Extensive research has focused on phenomena arising from the chirality of crystalline or magnetic structures. Recently, we have investigated the “nonlinear chiral thermoelectric (NCTE) Hall effect,” in which current flows in the direction of the cross product of the electric field and the temperature gradient in a material with a chiral structure. Despite its importance for device applications such as heat flow sensors and logic circuits, there are no quantitative demonstrations in actual materials. We investigate the NCTE Hall effect and the second-order response to the electric field in Te, which hosts the chiral crystal structure, based on ab initio calculations and symmetry argument. We clarify that the NCTE Hall current can flow parallel to the chiral axis, whereas such behavior is absent for the second-order response to the DC electric field. Quantitative estimation predicts the large NCTE Hall current, which is sufficiently detectable in experiments, and the orbital magnetic moment will play an important role in the vicinity of the top of the valence band.

The recent discovery of two-dimensional (2D) long-range magnets provides a wide platform to develop nonvolatile spintronic devices at the limit of miniaturization, and the contacts between 2D magnets and metals are crucial as the spintronic device performances are currently plagued by the Fermi-level pinning (FLP) effect, magnetic phase transition temperature, and tunneling resistance. Hence, a detailed atomic-scale understanding of the van der Waals (vdWs) ferromagnetic contacts to the 2D metals is a necessity. Herein, we propose a series of 2D metals vdWs contacts to 2D ferromagnetic monolayer ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$ (CGT) as the example to investigate the characteristics. The calculations reveal that strong FLP effects are observed in the Ohmic metal contacts to ${\mathrm{TaS}}_2, {\mathrm{VSe}}_2, {\mathrm{NbS}}_2, {\mathrm{VS}}_2$, and ${\mathrm{MoS}}_2$, while the Schottky metal contacts to ${\mathrm{TaSe}}_2$ and ${\mathrm{NbSe}}_2$ are weak. Further investigations uncover that the origin of strong FLP is the interfacial potential step $\mathrm{\Delta }V$. The magnetic phase transition based on Monte Carlo (MC) simulations demonstrates that interface charge injection and lattice mismatch jointly determine the Curie temperature ($T_{\mathrm{c}}$) of heterostructures, and the discovered supreme $T_{\mathrm{c}}$ approximately 97 K of $\mathrm{CGT}\text{/}{\mathrm{TaSe}}_2$ reach three times the $T_{\mathrm{c}}$ approximately 34 K of free-standing CGT. Furthermore, interfacial transports and magnetic anisotropy energy (MAE) were calculated and screened. Our studies can provide potential guidance for designing multifunctional 2D spintronic devices with selective contacts in the future.

The first-order transition line in the H-T phase diagram of itinerant electron metamagnets terminates at the critical end point—analogous to the critical point on the gas-liquid condensation line in the p-T phase diagram. To unravel the impact of critical magnetic fluctuations on the crystal lattice of a metamagnet at the critical end point, we performed an ultrasonic study of the itinerant electron metamagnet ${\mathrm{UTe}}_2$ across varying temperatures and magnetic fields. At temperatures exceeding 9 K, a distinct V-shaped anomaly emerges, precisely centered at the critical field of the metamagnetic transition in the isothermal field dependence of elastic constants. This anomaly arises from lattice instability, triggered by critical magnetic fluctuations via strong magnetoelastic interactions. Remarkably, this effect is maximized precisely at the critical-end-point temperature. Comparative measurements of another itinerant metamagnet, UCoAl, reveal intriguing commonalities. Despite significant differences in the paramagnetic ground state, lattice symmetry, and the expected metamagnetic transition process between ${\mathrm{UTe}}_2$ and UCoAl, both exhibit similar anomalies in elastic properties near the critical end point.

Topological superconductors present an ideal platform for exploring nontrivial superconductivity and realizing the Majorana boundary modes. However, finding a single-phase topological material with nontrivial superconducting states has been a challenge. Here, we predict nontrivial superconductivity in the pristine chiral metal RhGe with a transition temperature of 5.8 K. Chiral symmetries in RhGe enforce multifold Weyl fermions at high-symmetry momentum points and spin-polarized Fermi arc states that span the entire surface Brillouin zone. These bulk and surface chiral states support multiple type-II van Hove singularities that enhance superconductivity in RhGe. Our analysis of superconducting pairing symmetries involving Chiral Fermi pockets in RhGe indicates the presence of nontrivial superconducting pairing. Our study establishes RhGe as a promising candidate material for hosting mixed-parity pairing and topological superconductivity.

Two-dimensional (2D) ferromagnets with controlled magnetic anisotropy energy (MAE) provide the opportunity to develop emergent magnetic tunnel junctions (MTJs), enabling more energy-efficient memory devices with robust storage stability and low power consumption. Employing first-principles calculations, we study the effect of surface hydrogenation as well as the ferroelectric polarization of ${\mathrm{In}}_2{\mathrm{Se}}_3$ on the magnetic properties of layered ${\mathrm{MnGeSe}}_3$ (MGS). Electron injection by hydrogenation triggers a phase transition and spin reorientation with large perpendicular magnetic anisotropy for the functionalized MGS. Notably, our results demonstrate the feasibility to achieve the controlled MAE through the ferroelectric switching of 2D ${\mathrm{In}}_2{\mathrm{Se}}_3$ substrate and strain effect, while the multiferroic heterostructures yield distinct strain dependences of the MAE depending on the surface hydrogenation. The underlying mechanism is their synergistic effects of the competitive spin-orbit coupling strength between the modified Se-derived $p$ orbitals. These findings provide an effective strategy to modulate the 2D magnetism of MGS, which may lead to practical applications for the next-generation magnetoelectric memory device.

With recent advances in strain engineering and its widespread applications, it is becoming increasingly important to understand the effect of biaxial strain on the most common structural phase of perovskites—the orthorhombic $Pnma$ structure. In this work, by using a combination of group theory and first-principles density functional theory, we study the effect of biaxial strain on (001)- and (111)-oriented ${\mathrm{CaTiO}}_3, {\mathrm{SrSnO}}_3$, and ${\mathrm{SrZrO}}_3$ films to find phenomena common in different compounds and strain planes. We observe manifestly different behaviors depending on the strain orientation, with common trends emerging between different materials. In addition to the many different structural phases previously observed in individual compounds, we identify a transition between two different phases with the same space group name ($P{2}_1/c$) but different symmetries in (111)-strained materials. We also find that allowing the relaxation of the out-of-plane monoclinic angles, often ignored in first-principles studies, leads to significant stabilization of certain phases and is essential to correctly determine the structural ground state.

Magnetron sputtering inherently exhibits the advantage of dislodging particles from the target in a ratio equivalent to the target stoichiometry. Nevertheless, film compositions often deviate due to element-dependent scattering with the working gas, necessitating the adjustment of the sputtering process. In this work, we explore an unconventional approach to addressing this issue, involving the employment of an off-stoichiometric target. The required composition is obtained through an iterative process, which is demonstrated by ${\mathrm{Fe}}_2\mathrm{VAl}$ and ${\mathrm{Fe}}_2{\mathrm{V}}_{0.9}{\mathrm{Ti}}_{0.1}\mathrm{Al}$ films as case studies. Ultimately, the correct stoichiometry is obtained from ${\mathrm{Fe}}_{1.86}{\mathrm{V}}_{1.15}{\mathrm{Al}}_{0.99}$ and ${\mathrm{Fe}}_{1.88}{\mathrm{V}}_{1.02}{\mathrm{Ti}}_{0.13}{\mathrm{Al}}_{0.97}$ targets, respectively. Despite the thermoelectric properties falling below expectations, mainly due to imperfect film crystallization, the strategy successfully achieved the desired stoichiometry, enabling accurate film synthesis without the need for advanced sputtering setups.

Thermoelectric materials can utilize the Seebeck effect to convert electrical into thermal energy and vice versa. State-of-the-art research focuses on semiconductors as the band gap in their electronic density of states results in large values of the Seebeck coefficient. However, recent results suggest that certain metallic alloys such as ${\mathrm{Ni}}_x{\mathrm{Au}}_{1-x}$ can also feature promising thermoelectric properties, relevant for technological applications [Sci. Adv. 9, eadj1611 (2023)]. In this work, we study the thermoelectric properties of ${\mathrm{Ni}}_x{\mathrm{Au}}_{1-x}$ films on different substrates, with additional focus on a cost-efficient synthesis. Ultimately, a large power factor of $11.2\text{mW}/\text{m}{\text{K}}^2$ is achieved at $614\text{K}$ in ${\mathrm{Ni}}_{0.27}{\mathrm{Au}}_{0.73}$. Furthermore, by neglecting the phonon contribution to thermal conduction, which is negligibly small in these metallic systems well-obeying the Wiedemann-Franz law, a figure of merit of $zT=0.15$ is obtained at $763\text{K}$.

In ferromagnetic oxide epitaxial multilayers, magnetic properties and interlayer coupling are determined by a variety of factors. Beyond the contribution of interlayer exchange coupling, strain and interfacial effects, such as structural reconstructions or charge transfer, play significant roles, resulting in complex magnetic behavior. In this study, the interlayer coupling of ferromagnetic ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{Mn}}_{0.95}{\mathrm{Ru}}_{0.05}{\mathrm{O}}_3$ (LSMRO) layers (8 nm thick) was investigated, when separated by epitaxial spacers of paramagnetic metallic ${\mathrm{LaNiO}}_3$ (LNO), in stacks exhibiting perpendicular magnetic anisotropy. By varying the thickness of the spacer, it was found that the coupling between two LSMRO layers changes from antiferromagnetic (with a 4-unit-cell-thick LNO spacer) to ferromagnetic (with a 6-unit-cell-thick LNO spacer). For multilayers comprising five LSMRO layers and a 4-unit-cell-thick LNO spacer, the antiferromagnetic coupling was preserved. However, the effective magnetic anisotropy changed, causing the magnetization to cant more towards the in-plane direction. This behavior was corroborated by X-ray magnetic circular dichroism (XMCD) investigations at the Mn and Ni $L_3$ edges. The XMCD results indicated that the 4-unit-cell-thick LNO spacer in the multilayer become magnetically ordered, closely following the magnetization of adjacent LSMRO layers.

Single-crystalline ferroelectric (FE) perovskites show a large electrocaloric effect at electric field-induced phase transitions, promising for solid-state cooling technologies. However, paraelectric-FE transition temperatures are often too high for practical applications, and lower transitions are underrepresented in literature. Particularly, the role of thermal hysteresis and electric field direction on the caloric response is critical, especially for polycrystalline materials, but not yet fully understood. Using ab initio-based coarse-grained molecular dynamics simulations, we show how transition temperatures depend on the direction of the applied field. Also, we reveal that the choice of electric field direction can reduce thermal hysteresis and can adjust the temperature ranges where large and reversible caloric responses occur. Furthermore, we propose a phenomenological descriptor for the qualitative changes in transition temperature with field direction. This descriptor is valid for both ${\mathrm{BaTiO}}_3$ and ${\mathrm{PbTiO}}_3$, even though both materials show different microscopic electric field coupling. Finally, we identify favorable temperature and texturing conditions for large and reversible caloric responses in polycrystals.

Single crystals of ${\mathrm{EuIn}}_4$ were grown and ${}^{151}\mathrm{Eu}$ Mössbauer spectroscopy, combined with temperature-dependent electrical resistance, specific heat, and anisotropic magnetization measurements have been used to investigate the magnetic ordering of monoclinic ${\mathrm{EuIn}}_4$. We find two closely spaced magnetic transitions (at $\sim 10\mathrm{K}$ and $\sim 11\mathrm{K}$). The initial ordering leads to an incommensurate sinusoidally modulated structure that squares up rapidly on cooling through the lower (10 K) transition. Well above the magnetic transitions, we observe an additional transition at $\sim 130\mathrm{K}$ which may also involve two closely spaced events. This upper transition(s) is most likely structural and offers no suggestion of magnetic nature either in magnetization or Mössbauer data.

In the spinel ${\mathrm{CuIr}}_2{\mathrm{S}}_4$ an exotic, orbitally driven metal-insulator (MI) transition is observed at $T_{\mathrm{MI}}\sim 230\mathrm{K}$. However, spectroscopic investigations presently do not agree with respect to the role of related lattice distortions and dynamic effects. Here, we present a detailed study of single-crystalline ${\mathrm{CuIr}}_2{\mathrm{S}}_4$ from different batches comparing detailed high- and low-temperature phonon spectra. An analysis using dynamic lattice calculations confirms a low-temperature collectively distorted structure according to previous synchrotron x-ray studies. The related isomorphic $\mathrm{I}{\mathrm{r}}^{3+}$ and $\mathrm{I}{\mathrm{r}}^{4+}$ octamers' formation and spin dimerization agree well with the proposed $P\overline{1}$ symmetry. Thereby, previous discrepancies are resolved.

The 2H, 1T, and their distorted structures are known as prototype structures of $A{B}_2$ monolayers. Here, we study a puckered (PCK) structure that is truncated from the (110) surface of fluorite-type materials. 53 fluorite-type materials are investigated based on first-principles approach. The formation energy calculations indicate that seven systems form the PCK structure in the monolayer limit, while other systems form either 1T, 2H, or distorted 1T structures. The PCK structures of ${\mathrm{PbF}}_2$ and ${\mathrm{Ga}}_2\mathrm{Au}$ exhibit negative Poisson's ratio (NPR) in the out-of-plane direction. We explain the NPR by an analytical model assuming a constant interatomic distance under the in-plane strain. In addition, we demonstrate that the appearance of NPR is correlated with non-ionic character of the system, which is based on the surface energy calculations and the Born effective charge analyses. We also find that ${\mathrm{PRh}}_2$ in the PCK structure is highly distorted.

The correlation between magnetism and nontrivial topological band structure serves as a unique venue for discovering exotic topological properties. Combining magnetotransport measurements and first-principles calculations, we unveil herein that the hexagonal EuCuP holds a topologically trivial state in the paramagnetic structure, while strong magnetization dependent anisotropic topological states in the spin-polarization structures. Specifically, it hosts a trivial topological state in the in-plane spin-polarization structure, while a Weyl semimetal state in the out-of-plane spin-polarization structure. Our scaling analysis suggests that the intrinsic Berry curvature in the spin-polarization structures can account for the observed large anisotropic anomalous Hall effect. First-principles calculations show that the magnetization and the spin-orbit coupling simultaneously play essential roles for the appearance of the four pairs of Weyl points in the out-of-plane spin-polarization structure. Our work therefore establishes in EuCuP the intimate relation between magnetism and the nontrivial topological states, which would be instructive for future study on this key issue of topological physics.

Coupled first-order magnetostructural transformations (FOMSTs) with narrow widths governed by low external stimuli play a crucial role in magnetic refrigeration for ferromagnetic hexagonal systems. In this work, we report a family of magnetocaloric materials named boron (B)-doped ${\left(\mathrm{MnNiSi}\right)}_{0.67}{\left(\mathrm{F}{\mathrm{e}}_2\mathrm{Ge}\right)}_{0.33}$ compounds that are devoid of rare-earth elements. Our results show that varying B concentrations up to 5 at. % can tailor the robust FOMSTs between the low-temperature ferromagnetic orthorhombic phase and the high-temperature paramagnetic hexagonal phase in a wider temperature regime. A dramatic change in hysteresis ($\mathrm{\Delta }{T}_{\mathrm{hys}}$) from ∼25 K for $x=0$ to ∼8 (9) K as well as increases in the saturation magnetization for specific 2 (3) at. % of B dopants is pronounced. Henceforth, the origin of the reducing hysteresis is illustrated based on the geometrical compatibility conditions $({\lambda }_2\sim 1)$ between the austenite and martensite phases using temperature-dependent powder x-ray diffraction analysis. Moreover, we found the samples performed with good functional stability from the thermal cycling run. The branch of these B doping materials exhibits robust features of a large magnetocaloric effect (MCE) over an extensive temperature range (∼71 K) and temperature-averaged magnetic entropy change at a lower magnetic field change of 2 T. These several tangible benefits, such as reduced $\mathrm{\Delta }{T}_{\mathrm{hys}}$, geometrical compatibility, and robust MCE properties are first reported in the studied hexagonal system. Therefore, our results offer a viable approach to improve the cascading of these materials towards the application of cooling technology.