Mansi Tarani (Tata Institute of Fundamental Research Hyderabad, India)
LinkedIn: Mansi Tarani
Abstract: NMR is a powerful technique to investigate the structure and dynamics of molecules by manipulating nuclear spins. In the zero- to ultra-low-field (ZULF) regime (≤ few tens of μT), spin dynamics are dominated by spin-spin interactions rather than Zeeman interactions. In this regime, the Larmor frequency lies in the range from Hz to a few kHz; consequently, spins can be manipulated using external DC magnetic fields. As pickup coils are less sensitive to such low frequencies, detection is done using highly sensitive magnetometers. In this work, we use commercial magnetometer (QuSpin) along with a home-built atomic magnetometer (AM) (sensitivity ~ 1pT/√Hz, dynamic range ~ 20μT, bandwidth ~ 24kHz and response time ~ 200 μs), which enables detection of system response in the range of a few kHz with short transverse relaxation times. We explored NMR spectra of different liquid samples over a magnetic field range from 50nT to 10μT. As the magnetic field strength increased, the spin coherence time decreased due to increasing field inhomogeneity across the sample. To refocus the signal, we used CPMG pulse sequence and further enhanced SNR by the introduction of phase cycling, which eliminated the correlated noise across successive scans. We also investigated the spin-spin (T2) and spin–lattice (T1) relaxation times. We observed an increase in (T2) time compared to high-field NMR because various dephasing effects become weaker in this regime. This work demonstrates the potential of ZULF NMR for precision relaxation studies and provides a pathway toward portable, low-cost spectroscopic and sensing applications.
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