• Open Access

Anisotropic Magnetoresistance in Antiferromagnetic Sr2IrO4

C. Wang, H. Seinige, G. Cao, J.-S. Zhou, J. B. Goodenough, and M. Tsoi
Phys. Rev. X 4, 041034 – Published 19 November 2014
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Abstract

We report point-contact measurements of anisotropic magnetoresistance (AMR) in a single crystal of antiferromagnetic Mott insulator Sr2IrO4. The point-contact technique is used here as a local probe of magnetotransport properties on the nanoscale. The measurements at liquid nitrogen temperature reveal negative magnetoresistances (up to 28%) for modest magnetic fields (250 mT) applied within the IrO2 ab plane and electric currents flowing perpendicular to the plane. The angular dependence of magnetoresistance shows a crossover from fourfold to twofold symmetry in response to an increasing magnetic field with angular variations in resistance from 1% to 14%. We tentatively attribute the fourfold symmetry to the crystalline component of AMR and the field-induced transition to the effects of applied field on the canting of antiferromagnetic-coupled moments in Sr2IrO4. The observed AMR is very large compared to the crystalline AMRs in 3d transition metal alloys or oxides (0.1%–0.5%) and can be associated with the large spin-orbit interactions in this 5d oxide while the transition provides evidence of correlations between electronic transport, magnetic order, and orbital states. The finding of this work opens an entirely new avenue to not only gain a new insight into physics associated with spin-orbit coupling but also to better harness the power of spintronics in a more technically favorable fashion.

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  • Received 11 April 2014

DOI:https://doi.org/10.1103/PhysRevX.4.041034

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Authors & Affiliations

C. Wang1,2, H. Seinige1,2, G. Cao3, J.-S. Zhou2, J. B. Goodenough2, and M. Tsoi1,2

  • 1Physics Department, University of Texas at Austin, Austin, Texas 78712, USA
  • 2Texas Materials Institute, University of Texas at Austin, Austin, Texas 78712, USA
  • 3Center for Advanced Materials, Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA

Popular Summary

Antiferromagnetic spintronics is a new emerging field of materials science and device physics that explores the unique properties of antiferromagnets and their implementation as active ingredients in spintronic applications.

Antiferromagnetic materials share a number of useful functionalities with ferromagnets, such as spin-transfer torque, and they exhibit unique interactions with ferromagnets. Moreover, they are instrumental in minimizing the cross talk between nanodevices since antiferromagnets do not produce stray magnetic fields. One of the goals of antiferromagnetic spintronics has been finding an efficient method for monitoring magnetic order in antiferromagnets. Anisotropic magnetoresistance (AMR) and tunneling AMR are very promising candidates for monitoring magnetic order. The antiferromagnetic iridate Sr2IrO4—characterized by tetragonal crystallographic structure—-is a particularly interesting material for such studies. The strong spin-orbit interaction in this and other iridates drives many fascinating phenomena, including the Jeff=1/2 Mott state, possible superconductivity, and topological insulator and spin liquid behaviors, which makes these iridates an attractive realm for studying physics driven by spin-orbit interactions.

We present the first observation of point-contact AMR Sr2IrO4, which can potentially be used to sense the antiferromagnetic order parameter in spintronic nanodevices. The point-contact technique allows us to probe extremely small volumes and, therefore, measures electronic transport on a microscopic scale. Point-contact measurements (a Cu tip with single crystals of Sr2IrO4) reveal a large AMR with an intriguing angular transition from fourfold to twofold symmetry in response to an increasing magnetic field (up to 0.3 T). We tentatively attribute the fourfold symmetry to the crystalline component of AMR and the field-induced transition to the effects of an applied field on the canting of antiferromagnetic-coupled moments in Sr2IrO4. The observed AMR is very large (14%) compared with the crystalline AMR in 3d transition-metal alloys/oxides (0.1%--0.5%)—-perhaps because of the large spin-orbit interactions in Sr2IrO4, a 5d oxide. The transition provides evidence of correlations among electronic transport, magnetic order, and orbital states.

Our findings pave the way for gaining new insights into the physics associated with spin-orbit coupling and also for better harnessing the power of spintronics in a more technically favorable manner.

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Vol. 4, Iss. 4 — October - December 2014

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