Field-induced breaking of Tτ symmetry and anomalous Hall effect

Determine whether a sufficiently strong magnetic field generates a net out-of-plane Ce moment in CeNiAsO, thereby producing an FMz state that breaks the combined time-reversal and translation symmetry Tτ and causes the observed anomalous Hall effect.

Background

CeNiAsO exhibits two anomalous Hall-effect loops at low temperature in its commensurate antiferromagnetic phase. The authors associate the onset of the Hall response with a field-driven reorientation of the Ce moments, inferred from the rapid decrease of the 75As NMR central-peak splitting above approximately 13 T.

The proposed mechanism is that a sufficiently large field produces a net out-of-plane moment, changing the canted antiferromagnetic configuration into an FMz-like state and breaking Tτ symmetry. The passage is explicitly framed as a conjecture rather than as an established result, so the field-induced magnetic structure and its symmetry-based explanation remain unresolved.