SQUID detected NMR and NQR. Superconducting Quantum Interference Device

Area of Science:

• Physics
• Spectroscopy
• Materials Science

Background:

• Superconducting QUantum Interference Devices (SQUIDs) are highly sensitive magnetic flux detectors.
• Traditional NMR/NQR spectrometers have limitations in sensitivity and frequency range.
• SQUID-based flux transformers offer enhanced sensitivity for low-frequency magnetic measurements.

Purpose of the Study:

• To develop and demonstrate a SQUID-based spectrometer for continuous-wave (cw) and pulsed Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR).
• To exploit the SQUID's sensitivity for novel spectroscopic techniques and imaging.
• To measure relaxation times and acquire multi-dimensional spectra.

Main Methods:

• Utilizing a niobium wire coil coupled to a thin-film superconducting coil on a SQUID as a flux transformer.
• Employing a cw spectrometer to monitor static magnetization changes induced by RF irradiation.
• Implementing a pulsed spectrometer with spin-echo techniques and two-frequency pulses for advanced measurements.

Main Results:

• Successful detection of NQR in 27Al and 11B, and enhanced 14N signal detection.
• Measurement of 14N NQR relaxation times in NH4ClO4 (T1 = 63±6 ms, T2 = 22±2 ms).
• Acquisition of a two-dimensional NQR spectrum and detection of low-frequency 129Xe NMR (down to 200 Hz).
• Demonstration of NMR imaging and detection in small samples at room and low temperatures.

Conclusions:

• SQUID-based spectrometers provide exceptional sensitivity and broad frequency response for NMR and NQR.
• The technology enables advanced spectroscopic techniques, including multi-dimensional analysis and relaxation time measurements.
• SQUID NMR/NQR shows promise for high-resolution imaging and analysis of diverse samples, even at the microscale.