Hyperfine interactions of Er3+ ions in Y2SiO5 : Electron paramagnetic resonance in a tunable microwave cav

Abstract

The hyperfine structure of the ground state of erbium doped yttrium orthosilicate is analyzed with the use of electron paramagnetic resonance experiments in a tunable microwave resonator. This work was prompted by the disagreement between a recent measurement made in zero magnetic field and a previously published spin Hamiltonian which. The ability to vary magnetic field strength, resonator frequency, and the orientation of our sample enabled us to monitor how the frequencies of hyperfine transitions change as a function of a vector magnetic field. We arrived at a different set of spin Hamiltonian parameters, which are also broadly consistent with the existing data. We discuss the reliability of our new spin Hamiltonian parameters to make predictions outside the magnetic field and frequency regimes of our data. We also discuss why it proved to be difficult to determine spin Hamiltonian parameters for this material, and present data collection strategies that improve the model reliability.

Electron paramagnetic resonance spectroscopy of Er3+:Y2SiO5 using a Josephson bifurcation amplifier: Observation of hyperfine and quadrupole structures

“…The results confirm the improved spin Hamiltonian parameters [13] compared to parameters obtained using single-frequency conventional EPR [36], as well as the advantages of field and frequency-dependent EPR for anisotropic multilevel spin systems. We also note that our JBA-EPR frequency range is significantly broader than the 3 to 5 GHz tunable cavity used to derive the g, A, and Q values [13]; thus we should be able to improve these parameters even further by also performing EPR at different B 0 orientations (e.g., by using a vector magnet [40]). Indeed, while the agreement between simulated and measured transitions for 167 Er isotopes in site 2 is very good overall, we observed small differences (< 100 MHz) between the simulated and measured 167 Er site 1 transitions below 2 GHz.…”

“…By fitting the peak frequencies as a function of B 0 we extract g = (7.8±0.1) and (16.2 ± 0.2) for sites 1 and 2, respectively. These values are slightly higher than the expected g ≈ 7.0 and 15 for the direction of B 0 [13,36,37]. These can be attributed to ≈ 10% enhancement of the magnetic field near the superconducting film due to Meissner effect, comparable to previous reports on superconducting waveguides [17].…”

“…However, these EPR schemes typically only allow magnetic field-dependent study, because the operating frequency range is limited to frequencies near the resonator's resonance. Frequency and magnetic field-dependent EPR spctroscopy can be advantageous when compared to conventional, single-frequency EPR, in the characterization of more complicated materials [11][12][13], e.g., anisotropic materials, systems with electron spin S > 1/2 (zerofield interactions), or systems with nuclear spin I > 0 (hyperfine and quadrupole interactions). Efforts to extend the frequency range include using a tunable resonator [8,13,14], a resonator with multiple narrowly spaced modes (e.g., a whispering gallery mode resonator [15,16]), or a broadband waveguide [12,17].…”

“…We simulated the expected transition frequencies and spectra using the EASYSPIN package [38]. We considered all Er sites and subclasses, used the most recently reported g, A, and Q values from EPR using a tunable cavity [13], and included B 0 enhancement effects discussed previously. Lines in Fig.…”

“…However, some of the observed transtitions (e.g. those marked by yellow arrows) do not correspond to Er transitions and can instead be attributed to additional impurities in the YSO crystal [13,39].…”