Picoscale Magnetoelasticity Governs Heterogeneous Magnetic Domains in a Noncentrosymmetric Ferromagnetic Weyl Semimetal

Abstract

Magnetic Weyl semimetals are predicted to host emergent electromagnetic fields at heterogeneous strained phases or at the magnetic domain walls. Tunability and control of the topological and magnetic properties are crucial for revealing these phenomena, which are not well understood or fully realized yet. Here, a scanning superconducting quantum interference device microscope is used to image spontaneous magnetization and magnetic susceptibility of CeAlSi, a noncentrosymmetric ferromagnetic Weyl semimetal candidate. Large metastable domains are observed alongside stable ferromagnetic domains. The metastable domains most likely embody a type of frustrated or glassy magnetic phase, with excitations that may be of an emergent and exotic nature. Evidence is found that the heterogeneity of the two types of domains arises from magnetoelastic or magnetostriction effects. It is shown how these domains form, how they interact, and how they can be manipulated or stabilized with lattice strains estimated to be on picometer levels. This knowledge can be used in designing and fabricating devices made from CeAlSi and related materials for magnetic field sensing and magnetic memory applications.

Pressure tuning domain-wall chirality in noncentrosymmetric magnetic Weyl semimetal CeAlGe

“…Recently, similar LTHE was also reported in CeAlSi [23,24], a type-I magnetic WSM isostructural to CeAlGe, but there the ground magnetic structure is an in-plane noncollinear ferromagnetic order below 8.2 K [23]. In CeAlSi, picoscalemagnetoelasticity governing heterogeneous magnetic domains have been observed by B. Xu et al using scanning SQUID microscope [30]. Vector MOKE measurements further confirmed two kinds of DWs with distinct topology in CeAlSi [31]: a non-chiral DW that form parallel GPa, the highest pressure we can reach, the first LTHE is observed between 0 and 0.5 T, while the second one is visible in the range 0.8≤H≤1.7 T. To the best of our knowledge, such kind of LTHE evolution with pressure has never been reported in any other materials including the structural analog CeAlSi where pressure only weakens the LTHE [24].…”

“…In addition, the inclusion of rare-earth elements endows them with strong magnetoelastic coupling and thus high tunability, providing an ideal platform to investigate the pressure-controlled DW landscapes. Although recent singular angular magnetoresistance [29], scanning superconducting quantum interference device (SQUID) microscope [30] and vector magneto-optical Kerr effect (MOKE) [31] measurements have confirmed the existence of magnetic DWs in CeAlGe and CeAlSi, the effect of pressure on these DWs has been seldom studied [24].…”

Tuning the nontrivial topological properties of the Weyl semimetal CeAlSi

“…An important property for the topological behaviors is the presence of a magnetoelastic coupling, in which the internal fields of the FM order generate picometer displacements in the unit cell [46]. These lead to strains in the domain walls and create magnetic phases with different textures [46].…”

“…An important property for the topological behaviors is the presence of a magnetoelastic coupling, in which the internal fields of the FM order generate picometer displacements in the unit cell [46]. These lead to strains in the domain walls and create magnetic phases with different textures [46]. In fact, it is theoretically predicted that magnetic WSMs can host nontrivial domain walls [47] and chiral domain walls were indeed recently detected in CeAlSi [48].…”

“…Furthermore, nontrivial domain walls are predicted to exist in magnetic WSMs [47]. It is conceivable that the internal fields already create tiny displacements at ambient pressure leading to differently oriented magnetic regions due to the presence of strain at domain walls via magnetostriction/magnetoelastic effects [46]. A compression of the sample by the application of hydrostatic pressure could then effectively change the landscape of the mag- netic domain walls in CeAlSi, modifying its topological properties.…”