arXiv subjects

Tyler J. Slade

Publications and source records attributed to Tyler J. Slade.

At least 19 recordsLinked to original sources

arXiv2026

Chiral Magnon Mixing by Symmetry-Breaking in Collinear Ferrimagnets

Magnons in ferromagnets possess spin angular momentum defined by right-handed precession of the moment around the magnetization direction. In antiferromagnets with no net magnetization, left-and right-handed magnons are degenerate in the absence of an applied field. Ferrimagnets possess uncompensated magnetic sublattices, which should natively possess right-and left-handed magnons where their energy is split by the internal molecular field. Here, we show that RMn6Sn6 (R = Tb, Er) ferrimagnets possess right and left-handed magnon bands that cross at finite momentum (k) within the basal plane, defining modes with opposite dynamical chirality. Depending on the symmetry of the ferrimagnetic order, which may be manipulated by varying the rare-earth magnetic anisotropy or with applied field, the band crossing may remain a nodal line or may be gapped. The gapped modes contain hybridized chiral excitations whose chirality becomes k-dependent.

cond-mat.str-el↗

arXiv2026

Complex crystal structure prediction using ML-enhanced multi-minima iterative genetic algorithm

Current machine learning (ML) approaches for materials discovery rely heavily on known structural databases, limiting their ability to identify entirely novel structure types. In this work, we develop a multi-minima iterative genetic algorithm (MMIGA) that integrates an artificial-neural-network machine learning (ANN-ML) interatomic potential with an iterative, metadynamics-inspired penalty scheme. We demonstrate the robustness of this method on a complex ternary La-Co-Pb system, characterized by Co-Pb immiscibility and an intricate energy landscape. The ML-enhanced MMIGA successfully predicts the ground-state Pbam structure of the recently synthesized La4Co4Pb antagonistic-pair-phase, a novel structure missed by previous database-reliant ML predictions, while also identifying multiple metastable competing phases. Additionally, we challenged the MMIGA method to predict the structure of La5CoPb2 antagonistic-pair-phase, a new compound discovered during earlier attempts to synthesize the predicted phase La3CoPb. With only knowledge of the composition, our MMIGA approach successfully predicts the orthorhombic structure of La5CoPb2, producing an exact match with the structure independently determined by x-ray diffraction. By efficiently mapping both global minimum and relevant competing metastable states, this approach provides critical theoretical insights into phase selection for novel quantum and magnetic materials.

cond-mat.mtrl-sci↗

arXiv2026

Observation of Flat Bands in Type-II Weyl Semimetal TaRhTe$_{4}$

Flat bands have been theoretically predicted for decades but have only recently been realized in quantum materials such as magic-angle twisted bilayer graphene, kagome and Lieb lattices, and rare-earth metal compounds. To date, only twisted layered materials have enabled tuning of flat-band energies near the electronic chemical potential, thereby influencing transport and thermodynamic properties. Here, we report the presence of flat bands near the chemical potential in bulk TaRhTe$_{4}$, a noncentrosymmetric van-der Waals type-II Weyl semimetal. Flat bands are rarely observed in Weyl semimetals, particularly in nonmagnetic bulk systems, and the observed flat bands were not predicted by density functional theory calculations. TaRhTe$_{4}$ therefore provides a platform in which nontrivial topology coexists with flat bands near the Fermi level, as evidenced by our angle-resolved photoemission spectroscopy measurements.

cond-mat.mtrl-sci↗

arXiv2026

Physical properties of R$_2$Co$_6$Al$_{20-\delta}$ (R = Gd-Tm, Y) single crystals

Rare-earth (R) based intermetallic compounds can often exhibit diverse physical properties and distinct magnetic anisotropies. A Notable example are the light rare earth members of the mono-clinic, R$_2$Co$_6$Al$_{19}$ series that are known to display a range of physical properties, from non-Fermi liquid behavior to antiferromagnetic (AFM) ordering, with properties that vary depending on R. In this work, we have extended this series to the heavy rare earths and systematically investigate the synthesis, crystal structure, and physical properties of single crystals of R$_2$Co$_6$Al$_{20-\delta}$ for R = Gd - Tm and Y. Single crystal X-ray diffraction reveals that these materials adopt an orthorhombic Imma-type structure with delta varying non-monotonically across the heavy rare earths; ranging from 0.73 for Dy to 0.91 for Gd. Temperature-dependent specific heat, resistivity, and magnetization measurements demonstrate AFM ordering in all materials, with the Neel temperature (TN) ranging from 1.8 K for Ho to 11.8 K for Tb. Notably, Gd and Tb-based materials exhibit two distinct AFM transitions, separated by approximately 2 - 3 K. These findings establish the heavy rare-earth members of the R2Co6Al20-delta series as anisotropic antiferromagnets with strong crystal electric field effects and exchange anisotropy. The observed deviation from de Gennes scaling and the anisotropy crossover across the series highlight the important interplay between RKKY exchange and crystal electric field interactions in this orthorhombic system.

cond-mat.mtrl-sci↗

arXiv2026

Itinerant antiferromagnetism in the antagonistic pair compound Y$_4$Co$_3$Ag

Low dimensional crystallographic motifs have long been associated with desirable physical properties. The confinement of electrons to low dimensions is thought to enhance quantum fluctuations and may promote correlated phenomena. Here, using the antagonistic pair concept, we add Y to the immiscible Co-Ag pair to discover Y$_4$Co$_3$Ag. This compound adopts a monoclinic $I$2/$m$ structure consisting of Y channels that are filled by one-dimensional zigzag and hexagonal Co chains, which extend along the crystallographic $b$-axis with no nearest neighbor contacts between Co and Ag atoms. Transport, magnetic, and specific heat measurements reveal that Y$_4$Co$_3$Ag orders antiferromagnetically at $T_N=14.9$ K with an effective magnetic moment $\mu_{\text{eff}}$ = 1.4 $\mu_{\text{B}}$/Co. Specific heat measurements show only a small entropy loss on the order of $0.1\,R\ln2$ associated with magnetic order, and magnetization isotherms, in DC fields up to 70 kOe at 1.8 K and in pulsed fields up to 600 kOe at 500 mK, indicate a small ordered moment of less than 0.2 $\mu_B$/Co. Taken together, our results imply the presence of small, itinerant moments and strong fluctuations in Y$_4$Co$_3$Ag, suggesting that Y$_4$Co$_3$Ag may be a promising candidate material to investigate itinerant magnetic interactions in a quasi-one dimensional system.

cond-mat.str-el↗

arXiv2025

Structural phase transitions in the van der Waals ferromagnets Fe$_x$Pd$_{y}$Te$_2$

Here, we provide a detailed study of the crystal structure and physical properties of the recently discovered vdW ferromagnet FePd$_2$Te$_2$. We find this compound has a relatively wide width of formation, and grow single crystals with compositions Fe$_x$Pd$_{y}$Te$_2$ where $x$ ranges from 0.9 to 1.1 and $y$ from 1.8 to 2.5, respectively. Temperature-dependent X-ray diffraction and transport measurements reveal that a first-order structural transition occurs in the range of $T$ = 360-420 K. Above the transition, the compounds with Pd fraction $y>2$ adopt a disordered derivative of the tetragonal FeTe structure, with the Fe layer showing mixed Fe/Pd occupancy and the extra Pd atoms partially occupying interstitial sites. Below 370 K, the structure is incommensurately modulated. For $y<2$, the composition Fe$_{1.1}$Pd$_{1.8}$Te$_2$ has monoclinic symmetry at room temperature that is consistent with the reported structure of FePd$_2$Te$_2$. This phase undergoes a structural transition at 420 K for which the high temperature structure is yet to be determined; however, based on the similarities with the $y > 2$ compounds, we speculate that this composition also adopts a tetragonal structure above 420\,K. All compounds investigated in the Fe$_x$Pd$_{y}$Te$_2$ series show metallic behavior, with magnetic characterization indicating that they are easy-plane, hard, ferromagnets with $T_C$ spanning 98--180 K. Both the critical temperature for the structural transition and the Curie temperature are moderately suppressed with increasing Pd fraction $y$ and corresponding decreasing Fe fraction $x$, indicating that synthetic control over $x$ and $y$ paves way for the further exploration of these compounds.

cond-mat.str-el↗

arXiv2025

Hidden symmetry-breaking in a kagome Ising ferromagnet

Kagome metals can host unconventional electronic phenomena that emerge from their frustrated lattice geometry and associated band topology. Correlated electronic orders, such as charge-density waves and superconductivity, are observed to intertwine with subtle time-reversal symmetry breaking whose microscopic origin is not currently understood. Here, we provide evidence for such time-reversal symmetry breaking in the kagome metal TbV$_6$Sn$_6$ arising from staggered magnetic moments within the kagome layers. TbV$_6$Sn$_6$ consists of metallic V kagome layers separated by Tb triangular layers that host Ising ferromagnetic order. Deep in the ferromagnetic state, the Tb Ising doublet ground state should display a single, dispersionless spin-flip excitation. Instead, inelastic neutron scattering reveals two sharp excitations associated with inequivalent Tb sites, demonstrating that a symmetry-broken phase coexists with Ising ferromagnetism. No additional structural or magnetic phase transitions are detected, and first-principles calculations rule out lattice distortions as the origin of the splitting. We attribute this effect to time-reversal symmetry breaking encoded by small V moments that couple to the Tb sublattice and leave a measurable spectral fingerprint. Our results establish rare-earth local moment spectroscopy as a sensitive probe of subtle broken symmetries and highlight an unexpected interplay between kagome magnetism and rare-earth local moment magnetism.

cond-mat.str-el↗

arXiv2025

Suppression of the valence transition in solution-grown single crystals of Eu$_2$Pt$_6$Al$_{15}$

The study of Eu intermetallic compounds has allowed the exploration of valence fluctuations and transitions in 4f electron systems. Recently, a Eu$_2$Pt$_6$Al$_{15}$ phase synthesized by arc-melting followed by a thermal treatment was reported [M. Radzieowski \textit{et al.}, J Am Chem Soc 140(28), 8950-8957 (2018)], which undergoes a transition upon cooling below 45~K that was interpreted as a valence transition from Eu$^{2+}$ to Eu$^{3+}$. In this paper, we present the discovery of another polymorph of Eu$_2$Pt$_6$Al$_{15}$ obtained by high temperature solution growth, which presents different physical properties than the arc-melted polycrystalline sample. Despite the similarities in crystal structure and chemical composition, the Eu valence transition is almost fully suppressed in the solution-grown crystals, allowing the moments associated with the Eu$^{2+}$ state to order antiferromagnetically at around 14~K. A detailed analysis of the crystal structure using single crystal X-ray diffraction reveals that, although the solution grown crystals are built from the same constituent layers as the arc-melted samples, these layers present a different stacking. The effect of different thermal treatments is also studied. Different anneal procedures did not result in significant changes in the intrinsic properties, and only by arc-melting and quenching the crystals we were able to convert them into the previously reported polymorph.

cond-mat.mtrl-sci↗

arXiv2025

Charge density wave in intermetallic oxides R$_5$Pb$_3$O (R = La and Ce)

The R$_5$Pb$_3$O family was discovered decades ago, but has remained largely unexplored. Here, we report single crystal growth and basic characterization for the La and Ce members of this family. At room temperature, these compounds adopt a tetragonal structure (I4/mcm), where R and Pb atoms form linear chains along the c-axis. We identify a second-order structural phase transition at 260 K and 145 K for R = La and Ce, respectively. Single crystal X-ray diffraction reveals a lattice modulation below the transition temperature, resulting in R-Pb pairs in the z direction. The broken symmetry in the low-temperature phases results in a primitive structure with space group P4/ncc. Transport and diffraction measurements, in agreement with density functional theory calculations, support that the R$_5$Pb$_3$O (R = La and Ce) series hosts an electron-phonon coupling driven charge density wave (CDW) at low temperatures. The CDW ordering temperature is suppressed by more than 100 K by the La to Ce substitution, suggesting high pressure-sensitivity. Therefore, this family offers the potential for investigating competing orders in oxides, with heavier rare-earth members still to be explored.

cond-mat.mtrl-sci↗

arXiv2025

Quantum critical point followed by Kondo-like behavior due to Cu substitution in itinerant, antiferromagnet ${\text{La}_{2}\text{(Cu}_{x}\text {Ni}_{1-x})_7}$

$\text{La}_2 \text{Ni}_7$ is an itinerant magnetic system with a small ordered moment of $\sim$ 0.1 $\mu_{B}/\text{Ni}$ and a series of antiferromagnetic (AFM) transitions at $T_1$ = 61.0 K, $T_2$ = 56.5 K and $T_3$ = 42.2 K. $M(H)$, and $\rho(H)$ isotherms as well as constant field $M(T)$ and $\rho(T)$ measurements on single crystalline samples manifest a complex, anisotropic $H-T$ phase diagram with multiple phase lines. Here we present the growth and characterization of single crystals of the ${\text{La}_{2}\text{(Cu}_{x}\text {Ni}_{1-x})_7}$ series for 0 $\leq x \leq$ 0.181. We measured powder x-ray diffraction, and composition, as well as anisotropic $R(H,T)$, $M(H,T)$, and $C_p(T)$ on these single crystals. Using the measured data, we infer a $(T-x)$ phase diagram to study the evolution of the AFM ordering upon Cu substitution. For ${0 \leq x \leq 0.097}$, the system remains magnetically ordered at base temperature with $x \leq$ 0.012, showing signs of multiple AFM ordering temperatures. For the higher substitution levels, ${0.125 \leq x \leq 0.181}$, there are no signatures of magnetic ordering, but anomalous features in $R(T)$ and $C_p(T)$ data are observed which are consistent with the Kondo effect in this system. The intermediate $x$ = 0.105 sample lies between the magnetic ordered and the Kondo regime and is in the vicinity of the AFM-quantum critical point (QCP). Thus, ${\text{La}_{2}\text{(Cu}_{x}\text {Ni}_{1-x})_7}$ is an example of a small moment system that can be tuned through a QCP. Given these data combined with the fact that the $\text{La}_2 \text{Ni}_7$ structure has kagome-like, Ni-sublattices running perpendicular to the crystallographic $c$ axis, and a predicted $3d$-electron flat band that contributes to the density of states near the Fermi energy, ${\text{La}_{2}\text{(Cu}_{x}\text {Ni}_{1-x})_7}$ becomes a promising system to host and study exotic physics.

cond-mat.str-el↗

arXiv2025

Superconducting dome and structural changes in LaRu$_3$Si$_2$ under pressure

LaRu$_3$Si$_2$ is of current research interest as a kagome metal with a superconducting transition temperature, $T_c\sim$7 K and higher temperature charge density wave (CDW) orders. Here we report electrical transport and X-ray diffraction measurements on LaRu$_3$Si$_2$ under pressure up to 65 GPa and 35 GPa respectively. The superconducting transition temperature $T_c$ first gets slightly enhanced and reaches a maximum $\sim$8.7 K at $\sim$8.5 GPa. With further applied pressure, $T_c$ is initially gradually suppressed, then more rapidly suppressed, followed by gradual suppression, revealing a superconducting dome. Two possible pressure-induced structural phase transitions are also observed at room temperature, from original hexagonal phase to another hexagonal structure above $\sim$11.5 GPa, and further to a structure with lower symmetry above $\sim$23.5 GPa. These transition pressures roughly correlate with features found in our pressure dependent transport data.

cond-mat.supr-con↗

arXiv2025

Use of frit-disc crucible sets to make solution growth more quantitative and versatile

The recent availability of step-edge, frit-disc crucible sets (generally sold as Canfield Crucible Sets or CCS) has led to multiple innovations associated with our group's use of solution growth. Use of CCS allows for the clean separation of liquid from solid phases during the growth process. This clean separation enables the reuse of the decanted liquid, either allowing for simple, economic, savings associated with recycling expensive precursor elements or allowing for the fractionation of a growth into multiple, small steps, revealing the progression of multiple solidifications. Clean separation of liquid from solid phases also allows for the determination of the liquidus line (or surface) and the creation, or correction, of composition-temperature phase diagrams. The reuse of clean decanted liquid has also allowed us to prepare liquids ideally suited for the growth of large single crystals of specific phases by tuning the composition of the melt to the optimal composition for growth of the desired phase, often with reduced nucleation sites. Finally, we discuss how solution growth and CCS use can be harnessed to provide a plethora of composition-temperature data points defining liquidus lines or surfaces with differing degrees of precision to either test or anchor artificial intelligence and/or machine learning based attempts to augment and extend the limited experimentally determined data base.

cond-mat.mtrl-sci↗

arXiv2024

Tuning the structure and superconductivity of SrNi$_2$P$_2$ by Rh substitution

SrNi$_2$P$_2$ is unique among the ThCr$_2$Si$_2$ class since it exhibits a temperature induced transition upon cooling from an uncollapsed tetragonal (ucT) state to a one-third-collapsed orthorhombic (tcO) state where one out of every three P-rows bond across the Sr layers. This compound is also known for exhibiting bulk superconductivity below 1.4 K at ambient pressure. In this work, we report on the effects of Rh substitution in Sr(Ni$_{1-x}$Rh$_x$)$_2$P$_2$ on the structural and superconducting properties. We studied the variation of the nearest P-P distances as a function of the Rh fraction at room temperature, as well as its temperature dependence for selected compositions. We find that increasing the Rh fraction leads to a decrease in the transition temperature between the ucT and tcO states, until a full suppression of the tcO state for $x\geq 0.166$. The superconducting transition first remains nearly insensitive to the Rh fraction, and then it increases to 2.3 K after the tcO state is fully suppressed. These results are summarized in a phase diagram, built upon the characterization by energy dispersive x-ray spectroscopy, x-ray diffraction, resistance, magnetization and specific heat measurements done on crystalline samples with varying Rh content. The relationship between band structure, crystal structure and superconductivity is discussed based on previously reported band structure calculations on SrRh$_2$P$_2$. Moreover, the effect of Rh fraction on the stress-induced structural transitions is also addressed by means of strain-stress studies done by uniaxial compression of single-crystalline micropillars of Sr(Ni$_{1-x}$Rh$_x$)$_2$P$_2$.

cond-mat.supr-con↗

arXiv2024

Nature of quantum criticality in the Ising ferromagnet TbV$_6$Sn$_6$

TbV$_6$Sn$_6$ is a topological metal where ferromagnetic Tb ions with strong uniaxial magnetic anisotropy interact with V kagome layers. Inelastic neutron scattering (INS) measurements show that the Tb ions adopt an Ising doublet ground state. Here, we consider whether a transverse magnetic field can drive TbV$_6$Sn$_6$ toward a quantum critical point, providing a rare example of transverse-field Ising criticality in a metallic compound. High-field magnetization measurements reveal a first-order-like spin-reorientation transition at 25.6 T. Our INS-based magnetic model finds that this is caused by an avoided crossing of an excited-state singlet with the ground-state doublet. Surprisingly, our model predicts that quantum critical and tricritical points are accessible within the range of experimentally determined model parameters and may be reached by varying the direction of an applied magnetic field.

cond-mat.str-el↗

arXiv2024

Design and Predict Tetragonal van der Waals Layered Quantum Materials of MPd$_5$I$_2$ (M=Ga, In and 3$d$ Transition Metals)

Quantum materials with stacked van der Waals (vdW) layers hosting non-trivial band structure topology and magnetism have shown many interesting properties. Using high throughput density functional theory calculations, we design and predict tetragonal vdW-layered quantum materials in the MPd$_5$I$_2$ structure (M=Ga, In and 3d transition metals). We show that besides the known AlPd$_5$I$_2$, the -MPd$_5$- structural motif of three-atomic-layer slabs separated by two I layers can accommodate a variety of metal atoms giving arise to topologically non-trivial features and highly tunable magnetic properties in both bulk and single layer 2D structures. Among them, TiPd$_5$I$_2$ and InPd$_5$I$_2$ host a pair of Dirac points and likely an additional strong topological insulator state for the band manifolds just above and below the top valence band, respectively, with their single layers hosting or near quantum spin Hall states. CrPd$_5$I$_2$ is a ferromagnet with a large out-of-plane magneto-anisotropy energy, desirable for rare-earth-free permanent magnets.

cond-mat.mtrl-sci↗

arXiv2024

New insight into tuning magnetic phases of $R$Mn$_6$Sn$_6$ kagome metals

Predicting magnetic ordering in kagome compounds offers the possibility of harnessing topological or flat-band physical properties through tuning of the magnetism. Here, we examine the magnetic interactions and phases of ErMn$_6$Sn$_6$ which belongs to a family of $R$Mn$_6$Sn$_6$, $R=$ Sc, Y, Gd--Lu, compounds with magnetic kagome Mn layers, triangular $R$ layers, and signatures of topological properties. Using results from single-crystal neutron diffraction and mean-field analysis, we find that ErMn$_6$Sn$_6$ sits close to the critical boundary separating the spiral-magnetic and ferrimagnetic ordered states typical for nonmagnetic versus magnetic $R$ layers, respectively. Finding interlayer magnetic interactions and easy-plane Mn magnetic anisotropy consistent with other members of the family, we predict the existence of a number of temperature and field dependent collinear, noncollinear, and noncoplanar magnetic phases. We show that thermal fluctuations of the Er magnetic moment, which act to weaken the Mn-Er interlayer magnetic interaction and quench the Er magnetic anisotropy, dictate magnetic phase stability. Our results provide a starting point and outline a multitude of possibilities for studying the behavior of Dirac fermions in $R$Mn$_6$Sn$_6$ compounds with control of the Mn spin orientation and real-space spin chirality.

cond-mat.str-el↗

arXiv2024

Effect of Ni substitution on the fragile magnetic system ${\text{La}_{5}\text{Co}_{2}\text {Ge}_{3}}$

$\text{La}_{5}\text{Co}_{2}\text{Ge}_{3}$ is an itinerant ferromagnet with a Curie temperature, $T_C$, of $\sim$ 3.8 K and a remarkably small saturated moment of 0.1 $\mu_{B}/\text{Co}$. Here we present the growth and characterization of single crystals of the ${\text{La}_{5}\text{(Co}_{1-x}\text {Ni}_{x})_2\text {Ge}_{3}}$ series for 0.00 $\leq x \leq$ 0.186. We measured powder X-ray diffraction, composition as well as anisotropic temperature dependent resistivity, temperature and field dependent magnetization along with heat capacity on these single crystals. We also measured muon-spin rotation/relaxation ($\mu \text{SR}$) for some Ni substitutions ($x$ = 0.027, 0.036, 0.074) to study the evolution of internal field with Ni substitution. Using the measured data we infer a low temperature, transition temperature-composition phase diagram for ${\text{La}_{5}\text{(Co}_{1-x}\text {Ni}_{x})_2\text {Ge}_{3}}$. We find that $T_{C}$ is suppressed for low dopings, $x \leq 0.014 $; whereas for $0.036 \leq {x} \leq 0.186 $, the samples are antiferromagnetic with a Neel temperature, $T_{N}$, that goes through a weak and shallow maximum ($T_N \sim$ 3.4 K for $ x \sim$ 0.07) and then gradually decreases to 2.4 K by $x$ = 0.186. For intermediate Ni substitutions, $0.016 \leq {x} \leq 0.027 $, two transition temperatures are inferred with $T_N > T_C$. Whereas the $T-x$ phase diagram for ${\text{La}_{5}\text{(Co}_{1-x}\text {Ni}_{x})_2\text {Ge}_{3}}$ and the $T-p$ phase diagram determined for the parent $\text{La}_{5}\text{Co}_{2}\text{Ge}_{3}$ under hydrostatic pressure are grossly similar, changing from a low doping or low pressure ferromagnetic (FM) ground state to a high doped or pressure antiferromagnetic (AFM) state, perturbation by Ni substitution enabled us to identify an intermediate doping regime where both FM and AFM transitions occur.

cond-mat.str-el↗

arXiv2024

La$_4$Co$_4$X (X = Pb, Bi, Sb): a demonstration of antagonistic pairs as a route to quasi-low dimensional ternary compounds

We outline how pairs of strongly immiscible elements, referred to here as antagonistic pairs, can be used to synthesize ternary compounds with quasi-reduced dimensional motifs. By identifying third elements that are compatible with a given antagonistic pair, ternary compounds can be formed in which the third element segregates the immiscible atoms into spatially separated substructures. Quasi-low dimensional structural units are a natural consequence of the immiscible atoms seeking to avoid contact in the solid-state. As proof of principle, we present the discovery and physical properties of La$_4$Co$_4$X (X = Pb, Bi, Sb), a new family of intermetallics based on the antagonistic pairs Co-Pb and Co-Bi. La$_4$Co$_4$X adopts a new orthorhombic crystal structure (space group Pbam) containing quasi-2D Co slabs and La-X layers that stack along the a-axis. Consistent with our proposal, the La atoms separate the Co and X substructures, ensuring there are no direct contacts between immiscible atoms. Within the Co slabs, the atoms occupy the vertices of corner sharing tetrahedra and triangles, and this motif produces flat electronic bands near the Fermi level that favor magnetism. The Co is moment bearing in La$_4$Co$_4$X, and we show that whereas La$_4$Co$_4$Pb behaves as a three dimensional antiferromagnet with T$_N$ = 220 K, La$_4$Co$_4$Bi and La$_4$Co$_4$Sb have behavior consistent with low dimensional magnetic coupling and ordering, with T$_N$ = 153 K and 143 K respectively. In addition to the Pb, Bi, and Sb based La$_4$Co$_4$X compounds, we were likely able to produce an analogous La$_4$Co$_4$Sn in polycrystalline form, although we were unable to isolate single crystals. We anticipate that using mutually compatible third elements with an antagonistic pair represents a generalizable design principle for discovering new materials and structure types containing low-dimensional substructures.

cond-mat.mtrl-sci↗