Eel Temperature Research Articles

Low-dimensional magnetism of BaCuTe2O6

X-ray diffraction, thermodynamic measurements, and density-functional band-structure calculations are used to study the magnetic behavior of BaCuTe$_{2}$O$_{6}$, a member of the $A$CuTe$_2$O$_6$ structural family that hosts complex three-dimensional frustrated spin networks with possible spin-liquid physics. Temperature-dependent magnetic susceptibility and heat capacity of the Ba compound are well described by the one-dimensional spin-$\frac12$ Heisenberg chain model reminiscent of the Sr analog SrCuTe$_2$O$_6$. While the intrachain coupling $J/k_{\rm B}\simeq 37$ K is reduced compared to 49 K in the Sr compound, the N\'eel temperature increases from 5.5 K (Sr) to 6.1 K (Ba). Unlike the Sr compound, BaCuTe$_2$O$_6$ undergoes only one magnetic transition as a function of temperature and shows signatures of weak spin canting. We elucidate the microscopic difference between the Sr and Ba compounds and suggest that one of the interchain couplings changes sign as a result of negative pressure caused by the Sr/Ba substitution. The N\'eel temperature of BaCuTe$_2$O$_6$ is remarkably insensitive to the magnetic dilution with Zn$^{2+}$ up to the highest reachable level of about 20%.

Role of NiO in the nonlocal spin transport through thin NiO films on Y3Fe5O12

In spin transport experiments with spin currents propagating through antiferromagnetic (AFM) material, the antiferromagnet is treated as a mainly passive spin conductor not generating nor adding any spin current to the system. The spin current transmissivity of the AFM NiO is affected by magnetic fluctuations, peaking at the N\'eel temperature and decreasing by lowering the temperature. In order to study the role of the AFM in local and nonlocal spin transport experiments, we send spin currents through NiO of various thickness placed on Y$_3$Fe$_5$O$_{12}$. The spin currents are injected either electrically or by thermal gradients and measured at a wide range of temperatures and magnetic field strengths. The transmissive role is reflected in the sign change of the local electrically injected signals and the decrease in signal strength of all other signals by lowering the temperature. The thermally generated signals, however, show an additional upturn below 100$\,$K which are unaffected by an increased NiO thickness. A change in the thermal conductivity could affect these signals. The temperature and magnetic field dependence is similar as for bulk NiO, indicating that NiO itself contributes to thermally induced spin currents.

Towards cubic symmetry for Ir4+ : Structure and magnetism of the antifluorite K2IrBr6

Crystal structure, electronic state of Ir$^{4+}$, and magnetic properties of the antifluorite compound K$_2$IrBr$_6$ are studied using high-resolution synchrotron x-ray diffraction, resonant inelastic x-ray scattering (RIXS), thermodynamic and transport measurements, and ab initio calculations. The crystal symmetry is reduced from cubic at room temperature to tetragonal below 170 K and eventually to monoclinic below 122 K. These changes are tracked by the evolution of the non-cubic crystal-field splitting $\Delta$ measured by RIXS. Non-monotonic changes in $\Delta$ are ascribed to the competing effects of the tilt, rotation, and deformation of the IrBr$_6$ octahedra as well as tetragonal strain on the electronic levels of Ir$^{4+}$. The N\'eel temperature of $T_N=11.9$ K exceeds that of the isostructural K$_2$IrCl$_6$, and the magnitude of frustration on the fcc spin lattice decreases. We argue that the replacement of Cl by Br weakens electronic correlations and enhances magnetic couplings.

Field-induced successive phase transitions in the J1−J2 buckled honeycomb antiferromagnet Cs3Fe2Cl9

The magnetic properties of ${\mathrm{Cs}}_{3}{\mathrm{Fe}}_{2}{\mathrm{Cl}}_{9}$ single crystals were investigated by magnetic and thermal measurements. The crystal structure of ${\mathrm{Cs}}_{3}{\mathrm{Fe}}_{2}{\mathrm{Cl}}_{9}$ consists of a bilayer triangular lattice of ${\mathrm{Fe}}^{3+}$ ions. The analysis of magnetic susceptibility clarified that the intra- and interdimer interactions are comparable with each other, and ${\mathrm{Cs}}_{3}{\mathrm{Fe}}_{2}{\mathrm{Cl}}_{9}$ is regarded as a spin-5/2 ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ buckled honeycomb antiferromagnet with the ferromagnetic interlayer interaction ${J}_{3}$. The susceptibility for the magnetic field $H||c$ axis exhibits a sudden drop at the N\'eel temperature ${T}_{\mathrm{N}}=5.4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, indicating a first-order magnetic phase transition. One of the characteristic features is the linear temperature dependence below ${T}_{\mathrm{N}}$. Furthermore, ${\mathrm{Cs}}_{3}{\mathrm{Fe}}_{2}{\mathrm{Cl}}_{9}$ undergoes successive magnetic phase transitions in high magnetic fields along the $c$ axis. We obtained a rich H-T phase diagram in which the ${M}_{\mathrm{s}}/2$ magnetization-plateau phase is included. These unique magnetic behaviors probably originate from the competition of magnetic interactions and the easy-axis anisotropy in the antiferromagnetic ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ buckled honeycomb network.

Electrocaloric effects in multiferroics

An atomistic effective Hamiltonian is used to compute electrocaloric (EC) effects in rare-earth substituted BiFeO$_{3}$ multiferroics. A phenomenological model is then developed to interpret these computations, with this model indicating that the EC coefficient is the sum of two terms, that involve electric quantities (polarization, dielectric response), the antiferromagnetic order parameter, and the coupling between polarization and antiferromagnetic order. The first one depends on the polarization and dielectric susceptibility, has the analytical form previously demonstrated for ferroelectrics, and is thus enhanced at the ferroelectric Curie temperature. The second one explicitly involves the dielectric response, the magnetic order parameter and a specific magnetoelectric coupling, and generates a peak of the EC response at the N\'eel temperature. These atomistic results and phenomenological model may be put in use to optimize EC coefficients.

Magnetocapacitance effect and magnetoelectric coupling in type-II multiferroic HoFeWO6

We have investigated the multiferroicity and magnetoelectric (ME) coupling in $\mathrm{Ho}\mathrm{Fe}\mathrm{W}{\mathrm{O}}_{6}$. With a noncentrosymmetric polar structure (space group Pna${2}_{1}$) at room temperature, this compound shows an onset of electric polarization with an antiferromagnetic ordering at the N\'eel temperature (${T}_{N}$) of 17.8 K. The magnetic properties of the polycrystalline samples were studied by DC and AC magnetization and heat capacity measurements. The metamagnetic behavior at low temperatures was found to be directly related to the dielectric properties of the compound. In particular, field-dependent measurements of capacitance show a magnetocapacitance (MC) effect with double-hysteresis loop behavior in direct correspondence with the magnetization. Our x-ray diffraction results show the Pna${2}_{1}$ structure down to 8 K and suggest the absence of a structural phase transition across ${T}_{N}$. Soft x-ray absorption spectroscopy and soft x-ray magnetic circular dichroism (XMCD) measurements at the Fe $L{}_{2,3}$ and Ho $M{}_{4,5}$ edges revealed the oxidation state of Fe and Ho cations to be $3+$. Fe $L{}_{2,3}$ XMCD further shows that ${\mathrm{Fe}}^{3+}$ cations are antiferromagnetically ordered in a noncollinear fashion with spins arranged ${90}^{\ensuremath{\circ}}$ with respect to each other. Our findings show that $\mathrm{Ho}\mathrm{Fe}\mathrm{W}{\mathrm{O}}_{6}$ is a type-II multiferroic exhibiting a MC effect. The observed MC effect and the change in polarization by the magnetic field, as well as their direct correspondence with magnetization, further support the strong ME coupling in this compound.

Correlation between antiferromagnetic and Mott states in spin orbit coupled Sr2IrO4 : A study of Sr2Ir1−xMxO4 ( M=Fe or Co)

${\mathrm{Sr}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ is an archetypal spin-orbit-coupled Mott insulator with an antiferromagnetic state below 240 K. Here we report results of our study on single crystals of ${\mathrm{Sr}}_{2}{\mathrm{Ir}}_{1\ensuremath{-}x}\mathbf{F}{\mathbf{e}}_{x}{\mathrm{O}}_{4}$ ($0\ensuremath{\le}x<0.32$) and ${\mathrm{Sr}}_{2}{\mathrm{Ir}}_{1\ensuremath{-}x}\mathbf{C}{\mathbf{o}}_{x}{\mathrm{O}}_{4}$ ($0\ensuremath{\le}x<0.22$). Fe doping retains the antiferromagnetic state but simultaneously precipitates an emergent metallic state whereas Co doping causes a rapid collapse of both the antiferromagnetic and Mott states, giving rise to a confined metallic state featuring a pronounced linearity of the basal-plane resistivity up to 700 K. The results indicate tetravalent ${\mathrm{Fe}}^{4+}(3{d}^{4})$ ions in the intermediate spin state with $S=1$ and ${\mathrm{Co}}^{4+}(3{d}^{5})$ ions in the high spin state with $S=5/2$ substituting for ${\mathrm{Ir}}^{4+}(5{d}^{5})$ ions in ${\mathrm{Sr}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$, respectively. The effective magnetic moment closely tracks the N\'eel temperature as doping increases, suggesting that the spin state of the dopant predominately determines the magnetic properties in doped ${\mathrm{Sr}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$. Furthermore, all relevant properties including charge-carrier density (e.g., ${10}^{28}/{\mathrm{m}}^{3}$), Sommerfeld coefficient (e.g., $19\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/\mathrm{mole}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{2}$), and Wilson ratio (e.g., 2.6) consistently demonstrate an emergent metallic state that is both robust and highly correlated in the two systems, arising from the percolation of bound states and the weakening of structural distortions. This study strongly indicates that the antiferromagnetic and Mott states are correlated in an unconventional manner in ${\mathrm{Sr}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$.

Atomistic simulations of the magnetic properties of IrxMn1−x alloys

Iridium manganese (IrMn) is arguably the most important antiferromagnetic material for device applications due to its metallic nature, high N\'eel temperature, and exceptionally high magnetocrystalline anisotropy. Despite its importance, its magnetic properties are poorly understood due to its intrinsic complexity and the interplay between structural and magnetic properties. Here we present a unifying atomistic model of ${\mathrm{Ir}}_{x}{\mathrm{Mn}}_{(1\ensuremath{-}x)}$ alloys which reproduces the key experimental facts of the material, while providing unprecedented understanding of the compositional and structural origins of its magnetic ground state and thermodynamic properties. We find that the N\'eel temperature is strongly dependent on the nature of the ground-state magnetic order which varies with $x$ from a triangular to tetrahedral spin structure, leading to different levels of geometric spin frustration. The N\'eel temperature increases linearly with manganese concentration for the disordered phase, while the ordered phases show a peak for ${\mathrm{Ir}}_{50}{\mathrm{Mn}}_{50}$ followed by a decrease due to increased spin frustration. The ground-state tetrahedral spin structure of the disordered phase is composition independent for manganese concentrations in the 50--95% range, while the degree of spin order varies strongly in the same range. For low manganese concentrations, we find antiferromagnetic spin-glass and ferromagnetic ground-state spin structures. The magnetic anisotropy energy exhibits a complex dependence on the lattice symmetry, presenting easy-plane, cubic, and unconventional symmetries for the principal phases, and a similarly complex variation of magnitude. The complexity of behavior represents a dual blessing and a curse in that the properties of a particular sample depend strongly on the degree of order and composition, while also providing a large state space to engineer an antiferromagnet with optimal symmetry, magnetic anisotropy, and thermal stability. Such effects are important for the future development of nanoscale sensor devices and antiferromagnetic spintronics.

Flat-band-induced non-Fermi-liquid behavior of multicomponent fermions

We investigate multicomponent fermions in a flat band and predict experimental signatures of non-Fermi liquid behavior. We use dynamical mean-field theory to obtain the density, double occupancy and entropy in a Lieb lattice for $\mathcal{N} = 2$ and $\mathcal{N} = 4$ components. We derive a mean-field scaling relation between the results for different values of $\mathcal{N}$, and study its breakdown due to beyond-mean field effects. The predicted signatures occur at temperatures above the N\'eel temperature and persist in presence of a harmonic trapping potential, thus they are observable with current ultracold gas experiments.

Sb−5s lone pair dynamics and collinear magnetic ordering in Ba2FeSbSe5

Neutron diffraction and X-ray pair distribution function (XPDF) experiments were performed in order to investigate the magnetic and local crystal structures of Ba2FeSbSe5 and to compare them to the average (i.e. long-range) structural model, previously obtained by single crystal X-ray diffraction. Changes in the local crystal structure (i.e. in the second coordination sphere) are observed upon cooling from 295 K to 95 K resulting in deviations from the average (i.e. long-range) crystal structure. This work demonstrates, that these observations cannot be explained by local or long-range magnetoelastic effects involving Fe-Fe correlations. Instead, we found, that the observed differences between local and average crystal structure can be explained by Sb-5s lone pair dynamics. We also find, that below the N\'eel temperature (TN = 58 K), the two distinct magnetic Fe3+ sites order collinearly, such that a combination of antiparallel and parallel spin arrangements along the b-axis results. The nearest-neighbor arrangement (J1 = 6 {\AA}) is fully antiferromagnetic, while next-nearest-neighbor interactions are ferromagnetic in nature.

Spin-phonon coupling and magnon scattering in few-layer antiferromagnetic FePS3

Temperature-dependent Raman spectroscopic studies of spin-phonon (SP) coupling and magnon scattering in bulk and few-layer (FL) antiferromagnet (AFM) ${\text{FePS}}_{3}$ with N\'eel temperature (${T}_{N}$) $\ensuremath{\approx}$ 120 K were performed. Bulk and FL (2--5 atomic layers) samples show four distinct modes at room temperature between 150 and $400 {\text{cm}}^{\ensuremath{-}1}$ and a broad peak at $\ensuremath{\approx}105 {\text{cm}}^{\ensuremath{-}1}$. On lowering the temperature, three distinct phenomena are observed. First, we see the SP coupling, identified by the deviation from the usual two- or three-phonon anharmonic behavior of the higher wave number peaks ($\ensuremath{\ge}150 {\text{cm}}^{\ensuremath{-}1}$) at or below ${T}_{N}$. The strength of SP coupling can be calculated for bulk and FL flakes considering mean-field approximations. Secondly, we see the spin ordering marked by the evolution of three peaks at lower wave numbers (around $105 {\text{cm}}^{\ensuremath{-}1}$) below ${T}_{N}$ due to incommensurate magnetic cells at low temperature. Thirdly, magnon excitation in FL pristine ${\text{FePS}}_{3}$ is detected by the emergence of a distinct peak at $120 {\text{cm}}^{\ensuremath{-}1}$ ($\ensuremath{\sim}3.6$ THz) at a temperature much lower than ${T}_{N}$ ($\ensuremath{\approx}60$ K). Tracking the magnon mode in the designed van der Waals heterostructures with ${\text{Bi}}_{2}{\text{Te}}_{3}$ and ${\text{Cr}}_{2}{\text{Ge}}_{2}{\text{Te}}_{6}$ reveal interfacial electron and hole transfer from ${\text{FePS}}_{3}$, respectively. Raman spectroscopy can thus predict the magnetic transition temperature of FL magnetic insulators via SP coupling, zone-boundary phonons, and magnons. Quasi-two-dimensional AFMs and their heterostructures involving different electronic and magnetic orders may be promising candidates for ultrafast magnon transport involving magnetoelastic waves.

Topological surface states of MnBi2Te4 at finite temperatures and at domain walls

MnBi$_2$Te$_4$ has recently been the subject of intensive study, due to the prediction of axion insulator, Weyl semimetal, and quantum anomalous Hall insulator phases, depending on the structure and magnetic ordering. Experimental results have confirmed some aspects of this picture, but several experiments have seen zero-gap surfaces states at low temperature, in conflict with expectations. In this work, we develop a first-principles-based tight-binding model that allows for arbitrary control of the local spin direction and spin-orbit coupling, enabling us to accurately treat large unit-cells. Using this model, we examine the behavior of the topological surface state as a function of temperature, finding a gap closure only above the N\'eel temperature. In addition, we examine the effect of magnetic domains on the electronic structure, and we find that the domain wall zero-gap states extend over many unit-cells. These domain wall states can appear similar to the high temperature topological surface state when many domain sizes are averaged, potentially reconciling theoretical results with experiments.

Pressure-tuned spin switching in compensated GdCrO3 ferrimagnet

The effect of hydrostatic pressure on antiferromagnetic ordering of Cr spins, magnetic compensation, and exotic spin switching in the single-crystal $\mathrm{GdCr}{\mathrm{O}}_{3}$ ferrimagnet is studied. The N\'eel temperature ${T}_{\mathrm{N}}=168\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ increases under pressure with the rate of 0.42 K/kbar, and the compensation temperature ${T}_{\mathrm{comp}}=144\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at which the canted ferromagnetic moment of Cr spins and antiparallel polarized moment of Gd spins cancel each other also increases by 0.3 K/kbar. It was found that the spin switching temperature ${T}_{\mathrm{sw}}$, at which the ferromagnetic moment is reversed, noticeably increases under pressure, and the spin switching energy required for magnetization reversal reduces significantly because of a decrease in magnetic anisotropy. Due to this mechanism, the spin switching line, described in the $T$\ensuremath{-}$H$ diagram by a certain ratio of switching energy to canted ferromagnetic moment, is shifted under pressure towards higher temperatures. Thus, switching between two opposite spin configurations in the $\mathrm{GdCr}{\mathrm{O}}_{3}$ ferrimagnet can be controlled by both applied magnetic field and external pressure.

Structural and magnetic properties of two-dimensional layered BiFeO3 from first principles

Using first-principles calculations, we predict a unique $\mathrm{BiFe}{\mathrm{O}}_{3}$ (BFO) phase, which is coined $I$-BFO, with layered characteristics based on the ilmenite structure. The interactions between interlayer bismuth atoms make it easy to exfoliate monolayer BFO with a configuration in which Bi ions are above and below two-dimensional (2D) iron-oxygen octahedra sharing common edges. The calculated phonon spectra reveal the dynamic stability of both bulk and monolayer forms of $I$-BFO. Combining total energy computation and crystal structure search, we corroborate that the $I$-BFO monolayer maintains the lowest-energy ground state, as compared to other 2D BFO exfoliations. We also discover that monolayer $I$-BFO is a robust antiferromagnetic material with a N\'eel temperature (${T}_{N}$) of 4 K in the fully relaxed case. Such ${T}_{N}$ can be prominently improved by strain, for example, ${T}_{N}=25\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 6% tension. Furthermore, our electronic structure calculations with PBE and hybrid HSE functionals show the $I$-BFO monolayer to be an indirect-gap semiconductor. Finally, we indicate that other ternary $AB{\mathrm{O}}_{3}$ compounds also have the potential to produce layered materials from the ilmenite structure. This work thus provides guidance to explore unconventional layered materials, and further broadens the application of BFO and other promising ilmenite oxides in two dimensions.

Magnetic and electronic phases of U2Rh3Si5

We present a detailed study of the magnetic and electronic properties of ${\mathrm{U}}_{2}{\mathrm{Rh}}_{3}{\mathrm{Si}}_{5}$, a material that has been demonstrated to exhibit a first-order antiferromagnetic phase transition. From a high-magnetic-field study, together with extensive experiments in moderate fields, we establish the magnetic phase diagrams for all crystallographic directions. The possibility of an electronic phase in a narrow interval above the N\'eel temperature as a precursor of a magnetic phase is discussed.

Designing frustration in two-dimensional magnetic systems via the application of uniaxial strain

First principles are used and combined with Monte Carlo simulations to predict that the application of compressive uniaxial strains in two-dimensional $\mathrm{CrGe}{\mathrm{Te}}_{3}$ can tune the underlying magnetic parameters in such a way that the system undergoes a phase transition from ferromagnetic (FM) to antiferromagnetic (AFM) phases, with the border between these being a region of high frustration. Such latter region can be the playground for fine-tuning the system to exhibit exotic states. Moreover, we also show and explain that such uniaxial strains also dramatically tune the critical temperatures, namely N\'eel temperatures for the AFM phase and Curie temperatures for the FM phase, which is of obvious technological and fundamental significance.

Metamagnetic transitions and magnetoelectricity in the spin-1 honeycomb antiferromagnet Ni2Mo3O8

Earlier neutron scattering studies suggested the coexistence of complex stripelike and zigzaglike antiferromagnetic orders in polar honeycomb lattice ${\mathrm{Ni}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$, while its magnetoelectric (ME) behavior as an emergent effect is thus of high interest. Here we report our observations of two metamagnetic transitions and novel ME responses of ${\mathrm{Ni}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ single crystals against high magnetic field $H$ up to \ensuremath{\sim}60 T. The $c$-axis (polar axis) spontaneous electric polarization ${P}_{\mathrm{spin}}$, emerging at the magnetic N\'eel temperature ${T}_{N}\ensuremath{\sim}5.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and its remarkable response to $H$ applied along the $c$ axis ($H//c$) and $a$ axis ($H//a$), respectively, provide the clear evidence for the magnetism-driven ferroelectricity. While the magnetism exhibits the in-plane anisotropy to some extent, the magnetic field dependencies of magnetization and electric polarization in the low-field region and high-field region are distinctly different. In the low-field region where a weak spin-flop type metamagnetic transition occurs, the electric polarization response shows the parabolic dependence of magnetic field applied along both the $c$ axis and in-plane $a$ axis. The second metamagnetic transition happens when the magnetic field extends up to the high-field region where the magnetization and electric polarization response at low temperature are characterized by an extraordinarily broad plateau for the magnetic field along the $c$ axis but roughly linear dependence for field along the $a$ axis. These unusual phenomena are discussed, based on the symmetry-related local ME tensor analysis, and it is suggested that both the spin current and p-d hybridization mechanisms may contribute to the spontaneous electric polarization and ME responses. The present work demonstrates ${\mathrm{Ni}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ as a unique multiferroic and promising platform for exploring the rich spin-1 physics and ME phenomena in honeycomb lattice.

Rhombohedral distortion-driven ferroelectric order and exchange bias effect in geometrically frustrated ZnFe2O4

The rhombohedral distortion-driven occurrence of the spontaneous electric polarization at a reasonably high temperature $(T)$ and an exchange bias (EB) effect below the antiferromagnetic (AFM) N\'eel temperature $({T}_{N})$ are revealed in ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$. We observe the magnetic memory effect, suggesting a cooperative glassy magnetic state below ${T}_{N}$. The phase separation between the long-range AFM and the glassy magnetic component leads to the EB effect below ${T}_{N}$. The synchrotron diffraction studies confirm a structural transition to a polar $R3m$ structure from the cubic spinel structure, involving a strong rhombohedral distortion. This distortion correlates with the occurrence of the spontaneous electric polarization $(P)$ below $\ensuremath{\sim}110$ K $({T}_{\text{FE}1})$, which is accompanied by a short-range order (SRO). The $P$-value enhances further due to an additional rhombohedral distortion below ${T}_{N}$. A considerable magnetoelectric (ME) coupling is detected below ${T}_{\text{FE}1}$. The increase of $P$ is $\ensuremath{\sim}7.2$% for 5 T at the liquid nitrogen temperature. There has been a fundamental interest among the community in the unique result of the occurrence of ferroelectric (FE) order coexisting with SRO and having a significant ME coupling, which is accompanied by a strong rhombohedral structural distortion analogous to that observed in ${\mathrm{BiFeO}}_{3}$.

Classical and cubic Rashba effect in the presence of in-plane 4f magnetism at the iridium silicide surface of the antiferromagnet GdIr2Si2

We present a combined experimental and theoretical study of the two-dimensional electron states at the iridium-silicide surface of the antiferromagnet ${\mathrm{GdIr}}_{2}{\mathrm{Si}}_{2}$ above and below the N\'eel temperature. Using angle-resolved photoemission spectroscopy (ARPES) we find a significant spin-orbit splitting of the surface states in the paramagnetic phase. By means of ab initio density-functional-theory (DFT) calculations we establish that the surface electron states that reside in the projected band gap around the $\overline{\mathrm{M}}$ point exhibit very different spin structures which are governed by the conventional and the cubic Rashba effect. The latter is reflected in a triple spin winding, i.e., the surface electron spin reveals three complete rotations upon moving once around the constant energy contours. Below the N\'eel temperature, our ARPES measurements show an intricate photoemission intensity picture characteristic of a complex magnetic domain structure. The orientation of the domains, however, can be clarified from a comparative analysis of the ARPES data and their DFT modeling. To characterize a single magnetic domain picture, we resort to the calculations and scrutinize the interplay of the Rashba spin-orbit coupling field with the in-plane exchange field, provided by the ferromagnetically ordered $4f$ moments of the near-surface Gd layer.

Zero-field magnetic ground state of EuMg2Bi2

Layered trigonal EuMg$_2$Bi$_2$ is reported to be a topological semimetal that hosts multiple Dirac points that may be gapped or split by the onset of magnetic order. Here, we report zero-field single-crystal neutron-diffraction and bulk magnetic susceptibility measurements versus temperature $\chi(T)$ of EuMg$_2$Bi$_2$ that show the intraplane ordering is ferromagnetic (Eu$^{2+},\, S= 7/2$) with the moments aligned in the $ab$-plane while adjacent layers are aligned antiferromagnetically (i.e., A-type antiferromagnetism) below the N\'eel temperature.