Stripe helical magnetism and two regimes of anomalous Hall effect in NdAlGe

Hung-Yu Yang, Jonathan Gaudet, Rahul Verma, Santu Baidya, Faranak Bahrami, Xiaohan Yao, Cheng-Yi Huang, Lisa DeBeer-Schmitt, Adam A. Aczel, Guangyong Xu, Hsin Lin, Arun Bansil, Bahadur Singh, and Fazel Tafti

Phys. Rev. Materials 7, 034202 – Published 27 March 2023

Abstract

We report the magnetic and electronic transport properties of the inversion and time-reversal symmetry breaking Weyl semimetal NdAlGe. This material is analogous to NdAlSi, whose helical magnetism presents a rare example of a Weyl-mediated collective phenomenon, but with a larger spin-orbit coupling. Our neutron diffraction experiments revealed that NdAlGe, similar to NdAlSi, supports an incommensurate spin density wave ( $T_{inc} = 6.8$ K) whose spins are predominantly pointing along the out-of-plane direction and have a small helical spin canting of $3^{\circ}$ . The spin density wave has a long wavelength of $\approx 35$ nm and transitions to a commensurate ferrimagnetic state below $T_{com} = 5.1 K$ . Using small-angle neutron scattering, we showed that the zero-field cooled ferrimagnetic domains form stripes in real space with characteristic length scales of 18 and 72 nm parallel and perpendicular to the [110] direction, respectively. Interestingly, for the transport properties, NdAlSi does not exhibit an anomalous Hall effect (AHE) that is commonly observed in magnetic Weyl semimetals. In contrast to NdAlSi, we identify two different AHE regimes in NdAlGe that are, respectively, governed by intrinsic Berry curvature and extrinsic disorders/spin fluctuations. Our paper suggests that Weyl-mediated magnetism prevails in this group of noncentrosymmetric magnetic Weyl semimetals $NdAl X$ , but transport properties including AHE are affected by material-specific extrinsic effects such as disorders, despite the presence of prominent Berry curvature.

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Received 12 January 2023
Accepted 6 March 2023

DOI:https://doi.org/10.1103/PhysRevMaterials.7.034202

Physics Subject Headings (PhySH)

Anomalous Hall effect Helicoidal magnetic texture Magnetic domains RKKY interaction

Weyl semimetal

First-principles calculations Neutron diffraction Resistivity measurements Small angle neutron scattering

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Hung-Yu Yang ^1,*, Jonathan Gaudet^2,3, Rahul Verma⁴, Santu Baidya^5,6, Faranak Bahrami¹, Xiaohan Yao ¹, Cheng-Yi Huang⁷, Lisa DeBeer-Schmitt⁸, Adam A. Aczel⁸, Guangyong Xu², Hsin Lin⁹, Arun Bansil⁷, Bahadur Singh⁴, and Fazel Tafti¹

¹Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA
²NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
³Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
⁴Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Colaba, Mumbai 400005, India
⁵Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
⁶Department of Physics and Materials Science, Jaypee University of Information Technology, Waknaghat, Solan, Himachal Pradesh 173234, India
⁷Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
⁸Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
⁹Institute of Physics, Academia Sinica, Taipei 115201, Taiwan

^*Present address: Department of Electrical and Computer Engineering, University of California, Los Angeles, California 90095, USA; hungyuyang@g.ucla.edu