Magnetic Lattice Research Articles

Nuclear and magnetic spin structure of the antiferromagnetic triangular lattice compound LiCrTe2 investigated by mu ^+SR, neutron and X-ray diffraction

Two-dimensional (2D) triangular lattice antiferromagnets (2D-TLA) often manifest intriguing physical and technological properties, due to the strong interplay between lattice geometry and electronic properties. The recently synthesized 2-dimensional transition metal dichalcogenide LiCrTe_2, being a 2D-TLA, enriched the range of materials which can present such properties. In this work, muon spin rotation (mu ^+SR) and neutron powder diffraction (NPD) have been utilized to reveal the true magnetic nature and ground state of LiCrTe_2. From high-resolution NPD the magnetic spin order at base-temperature is not, as previously suggested, helical, but rather collinear antiferromagnetic (AFM) with ferromagnetic (FM) spin coupling within the ab-plane and AFM coupling along the c-axis. The value if the ordered magnetic Cr moment is established as mu _{textrm{Cr}}= 2.36~mu _{textrm{B}}. From detailed mu ^+SR measurements we observe an AFM ordering temperature T_{textrm{N}}approx 125 K. This value is remarkably higher than the one previously reported by magnetic bulk measurements. From mu ^+SR we are able to extract the magnetic order parameter, whose critical exponent allows us to categorize LiCrTe_2 in the 3D Heisenberg AFM universality class. Finally, by combining our magnetic studies with high-resolution synchrotron X-ray diffraction (XRD), we find a clear coupling between the nuclear and magnetic spin lattices. This suggests the possibility for a strong magnon–phonon coupling, similar to what has been previously observed in the closely related compound LiCrO_2.

Influence of gadolinium doped in nickel nanoferrites on structural, optical, electrical, and magnetic properties

The sonochemical reaction approach was used to make NiGdxFe2-xO4 nanoferrites (x = 0.01, 0.03, 0.05, 0.07, and 0.09). X-ray diffraction (XRD), ultra violet-diffuse reflectance spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, vibrating sample magnetometer, and electrochemical impedance spectroscopy were used to investigate the optical, magnetic, electrical, and structural properties of NiGdxFe2-xO4 nanoferrites. The creation of a cubic spinel structure was confirmed by analyzing the XRD pattern of these NiGdxFe2-xO4 nanoferrites. The average crystallite diameters of the nanoparticles for the compositions x = 0.01, 0.03, 0.05, 0.07, and 0.09 were 57, 53, 48, 45, and 41 nm, respectively. To investigate the dielectric behavior of the produced nanoferrites, an impedance study was performed. The addition of Gd to NiFe2-xO4 nanoparticles increased the dielectric characteristics of the produced nanoferrites, according to characterization experiments. A cation distribution has been proposed for the determination of various important theoretical parameters for these samples. The addition of Gd3+ nanoparticles has shown the ferromagnetic behavior at room temperature confirmed by VSM analysis. A specific correlation between magnetic interaction and lattice strain was observed in Gd3+ substituted nickel ferrite. An increase in Gd concentration in the manufactured nanoferrites resulted in a rise in saturation magnetization and a decrease in coercivity.

First-principles calculations to investigate physical properties of three magnetic sub lattice CaCu3Mn4-xIrxO12 (x = 0, 2 and 4) system via symmetry evaluation

Structural, electronic, elastic and magnetic properties of CaCu3Mn4-xIrxO12 (x = 0, 2 and 4) along with the optical properties of CaCu3Mn4O12 perovskites have been carried out in the framework of density functional theory (DFT). The investigation of structural optimization reveals that CaCu3Mn2Ir2O12 is stable in Pn-3 space group and CaCu3Mn4O12 and CaCu3Ir4O12 perovskites are stable in Im-3 space group. The cohesive energy and enthalpy of formation reveal the stability of these compound and shows that CaCu3Mn2Ir2O12 is more stable than the rest compounds. Substitution of Ir by Mn not only transforms these compounds from semiconductor to metallic nature but also transform the host compound from ferrimagnetic to anti-ferromagnetic via spin glass state. The DFT electronic behavior is also supported by the electrical resistivity. Elastic properties demonstrate the mechanical stability, anisotropic and ductile nature of these compounds. The optical properties indicate that CaCu3Mn4O12 is optically active for infrared electromagnetic radiations and could be used in optical devises. The ferrimagnetic ductile nature of CaCu3Mn4O12, spin glass and anti-ferromagnetic nature of CaCu3 Mn2Ir2O12 and CaCu3Ir4O12 makes these perovskites suitable candidates for spintronic and magnetic cloaking applications.

Modified Spin Textures in a 3D Magnetic Lattice

Modified Spin Textures Three dimensional magnetic nanostructures exhibit many new properties and phenomena due to the extra degree of freedom compared to two dimensional nanostructures. In article number 2200213, Vivian Ng and Ba Myint create a magnetic lattice by overlapping hour-glass structures arrays on a 2D antidot matrix through a self-aligned nanosphere lithography technique. The field reversal behaviour and magnetic properties of the 3D magnetic lattice are characterized by magnetic force microscopy and the spin-curvature display unique magnetic behaviour as a consequence of the interplay of magnetic coupling.

Magnetic Skyrmion Lattices in a Novel 2D‐Twisted Bilayer Magnet

AbstractMagnetic skyrmions are topologically protected spin swirling vertices, which are promising in device applications due to their particle‐like nature and excellent controlability. Magnetic skyrmions are extensively studied in a variety of materials and proposed to exist in the extreme 2D limit, i.e., in twisted bilayer CrI3 (TBCI). Unfortunately, the magnetic states of TBCIs with small twist angles are disorderly distributed ferromagnetic and antiferromagnetic (AFM) domains in recent experiments, and thus the method to get rid of disorders in TBCIs is highly desirable. Here, intralayer exchange interactions up to the third nearest neighbors without empirical parameters and very accurate interlayer exchange interactions are used to study the magnetic states of TBCIs. The functions of interlayer exchange interactions obtained using first‐principles calculations and stored in symmetry‐adapted artificial neural networks are proposed. Based on these, the subsequent Landau–Lifshitz–Gillbert equation calculations explain the disorderly distributed FM‐AFM domains in TBCIs with small twist angles and predict the orderly distributed skyrmions in TBCIs with large twist angles. This novel twisted 2D bilayer magnet can be used to design memory devices, monochromatic spin wave generators and many kinds of skyrmion lattices.

Magnetic triangular bubble lattices in bismuth-doped yttrium iron garnet

Magnetic bubbles have again become a subject of significant attention following the experimental observation of topologically nontrivial magnetic skyrmions. In recent work, tailoring the shape of the bubbles is considered a key factor for their dynamics in spintronic devices. In addition to the reported circular, elliptical, and square bubbles, here we observe triangular bubble domains in bismuth-doped yttrium iron garnet (Bi-YIG) using Kerr microscopy. The bubble domains evolve from discrete circular to latticed triangular and hexagonal shapes. Further, the orientation of the triangular bubbles in the hexagonal lattices can be flipped by decreasing the magnetic field. The sixfold in-plane magnetic anisotropy of Bi-YIG(111) crystal, which is presumably the mechanism underlying the triangular shape of the bubbles, is measured as 1179 erg/cm3. The study of the morphologies of topologically trivial bubbles in YIG offers insight into nontrivial spin textures, which is appealing for future spintronic applications.

Temperature- and field angular-dependent helical spin period characterized by magnetic dynamics in a chiral helimagnet MnNb3S6

The chiral magnets with topological spin textures provide a rare platform to explore topology and magnetism for potential application implementation. Here, we study the magnetic dynamics of several spin configurations on the monoaxial chiral magnetic crystal MnNb3S6 via broadband ferromagnetic resonance (FMR) technique at cryogenic temperature. In the high-field forced ferromagnetic state (FFM) regime, the obtained frequency f vs. resonance field Hres dispersion curve follows the well-known Kittel formula for a single FFM, while in the low-field chiral magnetic soliton lattice (CSL) regime, the dependence of Hres on magnetic field angle can be well-described by our modified Kittel formula including the mixture of a helical spin segment and the FFM phase. Furthermore, compared with the sophisticated Lorentz micrograph technique, the observed magnetic dynamics corresponding to different spin configurations allow us to obtain temperature- and field-dependent proportion of helical spin texture and helical spin period ratio L(H)/L(0) via our modified Kittel formula. Our results demonstrated that field- and temperature-dependent nontrivial magnetic structures and corresponding distinct spin dynamics in chiral magnets can be an alternative and efficient approach to uncovering and controlling nontrivial topological magnetic dynamics.

Gauge theory applied to magnetic lattices

The generalizations of micromagnetic exchange including higher order interactions are normally performed phenomenologically. In this paper we combine graph and gauge field theory to provide a new procedure to perform the continuum limit of the Heisenberg model. Our approach allows to simultaneously account for the symmetries of the crystal, the effect of spin-orbit coupling and their interplay. We obtain a micromagnetic theory accounting for the crystal symmetry constraints at all orders in exchange. The form of the micromagnetic Dzyaloshinskii-Moriya interaction in all 32 point groups is calculated at the first order.

Discovery of Charge Order and Corresponding Edge State in Kagome Magnet FeGe.

Kagome materials often host exotic quantum phases, including spin liquids, Chern gap, charge density wave, and superconductivity. Existing scanning microscopy studies of the kagome charge order have been limited to nonkagome surface layers. Here, we tunnel into the kagome lattice of FeGe to uncover features of the charge order. Our spectroscopic imaging identifies a 2×2 charge order in the magnetic kagome lattice, resembling that discovered in kagome superconductors. Spin mapping across steps of unit cell height demonstrates the existence of spin-polarized electrons with an antiferromagnetic stacking order. We further uncover the correlation between antiferromagnetism and charge order anisotropy, highlighting the unusual magnetic coupling of the charge order. Finally, we detect a pronounced edge state within the charge order energy gap, which is robust against the irregular shape fluctuations of the kagome lattice edges. We discuss our results with the theoretically considered topological features of the kagome charge order including unconventional magnetism and bulk-boundary correspondence.

Unraveling the Magnetic Ground State and Local Lattice Distortions in Z2XY-Type Full Heusler Compounds: An EXAFS Study

Unraveling the Magnetic Ground State and Local Lattice Distortions in Z₂XY-Type Full Heusler Compounds: An EXAFS Study

Analysis of time-of-flight small-angle neutron scattering data on mesoscopic crystals such as magnetic vortex lattices.

Bragg diffracted intensities and q values for crystalline structures with long repeat distances may be obtained by small-angle neutron scattering (SANS) investigations. An account is given of the methods, advantages and disadvantages of obtaining such data by the multichromatic time-of-flight method, compared with the more traditional quasi-monochromatic SANS method. This is illustrated with data obtained from high-magnetic-field measurements on magnetic vortex line lattices in superconductors on the former HFM/EXED instrument at Helmholtz-Zentrum Berlin. The methods have application to other mesoscopic crystalline structures investigated by SANS instruments at pulsed sources.

Transition metal dichalcogenide metaphotonic and self-coupled polaritonic platform grown by chemical vapor deposition

Transition metal dichalcogenides (TMDCs) have recently attracted growing attention in the fields of dielectric nanophotonics because of their high refractive index and excitonic resonances. Despite the recent realizations of Mie resonances by patterning exfoliated TMDC flakes, it is still challenging to achieve large-scale TMDC-based photonic structures with a controllable thickness. Here, we report a bulk MoS2 metaphotonic platform realized by a chemical vapor deposition (CVD) bottom-up method, supporting both pronounced dielectric optical modes and self-coupled polaritons. Magnetic surface lattice resonances (M-SLRs) and their energy-momentum dispersions are demonstrated in 1D MoS2 gratings. Anticrossing behaviors with Rabi splitting up to 170 meV are observed when the M-SLRs are hybridized with the excitons in multilayer MoS2. In addition, distinct Mie modes and anapole-exciton polaritons are also experimentally demonstrated in 2D MoS2 disk arrays. We believe that the CVD bottom-up method would open up many possibilities to achieve large-scale TMDC-based photonic devices and enrich the toolbox of engineering exciton-photon interactions in TMDCs.

Thermal Hysteresis and Ordering Behavior of Magnetic Skyrmion Lattices.

The physics of phase transitions in two-dimensional (2D) systems underpins research in diverse fields including statistical mechanics, nanomagnetism, and soft condensed matter. However, many aspects of 2D phase transitions are still not well understood, including the effects of interparticle potential, polydispersity, and particle shape. Magnetic skyrmions are chiral spin-structure quasi-particles that form two-dimensional lattices. Here, we show, by real-space imaging using in situ cryo-Lorentz transmission electron microscopy coupled with machine learning image analysis, the ordering behavior of Néel skyrmion lattices in van der Waals Fe3GeTe2. We demonstrate a distinct change in the skyrmion size distribution during field-cooling, which leads to a loss of lattice order and an evolution of the skyrmion liquid phase. Remarkably, the lattice order is restored during field heating and demonstrates a thermal hysteresis. This behavior is explained by the skyrmion energy landscape and demonstrates the potential to control the lattice order in 2D phase transitions.

Modified Spin Textures in a 3D Magnetic Lattice

New magnetic behavior of a 3D magnetic lattice created by stacking hour‐glass structures over a 2D antidot matrix is reported. The unique multivortices induced reversal process along the hard axis is reported for the 3D magnetic lattice. Further analysis with 3D Object Orientated MicroMagnetic Framework (OOMMF) simulation shows this magnetic behavior due to the magnetic coupling between the two building blocks: hour‐glass structures and 2D antidot. The reversal process for the 3D magnetic lattice along the easy axis shows abrupt coherent switching behavior, while the multivortices induced reversal process is observed for the hard axis. A new method of comparing the simulation and experimental result using a MATLAB divergence computation software is also reported. Good agreement between micromagnetic simulation and experimental results is observed via this method.

Magnetic properties of the triangular-lattice antiferromagnets Ba3RB9O18 (R=Yb, Er)

Frustration, spin correlations and interplay between competing degrees of freedom are some of the key ingredients that underlie exotic states with fractional excitations in quantum materials. Rare-earth based two dimensional magnetic lattice wherein crystal electric field, spin-orbit coupling, anisotropy and electron correlation between rare-earth moments offer a new paradigm in this context. Herein, we present crystal structure, magnetic susceptibility and specific heat accompanied by crystal electric field calculations on the polycrystalline sample of Ba3RB9O18 (R = Yb, Er) in which R3+ ions form a perfect triangular lattice without anti-site disorder. The localized R3+ spins show neither long-range order nor spin-glass state down to 1.9 K in Ba3RB9O18. Magnetization data reveal a pseudospin Jeff = 1/2 ( Yb3+) in the Kramers doublet state and a weak antiferromagnetic interaction between Jeff = 1/2 moments in the Yb variant. On the other hand, the effective moment {\mu}eff = 8.8 {\mu}B was obtained from the Curie-Weiss fit of the low-temperature susceptibility data of Er variant suggests the admixture of higher crystal electric field states with the ground state. The Curie-Weiss fit of low-temperature susceptibility data for Er system unveils the presence of a relatively strong antiferromagnetic interaction between Er3+ moments compared to its Yb3+ analog. Ba3ErB9O18 does not show long-range magnetic ordering down to 500 mK. Furthermore, our crystal electric field calculations based on magnetization data of Ba3ErB9O18 suggest the presence of a small gap between the ground and first excited Kramers doublets. The broad maximum around 4 K in magnetic specific heat in zero-field is attributed to the thermal population of the first CEF excited state in Ba3ErB9O18, which is consistent with our CEF calculations.

An emergence of chiral helimagnetism or ferromagnetism governed by Cr intercalation in a dichalcogenide CrNb3S6

A synthesis of single crystals of chiral dichalcogenides TM3X6 (T: 3d transition metal, M: Nb or Ta, X: S or Se) remains an intriguing issue for the investigation of emergent quantum properties such as chiral helimagnetism. In this study, we investigated a correlation between the quantity of Cr intercalation x and the magnetic property in single crystals of a chromium (Cr) intercalated chiral disulfide CrxNb3S6 in order to optimize the synthesis condition for the intercalation-controlled single crystals. The magnetic properties, including a magnetic transition temperature Tc, take different values depending on the samples. We systematically grew single crystals of CrxNb3S6 with x ranged from 0.89 to 1.03 and found that the amount of the Cr intercalation x is an essential factor in controlling the magnetic properties of the grown crystals. The magnetization anomaly, which appears in the temperature dependence as evidence of the formation of chiral magnetic soliton lattice (CSL), was observed only in a narrow region of x from 0.98 to 1.03. The single crystals with x being 0.98 and 0.99 showed the CSL behavior with the highest Tc of 133 K. These results indicate that the small number of defects on the sites for T ions dramatically affects the quality of the single crystals in the synthesis of TM3S6. We also discuss the importance of synthesizing enantiopure single crystals of chiral dichalcogenides in order to observe chiral physical properties unique to chiral compounds such as magneto-chiral effect and chiral-induced spin selectivity.

Polarization-independent resonant lattice Kerker effect in phase-change metasurface

Resonant lattice Kerker effect in periodic resonators is one of the most interesting generalizations of the Kerker effect that relates to various fascinating functionalities such as scattering management and Huygens metasurfaces. However, so far this effect has been shown to be sensitive to the incident polarization, restricting its applications. Here, we report, for the first time, polarization-independent resonant lattice Kerker effect in metasurfaces composed of periodic Ge2Se2Te5 (GST) disks. For such a metasurface of square lattice, the spectrally overlap of the electric dipole and magnetic dipole surface lattice resonances can be realized by choosing an appropriate GST crystalline fraction regardless of the incident polarization. The operation wavelength and the required GST crystalline fraction can be conveniently tuned over large ranges since these parameters scale linearly with the disk size and the lattice period, greatly facilitating the design. Making use of the obtained resonant lattice Kerker effect, we realize a reconfigurable and polarization-independent lattice Huygens’ metasurface with a dynamic phase modulation of close to 2π and high transmittance. This work will advance the engineering of the resonant lattice Kerker effect and promote its applications in phase modulation and wavefront control.

Hybridized magnetic lattice resonances for narrowband perfect absorption

The realization of multiple sharp collective resonances and their implications for ultrathin and narrowband perfect absorber without using back reflector is promising for the design of high performance nanophotonic devices. This study proposes and demonstrates that for double metallic/dielectric core/shell nanoparticle arrays, sharp hybridized magnetic lattice resonances can be excited and used to generate narrowband perfect absorption. Both coupled dipole approximation and full-wave simulations reveal that the magnetic (electric) coupling strength and coupling phase between the two nanoparticles in a unit cell can be effectively tuned by adjusting their relative positions, which leads to the selective excitation of the magnetic (electric) lattice modes for individual nanoparticle arrays or the hybridized magnetic (electric) lattice modes for the whole structures. When the hybridized magnetic lattice resonances are spectrally overlapping with electric modes by manipulating the lattice spacing, both balanced Kerker and critical coupling conditions are satisfied, thereby resulting in the formation of narrowband perfect absorptions. The flexible tunability of multiple sharp magnetic (electric) lattice resonances and the realization of narrowband perfect absorptions make the double nanoparticle arrays a promising platform for implications of linear and nonlinear nanophotonic devices.

Topological monopole's gauge field‐induced anomalous Hall effect in artificial honeycomb lattice

AbstractVortex magnetic structure in artificial honeycomb lattice provides a unique platform to explore emergent properties due to the additional Berry phase curvature imparted by chiral magnetization to circulating electrons via direct interaction. We argue that while the perpendicularly aligned magnetic component leads to the quantized flux of monopole at the center of the Berry sphere, the in‐plane vortex circulation of magnetization gives rise to unexpected nontrivial topological Berry phase due to the gauge field transformation. The unprecedented effect signifies the importance of vector potential in multiply connected geometrical systems. Experimental confirmations to proposed hypotheses are obtained from Hall resistance measurements on permalloy honeycomb lattice. Investigation of the topological gauge transformation due to the in‐plane chirality reveals anomalous quasi‐oscillatory behavior in Hall resistance as a function of perpendicular field. The oscillatory nature of is owed to the fluctuation in equilibrium current as a function of Fermi wave‐vector , envisaged under the proposed new formulation in this article. Our synergistic approach suggests that artificially tunable nanostructured material provides new vista to the exploration of topological phenomena of strong fundamental importance.Key PointsDemonstration of gauge field flux due to vortex magnetism.Anomalous Hall effect in magnetic honeycomb lattice.Topological monopole‐induced magnetic flux.

Tracking the evolution from isolated dimers to many-body entanglement in NaLuxYb1−xSe2

We synthesize homogeneous compositions of NaLu$_x$Yb$_{1-x}$Se$_2$, connecting non-magnetic NaLuSe$_2$ to the triangular lattice spin liquid candidate NaYbSe$_2$. Thermal and magnetic properties are studied as the system evolves from one with dilute magnetic defects to one of a dense magnetic lattice. The field and temperature dependent heat capacity show the carriers of entropy crossover from isolated magnetic ions to a correlated lattice borne from spin dimers. For the dilute system we estimate the single ion anisotropy $(g_\perp/g_\parallel =3.13)$ and also the dimer exchange couplings $J_\parallel(=5.4$~K) and $J_\perp(=9.6$~K), in order to draw comparison to the half-doped and full magnetic compounds.