The Absolute Direction of the Dzyaloshinskii-Moriya Interaction in Hematite Determined by Polarized Neutron Diffraction

Polarized neutron diffraction (PND) is a powerful method which provides direct access to the scattering con-tribution from nuclear-magnetic interference and thus reveals the phase difference between the nuclear andmagnetic structure. This technique can be utilized to gain a detailed insight in the microscopic spin orderingat the unit cell level even for complex magnetic structures. Since magnetic domains correspond to an overallphase shift between the nuclear and magnetic structure, PND also allows to resolve different magnetic domainconfigurations providing additional information at the mesoscopic scale. This qualifies PND as a versatile toolto simultaneously address a wide range of scientific issues. By conducting a detailed PND study of the proto-typical room-temperature weak ferromagnet α-Fe2O3 (hematite) we could solve the long standing problem ofinconsistent asymmetry signs observed within Friedel pairs in hematite. Moreover, using a detailed symme-try analysis the absolute direction of the Dzyaloshinskii-Moriya interaction (DMI) vector in α-Fe2O3 could bedetermined for the first time. This study is supported by a detailed refinement of the slightly canted magneticstructure and by numerical calculations. It can be used as a reference for further DMI sign determinations,reducing the experimental efforts to the measurement of one representative reflection, making it well suitedfor highly topical materials often requiring extreme sample environmen