Noncollinear Magnetic Structure Research Articles

Magnetotransport of SrIrO3-based heterostructures

Transition-metal oxide (TMO) based heterostructures provide fertile playground to explore or functionalize novel quantum materials. In this regard, the combination of 3d and 5d TMOs have gained special interest because of the simultaneous appearance of strong spin–orbit coupling and electron correlation at the interface of those heterostructures. Artificial breaking of the inversion symmetry in heterostructures may also result in a distinct interfacial Dzyaloshinskii-Moriya interaction (DMI) and the formation of non-collinear magnetic spin structures in case of magnetic TMOs. Among the 5d TMOs, SrIrO3 (SIO) has gained significant attention because of its large spin–orbit coupling and the semi-metallic ground state, which are highly susceptible to structural distortions. Here, we report on the preparation and the characterisation of structural, electronic and magnetic properties of epitaxial heterostructures consisting of the 5d TMO SIO and the 3d antiferromagnetic insulator LaFeO3.

Spin Elastodynamic Motive Force.

The spin-motive force (SMF) in a simple ferromagnetic monolayer caused by a surface acoustic wave is studied theoretically via spin-vorticity coupling (SVC). The SMF has two mechanisms. The first is the SVC-driven SMF, which produces the first harmonic electromotive force, and the second is the interplay between the SVC and the magnetoelastic coupling, which produces the dc and second harmonic electromotive forces. We show that these electric voltages induced by a Rayleigh-type surface acoustic wave can be detected in polycrystalline nickel. No sophisticated device structures, noncollinear magnetic structures, or strong spin-orbit materials are used in our approach. Consequently, it is intended to broaden the spectrum of SMF applications considerably.

Non-collinear magnetic structures in the magnetoelectric Swedenborgite CaBaFe4O7 derived by powder and single-crystal neutron diffraction

We have investigated the magnetic structures of the Swedenborgite compound CaBaFe_44O_77 using magnetic susceptibility and neutron diffraction experiments on powder and single-crystal samples. Below T_{N1}TN1 = 274 K the system orders in a ferrimagnetic structure with spins along the c axis and an additional antiferromagnetic component within the kagome plane which obviously cannot satisfy all exchange interactions. Competing single-ion anisotropy and exchange interactions lead to a transition into a multi-\mathbf{q}𝐪 conical structure at T_{N2}TN2 = 202 K. The derivation of the complex ordering scheme below T_{N2}TN2 is an important step towards the understanding of the magnetoelectric effect under magnetic fields in this polar ferrimagnet.

Thermoelectric properties plus phonon and de Haas\u2013van Alphen frequencies of hole/electron-doped hbox {CeIn}_3

We investigate temperature, pressure, and localization dependence of thermoelectric properties, phonon and de Haas–van Alphen (dHvA) frequencies of the anti-ferromagnetic (AFM) CeIn_3 using density functional theory (DFT) and local, hybrid, and band correlated functionals. It is found that the maximum values of thermopower, power factor, and electronic figure of merit of this compound occur at low (high) temperatures provided that the 4f-Ce electrons are (not) localized enough. The maximum values of the thermopower, power factor, electronic figure of merit (conductivity parameters), and their related doping levels (do not) considerably depend on the localization degree and pressure. The effects of pressure on these parameters substantially depend on the degree of localization. The phonon frequencies are calculated to be real which shows that the crystal is dynamically stable. From the phonon band structure, the thermal conductivity is predicted to be homogeneous. This prediction is found consistent with the thermal conductivity components calculated along three Cartesian directions. In analogous to the thermoelectric properties, it is found that the dHvA frequencies also depend on both pressure and localization degree. To ensure that the phase transition at Néel temperature cannot remarkably affect the results, we verify the density of states (DOS) of the compound at the paramagnetic phase constructing a non-collinear magnetic structure where the angles of the spins are determined so that the resultant magnetic moment vanishes. The non-collinear results reveal that the DOS and whence the thermoelectric properties of the compound are not changed considerably by the phase transition. To validate the accuracy of the results, the total and partial DOSs are recalculated using DFT plus dynamical mean-field theory (DFT+DMFT). The DFT+DMFT DOSs, in agreement with the hybrid DOSs, predict the Kondo effect in this compound.

Modulated Non-Collinear Magnetic Structure of (Co0.9757fe0.03)4nb2o9 as Revealed by Mössbauer Spectroscopy

In this work, we present detailed $^{57}$Fe M\"ossbauer spectroscopy investigations of (Co$_{0.97}$$^{57}$Fe$_{0.03}$)$_{4}$Nb$_{2}$O$_{9}$ compound to study its possible magnetic structures. We have shown that the previously reported magnetic structures can not satisfactorily describe our low temperature M\"ossbauer spectra. Therefore, in combination with theoretical calculations, we have proposed a modulated helicoidal magnetic structure that can be used to simulate the whole series of our low temperature M\"ossbauer spectra. Our results suggest that the combination of previously reported different magnetic structures are only approximations of the average magnetic structure from our modulated helicoidal model. We anticipate that the proposed modulated non-collinear magnetic structure might shed light on the understanding of the complex magnetoelectric effects observed in this system.

Lattice defects related magnetic and magnetocapacitance properties of multiferroic BaFe10.2Sc1.8O19 epitaxial thin films

Without changing the crystalline structure of BaFe10.2Sc1.8O19 (BFSO) epitaxial thin film, significant modulation of its saturation magnetization (from 75 to 180 emu/cc), magnetic anisotropy field (from 3590 to 1434 Oe) and multiferroic ordering temperature (from 207 to 306 K) can be realized with different densities of lattice defects (DLD). A defects-related effective magnetic field Heff is defined. Heff reduces obviously with increasing annealing temperature TA, agreeing well with the reduced DLD. The defects-related magnetic ordering of BFSO films is further verified in the magnetocapacitance devices. The magnetocapacitance for 1000 °C annealed film is more than 5 times larger than that of as-deposited film. This can be explained by the ultra-sensitive of non-collinear conical magnetic structure and spin-phonon coupling in BFSO to the DLD related local lattice structure. The above findings enable better understanding and usage of lattice defects on regulating the physical properties of multiferroic hexaferrite devices.

Mapping domain-wall topology in the magnetic Weyl semimetal CeAlSi

We report full vector mapping of local magnetization in CeAlSi, a Weyl semimetal in which both inversion and time-reversal symmetries are broken. The vector maps reveal unanticipated features both within domains and at their boundaries. Boundaries between domains form two kinds of walls with distinct topology and therefore different interactions with Weyl fermions. Domain walls aligned along the tetragonal axes, e.g. (100), exhibit emergent chirality forbidden by the bulk space group, while diagonal walls are non-chiral. Within the domains, we observe that the previously reported set of four easy axes aligned along the in-plane diagonals of the tetragonal structure actually split to form an octet with decreasing temperature below the magnetic transition. All the above phenomena are ultimately traced to the noncollinear magnetic structure of CeAlSi.

Unraveling complex magnetism in two-dimensional FeS2

Atomically thin two-dimensional (2D) magnets have given rise to emergent phenomena due to magnetic exchange and spin-orbit coupling showing great promise for realizing ultrathin device structures. In this paper, we critically examine the magnetic properties of 2D ${\mathrm{FeS}}_{2}$, a non van der Waals magnet, which has been recently claimed to exhibit room-temperature ferromagnetism in the (111) orientation. Our ab initio study based on collinear density functional theory has revealed the ground state as an antiferromagnetic one with an ordering temperature of around 100 K along with a signature of spin-phonon coupling, which may trigger a ferromagnetic coupling via strain. Moreover, our calculations based on spin spirals indicate the possibility of noncollinear magnetic structures, which is also supported by Monte Carlo simulations based on ab initio magnetic exchange parameters. This opens up an excellent possibility to manipulate magnetic structures by the application of directional strain.

Emergence of the topological Hall effect in a tetragonal compensated ferrimagnet Mn2.3Pd0.7Ga

Topological spin textures such as magnetic skyrmions have attracted considerable interest due to their potential application in spintronic devices. However, there still remain several challenges to overcome before their practical application, for instance, achieving high scalability and thermal stability. Recent experiments have proposed a new class of skyrmion materials in the Heusler family, Mn1.4Pt0.9Pd0.1Sn and Mn2Rh0.95Ir0.05Sn, which possess noncollinear magnetic structures. Motivated by these experimental results, we suggest another Heusler compound hosted by Mn3Ga to overcome the above limitations. We fabricate Mn3-xPdxGa thin films, focusing on the magnetic compensation point. In Mn2.3Pd0.7Ga, we find a spin-reorientation transition around TSR = 320 K. Below the TSR, we observe the topological Hall effect and a positive magnetic entropy change, which are the hallmarks of a chiral noncollinear spin texture. By integrating all the data, we determine the magnetic phase diagram, displaying a wide chiral noncollinear spin phase even at room temperature. We believe that this compensated ferrimagnet shows promise for opening a new avenue toward chiral spin-based, high-density, and low-power devices.

Phase transition in the 5d1 double perovskite Ba2CaReO6 induced by high magnetic field

Magnetic properties of an antiferromagnetic double perovskite oxide Ba2CaReO6, where Re6+ (5d1) ions with large spin-orbit coupling are arranged on the face-centered-cubic lattice, are investigated using pulsed high magnetic field up to 66 T. Magnetization and magnetostriction measurements have revealed a magnetic field induced phase transition at around 50 T. The phase transition accompanies a jump of magnetization and longitudinal magnetostriction of approximately 2 10^(-4) with the change of power law behavior, indicating sizable coupling between the electronic degrees of freedom and the lattice. The high field phase exhibits a magnetic moment approximately 0.2 {\mu}B, which is close to the values observed in 5d1 double perovskite oxides with non-collinear magnetic structure. We argue that Ba2CaReO6 is an antiferromagnet that sits close to the phase boundary between the collinear and non-collinear phases, providing the target material for investigating the interplay between spin-orbital entangled electrons and magnetic field.

Factors Governing the Propagation Direction and Spin-Rotation Plane of Noncollinear Magnetic Structures: A Helix vs Cycloid in Doubly Ordered Perovskites NaYMnWO6 and NaYNiWO6.

The magnetic structure of NaYMnWO6 was determined by neutron powder diffraction measurements. Below 9 K, the magnetic structure is a helix to wave vector k = (0, 0.447, 1/2), in contrast with NaYNiWO6, which shows a transverse spin density wave with k = (0.47, 0, 0.49). By analyzing the differences in the spin exchanges of NaYMnWO6 and NaYNiWO6, and in the magnetic anisotropies of the Mn2+ (d5, S = 5/2) and the Ni2+ (d2, S = 1) ions, we show what factors govern the propagation direction of a noncollinear magnetic structure and whether it becomes a helix or a cycloid.

Nanoscale Near-Field Steering of Magnetic Vortices

Magneto-optical approaches are promising for fast, precise handling of magnetic data. This study presents a scheme for precise spatiotemporal control of magnetic vortices or skyrmions via the magnetoelectric interaction, using the electric near fields around a biased nanoscale scanning tip. By balancing the topological Lorentz force with an attractive force due to the off-center tip above, magnetic textures can be trapped, accelerated, or stopped without undesirable effects such as transverse Hall drift. The method is applicable to a wide class of noncollinear magnetic structures, and points to the potential of functionalizing near fields for information storage and processing.

Noncollinear Magnetic Order in Two-Dimensional NiBr2 Films Grown on Au(111).

Metal halides are a class of layered materials with promising electronic and magnetic properties persisting down to the two-dimensional limit. While most recent studies focused on the trihalide components of this family, the rather unexplored metal dihalides are also van der Waals layered systems with distinctive magnetic properties. Here we show that the dihalide NiBr2 grows epitaxially on a Au(111) substrate and exhibits semiconducting and magnetic behavior starting from a single layer. Through a combination of a low-temperature scanning-tunneling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy, and photoemission electron microscopy, we identify two competing layer structures of NiBr2 coexisting at the interface and a stoichiometrically pure layer-by-layer growth beyond. Interestingly, X-ray absorption spectroscopy measurements revealed a magnetically ordered state below 27 K with in-plane magnetic anisotropy and zero-remanence in the single layer of NiBr2/Au(111), which we attribute to a noncollinear magnetic structure. The combination of such two-dimensional magnetic order with the semiconducting behavior down to the 2D limit offers the attractive perspective of using these films as ultrathin crystalline barriers in tunneling junctions and low-dimensional devices.

Topologically driven three-spin chiral exchange interactions treated from first principles

The mechanism behind the three-spin chiral interaction (TCI) included in the extended Heisenberg Hamiltonian and represented by an expression worked out recently (Phys.\ Rev.\ B, {\bf 101}, 174401 (2020)) is discussed. It is stressed that this approach provides a unique set of the multispin exchange parameters which are independent of each other either due to their different order of perturbation or due to different symmetry. This ensures in particular the specific properties of the TCI that were demonstrated previously via fully relativistic first principles calculations, and that result from the common influence of several issues not explicitly seen from the expression for the TCI parameters. Therefore, an interpretation of the TCI is suggested, showing explicitly its dependence on the relativistic spin-orbit coupling and on the topological orbital susceptibility (TOS). This is based on an expression for the TOS that is worked out on the same footing as the expression for the TCI. Using first-principles calculations we demonstrate in addition numerically the common topological properties of the TCI and TOS. To demonstrate the role of the relativistic spin-orbit coupling (SOC) for the TCI, a so-called topological' spin susceptibility (TSS) is introduced. This quantity characterizes the SOC induced spin magnetic moment on the atom in the presence of non-collinear magnetic structure, giving a connection between the TOS and TCI. Numerical results again support our conclusions.

Numerical hardware-efficient variational quantum simulation of a soliton solution

Implementing variational quantum algorithms with noisy intermediate-scale quantum machines of up to a hundred qubits is nowadays considered as one of the most promising routes towards achieving a quantum practical advantage. In multiqubit circuits, running advanced quantum algorithms is hampered by the noise inherent to quantum gates which distances us from the idea of universal quantum computing. Based on a one-dimensional quantum spin chain with competing symmetric and asymmetric pairwise exchange interactions, herein we discuss the capabilities of quantum algorithms with special attention paid to a hardware-efficient variational eigensolver. A delicate interplay between magnetic interactions allows one to stabilize a chiral state that destroys the homogeneity of magnetic ordering, thus making this solution highly entangled. Quantifying entanglement in terms of quantum concurrence, we argue that, while being capable of correctly reproducing a uniform magnetic configuration, the hardware-efficient ansatz meets difficulties in providing a detailed description to a noncollinear magnetic structure. The latter naturally limits the application range of variational quantum computing to solve quantum simulation tasks.

Mutual transformation of reversible and bound polarization in Y-type BaSrCo2Fe11AlO22 ceramics

The performance of continuously reversed polarization induced by non-collinear conical magnetic structures was investigated in Y-type BaSrCo2Fe11AlO22 ceramics. The electrical polarization induced by the non-collinear magnetic structures was categorized as reversible polarization and bound polarization. When the range of a circulating magnetic field H ≥ ±1.5 kOe, the P–H loops reached a saturated state and the saturated polarization increased linearly as the circulating magnetic field increased, which was ascribed to the bound polarization. During the continuous magnetic field cycle, a portion of the reversible polarization transformed into bound polarization and only the poling process can achieve inverse transformation. Therefore, the polarization attenuated exponentially as the number of the H cycles increased.

Electronic scattering off a magnetic hopfion

We study scattering of itinerant electrons off a magnetic hopfion in a three-dimensional metallic magnet described by a magnetization vector $\mathbf S(\mathbf r)$. A hopfion is a confined topological soliton of $\mathbf S(\mathbf r)$ characterized by an {\it emergent} magnetic field $B_\gamma(\mathbf r) \equiv \epsilon_{\alpha\beta\gamma} \,\mathbf S\cdot(\nabla_\alpha \mathbf S\times \nabla_\beta \mathbf S)/4 \neq 0$ with vanishing average value $\langle \mathbf B(\mathbf r)\rangle = 0$. We evaluate the scattering amplitude in the opposite limits of large and small hopfion radius $R$ using the eikonal and Born approximations, respectively. In both limits, we find that the scattering cross-section contains a skew-scattering component giving rise to the Hall effect within a hopfion plane. That conclusion contests the popular notion that the topological Hall effect in non-collinear magnetic structures necessarily implies $\langle \mathbf B(\mathbf r)\rangle \neq 0$. In the limit of small hopfion radius $pR \ll 1$, we expand the Born series in powers of momentum $p$ and identify different expansion terms corresponding to the hopfion anisotropy, toroidal moment, and skew-scattering.

The effects of indium doping on the electrical, magnetic, and magnetodielectric properties of M-type strontium hexaferrites

A series of indium-doped hexaferrite ceremics with composition of SrInxFe12-xO19 (x = 0, 1.8, 2.4 and 3.0) were synthesized by a solid-state reaction method. The samples have a single-phase magneto-plumbite structure, and their lattice parameters a and c gradually decrease with the doping indium amount. The indium doping can reduce the ceramic pores. The dielectric constant, dielectric loss, saturation magentization and coercivity also decrease with the indium concentration. The dielectric change with temperature under different frequencies and magnetic fields reveals that the magnetic field has a certain manipulation on the dielectric parameter. Indium doping induces the non-collinear magnetic structure, causing a magnetodielectric effect. The influence of the magnetic field on the magnetodielectric coefficient shows that the magnetodielectric coefficient changes from positive to negative for SrInxFe12-xO19 with x = 0.0, 2.4 and 3.0, while keeps negative in the whole temperature range for SrIn1.8Fe10.2O19. At the same time, the positive and negative magnetodielectric transition temperature is different for the samples with different doping amounts. The transition temperature of SrFe12O19 is between 50 K and 75 K, while that of SrInxFe12-xO19 (x = 2.4–3.0) is between 25 and 50 K. In addition, SrIn2.4Fe9.6O19 enjoys the magnetodielectric effect with remarkable twisted-butterfly loop at room temperature, which is an intrinsic effect confirmed by the fact that the magnetodielectric coefficient is invariable with frequency. Our results provide a helpful research basis for the magnetodielectric materials.

Influence of the Cubic Sublattice on Magnetic Coupling between the Tetrahedral Sites of Garnet.

We present a study on the nuclear and magnetic structures of two iron-based garnets with magnetic cations isolated on tetrahedral sites. Ca2YZr2Fe3O12 and Ca2LaZr2Fe3O12 offer an interesting comparison for examining the effect of increasing cation size within the diamagnetic backbone of the garnet crystal structure, and how such changes affect the magnetic order. Despite both systems exhibiting well-pronounced magnetic transitions at low temperatures, we also find evidence for diffuse magnetic scattering due to a competition between the nearest-neighbor, next nearest-neighbor, and so on, within the tetrahedral sites. This competition results in a complex noncollinear magnetic structure on the tetrahedral sublattice creating a mixture of ferro- and antiferromagnetic interactions above the long-range ordering temperature near 20 K and suggests that the cubic site of the garnet plays a significant role in mediating the superexchange interactions between tetrahedral cations.

Magnetic field-induced polarization reversal in Y-type hexaferrites Ba0.7 Sr1.3CoZnFe11AlO22 single crystals

Y-type hexaferrites with non-collinear conical magnetic structures, which induce electric polarization (P), are prospective single-phase multiferroics with broad applications, such as magnetic sensors, energy convertors, and memory devices, among others. Y-type hexaferrites have attracted considerable attention. In this study, we investigated the magnetoelectric properties of Ba0.7Sr1.3CoZnFe11AlO22 single crystals with Y-type hexaferrite structures by replacing half of Zn2+ ions with Co2+ ions. A transition from a screw order to the ferromagnetic is observed at TN2 = 356 K in Ba0.7Sr1.3CoZnFe11AlO22 single crystals. The electric polarization (P) and magnetoelectric coupling coefficient(α) reach a maximum of 130 μC/m2 and 16667 ps/m at T = 30 K and E = 880 kV/m, respectively. Most importantly, the in-plane Hab induced P can be fully reversed by applying in-plane Hab and it maintains a non-zero value even when the applied magnetic field is zero. Since the P does not decay and repeats many times under a fluctuating low magnetic field, it is important for potential applications in new types of non-volatile memory devices.