Capabilities of Compact High-Frequency EPR/ESE/ODMR Spectrometers Based on a Series of Microwave Bridges and a Cryogen-F
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Applied Magnetic Resonance
ORIGINAL PAPER
Capabilities of Compact High‑Frequency EPR/ESE/ODMR Spectrometers Based on a Series of Microwave Bridges and a Cryogen‑Free Magneto‑optical Cryostat R. A. Babunts1 · A. G. Badalyan1 · A. S. Gurin1 · N. G. Romanov1 · P. G. Baranov1 · A. V. Nalivkin2 · L. Yu. Bogdanov2 · D. O. Korneev2 Received: 27 June 2020 / Revised: 25 July 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract A magnetic resonance spectrometer operating at several fixed frequencies in the millimeter range is designed on the basis of a new generation of microwave bridges and a cryogen-free magneto-optical cryogenic system. The spectrometer allows measurements of EPR in continuous wave and pulse (free-induction decay, FID and electron spin echo, ESE) modes, photo-EPR, and optically detected magnetic resonance (ODMR) in a wide range of temperatures (1.5–300 K) and magnetic fields (up to 7 T with the ability to invert the field). It is based on a line of unified microwave bridges with a powerful oscillator and a superheterodyne receiver. Currently, they operate in W and D bands (at 94 and 130 GHz, respectively), but the frequency bands can be extended. In addition to highly stable fixed-frequency oscillators with narrow spectrum (better than − 100 dBc at 10 kHz offset at 94 GHz), they have variable frequency oscillators, which simplify tuning of the microwave circuit with a resonator and allow operation with frequency modulation when using a non-resonant microwave system. In the latter, it is possible to study large samples and quickly change the operating frequency of the spectrometer, simply replacing the microwave bridge. For all frequencies, the spectrometer uses common hardware and original software. The performance of the spectrometer at 94 GHz and 130 GHz was tested in measurements of CW-EPR, ESE and ODMR of NV defects in diamond single crystals, Tb3+ and C e3+ ions in yttrium aluminum garnet crystals, nitrogen donors, and V 3+ ions in 6H-SiC.
* R. A. Babunts [email protected] 1
Ioffe Institute, St. Petersburg 194021, Russia
2
DOK Company, St. Petersburg 193318, Russia
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1 Introduction Electron paramagnetic resonance (EPR), discovered by Zavoisky in Kazan (1944) [1], is currently a powerful analytical method available for physicists, chemists, and biologists. Over 75 years, EPR and related methods played a decisive role in the study of spin phenomena in condensed matter (semiconductors and dielectrics), biophysical objects, and living systems. EPR turned out to be one of the most informative tools for non-destructive diagnostics of the structural properties of atomic and molecular objects at the electronic level. Currently, there is growing interest in using high frequencies and strong magnetic fields in EPR spectroscopy, significantly exceeding the usual values of 9.5 GHz and 35 GHz (magnetic fields of 0.34 T and 1.25 T for g = 2, respectively). The main advantages of high-frequency EPR are high absolute
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