Roles of Destressing and Dzyaloshinskii-Moriya Interaction for Magnetic Reversal in α-Fe2O3

Abstract

Antiferromagnets are at the forefront of research in spintronics. Recent results demonstrate their high potential for revolutionizing memory technologies. However, many of the underlying phenomena remain to be explored. Here, we study the domain structure and magnetic reversal of the canted antiferromagnet α-Fe2O3. Using x-ray magnetic linear dichroism (XMLD) measurements, we observe a strongly field-dependent domain structure of α-Fe2O3 (see Fig. 1a).To study the magnetic field control of the Néel order and demagnetization process in more detail, we employ spin Hall magnetoresistance (SMR) measurements in α-Fe2O3/Pt bilayer devices. The angle-dependent SMR shows the characteristic saturated negative SMR signal of antiferromagnets (light red curve in Fig. 1b) in agreement with previous findings1,2. The dark red curve shows the remanent resistance as a function of the angle of the preceding saturating magnetic field. The data show a simple scaling between the saturated SMR signal and the remanent resistance by a factor of 5. This implies that the internal fields driving the demagnetization do not follow the crystal symmetry of α-Fe2O3.Furthermore, the Dzyaloshinskii-Moriya interaction (DMI) induces canting of the two magnetic sublattices giving rise to a ferromagnetic moment at room temperature. The ferromagnetic moment lifts the degeneracy of the sublattices and consequently the orientation of the Néel vector with respect to the applied magnetic field resulting in hysteresis in the SMR signal. The irreversibility upon switching the direction of the magnetic field elucidates the nature and formation of antiferromagnetic as well as ferromagnetic domain walls at low magnetic fields.The insights gained from our work serve as a foundation for further studies of electrical and optical manipulation of the domain structure of canted antiferromagnets.  Fig. 1: (a) XMLD image of the domain structure of α-Fe2O3 in zero magnetic field (left) and in 250 mT in-plane magnetic field (right). (b) Transverse remanent SMR signal Rrem (dark red) of α-Fe2O3/Pt Hall cross after H has been reduced from a saturated state Rsat (light red) to zero field as a function of angle of the applied magnetic field.