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Among the 3d transition metal ions doped polar Ni3TeO6, Mn-doped Ni3TeO6 has stimulated great interest due to its high magnetic ordering temperature and complex magnetic phases, but the mechanism of magnetoelectric (ME) coupling is far from understood. Herein we report our systematic investigation of the chemical control of magnetism, metamagnetic transition, and ME properties of Ni3-xMnxTeO6 single crystals in high magnetic field (H) up to 52 T. We present a previously unreported weak ferromagnetic behavior appeared in the ab plane below 9.5 K in addition to the incommensurate helical and commensurate collinear antiferromagnetic states. In the low-field region, a spin-flop type metamagnetic transition without any hysteresis occurs at Hc1 for H // c, while another metamagnetic transition accompanied with a change in electric polarization is observed at Hc2 in the high-field region both for H // c and H // ab above 30 K, which can be attributed to the sudden rotation of magnetic moments at Ni2 sites. The ME measurements reveal that a first-order ME effect is observed in the low-T and low-H regions, while a second-order ME coupling term appears above 30 K in the magnetic field range of Hc1 < H < Hc2 for H // c and H < Hc2 for H // ab, both becoming significant with increasing temperature. Eventually, they are dominated by the second-order ME effect near the antiferromagnetic transition temperature. The present work demonstrates that Ni3-xMnxTeO6 is an exotic magnetoelectric material compared with Ni3TeO6 and its derivatives, thereby providing insights to better understand the magnetism and ME coupling in Ni3TeO6 and its derivatives., Comment: 30 pages with 8 figures

The van der Waals (vdW) layered multiferroics, which host simultaneous ferroelectric and magnetic orders, have attracted attention not only for their potentials to be utilized in nanoelectric devices and spintronics, but also offer alternative opportunities for emergent physical phenomena. To date, the vdW layered multiferroic materials are still very rare. In this work, we have investigated the magnetic structure and magnetoelectric effects in Co5(TeO3)4Cl2, a promising new multiferroic compound with antiferromagnetic (AFM) Neel point TN = 18 K. The neutron powder diffraction reveals the non-coplanar AFM state with preferred Neel vector along the c-axis, while a spin re-orientation occurring between 8 K and 15 K is identified, which results from the distinct temperature dependence of the non-equivalent Co sites moment in Co5(TeO3)4Cl2. What is more, it is found that Co5(TeO3)4Cl2 is one of the best vdW multiferroics studied so far in terms of the multiferroic performance. The measured linear ME coefficient exhibits the emergent oscillation dependence of the angle between magnetic field and electric field, and the maximal value is as big as 45 ps/m. It is suggested that Co5(TeO3)4Cl2 is an appreciated platform for exploring the emergent multiferroicity in vdW layered compounds., Comment: 31 pages, 9 figures

Magnon frequency comb provides opportunities for exploring magnon nonlinear effects and measuring the transmission magnon frequency in magnets, whose controllability becomes vital for modulating the operating frequency and improving the measurement accuracy. Nevertheless, such controllable frequency comb remains to be explored. In this work, we investigate theoretically and numerically the skyrmion-induced magnon frequency comb effect generated by interaction between the magnon excitation mode and skyrmion breathing mode in synthetic ferrimagnets. It is revealed that both the skyrmion breathing mode and the magnon frequency gap closely depend on the net angular momentum {\delta}s, emphasizing the pivotal role of {\delta}s as an effective control parameter in governing the comb teeth. With the increase of {\delta}s, the skyrmion size decreases, which results in the enlargement of the breathing frequency and the distance between the comb teeth. Moreover, the dependences of the magnon frequency gap on {\delta}s and the inter-layer coupling allow one to modulate the comb lowest coherent frequency via structural control. Consequently, the coherent modes generated by the comb may range from gigahertz to terahertz frequencies, serving as a bridge between microwave and terahertz waves. Thus, this work represents a substantial advance in understanding the magnon frequency comb effect in ferrimagnets., Comment: 27 pages, 8 figures

Sr2IrO4 hosts a novel Jeff =1/2 Mott state and quasi-two-dimensional antiferromagnetic order, providing a unique avenue of exploring emergent states of matter and functions that are extraordinarily sensitive to any structural variations. While the correlation between the physical property and lattice structure in Sr2IrO4 has been a focused issue in the past decade, a common perception assumes that the magnetic ordering is essentially determined by the Ir-O-Ir bond angle. Therefore, a delicate modulation of this angle and consequently a major modulation of the magnetic ordering, by chemical doping such as Ga at Ir site, has been extensively investigated and well believed. In this work, however, we present a whole package of structure and magnetism data on a series of single crystal and polycrystalline Sr2Ir1-xGaxO4 samples, revealing the substantial difference in the N\'eel temperature TN between the two types of samples, and the TN value for the polycrystalline sample x = 0.09 is even 64 K higher than that of the single crystal sample x = 0.09 (deltaTN ~ 64 K at x = 0.09). Our systematic investigations demonstrate the crucial role of the c/a ratio in tuning the interlayer coupling and thereby the Neel point TN, i.e. a higher TN can be achieved as c/a is reduced. The notable differences in structural parameters between the two groups of samples are probably caused by additional strain due to the massive grain boundaries in polycrystalline samples. The present work suggests an additional ingredient of physics that is essential in modulating the emergent properties in Sr2IrO4 and probably other iridates.

Optical vortex, a light beam carrying orbital angular momentum (OAM) has been realized in experiments, and its interactions with magnets show abundant physical characteristics and great application potentials. In this work, we propose that optical vortex can control skyrmion ultrafast in antiferromagnets using numerical and analytical methods. Isolated skyrmion can be generated/erased in a very short time ~ps by beam focusing. Subsequently, the OAM is transferred to the skyrmion and results in its rotation motion. Different from the case of ferromagnets, the rotation direction can be modulated through tuning the light frequency in antiferromagnets, allowing one to control the rotation easily. Furthermore, the skyrmion Hall motion driven by multipolar spin waves excited by optical vortex is revealed numerically, demonstrating the dependence of the Hall angle on the OAM quantum number. This work unveils the interesting optical-controlled skyrmion dynamics in antiferromagnets, which is a crucial step towards the development of optics and spintronics., Comment: 19 pages, 6 figures

Magnetic skyrmions are magnetic textures with topological protection, which are expected to be information carriers in future spintronic devices. In this work, we propose a scheme to implement hybrid magnetic skyrmions (HMS) in ferrimagnets, and we study theoretically and numerically the dynamics of the HMS driven by spin-orbit torque. It is revealed that the skyrmion Hall effect depends on the skyrmion helicity and the net angular momentum ({\delta}s), allowing the effective modulation of the HMS motion through tuning Dzyaloshinskii-Moriya interaction and {\delta}s. Thus, the Hall effect can be suppressed through selecting suitable materials to better control the HMS motion. Moreover, Magnus force for finite {\delta}s suppresses the transverse motion and enhances the longitudinal propagation, resulting in the HMS dynamics in ferrimagnets faster than that in antiferromagnets., Comment: 25 pages, 6figures

Excitation and propagation of spin waves inside magnetic domain walls has received attention because of their potentials in spintronic and communication applications. Besides wave amplitude and frequency, spin-wave has its third character: handedness, whose manipulation is certainly of interest. We propose in this Letter that the handedness of low energy spin-wave excitations can be controlled by tuning the net angular momentum {\delta}s in a ferrimagnetic (FiM) domain wall, attributing to the inequivalent magnetic sublattices. The results indicate that the spin-wave dispersion depends on both {\delta}s and wave handedness. For a positive (negative) {\delta}s, a gapless dispersion is observed for the left-handed (righ-handed) spin waves, while a frequency gap appears for the right-handed (left-handed) spin waves. Thus a FiM wall could serve as a multifold filter of low energy spin-wave in which only spin waves with particular handedness can propagate. Furthermore, the energy consumption loss for spin-wave excitation in the wall is much lower than that inside the domain, while the group velocity is much faster too, demonstrating the advantages of domain walls serving as spin waveguides. Moreover, the current-induced spin-wave Doppler shift in the FiM wall is also revealed, and can be controlled by {\delta}s. This work unveils for the first time the interesting spin-wave dynamics in FiM domain walls, benefiting future spin-wave applications., Comment: Page 17, 5 figures

Searching for low-power-consuming and high-efficient methods for well controllable driving of skyrmion motion is one of the most concerned issues for future spintronic applications, raising high concern with an appreciated choice of magnetic media and driving scenario. In this work, we propose a novel scenario of spin wave driven skyrmion motion in a ferrimagnetic (FiM) lattice with the net angular momentum {\delta}s. We investigate theoretically the effect of both {\delta}s and the circular polarization of spin wave on the skyrmion dynamics. It is revealed that the momentum onto the skyrmion imposed by the excited spin wave can be partitioned into a ferromagnetic term plus an antiferromagnetic term. The ratio of these two terms and consequently the Hall angle of skyrmion motion can be formulated as the functions of {\delta}s, demonstrating the key role of {\delta}s as an effective control-parameter for the skyrmion motion. Moreover, the spin wave frequency dependent skyrmion motion is discussed, predicting the frequency enhanced skyrmion Hall motion. This work thus represents an essential contribution to understand the skyrmion dynamics in a FiM lattice., Comment: 25 pages, 4 figures

A theoretical study on the interplay of frustrated skyrmion and magnons is useful for revealing new physics and future experiments design. In this work, we investigated the magnon-driven dynamics of frustrated skyrmion in synthetic antiferromagnets, focusing on the effect of skyrmion precession. It is theoretically revealed that the scattering cross section of the injected magnons depends on the skyrmion precession, which in turn effectively modulates the skyrmion Hall motion. Specifically, the Hall angle decreases as the precession speed increases, which is also verified by the atomistic micromagnetic simulations. Moreover, the precession speed and the Hall angle of the frustrated skyrmion depending on the magnon intensity and damping constant are simulated, demonstrating the effective suppression of the Hall motion by the skyrmion precession. This work provides a comprehensive understanding of the magnon-skyrmion scattering in frustrated magnets, benefiting future spintronic and magnonic applications., Comment: 18 pages, 5 figures

The explosive growth of artificial intelligence and data-intensive computing has brought crucial challenge to modern information science and technology, i.e. conceptually new devices with superior properties are urgently desired. Memristor is recognized as a very promising circuit element to tackle the barriers, because of its fascinating advantages in imitating neural network of human brain, and thus realizing in-memory computing. However, there exist two core and fundamental issues: energy efficiency and accuracy, owing to the electric current operation of traditional memristors. In the present work, we demonstrate a new type of memristor, i.e. charge q and magnetic flux {\phi} space memristor, enabled by linear magnetoelectricity of Co4Nb2O9. The memory states show distinctly linear magnetoelectric coefficients with a large ratio of about 10, ensuing exceptional accuracy of related devices. The present q-{\phi} type memristor can be manipulated by magnetic and electric fields without involving electric current, paving the way to develop ultralow-energy-consuming devices. In the meanwhile, it is worth to mention that Co4Nb2O9 hosts an intrinsic compensated antiferromagnetic structure, which suggests interesting possibility of further integrating the unique merits of antiferromagnetic spintronics such as ultrahigh density and ultrafast switching. Linear magnetoelectricity is proposed to essential to the q-{\phi} type memristor, which would be accessible in a broad class of multiferroics and other magnetoelectric materials such as topological insulators. Our findings could therefore advance memristors towards new levels of functionality., Comment: 4 figures

Hexagonal rare-earth ferrite RFeO$_3$ family represents a unique class of multiferroics exhibiting weak ferromagnetism, and a strong coupling between magnetism and structural trimerization is predicted. However, the hexagonal structure for RFeO$_3$ remains metastable in conventional condition. We have succeeded in stabilizing the hexagonal structure of polycrystalline YbFeO$_3$ by partial Sc substitution of Yb. Using bulk magnetometry and neutron diffraction, we find that Yb$_{0.42}$Sc$_{0.58}$FeO$_3$ orders into a canted antiferromagnetic state with the Neel temperature $T_N$ ~ 165 K, below which the $Fe^{3+}$ moments form the triangular configuration in the $ab$-plane and their in-plane projections are parallel to the [100] axis, consistent with magnetic space group $P$6$_{3}$$c'm'$. It is determined that the spin-canting is aligned along the $c$-axis, giving rise to the weak ferromagnetism. Furthermore, the $Fe^{3+}$ moments reorient toward a new direction below reorientation temperature $T_R$ ~ 40 K, satisfying magnetic subgroup $P$6$_{3}$, while the $Yb^{3+}$ moments order independently and ferrimagnetically along the $c$-axis at the characteristic temperature $T_{Yb}$ ~ 15 K. Interestingly, reproducible modulation of electric polarization induced by magnetic field at low temperature is achieved, suggesting that the delicate structural distortion associated with two-up/one-down buckling of the Yb/Sc-planes and tilting of the FeO$_5$ bipyramids may mediate the coupling between ferroelectric and magnetic orders under magnetic field. The present work represents a substantial progress to search for high-temperature multiferroics in hexagonal ferrites and related materials.

The controllable magnetic skyrmion motion represents a highly concerned issue in preparing advanced skyrmion-based spintronic devices. Specifically, magnon-driven skyrmion motion can be easily accessible in both metallic and insulating magnets, and thus is highly preferred over electric current control further for the ultra-low energy consumption. In this work, we investigate extensively the dynamics of skyrmion motion driven by magnon in an antiferromagnet using the collective coordinate theory, focusing on the effect of magnon polarization. It is revealed that the skyrmion Hall motion driven by circularly polarized magnon becomes inevitable generally, consistent with earlier report. Furthermore, the elastic scattering theory and numerical results unveil the strong inter-dependence between the linearly polarized magnon and skyrmion motion, suggesting the complicated dependence of the skyrmion motion on the polarization nature of driving magnon. On the reversal, the scattering from the moving skyrmion may lead to decomposition of the linearly polarized magnon into two elliptically polarized magnon bands. Consequently, a net transverse force acting on skyrmion is generated owing to the broken mirror symmetry, which in turn drives a skyrmion Hall motion. The Hall motion can be completely suppressed only in some specific condition where the mirror symmetry is preserved. The present work unveils non-trivial skyrmion-magnon scattering behavior in antiferromagnets, advancing the antiferromagnetic spintronics and benefiting to high-performance devices., Comment: 22 pages,7 figures

A theoretical study on the dynamics of an antiferromagnetic (AFM) skyrmion is indispensable for revealing the underlying physics and understanding the numerical and experimental observations. In this work, we present a reliable theoretical treatment of the spin current induced motion of an AFM skyrmion in the absence and presence of pinning defect. For an ideal AFM system free of defect, the skyrmion motion velocity as a function of the intrinsic parameters can be derived, based on the concept that the skyrmion profile agrees well with the 360 domain wall formula, leading to an explicit description of the skyrmion dynamics. However, for an AFM lattice containing a defect, the skyrmion can be pinned and the depinning field as a function of damping constant and pinning strength can be described by the Thiele approach. It is revealed that the depinning behavior can be remarkably influenced by the time dependent oscillation of the skyrmion trajectory. The present theory provides a comprehensive scenario for manipulating the dynamics of AFM skyrmion, informative for future spintronic applications based on antiferromagnets., Comment: 17 pages, 4 figures, to be published in Physical Review B

LiOsO3 is the first experimentally confirmed polar metal. Previous works suggested that the ground state of LiOsO$_3$ is just close to the critical point of metal-insulator transition. In this work the electronic state of LiOsO$_3$ is tuned by epitaxial biaxial strain, which undergoes the Slater-type metal-insulator transition under tensile strain, i.e., the G-type antiferromagnetism emerges. The underlying mechanism of bandwidth tuning can be extended to its sister compound NaOsO$_3$, which shows an opposite transition from a antiferromagnetic insulator to a nonmagnetic metal under hydrostatic pressure. Our work suggests a feasible route for the manipulation of magnetism and conductivity of polar metal LiOsO$_3$., Comment: 10 pages, 4 figures

The ultrafast magnetic dynamics in compensated ferrimagnets not only provides information similar to antiferromagnetic dynamics, but more importantly opens new opportunities for future spintronic devices [Kim et al., Nat. Mater. 16, 1187 (2017)]. One of the most essential issues for device design is searching for low-power-consuming and high-efficient methods of controlling domain wall. In this work, we propose to use the voltage-controlled magnetic anisotropy gradient as an excitation source to drive the domain wall motion in ferrimagnets. The ultrafast wall motion under the anisotropy gradient is predicted theoretically based on the collective coordinate theory, which is confirmed by the atomistic micromagnetic simulations. The antiferromagnetic spin dynamics is realized at the angular momentum compensation point, and the wall shifting has a constant speed under small gradient and can be slightly accelerated under large gradient due to the broadened wall width during the motion. For nonzero net angular momentum, the Walker breakdown occurs at a critical anisotropy gradient significantly depending on the second anisotropy and interfacial Dzyaloshinkii-Moriya interaction, which is highly appreciated for further experiments including the materials selection and device geometry design. More importantly, this work unveils a low-power-consuming method of controlling the domain wall in ferrimagnets, benefiting to future spintronic applications., Comment: 20 pages, 5 figures

The radial velocity (RV) is a basic physical quantity which can be determined through Doppler shift of the spectrum of a star. The precision of RV measurement depends on the resolution of the spectrum we used and the accuracy of wavelength calibration. In this work, radial velocities of LAMOST-II medium resolution (R ~ 7500) spectra are measured for 1,594,956 spectra (each spectrum has two wavebands) through matching with templates. A set of RV standard stars are used to recalibrate the zero point of the measurement, and some reference sets with RVs derived from medium/high-resolution observations are used to evaluate the accuracy of the measurement. Comparing with reference sets, the accuracy of our measurement can get 0.0227 km s/1 with respect to radial velocities standard stars. The intrinsic precision is estimated with the multiple observations of single stars, which can achieve to 1.36 km s/1,1.08 km s/1, 0.91 km s/1 for the spectra at signal-to-noise levels of 10, 20, 50, respectively., Comment: published by ApJs. 13 pages, 13 figures

Experimental results have shown that the quaternary compound Cu2ZnSnSe4 is an excellent thermoelectric material. This inspires us to seek the other quaternary compounds with similar chemical formula to Cu2ZnSnSe4 as thermoelectric materials. In this paper, we use the first-principle method to systematically explore the electronic and phonon structures, mechanical, thermal and thermoelectric properties of p- and n-type Ag2XYSe4 (X=Ba, Sr; Y=Sn, Ge). It is found that the ZT maximum for n-type Ag2SrGeSe4 can reach up to 1.22 at 900 K, and those for p-type Ag2SrSnSe4, Ag2SrGeSe4 and Ag2BaSnSe4 can reach up to 1.20, 1.13 and 1.12, respectively. Our work not only shows that Ag2XYSe4 (X=Ba, Sr; Y=Sn, Ge) are a kind of potential thermoelectric materials, but also can inspire more theoretical and experimental researches on thermoelectric properties of quaternary compounds.

Searching for new methods controlling antiferromagnetic (AFM) domain wall is one of the most important issues for AFM spintronic device operation. In this work, we study theoretically the domain wall motion of an AFM nanowire, driven by the axial anisotropy gradient generated by external electric field, allowing the electro control of AFM domain wall motion in the merit of ultra-low energy loss. The domain wall velocity depending on the anisotropy gradient magnitude and intrinsic material properties is simulated based on the Landau-Lifshitz-Gilbert equation and also deduced using the energy dissipation theorem. It is found that the domain wall moves at a nearly constant velocity for small gradient, and accelerates for large gradient due to the enlarged domain wall width. The domain wall mobility is independent of lattice dimension and types of domain wall, while it is enhanced by the Dzyaloshinskii-Moriya interaction. In addition, the physical mechanism for much faster AFM wall dynamics than ferromagnetic wall dynamics is qualitatively explained. This work unveils a promising strategy for controlling the AFM domain walls, benefiting to future AFM spintronic applications., Comment: 17 pages, 5 figures

The pinning and depinning of antiferromagnetic (AFM) domain wall is certainly the core issue of AFM spintronics. In this work, we study theoretically the N\'eel-type domain wall pinning and depinning at a notch in an antiferromagnetic (AFM) nano-ribbon. The depinning field depending on the notch dimension and intrinsic physical parameters are deduced and also numerically calculated. Contrary to conventional conception, it is revealed that the depinning field is remarkably dependent of the damping constant and the time-dependent oscillation of the domain wall position in the weakly damping regime benefits to the wall depinning, resulting in a gradual increase of the depinning field up to a saturation value with increasing damping constant. A one-dimensional model accounting of the internal dynamics of domain wall is used to explain perfectly the simulated results. It is demonstrated that the depinning mechanism of an AFM domain wall differs from ferromagnetic domain wall by exhibiting a depinning speed typically three orders of magnitude faster than the latter, suggesting the ultrafast dynamics of an AFM system., Comment: 18 pages, 3 figures

In this work, we derive the Landau-Lifshitz-Bloch equation accounting for the multi-domain antiferromagnetic (AFM) lattice at finite temperature, in order to investigate the domain wall (DW) motion, the core issue for AFM spintronics. The continuity equation of the staggered magnetization is obtained using the continuum approximation, allowing an analytical calculation on the domain wall dynamics. The influence of temperature on the static domain wall profile is investigated, and the analytical calculations reproduce well earlier numerical results on temperature gradient driven saturation velocity of the AFM domain wall, confirming the validity of this theory. Moreover, it is worth noting that this theory could be also applied to dynamics of various wall motions in an AFM system. The present theory represents a comprehensive approach to the domain wall dynamics in AFM materials, a crucial step toward the development of AFM spintronics., Comment: 25 pages, 4 figures

LiOsO$_3$ is the first experimentally confirmed polar metal with ferroelectric-like distortion. One puzzling experimental fact is its paramagnetic state down to very low temperature with negligible magnetic moment, which is anomalous considering its $5d^3$ electron configuration since other osmium oxides (e.g. NaOsO$_3$) with $5d^3$ Os ions are magnetic. Here the magnetic and electronic properties of LiOsO$_3$ are re-investigated carefully using the first-principles density functional theory. Our calculations reveal that the magnetic state of LiOsO$_3$ can be completely suppressed by the spin-orbit coupling. The subtle balance between significant spin-orbit coupling and weak Hubbard $U$ of $5d$ electrons can explain both the nonmagnetic LiOsO$_3$ and magnetic NaOsO$_3$. Our work provides a reasonable understanding of the long-standing puzzle of magnetism in some osmium oxides., Comment: 10 pages, 7 figures

Ca$_3$Ti$_2$O$_7$ is an experimentally confirmed hybrid improper ferroelectric material, in which the electric polarization is induced by a combination of the coherent TiO$_6$ octahedral rotation and tilting. In this work, we investigate the tuning of ferroelectricity of Ca$_3$Ti$_2$O$_7$ using iso-valent substitutions on Ca-sites. Due to the size mismatch, larger/smaller alkaline earths prefer $A$'/$A$ sites respectively, allowing the possibility for site-selective substitutions. Without extra carriers, such site-selected iso-valent substitutions can significantly tune the TiO$_6$ octahedral rotation and tilting, and thus change the structure and polarization. Using the first-principles calculations, our study reveals that three substituted cases (Sr, Mg, Sr+Mg) show divergent physical behaviors. In particular, (CaTiO$_3$)$_2$SrO becomes non-polar, which can reasonably explain the suppression of polarization upon Sr substitution observed in experiment. In contrast, the polarization in (MgTiO$_3$)$_2$CaO is almost doubled upon substitutions, while the estimated coercivity for ferroelectric switching does not change. The (MgTiO$_3$)$_2$SrO remains polar but its structural space group changes, with moderate increased polarization and possible different ferroelectric switching paths. Our study reveals the subtle ferroelectricity in the $A_3$Ti$_2$O$_7$ family and suggests one more practical route to tune hybrid improper ferroelectricity, in addition to the strain effect.

In this work, we study the microscopic dynamics of distorted skyrmions in strained chiral magnets [K. Shibata et al., Nat. Nanotech. 10, 589 (2015)] under gradient magnetic field or electric current by Landau-Lifshitz-Gilbert simulations of the anisotropic spin model. It is observed that the dynamical responses are also anisotropic, and the velocities of the distorted skyrmions are periodically dependent on the directions of the external stimuli. Furthermore, in addition to the uniform motion, our work also demonstrates anti-phase harmonic vibrations of the two skyrmions in nanostripes, and the frequencies are mainly determined by the exchange anisotropy. The simulated results are well explained by Thiele theory, which may provide useful information in understanding the dynamics of the distorted skyrmions in strained chiral magnets., Comment: 17 pages, 5 figures

In this work, we study the microwave field driven antiferromagnetic domain wall motion in an antiferromagnetic nanowire, using the numerical calculations based on a classical Heisenberg spin model. We show that a proper combination of a static magnetic field plus an oscillating field perpendicular to the nanowire axis is sufficient to drive the domain wall propagation along the nanowire with the axial magnetic anisotropy. More importantly, the drift velocity at the resonance frequency is comparable to that induced by temperature gradients, suggesting that microwave field can be a very promising tool to control domain wall motions in antiferromagnetic nanostructures. Furthermore, the dependences of resonance frequency and drift velocity on the static and oscillating fields, the axial anisotropy, and the damping constant are discussed in details. This work provides useful information for the spin dynamics in antiferromagnetic nanostructures for spintronics applications., Comment: 16 pages, 5 figures

The study of skyrmion/antiskyrmion motion in magnetic materials is very important in particular for the spintronics applications. In this work, we study the dynamics of isolated skyrmions and antiskyrmions in frustrated magnets driven by magnetic field gradient, using the Landau-Lifshitz-Gilbert simulations on the frustrated classical Heisenberg model on the triangular lattice. A Hall-like motion induced by the gradient is revealed in bulk system, similar to that in the well-studied chiral magnets. More interestingly, our work suggests that the lateral confinement in nano-stripes of the frustrated system can completely suppress the Hall motion and significantly speed up the motion along the gradient direction. The simulated results are well explained by the Thiele theory. It is demonstrated that the acceleration of the motion is mainly determined by the Gilbert damping constant, which provides useful information for finding potential materials for skyrmion-based spintronics., Comment: 15 pages, 4 figures

In this work, we study the magnetic orders of the classical spin model with the anisotropic exchange and Dzyaloshinskii-Moriya interactions in order to understand the uniaxial stress effect in chiral magnets such as MnSi. Variational zero temperature (T) calculated results demonstrate that various helical orders can be developed depending on the magnitude of the interaction anisotropy, consistent with the experimental observations at low T. Furthermore, the creation and annihilation of the skyrmions by the uniaxial pressure can be also qualitatively reproduced in our Monte Carlo simulations. Thus, our work suggests that the interaction anisotropy tuned by applied uniaxial stress may play an essential role in modulating the magnetic orders in strained chiral magnets., Comment: 21 pages, 5 figures, to be published in Scientific Reports

We study the thermal phase transitions of the four-fold degenerate phases (the plaquette and single stripe states) in two-dimensional frustrated Ising model on the Shastry-Sutherland lattice using Monte Carlo simulations. The critical Ashkin-Teller-like behavior is identified both in the parameter regions with the plaquette and single stripe phases, respectively. The four-state Potts-critical end points differentiating the continuous transitions from the first-order ones are estimated based on finite-size scaling analyses. Furthermore, similar behavior of the transition to the four-fold single stripe phase is also observed in the anisotropic triangular Ising model. Thus, this work clearly demonstrates that the transitions to the four-fold degenerate states of two-dimensional Ising antiferromagnets exhibit similar transition behavior., Comment: To be published in Physical Review E

We present a comprehensive study of the magnetic properties of the long-range ordered quasi-one dimensional $J_{1}$-$J_{2}$ systems with a newly developed torque equilibrium spin-wave expansion approach, which can describe the spin Casimir and magnon decay effects in a unified framework. While the framework does not lose the generality, our discussion will be restricted to two representative types of inter-chain coupling systems: $J_{3}$- or $J_{4}$-system respectively. In spite of the long-range spiral order, the dynamical properties of these systems turn out to be highly nontrivial due to the incommensurate noncollinear spin configuration and the strong quantum fluctuation effects enhanced by the frustration and low-dimensionality. Both the systems show prominent spin Casimir effects induced by the vacuum fluctuation of the spin waves and related modification of the ordering vector, Lifshitz point's position and sublattice magnetization. Significant and spontaneous magnon decay effects are manifested in the quantum corrections to the excitation spectrum. By adjusting the strength of magnetic anisotropy and varying the approximation scheme, it is revealed that these striking distinct features are quite robust and have deep connection with both the spin Casimir and the magnon decay effects. Thus these special consequences of the inter-chain coupling on the spin wave dynamics may be served as a set of probes for different types of inter-chain couplings in experiments. At last, to guide experimental measurements such as inelastic neutron scattering in realistic materials and complement our theoretical framework, we develop the analytical theory of the dynamical structure factor within the torque equilibrium formulism and provide the explicit results of the quasi-one dimensional $J_{1}$-$J_{2}$ systems.

In this work, we study the doping effects on the magnetic states of CuCrO2 based on the classical frustrated spin model [Lin et al., Phys. Rev. B 89, 220405(R) (2014)]. Several experimental observations can be well reproduced by the Monte Carlo simulations of the modified spin models. Our work suggests that the disorder induced by V/Al doping cooperated with the frustration in the system may contribute to the emergence of the spin glass state. Furthermore, the hole-doping by Mg2+ substituting Cr3+ enhances the quantum fluctuations and bond disorder which modulate the biquadratic exchanges, and in turn results in the promotion of the spiral phase, consistent with the experimental report., Comment: 19 pages, 7 figures, to be published in Physical Review B

In this work, we study the magnetization behaviors of the classical Ising model on the triangular lattice using Monte Carlo simulations, and pay particular attention to the effect of further-neighbor interactions. Several fascinating spin states are identified to be stabilized in certain magnetic field regions, respectively, resulting in the magnetization plateaus at 2/3, 5/7, 7/9 and 5/6 of the saturation magnetization MS, in addition to the well known plateaus at 0, 1/3 and 1/2 of MS. The stabilization of these interesting orders can be understood as the consequence of the competition between Zeeman energy and exchange energy., Comment: 17 pages, 5 figures, to be published in Journal of Physics: Condensed Matter

In this work, we study a biquadratic Heisenberg model with coupled orbital degree of freedom using Monte Carlo simulation in order to investigate the phase transitions in iron-based superconductors. The antiferro-quadrupolar state, which may be related to the magnetism of FeSe [Phys. Rev. Lett. 115, 116401 (2015)], is stabilized by the anisotropic biquadratic interaction induced by a ferro-orbital-ordered state. It is revealed that the orbital and nematic transitions occur at the same temperature for all the cases, supporting the mechanism of the orbital-driven nematicity as revealed in most recent experiments [Nat. Mater. 14, 210 (2015)]. In addition, it is suggested that the orbital interaction may lead to the separation of the structural and magnetic phase transitions as observed in many families of iron pnictides., Comment: 20 pages, 7 figures, to be published in Physical Review B

In this work, we investigate the phase transitions and critical behaviors of the frustrated J1-J2-J3 Ising model on the square lattice using Monte Carlo simulations, and particular attention goes to the effect of the second next nearest neighbor interaction J3 on the phase transition from a disordered state to the single stripe antiferromagnetic state. A continuous Ashkin-Teller-like transition behavior in a certain range of J3 is identified, while the 4-state Potts-critical end point [J3/J1]C is estimated based on the analytic method reported in earlier work [Jin et al., Phys. Rev. Lett. 108, 045702 (2012)]. It is suggested that the interaction J3 can tune the transition temperature and in turn modulate the critical behaviors of the frustrated model. Furthermore, it is revealed that an antiferromagnetic J3 can stabilize the staggered dimer state via a phase transition of strong first-order character., Comment: 20 pages, 10 figures. To be published in Physical Review E

Hexagonal LuFeO$_3$ has drawn a lot of research attention due to its contentious room-temperature multiferroicity. Due to the unstability of hexagonal phase in the bulk form, most experimental studies focused on LuFeO$_3$ thin films which can be stabilized by strain using proper substrates. Here we report on the hexagonal phase stabilization, magnetism, and magnetoelectric coupling of bulk LuFeO$_3$ by partial Sc-substitution of Lu. First, our first-principles calculations show that the hexagonal structure can be stabilized by partial Sc substitution, while the multiferroic properties including the noncollinear magnetic order and geometric ferroelectricity remain robustly unaffected. Therefore, Lu$_{1-x}$Sc$_x$FeO$_3$ can act as a platform to check the multiferroicity of LuFeO$_3$ and related materials in the bulk form. Second, the magnetic characterizations on bulk Lu$_{1-x}$Sc$_x$FeO$_3$ demonstrate a magnetic anomaly (probable antiferromagnetic ordering) above room temperature, $\sim425-445$ K, followed by magnetic transitions in low temperatures ($\sim167-172$ K). In addition, a magnetoelectric response is observed in the low temperature region. Our study provides useful information on the multiferroic physics of hexagonal $R$FeO$_3$ and related systems., Comment: 21 pages, 8 figures

The intrinsic noncollinear spin patterns in rare-earth pyrochlore are physically interesting, hosting many emergent properties, e.g. spin ice and monopole-type excitation. Recently, the magnetic monopole excitation of spin ice systems was predicted to be magnetoelectric active, while rare experimental works have directly confirmed this scenario. In this work, we performed systematic experimental investigation on the magnetoelectricity of Dy$_2$Ti$_2$O$_7$ by probing the ferroelectricity, spin dynamics, and dielectric behaviors. Two ferroelectric transitions at $T_{c1}$=25 K and $T_{c2}$=13 K have been observed. Remarkable magnetoelectric coupling is identified below the lower transition temperature, with a significant suppression of the electric polarization upon applied magnetic field. It is surprised that the lower ferroelectric transition temperature just coincides with the Ising-spin paramagnetic transition point, below which the quasi-particle-like monopoles are populated, indicating implicit correlation between electric dipoles and spin moments. The possible magnetoelectric mechanisms have also been discussed although a decent theory remains unavailable up to date. Our results will stimulate more investigations to explore multiferroicity in these spin ice systems and other frustrated magnets., Comment: 25 pages, 10 figures

The copper silver selenide has two phases: the low-temperature semimetal phase ({\alpha}-CuAgSe) and high-temperature phonon-glass superionic phase (\b{eta}-CuAgSe). In this work, the electric transport and thermoelectric properties of the two phases are investigated. It is revealed that the \b{eta}-CuAgSe is a p-type semiconductor and exhibits low thermal conductivity while the {\alpha}-CuAgSe shows metallic conduction with dominant n-type carriers and low electrical resistivity. The thermoelectric figure of merit zT of the polycrystalline \b{eta}-CuAgSe at 623 K is ~0.95, suggesting that superionic CuAgSe can be a promising thermoelectric candidate in the intermediate temperature range., Comment: 14 pages, 6 figures

Double-perovskite A2BB'O6 oxides with magnetic B and B' ions and E*-type antiferromagnetic order (E*-AFM, i.e. the ++-- structure) are believed to exhibit promising multiferroic properties, and Y2CoMnO6 (YCMO) is one candidate in this category. However, the microscopic origins for magnetically induced ferroelectricity in YCMO remain unclear. In this work, we perform detailed symmetry analysis on the exchange striction effect and lattice distortion, plus the first-principles calculations on YCMO. The E*-AFM state as the ground state with other competing states such as ferromagnetic and A-antiferromagnetic orders is confirmed. It is revealed that the ferroelectricity is generated by the exchange striction associated with the E*-AFM order and chemically rdered Mn/Co occupation. Both the lattice symmetry consideration and first-principles calculations predict that the electric polarization aligns along the b-axis. The calculated polarization reaches up to 0.4682 uC/cm2, mainly from the ionic displacement contribution. The present work presents a comprehensive understanding of the multiferroic mechanisms in YCMO and is of general significance for predicting emergent multiferroicity in other double-perovskite magnetic oxides., Comment: 9 pages,8 figures, 2 tables