Detecting weak magnetic fields at hertz frequencies is central to biomagnetism, geophysical sensing, and searches for new physics, yet it remains challenging because of technical systematics and environmental noise. Here, we realize a continuously operating molecular magnetic amplifier. Signal amplification by reversible exchange (SABRE) parahydrogen-based hyperpolarization maintains non-equilibrium spin order at zero field, turning scalar-coupled nuclear spins in liquid state molecules into an active, frequency-selective gain medium. Measurements of its complex magnetic susceptibility ($\chi$) reveal an intrinsic response of $ | \chi | \approx$ 10. By feeding the collectively generated magnetic field back to the spins below the threshold for self-sustained $J$-oscillation, we extend the effective spin coherence and cooperatively enhance the susceptibility up to $ | \chi | \approx$ 80. Near threshold, this produces approximately fourfold amplification of a weak (20 pT) magnetic field at 3.37 Hz at the sensor location. These results establish hyperpolarized molecules as a tunable active magnetic medium for narrowband quantum sensing and precision measurement.
Nitrogen-vacancy (NV) centers in diamond are promising quantum sensors for AC magnetic fields. However, conventional dynamical-decoupling-based magnetometry becomes technically demanding at high frequencies because of the requirement for increasingly short and high-power microwave pulses. This paper describes an AC mag...
Ryusei Okaniwa, R. Suzuki, Yuichiro Matsuzaki et al.· 0 citations
Hyperpolarization approaches in magnetic resonance overcome sensitivity limitations imposed by thermal magnetization and are integral to many modern applications. We begin with an overview of hyperpolarization. We then focus on one method, SABRE, which uses parahydrogen to form hydride transition metal complexes, follo...
L. Smith, Warren S. Warren· Science Advances· 0 citations
Spatiotemporal microwave magnetic-field imaging reveals current flow in high-frequency circuits and nonequilibrium spin dynamics, yet probes rarely combine calibrated spectral readout, optics-free operation and transient mapping at room temperature. Here ferrimagnetic order in yttrium iron garnet supports coherent coup...
Chun-Ke Wei, Z.-J. Chen, J. Song et al.· 0 citations
We demonstrate a novel magnetometer that utilizes the Langevin nonlinear magnetization of superparamagnetic nanoparticles as the sensing medium. The magnetic sensor exploits the even-order harmonics of the magnetization response, particularly the second harmonic, which is proportional to the local magnetic field compon...
M. Jurj, C. McDonough, C. Bastajian et al.· 0 citations
Electrical detection of antiferromagnetic order is a critical challenge for antiferromagnetic spintronics owing to their vanishing macroscopic magnetisation. While magnetic resonance has demonstrated sub-terahertz antiferromagnetic spin pumping and nonlinear magnon dynamics, its application to electrically contacted on...
Yi-Fang Hao, Zhi-Yi Che, J. Brierley et al.· 0 citations
Nuclear magnetic resonance (NMR) spectroscopy is among the most powerful tools for determining molecular structure, yet its intrinsic sensitivity has long constrained what can be studied. Dynamic nuclear polarization (DNP) addresses this fundamental limitation by transferring the much larger polarization of electron sp...
R. Palani, R. Temkin, R. G. Griffin· Science Advances· 0 citations
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