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Aspects in Mining & Mineral Science

The Jahn-Teller Effect of Magnetic Center With 3d9 Ion - Cu2+ in ZnAl2sub>4 Spinel

Vladimir V Shapovalov1 and Vladimir A Shapovalov2*

1Department of Physics Queens College of the City University of New York, USA

2Galkin Donetsk Institute of Physics and Engineering, Russia

*Corresponding author:Vladimir A Shapovalov, Galkin Donetsk Institute of Physics and Engineering, Donetsk, 283048 Russia

Submission: August 14, 2024;Published: October 28, 2024

DOI: 10.31031/AMMS.2024.12.000796

ISSN 2578-0255
Volume12 Issue5

Opinion

ZnAl2O4 crystals with 0.1% Cu2+ ions were grown by spontaneous crystallization from a solution of oxides in molten salts. The size of the optically homogeneous crystals was 2·2·2mm. The EPR spectrum at helium temperature was a superposition of three axial spectra of Cu2+ ions, the axes of symmetry of which are mutually orthogonal and directed along three axes of the fourth order of the oxygen octahedron forming the first coordination sphere of the magnetic ion. The EPR spectrum is shown in Figure 1. The EPR spectrum of Cu2+ ion in the crystal of ZnAl2O4 has been investigated with ν=9.23GHz in the temperature range T=4.2295K.. It is shown that Cu2+ EPR spectrum in ZnAl2O4 can be represented as a superposition of two spectra: the Low-Temperature spectrum (LT) and High-Temperature (HT) spectrum. Figure 2 shows the spectra for T=20K and T=100K. The LT spectrum is typical of Cu2+ ions in the octahedral environment with strong Jahn-Teller effect. It is a superposition of three axial spectra with the axes of symmetry orthogonal one to another. The spin Hamiltonian of one of the magnetic centers is of the form

where β is the Bohr magneton, S=1/2 is the electronic spin, I=3/2 is the nuclear spin, g//=2.321±0.001, g=2.075±0.001, A=(153±7) 10-4cm-1, B=(9±2) 10-4cm-1.

Figure 1:Experimental EPR spectrum in ZnAl2O4+0.1% Cu2+ single crystals in the H//C4 field at =9.24GHz. T=4.2K.


The hyperfine structure of the EPR spectrum (Figure 2, lines 1,2,3,4, LT spectrum) corresponds to the magnetic center in the parallel orientation. The line width ΔH=33Oe. The intensive narrow peak (Figure 2, line 5, LT spectrum) is the EPR spectrum of the magnetic centers whose axes are normal to the magnetic field. The HT spectrum of Figure 2 is a relatively broad asymmetric line with the effective g-factor g=2.1±0.01. The line width varies from 0.45 to 0.6 kOe. The investigation of the temperature dependence of EPR spectrum shows that the temperature transformation of the spectrum are determined by a change in the integral intensities of the low- and high-temperature spectra. According to Figure 3, the integral intensity of the HT spectrum grows with temperature and that of the LT spectrum exponentially decreases. The parameter E0=12cm-1 stands for the effective energy of activation. For the Jahn- Teller magnetic center of the Cu2+ ion in ZnAl2O4 the value of this parameter is defined by the height of the potential barrier between the potential wells [1].

Figure 2:The temperature transformation of the spectrum is determined by a change in the integral intensities of the low- and high-temperature spectra.


Figure 3:The integral intensity of the HT spectrum grows with temperature and that of the LT spectrum exponentially decreases.


References

  1. Shapovalov VA, Shapovalov VV, Rafailovich M, Piechota S, Dmitruk AF, et al. (2013) Dynamic characteristic of molecular structure of poly(ortho-methoxyaniline) with magnetic probes. J Phys Chem C 117(15): 7830-7834.

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