7 April 2004 High-frequency two-dimensional EPR spectroscopy of Cr3+ and Ho3+ dimers in synthetic forsterite
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Abstract
An enormously high concentration of Cr3+-Cr3+ and Ho3+-Ho3+ dimers is found in synthetic forsterite doped by Cr or Ho ions, respectively. The measurements were performed by means of high-frequency two-dimensional EPR spectroscopy in the frequency region of 65-250 GHz at 4.2 K in magnetic fields up to 0.8 T. The analysis of the spin Hamiltonian parameters and rotational diagrams showed that the Cr3+-Cr3+ dimers are formed by a pair of Cr3+ ions with an Mg2+ vacancy between them replacing three Mg2+ ions in M1 positions situated in a quasi-one-dimensional chain aligned parallel to the crystal c-axis. It is found that the interaction between Cr3+ ions in the dimer is the ferromagnetic exchange with parameters Jz = 0.47 GHz and Jt = 0.79 GHz. Most probable structures of Ho3+-Ho3+ dimers consist of two Ho3+ ions coupled by the dipole-dipole interaction (Jz = 11.4 GHz) and situated in the M2 octahedral positions in the same bc-layer with a Mg2+ vacancy in the M1 position between them. The mechanism which favors the formation of dimers of trivalent impurity ions in forsterite is proposed. It is connected with the conservation of the overall charge balance under the substitution of three nearest neighboring Mg2+ cations by the two impurity ions with a Mg vacancy between them.
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A. V. Gaister, A. A. Konovalov, Gil'man S. Shakurov, K. A. Subbotin, Valery F. Tarasov, Evgenii V. Zharikov, "High-frequency two-dimensional EPR spectroscopy of Cr3+ and Ho3+ dimers in synthetic forsterite", Proc. SPIE 5478, Laser Optics 2003: Solid State Lasers and Nonlinear Frequency Conversion, (7 April 2004); doi: 10.1117/12.558454; https://doi.org/10.1117/12.558454
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