CeGaSi: Topological Magnetic Intermetallic

• CeGaSi is a noncentrosymmetric tetragonal intermetallic characterized by a polar LaPtSi-type structure, robust CEF-split 4f states, and nodal-line-metal features.
• It exhibits canted antiferromagnetism with easy-plane anisotropy, metamagnetic transitions, and a magnetic phase transition at 11 K.
• The material shows a large anomalous Hall effect dominated by skew scattering, linking its magnetic order with a topological band structure.

Searching arXiv for the specified CeGaSi paper and closely related context. to=arxiv_search 大发彩票网 天天爱彩票中奖led 山大发.json code {"^^^^^^^^2query2 (Swami et al., 28 Jul 2025) OR \2^^^^^^^^"Crystalline electric field and large anomalous Hall effect in the candidate topological material CeGaSi\"","max_results":5,"sort_by":"submittedDate","sort_order":"descending"} 泰皇്ത്രീassistant to=arxiv_search code to=arxiv_search code {"^^^^^^^^2query2 (Swami et al., 28 Jul 2025) OR \2query2^^^^} CeGaSi is a noncentrosymmetric tetragonal intermetallic, crystallizing in the LaPtSi-type structure, that combines strong crystalline-electric-field effects of CePRESERVED_PLACEHOLDER_^^^^2query2^^^^, low-temperature canted antiferromagnetism, anisotropic magnetotransport, and a large anomalous Hall response on top of a first-principles nodal-line-metal electronic structure (&&&^^^^2query2^^^^&&&). The material is characterized by a magnetic phase transition at PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^, pronounced easy-plane anisotropy, and anomalous Hall conductivities that remain large in the ordered state. In the reported picture, its phenomenology is governed by the interplay among polar crystal symmetry, crystal-field-split $4f$ states, magnetic order, and spin-orbit-coupled band topology.

^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^. Crystal structure and symmetry environment

CeGaSi crystallizes in space group $I4_1md$ (No. ^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2^^^^9) with point group $C_{4v}$ (&&&^^^^2query2^^^^&&&). Rietveld refinement at $300\,\mathrm{K}$ gives lattice parameters $a=b=4.2452\,\text{\AA}$ and $c=14.3443\,\text{\AA}$. Ce, Ga, and Si each occupy the Wyckoff $4a$ site $(0,0,z)$ and form alternating Ce–Ga–Si layers along the PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2^^^^ axis, producing a polar stacking without inversion symmetry.

This structural setting is central to the material’s classification as a polar tetragonal metal. The absence of inversion symmetry constrains both the allowed crystalline-electric-field (CEF) terms and the symmetry protection of the band structure. The reported nodal-line-like crossings and their evolution under spin-orbit coupling are therefore not independent of the crystal structure; they arise within the symmetry environment established by the polar LaPtSi-type lattice. A plausible implication is that CeGaSi belongs to the broader class of correlated noncentrosymmetric intermetallics in which magnetic and topological responses are tightly symmetry-coupled.

2. Crystalline-electric-field scheme of the CePRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^ multiplet

In tetragonal PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \22^^^^ symmetry, the CePRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^3 ion with PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^4 is described by the CEF Hamiltonian

PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^5

Fits to PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^6 and PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^7 yield

PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^8

and diagonalization gives the level sequence

PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^9

with an overall splitting of approximately $4f$^^^^2query2^^^^ (&&&^^^^2query2^^^^&&&).

The reported CEF analysis implies that the sixfold degenerate ground-state manifold of Ce$4f$^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^ splits into three Kramers doublets. This is the organizing principle for the compound’s anisotropic magnetic and thermodynamic behavior. The relatively large splitting places the first excited doublet well above the ordering scale, so the low-temperature physics is governed primarily by the ground-state doublet. This interpretation is reinforced thermodynamically by the magnetic entropy recovering approximately $4f$2 at $4f$3, consistent with ordering out of a Kramers-doublet manifold.

3. Magnetic susceptibility, metamagnetism, and canted antiferromagnetism

Above $4f$4, the magnetic susceptibility follows the modified Curie–Weiss form

$4f$5

with $4f$6, $4f$7, $4f$8, $4f$9, and $I4_1md$^^^^2query2^^^^ (&&&^^^^2query2^^^^&&&). The full CEF susceptibility is written as

$I4_1md$^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^

with molecular-field constants $I4_1md$2 and $I4_1md$3.

A sharp cusp in $I4_1md$4 at $I4_1md$5 marks the magnetic transition. Below $I4_1md$6, $I4_1md$7, demonstrating strong easy-plane anisotropy. At $I4_1md$8, $I4_1md$9 for $C_{4v}$^^^^2query2^^^^ shows two metamagnetic-like features at $C_{4v}$^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^ and $C_{4v}$2, interpreted as spin-flop behavior, and saturates near $C_{4v}$3. For $C_{4v}$4, two weaker transitions are observed together with quasi-saturation at $C_{4v}$5 at $C_{4v}$6. Hysteresis loops for both field orientations indicate a canted-antiferromagnetic ground state with a coexisting ferromagnetic component.

These results establish that CeGaSi is not a simple collinear antiferromagnet. The simultaneous presence of an antiferromagnetic transition, easy-plane anisotropy, low-field metamagnetic-like features, and hysteresis supports a canted configuration. The opposite signs of $C_{4v}$7 and $C_{4v}$8 further emphasize the directional competition between AFM-like and FM-like exchange tendencies. This suggests that the ordered state is shaped jointly by anisotropic exchange and the CEF-selected local-moment manifold.

4. Thermodynamic and charge-transport signatures of magnetic order

The total heat capacity between $C_{4v}$9 and $300\,\mathrm{K}$^^^^2query2^^^^ is fitted above $300\,\mathrm{K}$^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^ by

$300\,\mathrm{K}$2

yielding $300\,\mathrm{K}$3, $300\,\mathrm{K}$4, $300\,\mathrm{K}$5, and $300\,\mathrm{K}$6 (&&&^^^^2query2^^^^&&&). A $300\,\mathrm{K}$7-peak at $300\,\mathrm{K}$8 confirms bulk magnetic ordering. After subtraction of the LaGaSi reference, the magnetic contribution $300\,\mathrm{K}$9 shows a Schottky hump near $a=b=4.2452\,\text{\AA}$^^^^2query2^^^^, reproduced by a three-level model with $a=b=4.2452\,\text{\AA}$^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^ and $a=b=4.2452\,\text{\AA}$2. The magnetic entropy approaches approximately $a=b=4.2452\,\text{\AA}$3 by $a=b=4.2452\,\text{\AA}$4.

Electrical resistivity is metallic with $a=b=4.2452\,\text{\AA}$5, displays a broad hump near $a=b=4.2452\,\text{\AA}$6 attributed to CEF scattering, and exhibits a sharp drop at $a=b=4.2452\,\text{\AA}$7 as spin-disorder scattering freezes out. For $a=b=4.2452\,\text{\AA}$8, the low-temperature resistivity follows

$a=b=4.2452\,\text{\AA}$9

with $c=14.3443\,\text{\AA}$^^^^2query2^^^^, $c=14.3443\,\text{\AA}$^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^, and $c=14.3443\,\text{\AA}$2, signifying AFM-magnon scattering.

Magnetoresistance,

$c=14.3443\,\text{\AA}$3

is strongly anisotropic. For $c=14.3443\,\text{\AA}$4, it is negative at low fields and crosses to positive values at high fields; for $c=14.3443\,\text{\AA}$5, it remains positive at low temperature and high fields. In both orientations the maximum negative magnetoresistance occurs near $c=14.3443\,\text{\AA}$6, where it is attributed to suppression of spin-disorder scattering by the magnetic field.

Taken together, the heat-capacity, entropy, resistivity, and magnetoresistance data are internally consistent with a CEF-governed local-moment system that undergoes bulk antiferromagnetic ordering and retains strong coupling between spin disorder and charge transport. The broad feature near $c=14.3443\,\text{\AA}$7 in both $c=14.3443\,\text{\AA}$8 and $c=14.3443\,\text{\AA}$9 links the transport and thermodynamics directly to the same CEF excitation spectrum.

5. Anomalous Hall response and scattering mechanism

The Hall resistivity for $4a$^^^^2query2^^^^ ($4a$^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^) and $4a$2 ($4a$3) is described by

$4a$4

with positive $4a$5, corresponding to a hole-like carrier density $4a$6 and mobility $4a$7 at $4a$8 (&&&^^^^2query2^^^^&&&). In the ordered state, $4a$9.

The anomalous Hall component is analyzed through the scaling form

$(0,0,z)$^^^^2query2^^^^

for which $(0,0,z)$^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^, indicating that the anomalous Hall effect is dominated by skew scattering. At $(0,0,z)$2, the anomalous Hall conductivities are reported as

$(0,0,z)$3

The anomalous Hall angle $(0,0,z)$4 reaches a maximum near $(0,0,z)$5 and decreases above the ordering temperature.

A common simplification for magnetic topological metals is to treat a large anomalous Hall response as primarily intrinsic. In CeGaSi, the reported scaling analysis does not support that simplification: the dominant contribution is assigned to skew scattering rather than to the quadratic term associated with an intrinsic-plus-side-jump form. This does not negate the relevance of the band topology; rather, it indicates that the measured Hall response in the ordered state is controlled strongly by scattering processes tied to the magnetic background.

6. First-principles electronic structure and topological interpretation

First-principles calculations performed within GGA+$(0,0,z)$6 with $(0,0,z)$7 and a $(0,0,z)$8 supercell identify an AFM ground state denoted AFM-7 with spins along $(0,0,z)$9 (&&&^^^^2query2^^^^&&&). The optimized lattice parameters, PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2query2^^^^ and PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^, are reported to be in close agreement with experiment. The total density of states is metallic, with valence bands derived from Ce-PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query22^^^^/Ga-PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2^^^^3/Si-PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2^^^^4 states and conduction bands dominated by Ce PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2^^^^5 character.

In spin-polarized calculations without spin-orbit coupling, nodal-line-like crossings appear along PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2^^^^6–S at PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2^^^^7 and Z–PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2^^^^8 at PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2^^^^9. These crossings arise from band inversion and hybridization of Ce PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2CeGaSi (Swami et al., 28 Jul 2025) OR \2query2^^^^, PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2CeGaSi (Swami et al., 28 Jul 2025) OR \2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^, and PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2CeGaSi (Swami et al., 28 Jul 2025) OR \22^^^^ orbitals, and the nodal lines lie in the PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^3 plane. When spin-orbit coupling is included along PRESERVED_PLACEHOLDER_^^^^2CeGaSi (Swami et al., 28 Jul 2025) OR \2CeGaSi (Swami et al., 28 Jul 2025) OR \2^^^^4, these crossings become gapped, which is interpreted as nontrivial topology inherited from broken mirror and fourfold rotational symmetries of the polar lattice.

The designation of CeGaSi as a candidate topological material follows from this calculated nodal-line-metal electronic structure together with its SOC-induced gap opening. The key point is not the persistence of ideal symmetry-protected crossings in the fully spin-orbit-coupled state, but the coexistence of a topologically nontrivial band-structure tendency with magnetic order, CEF physics, and a strong anomalous Hall response. This suggests a magnetic–topological interplay in which the transport anomalies are embedded in a correlated, symmetry-broken electronic environment rather than in a weakly interacting topological semimetal alone.