Antiferromagnetic Spin Research Articles

Collective Monte Carlo updates through tensor network renormalization

We introduce a Metropolis-Hastings Markov chain for Boltzmann distributions of classical spin systems. It relies on approximate tensor network contractions to propose correlated collective updates at each step of the evolution. We present benchmark computations for a wide variety of instances of the two-dimensional Ising model, including ferromagnetic, antiferromagnetic, (fully) frustrated and Edwards-Anderson spin glass instances, and we show that, with modest computational effort, our Markov chain achieves sizeable acceptance rates, even in the vicinity of critical points. In each of the situations we have considered, the Markov chain compares well with other Monte Carlo schemes such as the Metropolis or Wolff’s algorithm: equilibration times appear to be reduced by a factor that varies between 4040 and 20002000, depending on the model and the observable being monitored. We also present an extension to three spatial dimensions, and demonstrate that it exhibits fast equilibration for finite ferro- and antiferromagnetic instances. Additionally, and although it is originally designed for a square lattice of finite degrees of freedom with open boundary conditions, the proposed scheme can be used as such, or with slight modifications, to study triangular lattices, systems with continuous degrees of freedom, matrix models, a confined gas of hard spheres, or to deal with arbitrary boundary conditions.

Efficient Spin-to-Charge Conversion via Altermagnetic Spin Splitting Effect in Antiferromagnet RuO_{2}.

The relativistic spin Hall effect and inverse spin Hall effect enable the efficient generation and detection of spin current. Recently, a nonrelativistic altermagnetic spin splitting effect (ASSE) has been theoretically and experimentally reported to generate time-reversal-odd spin current with controllable spin polarization in antiferromagnet RuO_{2}. The inverse effect, electrical detection of spin current via ASSE, still remains elusive. Here we show the spin-to-charge conversion stemming from ASSE in RuO_{2} by the spin Seebeck effect measurements. Unconventionally, the spin Seebeck voltage can be detected even when the injected spin current is polarized along the directions of either the voltage channel or the thermal gradient, indicating the successful conversion of x- and z-spin polarizations into the charge current. The crystal axes-dependent conversion efficiency further demonstrates that the nontrivial spin-to-charge conversion in RuO_{2} is ascribed to ASSE, which is distinct from the magnetic or antiferromagnetic inverse spin Hall effects. Our finding not only advances the emerging research landscape of altermagnetism, but also provides a promising pathway for the spin detection.

Even-odd effects in the J1−J2 SU(N) Heisenberg spin chain

The zero-temperature phase diagram of the ${J}_{1}\text{\ensuremath{-}}{J}_{2}\phantom{\rule{4pt}{0ex}}\mathrm{SU}(N)$ antiferromagnetic Heisenberg spin chain is investigated by means of complementary field theory and numerical approaches for general $N$. A fully gapped $\mathrm{SU}(N)$ valence bond solid made of $N$ sites is formed above a critical value of ${J}_{2}/{J}_{1}$ for all $N$. We find that the extension of this $N$-merized phase for larger values of ${J}_{2}$ strongly depends on the parity of $N$. For even $N$, the phase smoothly interpolates to the large ${J}_{2}$ regime where the model can be viewed as a zigzag $\mathrm{SU}(N)$ two-leg spin ladder. The phase exhibits both a $N$-merized ground state and incommensurate spin-spin correlations. In stark contrast to the even case, we show that the $N$-merized phase with odd $N$ has only a finite extent with no incommensuration. A gapless phase in the $\mathrm{SU}{(N)}_{1}$ universality class is stabilized for larger ${J}_{2}$ that stems from the existence of a massless renormalization group flow from $\mathrm{SU}{(N)}_{2}$ to $\mathrm{SU}{(N)}_{1}$ conformal field theories when $N$ is odd.

Magnetic excitation spectrum and Hamiltonian of the quantum spin chain compound BaCuTe2O6

The magnetic excitation spectrum and Hamiltonian of the quantum magnet BaCuTe2O6 is studied by inelastic neutron scattering (INS) and density functional theory (DFT). INS on powder and single crystal samples reveals overlapping spinon continuua - the spectrum of an antiferromagnetic spin-1/2 spin chain - due to equivalent chains running along the a, b, and c directions. Long-range magnetic order onsets below TN = 6.3 K due to interchain interactions, and is accompanied by the emergence of sharp spin-wave excitations which replace the continuua at low energies. The spin-wave spectrum is highly complex and was successfully modelled achieving excellent agreement with the data. The extracted interactions reveal an intrachain interaction, J3 = 2.9 meV, while the antiferromagnetic hyperkagome interaction J2, is the sub-leading interaction responsible for coupling the chains together in a frustrated way. DFT calculations reveal a similar picture for BaCuTe2O6 of dominant J3 and sub-leading J2 antiferromagnetic interactions and also indicate a high sensitivity of the interactions to small changes of structure which could explain the very different Hamiltonians observed in the sister compounds SrCuTe2O6 and PbCuTe2O6.

Low-frequency spin dynamics of the quasi-two-dimensional S = 12 antiferromagnet BaCdVO(PO4)2

A quasi-two-dimensional quantum magnet with competing ferro- and antiferromagnetic exchange interactions, $\mathrm{BaCdVO}{({\mathrm{PO}}_{4})}_{2}$, is studied using the magnetic resonance technique in a wide frequency range. The magnetic resonance spectra of the ordered phase confirm the collinear antiferromagnetic spin structure oriented along the $a$ axis. The frequency-field diagram of antiferromagnetic resonance demonstrates two low-frequency excitation branches with different energy gaps, indicating a biaxial nature of anisotropy. We observe a critical softening of the longitudinal resonance mode in a field of 3.8 T, which is the lower boundary of a previously proposed presaturation phase positioned below the saturation field of 6.5 T. An interpretation of the presaturation phase as a state with variable magnetization of spin-vacancy defects is proposed. It may be considered an alternative to the spin-nematic phase initially supposed.

Majorana lattice gauge theory: Symmetry breaking, topological order and intertwined orders all in one

The Majorana lattice gauge theory purely composed of Majorana fermions on square lattice is studied throughly. The ground state is obtained exactly and exhibits the coexistence of symmetry breaking and topological order. The Z_2Z2 symmetry breaking of matter fields leads to the intertwined antiferromagnetic spin order and \etaη-pairing order. The topological order is reflected in the Z_2Z2 quantum spin liquid ground state of gauge fields. The Majorana lattice gauge theory, alternatively can be viewed as interacting Majorana fermion model, is possibly realized on a Majorana-zero-mode lattice.

Probing the topologically trivial nature of end states in antiferromagnetic atomic chains on superconductors

Spin chains proximitized by s-wave superconductors are predicted to enter a mini-gapped phase with topologically protected Majorana modes (MMs) localized at their ends. However, the presence of non-topological end states mimicking MM properties can hinder their unambiguous observation. Here, we report on a direct method to exclude the non-local nature of end states via scanning tunneling spectroscopy by introducing a locally perturbing defect on one of the chain’s ends. We apply this method to particular end states observed in antiferromagnetic spin chains within a large minigap, thereby proving their topologically trivial character. A minimal model shows that, while wide trivial minigaps hosting end states are easily achieved in antiferromagnetic spin chains, unrealistically large spin-orbit coupling is required to drive the system into a topologically gapped phase with MMs. The methodology of perturbing candidate topological edge modes in future experiments is a powerful tool to probe their stability against local disorder.

Novel multiferroic nanoparticles Sm1−xHoxFeO3 as a heavy metal Cr6+ ion removal from water

Novel multiferroic nanoparticles Sm1−xHoxFeO3 have been prepared using a simple citrate auto-combustion method. According to the X-ray diffraction (XRD) data, the multiferroic samples had an orthorhombic single phase structure. The field emission scanning electron microscope (FESEM) illustrated that the nanoparticles possessed a cotton-like morphology with a porous nature. The vibrating sample magnetometer (VSM) demonstrates the antiferromagnetic (AFM) behavior of the samples. The maximum magnetization (Mm) of Sm0.95Ho0.05FeO3 is five times greater than that of SmFeO3. The ferroelectricity of Sm1−xHoxFeO3 has Г2-spin structure. The antiferromagnetic (AFM) spin canting has a great effect on both the magnetization and the ferroelectricity of the investigated perovskites. Sm1−xHoxFeO3; 0.0 ≤ x ≤ 0.10 samples are concluded to be novel single-phase multiferroic materials capable of adsorbing toxic chromium (Cr6+) metal ions from water. A hydrogen potential of pH 6 is the best condition for precipitating chromium ions. The adsorption of Cr6+ ions on Sm1−xHoxFeO3 was studied using the Langmuir and Freundlich isotherm models.

Topological Spin Textures in a Non-Collinear Antiferromagnet System.

Topologically protected magnetic "whirls" such as skyrmions in antiferromagnetic materials have recently attracted extensive interests due to their nontrivial band topology and potential application in antiferromagnetic spintronics. However, the room-temperature skyrmions in natural metallic antiferromagnetic materials with merit of probably conveniently electrical manipulation have not been reported. Here, we realize room-temperature skyrmions in a non-collinear antiferromagnet Mn3 Sn capped with a Pt overlayer. The evolution of spin textures from coplanar inverted triangular structures to Bloch-type skyrmions is achieved via tuning the magnitude of interfacial Dzyaloshinskii - Moriya interaction. Beyond that, the temperature can induce an unconventional transition from skyrmions to antiferromagnetic meron-like spin textures at approximately 220 K in our Mn3 Sn/Pt samples. Combining with the theoretical calculations, we find the transition is originated from the temperature dependence of antiferromagnetic exchange interaction between kagome sublayers within the Mn3 Sn crystalline unitcell. Our findings open the avenue for the development of topological spin-swirling-based antiferromagnetic spintronics. This article is protected by copyright. All rights reserved.

Inelastic neutron scattering in the weakly coupled triangular spin tube candidate CsCrF4

We performed inelastic neutron scattering (INS) experiments to measure spin dynamics on a polycrystalline sample of a spin tube candidate CsCrF$_{4}$. The compound exhibits a successive phase transition from a paramagnetic phase through an intermediate temperature (IT) phase of a 120$^{\circ}$ structure to a low temperature (LT) phase of another 120$^{\circ}$ structure. Elaborate comparison between observed and calculated neutron spectra in LT phase reveals that the spin Hamiltonian is identified as antiferromagnetic spin tubes including perturbative terms of intertube interaction, Dzyaloshinskii-Moriya interaction, and single ion anisotropy. A phase diagram for the ground state is classically calculated. A set of parameters in the spin Hamiltonian obtained from the INS spectra measured in LT phase is quite close to a boundary to the phase of the 120$^{\circ}$ structure of IT phase. The INS spectra measured in IT phase is, surprisingly, the same as those in LT phase in the level of powder averaged spectra, even though the magnetic structures in IT and LT phases are different. Identical dynamical structures compatible with two different static structures are observed. No difference in the observed spectra indicates no change of the spin Hamiltonian with the temperature, suggesting that the origin of the successive phase transition being order-by-disorder mechanism.

Spatial antiferromagnetic spin texture as a nano-oscillator

We report a theoretical study of the localized spatial magnetization configuration, which is a confined spin configuration of the target skyrmion/hopfion type in an antiferromagnet with perpendicular magnetic anisotropy, and then we solve the particular problem of self-oscillations of such a topological spin texture. Using the energy approach, a self-consistent account of inhomogeneity of the characteristics of the topological magnetic spin texture was carried out. On this basis, the equation of free oscillations of the confined spin configuration magnetization was derived and its quasi-classical solution was found. For a thin ring spin texture, the frequency, period of oscillations and relative amplitude of the main tone of oscillations are found. For the first time, we determined the topological mass, inertial mass and total energy of the main tone of oscillations of such spatial spin texture. The self-oscillatory process of a spatial spin texture is interpreted as a magnetic nano-oscillator.

Weak ferromagnetism at 48.5 K in rubidium-intercalated biphenyl

Aromatic hydrocarbon molecules with π-conjugated structure have great potential for the search of exotic states such as high temperature superconductivity and novel quantum magnetism. In this work, we found that high temperature weak ferromagnetism can be achieved by intercalating rubidium into the shortest poly(para-phenylene) molecule—biphenyl. Both dc and ac magnetic susceptibility measurements showed that the synthesized material exhibits a typical antiferromagnetic transition at 48.5 K, accompanying a ferromagnetic character in the magnetically ordered region. Combining theoretical calculations and Raman spectroscopic studies, it was found that the mole ratio between rubidium and biphenyl is 1:1, and the molecular magnetic moments are formed by transferring the Rb-5s electrons to the C-2p orbitals. The weak ferromagnetism is produced by intralayer spin-canted antiferromagnetic and interlayer ferromagnetic spin couplings. Our finding enriches the physicochemical functionality of biphenyl and opens a window for the search of π-electron organic magnets in poly(para-phenylene) molecules.

Magnetic Domain Change Induced by In‐Plane Electric Polarization Switching in Bi(Fe, Co)O3 Thin Film

AbstractPerovskite BiFe0.9Co0.1O3 with electric‐field‐induced magnetization reversal is a promising material for low‐power non‐volatile memory devices because spontaneous magnetization perpendicular to the electric polarization can be reversed by out‐of‐plane polarization reversal. In this study, magnetic and ferroelectric domain changes in BiFe0.9Co0.1O3 after applying an in‐plane electric field with counter electrodes fabricated by lithography is investigated. Electric poling can be performed up to 100 times via 71° polarization switching without disrupting the ferroelectric domains. It is determined that the correlation between the ferroelectric and magnetic domains is preserved, while in‐plane 71° polarization switching without reconstructing the ferroelectric domains does not change its out‐of‐plane magnetization. Lastly, possible differences in the antiferromagnetic spin vector and magnetization direction for in‐plane and out‐of‐plane 71° switching is discussed.

Memory of frozen and rotatable antiferromagnetic spins in epitaxial CoO(1 1 1)/Fe and NiO(1 1 1)/Fe bilayers

We combined X-ray magnetic linear and circular dichroism together with magnetooptic Kerr effect measurements in order to follow the magnetic properties of epitaxial CoO(111)/Fe(110) and NiO(111)/Fe(110) bilayers. We find that in both studied cases ferromagnetic sublayer plays a dominant role and determines the magnetic state of the neighboring antiferromagnet, however different interaction scenarios are observed. In CoO/Fe bilayers the antiferromagnetic spins are frozen and their orientation is imprinted by magnetization of Fe layer as the system passes the Néel temperature of CoO. For NiO/Fe bilayers, the antiferromagnetic spins are rotatable and always follow the reorientation of Fe magnetization that can be controlled by external magnetic field or via the temperature and thickness driven spin reorientation transition in Fe(110).

Interrelationships between nematicity, antiferromagnetic spin fluctuations, and superconductivity: Role of hotspots in FeSe1−xSx revealed by high pressure Se77 NMR study

The sulfur-substituted FeSe, FeSe$_{1-x}$S$_{x} $, is one of the unique systems that provides an independent tunability of nematicity, antiferromagnetism and superconductivity under pressure ($p$). Recently Rana et al. [Phys. Rev. B 101, 180503(R) (2020)] reported, from $^{77}$Se nuclear magnetic resonance (NMR) measurements on FeSe$_{0.91}$S$_{0.09}$ under pressure, that there exists a clear role of nematicity on the relationship between antiferromagnetic (AFM) spin fluctuations and superconducting transition temperature ($T_{\rm c}$) where the AFM spin fluctuations are more effective in enhancing $T_{\rm c}$ in the absence of nematicity than with nematicity. Motivated by the work, we carried out $^{77}$Se NMR measurements on FeSe$_{1-x}$S$_{x}$ with $x$= 0.15 and 0.29 under pressure up to 2.10 GPa to investigate the relationship in a wide range of $x$ in the FeSe$_{1-x}$S$_x$ system. Based on the new results together with the previously reported data for $x$=0 [P. Wiecki et al., Phys. Rev. B 96, 180502(R) (2017)] and 0.09 [K. Rana et al. Phys. Rev. B 101, 180503(R) (2020)], we established a $p$ - $x$ - temperature ($T$) phase diagram exhibiting the evolution of AFM spin fluctuations. From the systematic analysis of the NMR data, we found that the superconducting (SC) state in nematic state arises from a non Fermi liquid state with strong stripe-type AFM spin fluctuations while the SC state without nematicity comes from a Fermi liquid state with mild stripe-type AFM spin fluctuations. Furthermore, we show that the previously reported impact of nematicity on the relationship between AFM fluctuations and superconductivity holds throughout the wide range of $x$ from $x$ = 0 to 0.29 in FeSe$_{1-x}$S$_{x}$ under pressure. We discuss the origin of the role of nematicity in terms of the different numbers of hotspots on Fermi surfaces with and without nematicity.

The link between s and d components of electron boson coupling constants in one band d wave Eliashberg theory for high Tc superconductors

The phenomenology of overdoped high Tc uperconductors can be described by a one band d wave Eliashberg theory where the mechanism of superconducting coupling is mediated by antiferromagnetic spin fluctuations and whose characteristic energy Ω0 scales with Tc according to the empirical law Ω0 = 5.8 kBTc. This model presents universal characteristics that are independent of the critical temperature such as the link between the s and d components of electron boson coupling constants and the invariance of the ratio 2∆/kBTc. This situation arises from the particular structure of Eliashberg's equations which, despite being non-linear equations, present solutions with these simple properties.

Antiferromagnetic domain formation and spin frustration induced by adjacent paired screw dislocations in 10 monolayer-thick Cr(001) films

We investigated the growth and surface morphology of 10 monolayer (ML)-thick Cr(001) films on clean Au(001) surfaces. High quality epitaxial Cr(001) films with large atomically flat terraces and distinct surface states were successfully fabricated through growth at 300 K and subsequent post-annealing at 520 K. At 300 K, spin-polarized scanning tunneling microscopy images of both the topological and magnetic structures of this Cr film were obtained. The magnetic images exhibited the following features: (1) The layered antiferromagnetic (AF) order appeared in adjacent terraces and one ML-depth shallow hole in the terraces; (2) significant spin frustrations induced by adjacent paired screw dislocations caused the AF domain formation with 90 degrees quantum axis rotation and a large spin frustration area, not always limited in the vicinity of screw dislocations. The feature (2) was qualitatively reproduced by the micromagnetic simulation. These findings may be essential for the further development of spin-electronics utilizing thin AF films.

Electronic Structure and Properties of the Ground State of Fe–Pt Based Alloys

The properties of the ground state and the electronic structure of Fe2PtZ (Z = Ga, In, Ge, Si, Sn, Al) and FeRh1 – xPtx in the framework of the density functional theory implemented in the VASP software package alloys have been studied. Densities of electronic states for Fe2PtZ and FePt are obtained. It is shown that in Fe2PtIn and FePt high values of spin polarization are observed. It has been found that with increasing platinum concentration, the staggered antiferromagnetic spin configuration becomes unstable, and in the concentration range above 0.625, the antiferromagnetic configuration with layer-by-layer alternation of magnetic moment directions becomes advantageous. It was found that with a further increase in the platinum concentration, a ferromagnetic phase is observed.

Theoretical study on the magnetic properties of cathode materials in the lithium-ion battery.

The layered LiMO2 (M = Co, Ni, and Mn) materials are commonly used as the cathode materials in the lithium-ion battery due to the distinctive layer structure for lithium extraction and insertion. Although their electrochemical properties have been extensively studied, the structural and magnetic properties of LiNiO2 are still under considerable debate, and the magnetic properties of monoclinic LiMnO2 are seldom reported. In this work, a detailed study of LiNiO2, LiMnO2, and a half-doped material LiNi0.5Mn0.5O2 is performed via both first-principles calculations and Monte Carlo simulations based on the effective spin Hamiltonian model. Through considering different structures, it is verified that a structure with a zigzag-type pattern is the most stable one of LiNiO2. Moreover, in order to figure out the magnetic properties, the spin exchange interactions are calculated, and then magnetic ground states are predicted in these three systems. The results show that LiNiO2 forms a spiral order that is caused by the competition from both the short-range and long-range spin exchange interactions, whereas the magnetic ground state of LiMnO2 is collinearly antiferromagnetic due to its nearest and next-nearest neighbor antiferromagnetic spin exchange interactions. However, LiNi0.5Mn0.5O2 is collinearly ferrimagnetic because of the ferromagnetic nearest neighbor Ni-Ni and Mn-Mn exchange interactions. Our work demonstrates the competition between the different exchange interactions in these cathode materials, which may be relevant to the performance of the lithium-ion battery.

Theory of optical generation and detection of propagating magnons in an antiferromagnet

We report a theory of optical generation and detection of the propagating spin waves in antiferromagnetic materials relevant for ultrafast pump-probe experiments. We derive and solve the equations of motion for antiferromagnetic spins in response to the light-induced effective magnetic field in the linear regime. Different forms of the excitation and the properties of the generated spin waves are analyzed. We theoretically show the selective detection of the spin waves by the magneto-optical Kerr effect. The developed formalism is readily applicable to inform future experiments on antiferromagnetic optomagnonics.