Simultaneous Detection of H and D NMR Signals in a Micro-Tesla Field

Fast switching coil system for sample premagnetization in an unshielded ultra-low-field nuclear magnetic resonance experiment

We present a system developed to premagnetize liquid samples in an ultra-low-field nuclear magnetic resonance experiment. Liquid samples of a few milliliters are exposed to a magnetic field of about 70 mT, which is abruptly switched off, to leave a transverse microtesla field, where nuclei start precessing. An accurate characterization of the transients and intermediate field level enables a reliable operation of the detection system, which is based on an optical magnetometer.

Spurious ferromagnetic remanence detected by hybrid magnetometer

Nuclear magnetic resonance detection in ultra-low-field regime enables the measurement of different components of a spurious remanence in the polymeric material constituting the sample container. A differential atomic magnetometer detects simultaneously the static field generated by the container and the time-dependent signal from the precessing nuclei. The nuclear precession responds with frequency shifts and decay rate variations to the container magnetization. Two components of the latter act independently on the atomic sensor and on the nuclear sample. A model of the measured signal allows a detailed interpretation on the basis of the interaction geometry.

Scalar relaxation of NMR transitions at ultralow magnetic field

Nuclear magnetic resonance signals for ¹H in simple chlorinated, brominated and deuterated liquids were detected at field strengths between 1 nT and a few μT to investigate the influence of scalar relaxation of the second kind (SR2K). SR2K describes the acceleration in magnetization decay rate for a spin-1/2 nucleus that is scalar coupled to a fast-relaxing quadrupolar nucleus. In agreement with simple theoretical models, the experimental data show that couplings to nuclei with small, nonzero quadrupole moments (²H) give rise to higher transverse relaxation rates at ultralow field than rapidly relaxing quadrupolar nuclei (Cl and Br). This behavior is opposite to the case normally encountered in high-field NMR, and demonstrates that certain nuclei in the spin system may be "weakly coupled" or even decoupled when the applied magnetic field is zero. The results show that the capability for precision determination of NMR frequencies and molecular structural information depends strongly on the composition and topology of the nuclear spin system.

Sub-picotesla widely tunable atomic magnetometer operating at room-temperature in unshielded environments

We report on a single-channel rubidium radio-frequency atomic magnetometer operating in unshielded environments and near room temperature with a measured sensitivity of 130 fT/ Hz . We demonstrate consistent, narrow-bandwidth operation across the kHz-MHz band, corresponding to three orders of magnitude of the magnetic field amplitude. A compensation coil system controlled by a feedback loop actively and automatically stabilizes the magnetic field around the sensor. We measure a reduction in the 50 Hz noise contribution by an order of magnitude. The small effective sensor volume, 57 mm³, increases the spatial resolution of the measurements. Low temperature operation, without any magnetic shielding, coupled with the broad tunability, and low beam power, dramatically extends the range of potential field applications for our device.