It is important to distinguish three stages of the experiment: preparation, field variation, and detection, Fig. ). If a static magnetic field is applied during the pH 2 bubbling stage, we refer to this spin-order preparation as "SHEATH-pumping". In contrast, if no field is applied, we call it "zero-field (ZF) pumping". At the detection stage, the field need not to be the same as in the preparation stage nor should it have the same orientation. Depending on whether zero-or a small bias field (2 µT in this work) is applied during signal readout, the signal detection is categorized as "zero-field (ZF) detection" or "ultralow-field (ULF) detection".