Barnett effect as a new source of magnetic field in heavy-ion collisions

Abstract: The Barnett effect is a fundamental magnetomechanical phenomenon in which a ferromagnetic material becomes magnetized under rotation. Using a hadron resonance gas (HRG) model under rigid rotation, we compute the Barnett magnetization ($M_{\rm Barnett}$) and show that it produces a magnetic field ($B_{\text{ind}}$) comparable in magnitude to the well-known external field ($B_{\text{ext}}$) from spectator protons at low energy heavy-ion collisions. This finding establishes the Barnett effect as a previously overlooked but essential source of magnetization and magnetic field in the heavy-ion collisions, with profound implications for understanding spin dynamics and anomalous transport in quantum chromodynamics under extreme rotation.