Jungwoo Koo
Geometrically frustrated antiferromagnets have been the subject of extensivetheoretical and experimental works, mainly due to its disordered classical andquantum ground states whose short- or long-range order is determined by adelicate balance between (symmetric and antisymmetric) exchange interactionsand magnetic anisotropy. In addition, large anomalous Hall and Nernst effectsat room temperature have been evidenced from Mn3Sn[1] and Mn3Ge[2,3]. Theunexpected anomalous transport properties from these antiferromagnets areattributed to the inverse triangular spin structure in the basal plane. Moreover,the brokenPTsymmetry of the ground state allows the existence of gaplesselectronic excitations, i.e., the Weyl fermions, in the electronic band structuregiving rise to large anomalous Hall and Nernst conductivities. These materialsare currently of great interest to the topological magnetics community, dueboth to their fascinating Berry curvature driven magnetotransport propertiesand their potential applications in spintronic devices.Despite being an appealing system for the AFM spintronics research, all theintriguing transport properties of Mn3Sn and Mn3Ge were examined withsingle-crystal bulk specimens or polycrystalline thin films. Especially, owingto an ill-defined crystallographic property of polycrystalline thin films, therelationship of anomalous transport properties and the noncollinear AFM spinstructure has yet to be scrutinized thoroughly.In this talk, anomalous Hall and Nernst effects associated with the inversetriangular AFM spin structure of Mn3Sn thin films will be presented. Neutrondiffraction measurement of Mn3Sn thin film confirmed that the spin structureof our thin film is exactly the same type as the bulk specimen. Magnetic phasetransition from the inverse triangular spin structure to the helical order wasnot detected. Anomalous Hall and Nernst effects of Mn3Sn thin films weremeasured along the same crystallographic orientation as the single crystal bulkspecimens, e.g., AHE :I||[01 ̄10] andH||[2 ̄1 ̄10] and ANEQ||[0001] andH||[01 ̄10].Finally, noncollinear AFM domain wall switching and SMR experiments willbe discussed.
[1]S. Nakatsuji, N. Kiyohara, and T. Higo, Large anomalous hall effect in a non-collinear antiferromagnet at room temperature,Nature527, 212 (2015)[2]N. Kiyohara, T. Tomita, and S. Nakatsuji, Giant anomalous hall effect in the chiral antiferromagnet mn3ge, Physical ReviewApplied5, 10.1103/physrevapplied.5.064009 (2016)
[3]A. K. Nayak, J. E. Fischer, Y. Sun, B. Yan, J. Karel, A. C. Komarek, C. Shekhar, N. Kumar, W. Schnelle, J. K ̈ubler,C. Felser, and S. S. P. Parkin, Large anomalous hall effect driven by a nonvanishing berry curvature in the noncolinearantiferromagnet mn3ge, Science Advances2, e1501870 (2016)