Probing Magnetic Hysteresis at Amorphous Glass Interfaces via Quadrupolar-Enhanced ^{21}Ne Spin Relaxation.

The magnetic dynamics at the nanoscale interface of amorphous insulators sit at the intersection of advancing ultrasensitive quantum sensing and understanding condensed matter physics. While noble-gas spin relaxation offers a powerful approach to probe these interfaces, it has long been restricted to probing bulk paramagnetic backgrounds due to the deep penetration depths of traditional dipolar probes. In this Letter, we report the observation of nanotesla-level magnetic hysteresis and thermally activated relaxation growth in aluminosilicate glass cells using ^{21}Ne as a quadrupolar-enhanced quantum probe. The strong coupling between the nuclear electric quadrupole moment and the surface electric field gradient compresses the effective spin sampling depth to the nanometer scale [∼O(1)  nm]. By coupling Jiles-Atherton hysteresis dynamics with Cates diffusion and accounting for gas-phase thermal line broadening, we obtain a cross-cell average apparent activation energy of ⟨E_{act}⟩≈49.7  kJ/mol within the present relaxation model. The pronounced field-history dependence of the relaxation is consistent with localized magnetic inhomogeneity at the glass interface. The proposed methodology provides an in situ, nondestructive, depth-selective probe of magnetic behavior at otherwise inaccessible amorphous glass interfaces, with potential utility for identifying wall-related relaxation in ultrasensitive comagnetometers.