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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on NdAlSi by Materials Project

NdAlSi is hexagonal omega structure-derived structured and crystallizes in the tetragonal I4_1md space group. The structure is three-dimensional. Nd is bonded to six Al and six equivalent Si atoms to form a mixture of edge and face-sharing NdAl6Si6 cuboctahedra. There are two shorter (3.22 Å) and four longer (3.23 Å) Nd–Al bond lengths. There are four shorter (3.21 Å) and two longer (3.24 Å) Nd–Si bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded in a distorted trigonal planar geometry to six equivalent Nd and three equivalent Si atoms. There are one shorter (2.43 Å) and two longer (2.44 Å) Al–Si bond lengths. In the second Al site, Al is bonded in a distorted trigonal planar geometry to six equivalent Nd and three equivalent Si atoms. There are one shorter (2.43 Å) and two longer (2.44 Å) Al–Si bond lengths. Si is bonded in a distorted trigonal planar geometry to six equivalent Nd and three Al atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NdAlSi by Materials Project

NdAlSi is hexagonal omega structure-derived structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Nd is bonded to six equivalent Al and six equivalent Si atoms to form a mixture of face and edge-sharing NdAl6Si6 cuboctahedra. All Nd–Al bond lengths are 3.22 Å. All Nd–Si bond lengths are 3.22 Å. Al is bonded in a distorted trigonal planar geometry to six equivalent Nd and three equivalent Si atoms. All Al–Si bond lengths are 2.44 Å. Si is bonded in a distorted trigonal planar geometry to six equivalent Nd and three equivalent Al atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

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

Here, 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°. The spin density wave has a long wavelength of ≈35 nm and transitions to a commensurate ferrimagnetic state below T com =5.1K. 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 NdAlX, but transport properties including AHE are affected by material-specific extrinsic effects such as disorders, despite the presence of prominent Berry curvature.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Emergent electric field induced by dissipative sliding dynamics of domain walls in a Weyl magnet

The dynamic motion of topological defects in magnets induces an emergent electric field, as exemplified by the continuous flow of skyrmion vortices. However, the electrodynamics underlying this emergent field remains poorly understood. In this context, magnetic domain walls—one-dimensional topological defects with two collective modes, sliding and spin-tilt—offer a promising platform for exploration. Here we demonstrate that the dissipative motion of domain walls under oscillatory current excitation generates an emergent electric field. We image domain patterns and quantify the domain-wall length under applied magnetic fields in mesoscopic devices based on the magnetic Weyl semimetal NdAlSi. These devices exhibit exceptionally strong domain-wall scattering and a pronounced emergent electric field, as observed in the imaginary component of the complex impedance. Spin dynamics simulations reveal that domain-wall sliding dominates over spin-tilting, in which the phase delay of the domain-wall motion with respect to the driving force impacts the emergent electric field. Our findings establish domain-wall dynamics as a platform for studying emergent electromagnetic fields and motivate further investigations of the coupled motion of magnetic solitons and conduction electrons.

Yamada, Rinsuke [The University of Tokyo, Japan]↗
DOE OSTI2021

Dynamics of local magnetic moments induced by itinerant Weyl electrons

We derive the effective interactions between local magnetic moments which are mediated by Weyl electrons in magnetic topological semimetals. The resulting spin dynamics is governed by the induced Heisenberg, Kitaev, and Dzyaloshinskii-Moriya (DM) interactions with extended range and oscillatory dependence on the distance between the spins. These interactions are realized in multiple competing channels shaped by the multitude of Weyl nodes in the electron spectrum. Microscopic spins need to be spatially modulated with a channel-dependent wave vector in order to take advantage of the interactions. The DM vector is parallel to the displacement between the two interacting spins, and requires the presence of Weyl electron Fermi surfaces. Here, we also derive the Weyl-induced chiral three-spin interaction in the presence of an external magnetic field. This interaction has an extended range as well, and acts upon the spatially modulated spins in various channels. Its tendency is to produce a skyrmion lattice or a chiral spin liquid which exhibits topological Hall effect. Ultimately, the theory developed here addresses magnetic dynamics in relativistic metals even when chiral magnetism is microscopically precluded. We discuss insights into the ordered state of the magnetic Weyl semimetal NdAlSi.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗