Abstract
We report point-contact measurements of anisotropic magnetoresistance (AMR) in a single crystal of antiferromagnetic Mott insulator . 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 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 . The observed AMR is very large compared to the crystalline AMRs in transition metal alloys or oxides (0.1%–0.5%) and can be associated with the large spin-orbit interactions in this 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.
- Received 11 April 2014
DOI:https://doi.org/10.1103/PhysRevX.4.041034
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Published by the American Physical Society
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 —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 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 , 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 ) 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 . The observed AMR is very large (14%) compared with the crystalline AMR in transition-metal alloys/oxides (0.1%--0.5%)—-perhaps because of the large spin-orbit interactions in , a 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.