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.

![](https://assets.underline.io/uploads/markdown_image/1/image/d3101936d30b393ec81080a0faba3817.jpg)

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.

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

Antiferromagnets (AFs) are promising candidates for next generation spintronic devices. Hematite (α-Fe2O3), an easy-plane AF insulator with triaxial anisotropy, is one of the materials at the forefront of this effort, spurring discoveries of magnon-mediated long-distance spin transport and unambiguous control of the AF order by electrical current [1]. Contrary to ferromagnets, where domain structure is governed by long-range demagnetizing fields, the domain structure in AFs is controlled by destressing fields of magnetoelastic origin [2]. The electrical control of domains has been studied in AFs with an adjacent heavy metal as a source of interfacial anti-damping-like spin-orbit torque (SOT). But, AF switching has been shown to at least partially result from thermo-magnetoelastic torques, generated by current-induced temperature gradients [3,4]. The competition of a thermo-magnetoelastic torque and SOT complicates the fundamental understanding of the origin of domain re-distribution. In our work, we develop a method for discerning the two effects by heating a Pt device on α-Fe2O3 independently of the applied current. Implementing a combination of angle-dependent spin-Hall magnetoresistance (SMR) and current pulsing, we probe, respectively, the full and partial re-orientation of AF domains in epitaxial α-Fe2O3/Pt bilayers. We find that the origin of the current-induced switching signal, which results from domain re-orientation, is primarily of SOT origin in α-Fe2O3. The remanent switching amplitude (~5% of the expected signal amplitude) and a temperature-dependent study of key switching signatures reveals the existence of pinning barriers to domain wall motion. This study advances the understanding of current-induced effects in AF materials with low anisotropy and high magnetostriction, where magnetoelastic effects are thought to dominate.

**References:**

[1] Y. Cheng, S. Yu, M. Zhu, J. Hwang, and F. Yang, Phys. Rev. Lett. 124, 027202 (2020). [2] J. Fischer, O. Gomonay, R. Schlitz, K. Ganzhorn, N. Vlietstra, M. Althammer, H. Huebl, M. Opel, R. Gross, S. T. B. Goennenwein, and S. Geprägs, Phys. Rev. B 97, 014417 (2018). [3] H. Meer, F. Schreiber, C. Schmitt, R. Ramos, E. Saitoh, O. Gomonay, J. Sinova, L. Baldrati, and M. Kläui, Nano Lett. acs.nanolett.0c03367 (2020). [4] L. Baldrati, C. Schmitt, O. Gomonay, R. Lebrun, R. Ramos, E. Saitoh, J. Sinova, and M. Kläui, Phys. Rev. Lett. 125, 077201 (2020).

**Images:**

 Mechanism of Current-induced Magnetotransport in Epitaxial Antiferromagnetic α-Fe2O3

We study the magnetic reversal of the canted antiferromagnet α-Fe2O3. At room temperature, the Dzyaloshinskii-Moriya interaction (DMI) induces canting of the two magnetic sublattices MA and MB giving rise to a weak ferromagnetic (FM) moment m. We employ spin Hall magnetoresistance (SMR) measurements to study electrical and magnetic field control of the Néel order in α-Fe2O3/Pt bilayers. The angle-dependent magnetoresistance (ADMR) shows the characteristic saturated negative SMR signal of AFMs (dotted curve in figure 1) in agreement with previous findings1–4. We note that the FM moment lifts the degeneracy of the sublattices and consequently the orientation of the Néel vector with respect to the applied magnetic field. The solid blue curve in figure 1 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 ADMR signal and the remanent resistance by a factor of 5. The lack of signatures of anisotropy in the remanent signal implies that the relaxation of the SMR signal is dominated by destressing effects favoring an equilibrium state with multiple domains distributing the orientation of the Néel vector along random directions. Furthermore, we observe hysteresis in the SMR signal. The irreversibility upon switching the direction of the magnetic field in combination with investigating the transient effects of current-induced changes in the domain structure allows us to study the nature and formation of antiferromagnetic as well as ferromagnetic domain walls at low magnetic fields. Our work emphasizes the importance of the FM moment induced by DMI and the relaxation effects for the equilibrium domain structure in α-Fe2O3.

**References:**

1. Lebrun, R. et al. Anisotropies and magnetic phase transitions in insulating antiferromagnets determined by a Spin-Hall magnetoresistance probe. Commun. Phys. 2, 50 (2019). 2. Cheng, Y., Yu, S., Zhu, M., Hwang, J. & Yang, F. Electrical Switching of Tristate Antiferromagnetic Néel Order in a-Fe2O3 Epitaxial Films. Phys. Rev. Lett. 124, 027202 (2020). 3. Fischer, J. et al. Large Spin Hall Magnetoresistance in Antiferromagnetic a-Fe2O3/Pt Heterostructures. Phys. Rev. Appl. 13, 014019 (2020). 4. Zhang, P., Finley, J., Safi, T. & Liu, L. Quantitative Study on Current-Induced Effect in an Antiferromagnet Insulator/Pt Bilayer Film. Phys. Rev. Lett. 123, 247206 (2019).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/7877b8c698ce2bc70681f32ecc5f5632.jpg)
Transverse resistance (solid blue line) after H has been reduced from a saturated state (dotted blue line) to zero field as a function of angle of the applied magnetic field. The inset in the top right corner shows a schematic of the canting of the sublattice magnetization MA and MB due to DMI giving rise to the ferromagnetic moment m.

 Roles of Destressing, Pinning, and Weak Ferromagnetism for Magnetic Reversal in α-Fe2O3

In this work, we study the canted antiferromagnet α-Fe2O3. At room temperature, the Dzyaloshinskii-Moriya interaction (DMI) induces canting of the two magnetic sublattices MA and MB giving rise to a weak ferromagnetic (FM) moment m. We employ spin Hall magnetoresistance (SMR) measurements to study electrical and magnetic field control of the Néel order in α-Fe2O3/Pt bilayers. The angle-dependent magnetoresistance (ADMR) shows the characteristic saturated negative SMR signal of AFMs (red curve in figure 1) agreeing with previous findings1–4. We note that the FM moment lifts the degeneracy of the sublattices and consequently the orientation of the Néel vector with respect to the applied magnetic field. The blue curve in figure 1 shows the remanent resistance as a function of the angle of the preceding saturating magnetic field. The data shows a simple scaling between the saturated ADMR signal and the remanent resistance. The lack of signatures of anisotropy in the remanent signal implies that the relaxation of the SMR signal is dominated by destressing effects favoring an equilibrium state with multiple domains distributing the orientation of the Néel vector along different directions. Applying the insights from investigating the remanence of α-Fe2O3 with an external magnetic field on our current-induced switching experiments, we find that the fundamental limit of the switching efficiency is given by the magnitude of the remanence Furthermore, we observe hysteresis in the SMR signal. The irreversibility upon switching the direction of the magnetic field in combination with investigating the transient effects of current-induced changes in the domain structure allows us to study the nature and formation of domain walls at low magnetic fields. Our work emphasizes the importance of the FM moment induced by DMI and the relaxation effects for the equilibrium domain structure in α-Fe2O3.References: 1. Lebrun, R. et al. Anisotropies and magnetic phase transitions in insulating antiferromagnets determined by a Spin-Hall magnetoresistance probe. Commun. Phys. 2, 50 (2019). 2. Cheng, Y., Yu, S., Zhu, M., Hwang, J. & Yang, F. Electrical Switching of Tristate Antiferromagnetic Néel Order in a-Fe2O3 Epitaxial Films. Phys. Rev. Lett. 124, 027202 (2020). 3. Fischer, J. et al. Large Spin Hall Magnetoresistance in Antiferromagnetic a-Fe2O3/Pt Heterostructures. Phys. Rev. Appl. 13, 014019 (2020). 4. Zhang, P., Finley, J., Safi, T. & Liu, L. Quantitative Study on Current-Induced Effect in an Antiferromagnet Insulator/Pt Bilayer Film. Phys. Rev. Lett. 123, 247206 (2019).

Importance of the Ferromagnetic Moment Induced by Dzyaloshinskii-Moriya Interaction in a Canted Antiferromagnet for Electrical and Magnetic Field Control of the Néel Order

**Session chairs:** Jean Anne Incorvia, University of Texas at Austin and Vincent Baltz, Spintec



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Presentations

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

Mechanism of Current-induced Magnetotransport in Epitaxial Antiferromagnetic α-Fe2O3

Roles of Destressing, Pinning, and Weak Ferromagnetism for Magnetic Reversal in α-Fe2O3

Importance of the Ferromagnetic Moment Induced by Dzyaloshinskii-Moriya Interaction in a Canted Antiferromagnet for Electrical and Magnetic Field Control of the Néel Order

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