Recent advances in microresonators and supporting instrumentation for electron paramagnetic resonance spectroscopy

Abstract

Electron paramagnetic resonance (EPR) spectroscopy characterizes the magnetic properties of paramagnetic materials at the atomic and molecular levels. Resonators are an enabling technology of EPR spectroscopy. Microresonators, which are miniaturized versions of resonators, have advanced inductive-detection EPR spectroscopy of mass-limited samples. Here, we provide our perspective of the benefits and challenges associated with microresonator use for EPR spectroscopy. To begin, we classify the application space for microresonators and present the conceptual foundation for analysis of resonator sensitivity. We summarize previous work and provide insight into the design and fabrication of microresonators as well as detail the requirements and challenges that arise in incorporating microresonators into EPR spectrometer systems. Finally, we provide our perspective on current challenges and prospective fruitful directions.

Cryogenic platform to investigate strong microwave cavity-spin coupling in correlated magnetic materials

“…We were able to create a range of LGRs optimized to accommodate single crystal sizes ranging from 1 to 6 mm in diameter, with the primary constraint on smaller resonator sizes coming from machining limitations. While a particular lower bound on detectable sample size and spin density was not determined, previous work puts this limit around one microliter for basic LGRs [3].…”

“…In the k B T ≫ hν esr regime, thermal excitations lead to weak population differences and absorption between magnetic states [1]. By enhancing light-matter interactions, resonators produce a corresponding increase in microwave sensitivity, allowing small changes in sample inductance to be detected [3].…”

Scanning Spin Probe Based on Magnonic Vortex Quantum Cavities

“…The technological interest in EPR has led to the development of sophisticated and sensitive detection methods. These include optical techniques, such as using optically active atomic defects, − electrical detection of magnetic signals using scanning tunneling microscopy probes, − or mechanical sensing based on magnetic resonance force microscopy. , Among the inductive methods, pickup coils and superconducting quantum interference devices (SQUIDs) have been employed to characterize resonant phenomena in small paramagnetic crystals. , However, the most widespread inductive-EPR readout technique uses transmission lines and cavities. − This latter approach offers the advantage of confining light in the space domain, yielding increased light–matter interactions. In addition, the cavity’s quality factor can be further enhanced when using superconducting coplanar resonators instead of metallic three-dimensional cavities, yielding increased visibility.…”

“… 13 , 14 However, the most widespread inductive-EPR readout technique uses transmission lines and cavities. 15 − 17 This latter approach offers the advantage of confining light in the space domain, yielding increased light–matter interactions. In addition, the cavity’s quality factor can be further enhanced when using superconducting coplanar resonators instead of metallic three-dimensional cavities, 18 yielding increased visibility.…”

Order-of-magnitude SNR improvement for high-field EPR spectrometers via 3D printed quasi-optical sample holders

“…Therefore, maximizing the cross-polar-to-co-polar contrast also means maximizing the spectrometer's sensitivity. While typically capable of isolating the excitation polarization by about 30 dB (45,46), induction mode architectures still impart an undesirable background to EPR experiments, as the excitation power is typically much larger than the orthogonal induction-mode signal; as a result, improving induction-mode isolation for high-field and high-frequency experiments presents a potential avenue for improving HFEPR resolution and is a topic of interest for many researchers (37,(47)(48)(49)(50)(51)(52).…”