Single-crystal EPR studies of transition-metal ions in inorganic crystals at very high frequency |
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Authors: | S K Misra S I Andronenko K A Earle J H Freed |
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Institution: | 1. Physics Department, Concordia University, Montreal, Quebec, Canada 2. Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, USA
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Abstract: | Electron paramagnetic resonance (EPR) single-crystal rotation studies at very high frequency (249.9 GHz) of transition metal ions with electron spins greater than one-half are reported. At 249.9 GHz, the spectra are in the high-field limit despite large zero-field splittings. This leads to a considerable simplification of the spectra, and aids in their interpretation. Single-crystal 249.9 GHz EPR spectra of Ni2+ in Ni2CdCl6· 12H2O, Mn2+ (0.2%) in ZnV2O7, and Fe3+ (2%) in CaYA104 were recorded at 253 K in an external magnetic field of up to 9.2 T, along with those at X-band and Q-band frequencies at 295 K and lower temperatures. The goniometer used at 249.9 GHz for single-crystal rotation is based on a quasi-optical design and is an integral part of a special Fabry-Pérot resonator. The values of the spin-Hamiltonian parameters were estimated from a simultaneous fitting of all of the observed line positions at several microwave frequencies recorded at various orientations of each crystal with respect to the external magnetic field with least-squares fitting in conjunction with matrix diagonalization. Estimates of zero-field splitting parameterD at room temperature are: for Ni2+, about ?31 GHz (site I) and about ?7 GHz (site II); for Mn2+, about 6 GHz; and for Fe3+, about 29 GHz. |
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