Adjustable coupling and in situ variable frequency electron paramagnetic resonance probe with loop-gap resonators for...

Area of Science:

• Physical Chemistry
• Spectroscopy
• Materials Science

Background:

• Standard electron paramagnetic resonance (EPR) spectroscopy uses fixed frequency and variable magnetic field.
• Studying phenomena like avoided level crossings requires tuning frequency while keeping the magnetic field constant.
• Existing EPR techniques lack the capability for in-situ frequency tuning at cryogenic temperatures.

Purpose of the Study:

• To design and test a novel adjustable frequency and variable coupling EPR probe.
• To enable EPR experiments at cryogenic temperatures (as low as 1.8 K) with frequency tunability.
• To precisely map avoided crossings and determine tunnel splittings in molecular nanomagnets.

Main Methods:

• Developed an EPR probe utilizing loop-gap resonators (LGRs) with adjustable frequency.
• Frequency tuning achieved by adjusting a sapphire dielectric's position within the LGR gap.
• Variable microwave antenna coupling controlled by external micrometers outside the cryostat.

Main Results:

• The probe demonstrated frequency adjustment of over 1 GHz (>25%) around a central frequency of ~4 GHz.
• Operated successfully at temperatures as low as 1.8 K.
• Successfully mapped avoided crossings for the Ni4 molecular nanomagnet, yielding high-precision tunnel splitting data.

Conclusions:

• The developed adjustable frequency EPR probe is effective for low-temperature studies requiring frequency tuning.
• This technology allows for precise characterization of quantum phenomena like avoided level crossings.
• The probe offers a versatile tool for investigating molecular nanomagnets and other systems sensitive to magnetic field and frequency.