two singlet levels of different symmetry and is separated from the ground quasidoublet by ∼75 cm^{−1}. Behavior of all the detected levels is investigated in external magnetic fields**H** ⊥ *C* _{2} and **H** || *C* _{2}. Spectroscopic splitting factors are determined for the ground and excited levels of the Tb^{3+} ion in the KTb(WO_{4})_{2} crystal. Experimental data support the view that at low temperatures the case of Ising anisotropy is realized, and the crystal under study should be considered as a system of two-level magnetic ions.

The authors thank V. V. Eremenko, V. A. Pashchenko, and N. M. Nesterenko for the useful discussion and comments.

I. Introduction

II. Samples and measurement technique

III. Experimental data

IV. Discussion

V. Conclusion

### Key Topics

- Phonons
- 40.0
- Electron scattering
- 19.0
- Tensor methods
- 19.0
- Magnetic fields
- 17.0
- Ground states
- 10.0

## Figures

Behavior of the Raman spectrum in an external magnetic field **H**||*C* _{2} at 5 K. Experimental geometry is *Z*(*YZ*)*X*; symmetry of transitions is *B _{g} *. Spectral resolution is 1.8 cm

^{−1}.

Behavior of the Raman spectrum in an external magnetic field **H**||*C* _{2} at 5 K. Experimental geometry is *Z*(*YZ*)*X*; symmetry of transitions is *B _{g} *. Spectral resolution is 1.8 cm

^{−1}.

Behavior of the frequency (a), the integral intensity (b) for the Raman lines in an external magnetic field **H** || *C* _{2} at 5 K (▪–electronic transition 1, •–electronic transition 2, ○–phonon line with energy of 76.6 cm^{−1}, □–total intensity of the specified lines). Experimental geometry is *Z*(*YZ*)*X*; symmetry of transitions is *B _{g} *. Spectral resolution is 1.8 cm

^{−1}. Diagram of the observed transitions (c).

Behavior of the frequency (a), the integral intensity (b) for the Raman lines in an external magnetic field **H** || *C* _{2} at 5 K (▪–electronic transition 1, •–electronic transition 2, ○–phonon line with energy of 76.6 cm^{−1}, □–total intensity of the specified lines). Experimental geometry is *Z*(*YZ*)*X*; symmetry of transitions is *B _{g} *. Spectral resolution is 1.8 cm

^{−1}. Diagram of the observed transitions (c).

Behavior of the Raman spectrum in an external magnetic field **H**||*C* _{2} at 5 K. Experimental geometry is *Z*(*YY*)*X*; symmetry of transitions is A_{g}. Spectral resolution is 1.8 cm^{−1}. The calculated values of the energies of electronic transitions were obtained from the Lorentzian approximation of spectra and are shown by arrows in this and the subsequent figures.

Behavior of the Raman spectrum in an external magnetic field **H**||*C* _{2} at 5 K. Experimental geometry is *Z*(*YY*)*X*; symmetry of transitions is A_{g}. Spectral resolution is 1.8 cm^{−1}. The calculated values of the energies of electronic transitions were obtained from the Lorentzian approximation of spectra and are shown by arrows in this and the subsequent figures.

Behavior of the Raman spectrum in an external magnetic field **H**||*C* _{2} at 5 K: 0 (*1*), 5 (*2*), 10 (*3*), 15 (*4*), 20 (*5*), 25 (*6*), 30 (*7*) kOe. Experimental geometries *Z*(*YY*)*X* (a) and *Z*(*YZ*)*X* (b) correspond to the symmetries of transitions, *A _{g} * and

*B*, respectively. Spectral resolution is 1.8 cm

_{g}^{−1}. In this and the subsequent figures asterisks denote lines that are “leaking” through due to depolarization of the apparatus and do not belong to the vibrations corresponding to this symmetry.

Behavior of the Raman spectrum in an external magnetic field **H**||*C* _{2} at 5 K: 0 (*1*), 5 (*2*), 10 (*3*), 15 (*4*), 20 (*5*), 25 (*6*), 30 (*7*) kOe. Experimental geometries *Z*(*YY*)*X* (a) and *Z*(*YZ*)*X* (b) correspond to the symmetries of transitions, *A _{g} * and

*B*, respectively. Spectral resolution is 1.8 cm

_{g}^{−1}. In this and the subsequent figures asterisks denote lines that are “leaking” through due to depolarization of the apparatus and do not belong to the vibrations corresponding to this symmetry.

Behavior of the frequency (a), the integral intensity (b), and the half-width (c) of the Raman lines in an external magnetic field **H** || *C* _{2} at 5K (•–electronic transition with energy of 294 cm^{−1}, ○–phonon line with energy of 298.2 cm^{−1}). Experimental geometry is *Z*(*YZ*)*X*; symmetry of transitions is *B _{g} *.

Behavior of the frequency (a), the integral intensity (b), and the half-width (c) of the Raman lines in an external magnetic field **H** || *C* _{2} at 5K (•–electronic transition with energy of 294 cm^{−1}, ○–phonon line with energy of 298.2 cm^{−1}). Experimental geometry is *Z*(*YZ*)*X*; symmetry of transitions is *B _{g} *.

Behavior of the Raman spectrum in an external magnetic field **H**||*C* _{2} at 5 K: 0 (*1*), 5 (*2*), 10 (*3*), 15 (*4*), 20 (*5*), 25 (*6*), 30 (*7*) kOe. Experimental geometry is *Z*(*XZ*)*X* (a) and *Z*(*YZ*)*X* (b), the symmetry of transitions is *B _{g} *. Spectral resolution is 1.8 cm

^{−1}.

Behavior of the Raman spectrum in an external magnetic field **H**||*C* _{2} at 5 K: 0 (*1*), 5 (*2*), 10 (*3*), 15 (*4*), 20 (*5*), 25 (*6*), 30 (*7*) kOe. Experimental geometry is *Z*(*XZ*)*X* (a) and *Z*(*YZ*)*X* (b), the symmetry of transitions is *B _{g} *. Spectral resolution is 1.8 cm

^{−1}.

Behavior of the Raman spectrum (a) and the frequency of observed electronic transitions (b) in an external magnetic field **H** ⊥ *C* _{2} at 5 K: 0 kOe for KDy(WO_{4})_{2} (*1*); 0 (*2*), 10 (*3*), 20 (*4*), 30 (*5*) kOe for KTb(WO_{4})_{2}. Experimental geometry is *X*(*ZZ*)*Y*, the symmetry of transitions is *A _{g} *. Spectral resolution is 1.8 cm

^{−1}.

Behavior of the Raman spectrum (a) and the frequency of observed electronic transitions (b) in an external magnetic field **H** ⊥ *C* _{2} at 5 K: 0 kOe for KDy(WO_{4})_{2} (*1*); 0 (*2*), 10 (*3*), 20 (*4*), 30 (*5*) kOe for KTb(WO_{4})_{2}. Experimental geometry is *X*(*ZZ*)*Y*, the symmetry of transitions is *A _{g} *. Spectral resolution is 1.8 cm

^{−1}.

The behavior of the Raman spectrum (a) and the frequency of observed electronic transitions (b) in an external magnetic field **H** ⊥ *C* _{2} at 5K: 0 (*1*), 5 (*2*), 10 (*3*), 15 (*4*), 20 (*5*), 25 (*6*), 30 (*7*) kOe. Experimental geometries *X*(*ZZ*)*Y* and *X*(*YZ*)*Y* correspond to the *A _{g} * and

*B*symmetries of transitions, respectively. Spectral resolution is 1.8 cm

_{g}^{−1}.

The behavior of the Raman spectrum (a) and the frequency of observed electronic transitions (b) in an external magnetic field **H** ⊥ *C* _{2} at 5K: 0 (*1*), 5 (*2*), 10 (*3*), 15 (*4*), 20 (*5*), 25 (*6*), 30 (*7*) kOe. Experimental geometries *X*(*ZZ*)*Y* and *X*(*YZ*)*Y* correspond to the *A _{g} * and

*B*symmetries of transitions, respectively. Spectral resolution is 1.8 cm

_{g}^{−1}.

The behavior of electronic levels in an external magnetic field **H**||*C* _{2} at 5 K: •–*A _{g} * symmetry of transitions, ○–

*B*symmetry of transitions.

_{g}The behavior of electronic levels in an external magnetic field **H**||*C* _{2} at 5 K: •–*A _{g} * symmetry of transitions, ○–

*B*symmetry of transitions.

_{g}## Tables

The energy of electronic transitions in zero fields, their symmetry, and the spectroscopic splitting factor in a field **H** || *C* _{2}. The alleged separation into quasidoublets is displayed.

The energy of electronic transitions in zero fields, their symmetry, and the spectroscopic splitting factor in a field **H** || *C* _{2}. The alleged separation into quasidoublets is displayed.

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