Incommensurate Magnetic Order Research Articles

Incommensurate magnetic order in an axion insulator candidate EuIn2As2 investigated by NMR measurement

Magnetic topological insulators exhibit unique electronic states due to the interplay between the electronic topology and the spin structure. The antiferromagnetic metal EuIn2As2 is a prominent candidate material in which exotic topological phases, including an axion insulating state, are theoretically predicted depending on the magnetic structure of the Eu2+ moments. Here, we report experimental results of the nuclear magnetic resonance (NMR) measurements of all the nuclei in EuIn2As2 to investigate the coupling between the magnetic moments in the Eu ions and the conduction electrons in In2As2 layers and the magnetic structure. The 75As and 115In NMR spectra observed at zero external magnetic fields reveal the appearance of internal fields of 4.9 and 3.6 T, respectively, at the lowest temperature, suggesting a strong coupling between the conduction electrons in the In2As2 layer and the ordered magnetic moments in the Eu ions. The 75As NMR spectra under in-plane external magnetic fields show broad distributions of the internal fields produced by an incommensurate fan-like spin structure which turns into a forced ferromagnetic state above 0.7 T. We propose a spin reorientation process that an incommensurate helical state at zero external magnetic field quickly changes into a fan state by applying a slight magnetic field.

Incommensurate magnetic order: A fingerprint for electronic correlations in hole-doped cuprates

Incommensurate magnetic order: A fingerprint for electronic correlations in hole-doped cuprates

Concurrence of directional Kondo transport and incommensurate magnetic order in the layered material AgCrSe2

In this work, we report on the concurrent emergence of the directional Kondo behavior and incommensurate magnetic ordering in a layered material. We employ temperature- and magnetic field-dependent resistivity measurements, susceptibility measurements, and high resolution wavelength X-ray diffraction spectroscopy to study the electronic properties of AgCrSe2. Impurity Kondo behavior with a characteristic temperature of TK = 32 K is identified through quantitative analysis of the in-plane resistivity, substantiated by magneto-transport measurements. The excellent agreement between our experimental data and the Schlottmann’s scaling theory allows us to determine the impurity spin as S = 3/2. Furthermore, we discuss the origin of the Kondo behavior and its relation to the material’s antiferromagnetic transition. Our study uncovers a rare phenomenon—the equivalence of the Néel temperature and the Kondo temperature—paving the way for further investigations into the intricate interplay between impurity physics and magnetic phenomena in quantum materials, with potential applications in advanced electronic and magnetic devices.

Hourglasslike spin excitation in a doped Mott insulator

We examine the dynamical magnetic response in a two-component resonating-valence-bond (RVB) description of the doped Mott insulator. The half-filled antiferromagnetic phase described by the Schwinger-boson mean-field theory will evolve into a bosonic-RVB state in the superconducting phase upon doping, where the doped holes introduce another fermionic itinerant spinon which forms a BCS-like RVB order. The spin excitations are thus composed of a resonance-like mode from the former and a weak dispersive mode from the itinerant component at the mean-field level. These two-component spinons are shown to give rise to an hourglasslike spin excitation at the random-phase approximation level via an antiferromagnetic coupling between the two modes, which provides an unconventional explanation of the experimental observations in the cuprate. In particular, we also discuss an instability towards an incommensurate magnetic order in this theoretical framework. Published by the American Physical Society 2024

Truncated mass divergence in a Mott metal

The Mott metal-insulator transition represents one of the most fundamental phenomena in condensed matter physics. Yet, basic tenets of the canonical Brinkman-Rice picture of Mott localization remain to be tested experimentally by quantum oscillation measurements that directly probe the quasiparticle Fermi surface and effective mass. By extending this technique to high pressure, we have examined the metallic state on the threshold of Mott localization in clean, undoped crystals of NiS2. We find that i) on approaching Mott localization, the quasiparticle mass is strongly enhanced, whereas the Fermi surface remains essentially unchanged; ii) the quasiparticle mass closely follows the divergent form predicted theoretically, establishing charge carrier slowdown as the driver for the metal-insulator transition; iii) this mass divergence is truncated by the metal-insulator transition, placing the Mott critical point inside the insulating section of the phase diagram. The inaccessibility of the Mott critical point in NiS2 parallels findings at the threshold of ferromagnetism in clean metallic systems, in which criticality at low temperature is almost universally interrupted by first-order transitions or novel emergent phases such as incommensurate magnetic order or unconventional superconductivity.

Incommensurate Magnetic Order in Hole‐Doped Infinite‐Layer Nickelate Superconductors due to Competing Magnetic Interactions

AbstractThe discovery of superconductivity in hole‐doped infinite‐layer nickelates has fueled intense research to identify the critical factor responsible for high‐Tc superconductivity. Magnetism and superconductivity are closely entangled, and elucidating the magnetic interactions in hole‐doped nickelates is critical for understanding the pairing mechanism. Here, these calculations based on the generalized Bloch theorem (GBT) and magnetic force theorem (MFT) consistently reveal that hole doping stabilizes an incommensurate (IC) spin state and increases the IC wave vector continuously, in a way strikingly similar to hole‐doped cuprates. Going further, a nonlinear Heisenberg model including first‐neighbor and third‐neighbor in‐plane magnetic interactions is developed. The analytical solutions successfully reproduce GBT and MFT results and reveal that the competition between the two magnetic interactions is the decisive factor for the IC magnetic transition. Eventually, by analyzing the doping‐controlled spin splitting of band and orbital‐contributed exchange interactions, direct links between hole doping, magnetization, exchange constants, and magnetic order are established. This discovery of the IC spin state, new understanding of its electronic origin, and establishment of direct connection with the paring electrons radically change the current understanding of the magnetic properties in hole‐doped NdNiO2 and open new perspectives for the superconducting mechanism in nickelates superconductors.

The in- and out-of-plane magnetisation of highly underdoped YBa2Cu3O6+x single crystals

Previously we have shown how measurements of static magnetic susceptibility χc(T) of YBa2Cu3O6+x single crystals for magnetic fields applied along the c-axis, and χab(T) for fields in the ab-plane, can give useful information about their thermodynamic properties which are still being hotly debated. SQUID magnetometry above the superconducting (s/c) transition temperature Tc is used for larger crystals, while piezolever torque magnetometry gives χc(T)-χab(T) for tiny crystals. Here we present new data for more heavily under-doped crystals with hole concentrations per CuO2 plane, p =0.058 to 0.073. We again find that the T-dependent anisotropy well above Tc arises from the pseudogap and the g-factor anisotropy, while at lower T there are Gaussian s/c fluctuations with a strong cut-off. This is possibly a different region where neutron scattering studies give evidence for competition between incommensurate magnetic short-range order and superconductivity. We have studied crystals with three values of x, measuring χc(T) and χab(T) immediately after fixing x by quenching on to a copper block and again after allowing sufficient time at room temperature for the Cu-O chains to order. Thus, we report data for three pairs of underdoped (UD) crystals with Tc ranging from 13 to 36 K, namely UD13 and UD20, UD15 and UD30, UD23 and UD36. As found previously for polycrystalline samples, ordering the Cu-O chains increases Tc and substantially reduces the Curie term. These are isotropic, in contrast to the Pauli-like susceptibility from the CuO2 planes where there is g factor anisotropy, and this allows us to make a powerful novel analysis. At higher T, χc(T)- χab(T) varies as a + bT where the bT term arises from the pseudogap. At lower T, deviations from this behaviour are analysed in terms of 2D or 3D Gaussian s/c fluctuations to obtain in-plane coherence lengths and upper critical fields as T→0.

Orbitally driven spin reorientation in Mn-doped YBaCuFeO5

The oxygen-deficient layered perovskite YBaCuFeO5 (YBCFO) is a rare type-II multiferroic material where ferroelectricity, driven by incommensurate spiral magnetic order, is believed to be achievable up to temperatures higher than room temperature. A cycloidal spiral order rather than a helical spiral order is an essential ingredient for the existence of ferroelectricity in this material. Motivated by a recent experimental study on Mn-doped YBCFO where the spiral plane was observed to cant more towards the crystallographic c-axis upon Mn doping at Fe sites than in the parent compound, we performed a detailed theoretical investigation using density functional theory calculations to understand the mechanism behind such spin reorientation. Our total energy calculations, within the generalized gradient approximation plus U plus spin–orbit coupling approach, reveal that Fe/Cu spin moments indeed align more towards the c-axis in Mn-doped YBCFO than in the parent compound. The largest exchange interaction (Cu–Cu in the a−b plane) is observed to decrease systematically with Mn doping concentration, reflecting the lowering of the transition temperature seen in experiments. Further, the inter-bilayer Cu–Mn exchange interaction becomes ferromagnetic in Mn-doped YBCFO, whereas the corresponding Cu–Fe exchange is antiferromagnetic in the parent compound, giving rise to frustration in the commensurate magnetic order. Most importantly, our electronic structure calculations reveal that in Mn-doped YBCFO because of hybridization with the Mn dz2 orbital, the highest occupied Cu orbital becomes the dz2 orbital as opposed to the dx2−y2 orbital in the parent compound. Therefore, we believe that the occupancy of the out-of-plane-oriented Cu dz2 orbital in place of the planar dx2−y2 orbital along with the frustrating exchange interaction drives the spins to align along the c-axis in Mn-doped YBCFO.

Large Topological Hall Effect and Spiral Magnetic Order in the Weyl Semimetal SmAlSi

Weyl electrons are intensely studied due to novel charge transport phenomena such as chiral anomaly, Fermi arcs, and photogalvanic effect. Recent theoretical works suggest that Weyl electrons can also participate in magnetic interactions, and the Weyl-mediated indirect exchange coupling between local moments is proposed as a new mechanism of spiral magnetism that involves chiral electrons. Despite reports of incommensurate and non-collinear magnetic ordering in Weyl semimetals, an actual spiral order has remained hitherto undetected. Here, we present evidence of Weyl-mediated spiral magnetism in SmAlSi from neutron diffraction, transport, and thermodynamic data. We show that the spiral order in SmAlSi results from the nesting between topologically non-trivial Fermi pockets and weak magnetocrystalline anisotropy, unlike related materials (Ce,Pr,Nd)AlSi, where a strong anisotropy prevents the spins from freely rotating. We map the magnetic phase diagram of SmAlSi and reveal an A-phase where topological magnetic excitations may exist. This is corroborated by the observation of a topological Hall effect within the A-phase.

Interwoven atypical quantum states in CeLiBi2

Typically, exotic quantum phases reside in different materials, but they can coexist given ideal conditions. This underexplored regime is realized in CeLiBi${}_{2}$, which is found to exhibit multiple atypical quantum phases including incommensurate cycloidal magnetic order, hard-axis metamagnetism, large and linear magnetoresistance, and mobile ultralight carriers. These results indicate that CeLiBi${}_{2}$ is an ideal material to experimentally and theoretically explore simultaneous quantum phenomena and their interdependent relationships.

Incommensurate magnetic ordering in CrB2

Incommensurate magnetism in CrB2 is studied in terms of a spin model based on density functional theory calculations. Heisenberg exchange interactions derived from the paramagnetic phase using the disordered local moment (DLM) theory show significant differences compared with those resulting from the treatment of the material as a ferromagnet; of these two methods, the DLM theory is found to give a significantly more realistic description. We calculate strongly ferromagnetic interactions between Cr planes but largely frustrated interactions within Cr planes. Although we find that the ground state ordering vector is sensitive to exchange interactions over a large number of neighbour shells, the q-vector of the incommensurate spin spiral state is satisfactorily reproduced by the theory (0.213 compared with the known ordering vector along Γ–). The strong geometric frustration of the exchange interactions causes a rather low Néel temperature (about 97 K), also in good agreement with experiment.

Incommensurate Magnetic Order in Sm3BWO9 with Distorted Kagome Lattice

We investigate the magnetic ground state of Sm3BWO9 with a distorted kagome lattice. A magnetic phase transition is identified at T N = 0.75 K from the temperature dependence of specific heat. From 11B nuclear magnetic resonance measurements, an incommensurate magnetic order is shown by the double-horn type spectra under a c-axis magnetic field, and absence of line splitting is observed for field oriented within the ab-plane, indicating the incommensurate modulation of the internal field strictly along c-axis. From the spin dynamics, the critical slowing-down behavior is observed in the temperature dependence of 1/T 1 with μ 0 H⊥c-axis, which is completely absent in the case with μ 0 H||c-axis. Based on the local symmetry of 11B sites, we analyze the hyperfine coupling tensors and propose two constraints on the possible magnetic structure. The single ion anisotropy should play an important role in determination of contrasting ground states of Sm3BWO9 and Pr3BWO9.

First-principles study of the crystal and magnetic structures of multiferroic Cu2OCl2

Recently, the discovery of multiferroicity in pyrochlore-like compound Cu2OCl2 has generated significant interest, and several studies have been performed in this area. This transition metal oxychloride is unique because the divalent copper atoms create an correlated insulator and the pyrochlore lattice tends to frustrate spins. From neutron powder diffraction measurements, an incommensurate magnetic order of the ordering vector emerges below the Néel temperature of 70 K. At this temperature or slightly above, ferroelectricity (FE) or antiferroelectricity, accompanying a lattice distortion, has been observed. Experimentally, some discrepancies remain. In this paper, we report our first-principles simulation results by evaluating the possible lattice and spin spiral states. We found that the Fddd structure is not more stable than , which is supported by our reexamination of the x-ray diffraction data. In addition, we find that after we include magnetism in the calculation, it predicts that the lattice with a helical (proper screw) spin structure is energetically more stable than other spin configurations. Our results indicate charge-order-driven FE that subsequently induces magnetism.

The magnetic structure of DyFeO3 revisited: Fe spin reorientation and Dy incommensurate magnetic order

High resolution and high intensity neutron powder diffraction is used to study the ground state magnetic order and the spin reorientation transition in the orthoferrite DyFeO3. The transition from the high temperature k = 0 Γ4 (G x A y F z ) to the low temperature Γ1 (A x G y C z ) type order of the Fe-sublattice is found at T SR = 73 K and does not show any thermal hysteresis. Below T N2 = 4 K the Dy-sublattice orders in an incommensurate magnetic structure with k = [0, 0, 0.028] while the Fe-sublattice keeps its commensurate Γ1 type order. DyFeO3 is the first orthoferrite RFeO3 to possess an incommensurate magnetic order of the rare earth sublattice under zero field conditions; an important piece of information neglected in the recent discussion of its multiferroic properties.

Commensurate and incommensurate magnetic structure of the moderately frustrated antiferromagnet Li2M(WO4)2 with M=Co,Ni

We have investigated the magnetic structure of ${\mathrm{Li}}_{2}\mathrm{Co}{({\mathrm{WO}}_{4})}_{2}$ via magnetic susceptibility, and neutron diffraction measurements. Two magnetic transitions are observed in magnetic susceptibility at ${T}_{N1}\ensuremath{\sim}9.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{N2}\ensuremath{\sim}7.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Neutron diffraction reveals an incommensurate magnetic order with a wave vector ${k}_{\text{ICM}}=(\ensuremath{\sim}0.46,\ensuremath{\sim}0.27,\ensuremath{\sim}0.24$) between ${T}_{N1}$ and ${T}_{N2}$ and a commensurate magnetic order with a wave vector ${k}_{\text{CM}}=(0.5,0.25,0.25)$ below ${T}_{N2}$. The magnetic periodicity in the commensurate phase is four times larger than the nuclear unit cell length along the $b$- and $c$-axis directions with a saturated magnetic moment equal to $\ensuremath{\approx}2.92\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{B}$. Below ${T}_{N1}$, the ICM wave vector for ${\mathrm{Li}}_{2}\mathrm{Co}{({\mathrm{WO}}_{4})}_{2}$ varies with decreasing temperature and locked into commensurate at ${T}_{N2}$, whereas weaker temperature dependence of ${k}_{\text{ICM}}=(0.46,0.17,0.33)$ is observed for ${\mathrm{Li}}_{2}\mathrm{Ni}{({\mathrm{WO}}_{4})}_{2}$.

Incommensurate magnetic order in rare earth and transition metal compounds with local moments

Within the framework of the s–d(f) exchange model in the mean-field approximation for square, simple cubic, body-centered and face-centered cubic lattices, the formation of a ferromagnetic, spiral, and commensurate antiferromagnetic (AFM) order is investigated. The possibility of the formation of inhomogeneous states (magnetic phase separation), which necessarily arises during first-order phase transitions in the electron filling parameter, is taken into account. The saturation of the AFM and spiral states is studied depending on the parameters of the model. The results obtained include a rich variety of magnetic structures and phase transitions, allowing the interpretation of magnetic properties of semiconducting and metallic systems containing magnetic atoms.

Elastic and magnetic properties of Tb-MnO based thin films

We report on the elastic and magnetic properties of multiferroic Tb0.3Mn20.9O78.8 thin films. The films were deposited on (001) Si using radio frequency magnetron (RF) sputtering at 50 W and ambient temperature. The elastic properties have been established by surface Brillouin scattering (SBS) after fitting the discrete phonon dispersion in the k||d range of 0 – 5 by surface Elastodynamic Green’s function. The uncertainties in elastic constants values were obtained from Taylor series expansion of the phonon phase velocity as a function of C11 and C44 values and subsequently fitted by the least-squares method. The optimum primary elastic constants and their uncertainties were determined as C11 = 180 ± 4.9 GPa and C44 = 43.0 ± 0.89 GPa. The derived elastic constants show that the films are ductile. Using a vibrating sample magnetometer (VSM), the films have been noted to behave like soft ferromagnetic materials at T⩽150 K. Incommensurate magnetic ordering and spin-glass behaviors have also been observed.

Presaturation phase in the frustrated ferro-antiferromagnet Pb2VO(PO4)2

Magnetization, magnetic torque, neutron diffraction and NMR experiments are used to map out the $H$$-$$T$ phase diagram of the prototypical quasi-two-dimensional ferro-antiferromagnet Pb$_2$VO(PO$_4$)$_2$ in magnetic fields up to 27 T. When the field is applied perpendicular to the axis of magnetic anisotropy, a new magnetic state emerges through a discontinuous transition and persists in a narrow field range just below saturation. The measured NMR spectra suggest a complex and possibly incommensurate magnetic order in that regime.

Spin and charge fluctuations in the two-band Hubbard model

A model of CuO$_2$ planes of cuprate perovskites, containing $d_{x^2-y^2}$ copper orbitals and symmetric combinations of oxygen $p_\sigma$ orbitals, is investigated using the strong coupling diagram technique. This approach allows one to take into account the interactions of carriers with spin and charge fluctuations of all ranges. Derived equations for Green's function are self-consistently solved for the set of parameters corresponding to hole- and electron-doped cuprates. It is shown that the mentioned interactions lead to the appearance of spin polarons -- bound states of carriers with spin excitations, which show themselves as sharp peaks of the density of states and spectral functions at the Fermi level. Hole and electron doping are strongly asymmetric. This, in particular, manifests itself in the antiferromagnetic response for the electron-doped case and in an incommensurate magnetic ordering for hole doping. In the latter case, the incommensurability parameter grows with doping. The double occupancy shows that the electron-doped system retains strong correlations up to the concentration 0.23, while for hole doping the correlations decay rapidly. These results are in agreement with experimental observations in cuprates.

Momentum-Dependent Magnon Lifetime in the Metallic Noncollinear Triangular Antiferromagnet CrB_{2}.

Noncollinear magnetic order arises for various reasons in several magnetic systems and exhibits interesting spin dynamics. Despite its ubiquitous presence, little is known of how magnons, otherwise stable quasiparticles, decay in these systems, particularly in metallic magnets. Using inelastic neutron scattering, we examine the magnetic excitation spectra in a metallic noncollinear antiferromagnet CrB_{2}, in which Cr atoms form a triangular lattice and display incommensurate magnetic order. Our data show intrinsic magnon damping and continuumlike excitations that cannot be explained by linear spin wave theory. The intrinsic magnon linewidth Γ(q,E_{q}) shows very unusual momentum dependence, which our analysis shows to originate from the combination of two-magnon decay and the Stoner continuum. By comparing the theoretical predictions with the experiments, we identify where in the momentum and energy space one of the two factors becomes more dominant. Our work constitutes a rare comprehensive study of the spin dynamics in metallic noncollinear antiferromagnets. It reveals, for the first time, definite experimental evidence of the higher-order effects in metallic antiferromagnets.