Electron paramagnetic resonance of exchange-coupled [Fe+—Fe2+] pairs in BaF2: Fe crystal

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Abstract

The study of exchange-coupled [Fe+ - Fe2+] pairs found by authors of the work [1] in X-ray irradiated BaF2:Fe crystals is continued by the EPR method. It is confirmed that the electron spin multiplet S = 7/2 corresponds to the basic state of the studied pairs, split by the anisotropic part of the exchange interaction and the crystal field so that the Kramers doublet turned out to be the ground one. It was found that the energy interval to the next spin doublet corresponds approximately to 125 GHz. It was found that the nearest ligands of iron ions in an exchange-coupled pair [Fe+ - Fe2+] are eight fluorine ions registered in the EPR spectra as structurally equivalent. The parameters of the superhyperfine interaction with the magnetic moments of the nuclei of these ligand ions have been determined. It is shown that the observed experimental facts clearly indicate that the exchange between iron ions in the studied pairs is realized mainly by the mechanism of double Zener exchange.

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About the authors

R. B. Zaripov

Federal Research Center “Kazan Scientific Center of the Russian Academy of Sciences”

Email: ulvlad@inbox.ru

Zavoisky Physical-Technical Institute

Russian Federation, Kazan

V. A. Ulanov

Federal Research Center “Kazan Scientific Center of the Russian Academy of Sciences”; Kazan State Power Engineering University

Author for correspondence.
Email: ulvlad@inbox.ru

Zavoisky Physical-Technical Institute

Russian Federation, Kazan; Kazan

R. R. Zainullin

Kazan State Power Engineering University

Email: ulvlad@inbox.ru
Russian Federation, Kazan

R. I. Kalimullin

Kazan State Power Engineering University

Email: ulvlad@inbox.ru
Russian Federation, Kazan

References

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Supplementary files

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2. Fig. 1. EPR spectra of perpendicularly oriented radiation exchange-coupled pairs of iron ions in a BaF2:Fe crystal in the orientation →H0|| <100> (δ1 is the spectral splitting caused by the SFBR with each of the eight magnetically equivalent nuclei of the ligand fluorine ions, numbers 1 and 2 correspond to the EPR frequencies fmw.1 = 9732.5 MHz and fmw.2 = 342501 MHz, T = 80 K).

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3. Fig. 2. EPR spectrum of perpendicularly oriented radiation exchange-coupled pairs of iron ions in a BaF2:Fe crystal in the orientation →H0|| <100> (δ1 and δ2 are spectral splittings caused by the SFH with each of the two quartets of magnetically equivalent nuclei of ligand fluorine ions, respectively; the upper part of the figure shows diagrams that facilitate the interpretation of this spectrum and are constructed in accordance with the algorithm from [12], numbers 1, 4 and 6 correspond to the sequence of consideration of splittings, resonance frequency fmw = 9732.5 MHz).

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4. Fig. 3. EPR spectrum of parallel oriented radiation exchange-coupled pairs of iron ions in a BaF2:Fe crystal in the orientation →H0|| <100> (recorded at a frequency of fmw = 34250.1 MHz at a temperature of T = 80 K, δ4 is the spectral splitting in this orientation, caused by the SFBR with each of the eight magnetically equivalent nuclei of the ligand fluorine ions).

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5. Fig. 4. Angular dependences of the positions of the centers of gravity of the EPR spectra of three ensembles of structurally equivalent radiation exchange-coupled pairs of iron ions, recorded in the X- (a) and Q- (b) ranges at a temperature of 80 K and corresponding to the rotation of the sample around the crystallographic axis <110> (in this case, the vector of the external magnetic field strength →H0 remained perpendicular to the axis of rotation and at θ = 0° turned out to be parallel to the axis <001>, curve number 1 determines the positions of the EPR spectra of two ensembles of pairs that remain magnetically equivalent during rotation, and curve 2 corresponds to the third ensemble of pairs, in which the tetragonal axis of symmetry at θ = 0° turns out to be parallel to the vector →H0).

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6. Fig. 5. Simplified geometric model of the molecular structure of an exchange-coupled pair of iron impurity ions in a BaF2 crystal and the directions of the axes of two Cartesian coordinate systems convenient for calculating the parameters of the SSTS.

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