Magnetoresistive Switching and Topological Hall Effect Controlled by Novel Magnetic Textures

Understanding the origin and properties of magnetoresistance in topological systems is a topic of high interest currently, and we discuss work on two materials in this category. CeAlGe(Si) orders ferrimagnetically below 5.4 K, with two inequivalent Ce sites with different moments that are oriented in the a-b tetragonal plane. For a magnetic field applied in this plane the magnetoresistance appears to diverge when parallel to the [1,0,0] and comparable directions, in a very narrow angular range—singular angular magnetoresistance (SAMR) [1]. Neutron diffraction was employed to determine the magnetic structure, and this combined with theory led to understanding that the SAMR results from switching of domains coupled with Fermi surface mismatch near Weyl nodes. The second material is YMn$_{6}$Sn$_{6}$, which orders antiferromagnetically at 340 K and exhibits quite a variety of magnetic structures as a function of temperature and magnetic field, mostly incommensurate, revealed by neutron scattering. Only one such structure—the transverse conical spiral—exhibits a topological Hall effect, and this is only observed at elevated temperatures. Detailed theoretical calculations explain not only all the observed phases but also the topological Hall effect, which originates via a new mechanism of thermally induced magnons.[2,3]

[1] Singular Angular Magnetoresistance in a Magnetic Nodal Semimetal, T. Suzuki, L. Savary, J.-P. Liu, J. W. Lynn, L. Balents, and J. G. Checkelsky, Science 365, 377 (2019).
[2] Competing magnetic states and fluctuation-driven scalar spin chirality in the kagome metal YMn6Sn6, Nirmal J. Ghimire, Rebecca L. Dally, L. Poudel, D. C. Jones, D. Michel, N. Thapa Magar, M. Bleuel, Michael A. McGuire, J. S. Jiang, John F. Mitchell, Jeffrey W. Lynn, and I. I. Mazin, Science Advances 6, eabe2680 (2020).
[3] Chiral properties of the zero-field spiral state and field-induced magnetic phases of the itinerant kagome metal YMn6Sn6, Rebecca L. Dally, Jeffrey W. Lynn, Nirmal J. Ghimire, Dina Michel, Peter Siegfried, and Igor I. Mazin, Phys. Rev. B 103, 094413 (2021).