Pressure-induced magnetic phase and structural transition in SmSb_(2)

Motivated by the recent discovery of unconventional superconductivity around a magnetic quantum critical point in pressurized CeSb_(2),here we present a high-pressure study of an isostructural antiferromagnetic(AFM) SmSb_(2) through electrical transport and synchrotron x-ray diffraction measurements.At P_(C)~2.5 GPa,we found a pressure-induced magnetic phase transition accompanied by a Cmca→P4/nmm structural phase transition.In the pristine AFM phase below P_(C),the AFM transition temperature of SmSb_(2) is insensitive to pressure;in the emergent magnetic phase above P_(C),however,the magnetic critical temperature increases rapidly with increasing pressure.In addition,at ambient pressure,the magnetoresistivity(MR) of SmSb_(2) increases suddenly upon cooling below the AFM transition temperature and presents linear nonsaturating behavior under high field at 2 K.With increasing pressure above P_(C),the MR behavior remains similar to that observed at ambient pressure,both in terms of temperature-and field-dependent MR.This leads us to argue an AFM-like state for SmSb_(2) above P_(C).Within the investigated pressure of up to 45.3 GPa and the temperature of down to 1.8 K,we found no signature of superconductivity in SmSb_(2).

Negative magnetoresistance in the antiferromagnetic semimetal V_(1/3)TaS_(2)

Intercalated transition metal dichalcogenides(TMDCs)attract much attention due to their rich properties and potential applications.In this article,we grew successfully high-quality V_(1/3)TaS_(2) crystals by a vapor transport method.We measured the magnetization,longitudinal resistivityρxx(T,H),Hall resistivityρxy(T,H),as well as performed calculations of the electronic band structure.It was found that V_(1/3)TaS_(2) is an A-type antiferromagnet with the Neel temperature T_(N)=6.20 K,and exhibits a negative magnetoresistance(MR)near T_(N).Both band structure calculations and Hall resistivity measurements demonstrated it is a magnetic semimetal.

Spin gap in quasi-one-dimensional S=3/2 antiferromagnet CoTi2O5

Quasi-one-dimensional(1D)antiferromagnets are known to display intriguing phenomena especially when there is a spin gap in their spin-excitation spectra.Here we demonstrate that a spin gap exists in the quasi-1D Heisenberg antiferromagnet CoTi2O5 with highly ordered Co2+/Ti4+occupation,in which the Co2+ions with S=3/2 form a 1D spin chain along the a-axis.CoTi2O5 undergoes an antiferromagnetic transition at TN~24 K and exhibits obvious anisotropic magnetic susceptibility even in the paramagnetic region.Although a gapless magnetic ground state is usually expected in a quasi-1D Heisenberg antiferromagnet with half-integer spins,by analyzing the specific heat,the thermal conductivity,and the spin-lattice relaxation rate(1/T1)as a function of temperature,we found that a spin gap is opened in the spin-excitation spectrum of CoTi2O5 around TN,manifested by the rapid decrease of magnetic specific heat to zero,the double-peak characteristic in thermal conductivity,and the exponential decay of 1/T1 below TN.Both the magnetic measurements and the first-principles calculations results indicate that there is spin-orbit coupling in CoTi2O5,which induces the magnetic anisotropy in CoTi2O5,and then opens the spin gap at low temperature.

Coexistence of antiferromagnetism and unconventional superconductivity in a quasi-one-dimensional flat-band system:Creutz lattice

We study the coexistence of antiferromagnetism and unconventional superconductivity on the Creutz lattice which shows strictly flat bands in the noninteracting regime.The famous renormalized mean-field theory is used to deal with strong electron-electron repulsive Hubbard interaction in the effective low-energy t-J model,the superfluid weight of the unconventional superconducting state has been calculated via the linear response theory.An unconventional superconducting state with both spin-singlet and staggered spin-triplet pairs emerges beyond a critical antiferromagnetic coupling interaction,while antiferromagnetism accompanies this state.The superconducting state with only spin-singlet pairs is dominant with paramagnetic phase.The A phase is analogous to the pseudogap phase,which shows that electrons go to form pairs but do not cause a supercurrent.We also show the superfluid behavior of the unconventional superconducting state and its critical temperature.It is proven directly that the flat band can effectively raise the critical temperature of superconductivity.It is implementable to simulate and control strongly-correlated electrons'behavior on the Creutz lattice in the ultracold atoms experiment or other artificial structures.Our results may help the understanding of the interplay between unconventional superconductivity and magnetism.

In-phase and out-of-phase spin pumping effects in Py/Ru/Pysynthetic antiferromagnetic structures

The spin pumping effect in magnetic heterostructures and multilayers is a highly effective method for the generationand transmission of spin currents. In the increasingly prominent synthetic antiferromagnetic structures, the two ferromagneticlayers demonstrate in-phase and out-of-phase states, corresponding to acoustic and optical precession modes. Withinthis context, our study explores the spin pumping effect in Py/Ru/Py synthetic antiferromagnetic structures across differentmodes. The heightened magnetic damping resulting from the spin pumping effect in the in-phase state initially decreaseswith increasing Py thickness before stabilizing. Conversely, in the out-of-phase state, the amplified damping exceeds thatof the in-phase state, suggesting a greater spin relaxation within this configuration, which demonstrates sensitivity to alterationsin static exchange interactions. These findings contribute to advancing the application of synthetic antiferromagneticstructures in magnonic devices.

Influence of exchange bias on spin torque ferromagnetic resonance for quantification of spin–orbit torque efficiency

Antiferromagnet(AFM)/ferromagnet(FM)heterostructure is a popular system for studying the spin–orbit torque(SOT)of AFMs.However,the interfacial exchange bias field induces that the magnetization in FM layer is noncollinear to the external magnetic field,namely the magnetic moment drag effect,which further influences the characteristic of SOT efficiency.In this work,we study the SOT efficiencies of IrMn/NiFe bilayers with strong interfacial exchange bias by using spin-torque ferromagnetic resonance(ST-FMR)method.A full analysis on the AFM/FM systems with exchange bias is performed,and the angular dependence of magnetization on external magnetic field is determined through the minimum rule of free energy.The ST-FMR results can be well fitted by this model.We obtained the relative accurate SOT efficiencyξ_(DL)=0.058 for the IrMn film.This work provides a useful method to analyze the angular dependence of ST-FMR results and facilitates the accurate measurement of SOT efficiency for the AFM/FM heterostructures with strong exchange bias.

Spin-orbit torque effect in silicon-based sputtered Mn_(3)Sn film

Noncollinear antiferromagnet Mn_(3)Sn has shown remarkable efficiency in charge-spin conversion,a novel magnetic spin Hall effect,and a stable topological antiferromagnetic state,which has resulted in great interest from researchers in the field of spin-orbit torque.Current research has primarily focused on the spin-orbit torque effect of epitaxially grown noncollinear antiferromagnet Mn_(3)Sn films.However,this method is not suitable for large-scale industrial preparation.In this study,amorphous Mn_(3)Sn films and Mn_(3)Sn/Py heterostructures were prepared using magnetron sputtering on silicon substrates.The spin-torque ferromagnetic resonance measurement demonstrated that only the conventional spin-orbit torque effect generated by in-plane polarized spin currents existed in the Mn_(3)Sn/Py heterostructure,with a spin-orbit torque efficiency of 0.016.Additionally,we prepared the perpendicular magnetized Mn_(3)Sn/CoTb heterostructure based on amorphous Mn_(3)Sn film,where the spin-orbit torque driven perpendicular magnetization switching was achieved with a lower critical switching current density(3.9×10^(7)A/cm^(2))compared to Ta/CoTb heterostructure.This research reveals the spin-orbit torque effect of amorphous Mn_(3)Sn films and establishes a foundation for further advancement in the practical application of Mn_(3)Sn materials in spintronic devices.

Magnetism, heat capacity, magnetocaloric effect, and magneto-transport properties of heavy fermion antiferromagnet CeGaSi

We synthesize high-quality single crystal of CeGaSi by a Ga self-flux method and investigate its physical properties through magnetic susceptibility,specific heat and electrical resistivity measurements as well as high pressure effect.Magnetic measurements reveal that an antiferromagnetic order develops below T_(m)~10.4 K with magnetic moments orientated in the ab plane.The enhanced electronic specific heat coefficient and the negative logarithmic slope in the resistivity of CeGaSi indicate that the title compound belongs to the family of Kondo system with heavy fermion ground states.The max magnetic entropy change-ΔS_(M)^(max)(μ_(0)H⊥c,μ_(0)H=7 T) around T_(m) is found to reach up to 11.85 J·kg^(-1)·K^(-1).Remarkably,both the antiferromagnetic transition temperature and-ln T behavior increase monotonically with pressure applied to 20 kbar(1 bar=10~5 Pa),indicating that much higher pressure will be needed to reach its quantum critical point.

Angular and planar transport properties of antiferromagnetic V_(5)S_(8)

Systemically angular and planar transport investigations are performed in layered antiferromagnetic(AF)V_(5)S_(8).In this AF system,obvious anomalous Hall effect(AHE)is observed with a large Hall angle of 0.1 compared to that in ferromagnetic(FM)system.It can persist to the temperatures above AF transition and exhibit strong angular field dependence.The phase diagram reveals various magnetic states by rotating the applied field.By analyzing the anisotropic transport behavior,magnon contributions are revealed and exhibit obvious angular dependence with a spin-flop vanishing line.The observed prominent planar Hall effect and anisotropic magnetoresisitivity exhibit two-fold systematical angular dependent oscillations.These behaviors are attributed to the scattering from spin–orbital coupling instead of nontrivial topological origin.Our results reveal anisotropic interactions of magnetism and electron in V5S8,suggesting potential opportunities for the AF spintronic sensor and devices.

Low-energy spin dynamics in a Kitaev material Na_(3)Ni_(2)BiO_(6) investigated by nuclear magnetic resonance

We perform ^(23)Na nuclear magnetic resonance(NMR) and magnetization measurements on an S=1,quasi-2D honeycomb lattice antiferromagnet Na_(3)Ni_(2)BiO_(6).A large positive Curie-Weiss constant of 22.9 K is observed.The NMR spectra at low fields are consistent with a zigzag magnetic order,indicating a large easy-axis anisotropy.With the field applied along the c*axis,the NMR spectra confirm the existence of a 1/3-magnetization plateau phase between 5.1 T and 7.1 T.The transition from the zigzag order to the 1/3-magnetization plateau phase is also found to be a first-order type.A monotonic decrease of the spin gap is revealed in the 1/3-magnetization plateau phase,which reaches zero at a quantum critical field H_(C)≈8.35 T before entering the fully polarized phase.These data suggest the existence of exchange frustration in the system along with strong ferromagnetic interactions,hosting the possibility for Kitaev physics.Besides,well below the ordered phase,the 1/T_(1) at high fields shows either a level off or an enhancement upon cooling below 3 K,which suggests the existence of low-energy fluctuations.

Stacking-dependent exchange bias in two-dimensional ferromagnetic/antiferromagnetic bilayers

A clear microscopic understanding of exchange bias is crucial for its application in magnetic recording, and further progress in this area is desired. Based on the results of our first-principles calculations and Monte Carlo simulations,we present a theoretical proposal for a stacking-dependent exchange bias in two-dimensional compensated van der Waals ferromagnetic/antiferromagnetic bilayer heterostructures. The exchange bias effect emerges in stacking registries that accommodate inhomogeneous interlayer magnetic interactions between the ferromagnetic layer and different spin sublattices of the antiferromagnetic layer. Moreover, the on/off switching and polarity reversal of the exchange bias can be achieved by interlayer sliding, and the strength can be modulated using an external electric field. Our findings push the limits of exchange bias systems to extreme bilayer thickness in two-dimensional van der Waals heterostructures, potentially stimulating new experimental investigations and applications.

Antiferromagnetic spin dynamics in exchanged-coupled Fe/GdFeO_(3) heterostructure

We investigate the ultrafast spin dynamics of an antiferromagnet in a ferromagnet/antiferromagnet heterostructure Fe/GdFeO_(3) via an all-optical method.After laser irradiation,the terahertz spin precession is hard to be excited in a bare GdFeO_(3) without spin reorientation phase but efficiently in Fe/GdFeO_(3).Both quasi-ferromagnetic and impurity modes,as well as a phonon mode,are observed.We attribute it to the optical modification of interfacial exchange coupling between Fe and GdFeO3.Moreover,the excitation efficiency of dynamics can be modified significantly via the pump laser influence.Our results elucidate that the interfacial exchange coupling is a feasible stimulation to efficiently excite terahertz spin dynamics in antiferromagnets.It will expand the exploration of terahertz spin dynamics for antiferromagnet-based opto-spintronic devices.

关于Planar Ferromagnets and Antiferromagnets泛函的径向极小元的注记

就Bethuel,Brezis和Helein提出的问题讨论了Planar Ferromagnets and Antiferromagnets泛函在H={u(x)=(sinf(r)|xx|,cosf(r))∈H1(B1,S2);f(0)=0,f(1)=2π,r=|x|}中的径向极小元的一些性质,其中包括此泛函的径向极小元的零点的分布及若干个上界估计,并给出了这一问题的肯定回答.

Magnetic properties of the double perovskite compound Sr2YRuO6

We study the magnetic properties of the double perovskite ruthenate compound Sr2YRuO6 using Monte Carlo simulations(MCS).We elaborate the ground state phase diagrams for all possible and stable configurations.The magnetizations and the susceptibilities as a function of temperature for the studied system are also reported.The effects of the exchange coupling interactions and the crystal field are examined and discussed.On the other hand, since the compound Sr2YRuO6 exhibits an antiferromagnetic behavior, we find its Néel temperature, TN≈ 31 K, which is in good agreement with the experimental results in the literature.To complete this study, the hysteresis loops and the coercive field as a function of the external magnetic field are also obtained for fixed values of the physical parameters.

Spin transport in antiferromagnetic insulators

Electrical spin,which is the key element of spintronics,has been regarded as a powerful substitute for the electrical charge in the next generation of information technology,in which spin plays the role of the carrier of information and/or energy in a similar way to the electrical charge in electronics.Spin-transport phenomena in different materials are central topics of spintronics.Unlike electrical charge,spin transport does not depend on electron motion,particularly spin can be transported in insulators without accompanying Joule heating.Therefore,insulators are considered to be ideal materials for spin conductors,in which magnetic insulators are the most compelling systems.Recently,we experimentally studied and theoretically discussed spin transport in various antiferromagnetic systems and identified spin susceptibility and the Néel vector as the most important factors for spin transport in antiferromagnetic systems.Herein,we summarize our experimental results,physical nature,and puzzles unknown.Further challenges and potential applications are also discussed.

Quantum Nucleation of Antiferromagnetic Bubbles with Tetragonal and Hexagonal Symmetries

We study the quantum nucleation in a nanometer-scale antiferromagnet placed in a magnetic field at an arbitrary angle. We consider the magnetocrystalline anisotropy with tetragonal symmetry and that with hexagonal symmetry, respectively. Different structures of the tunneling barriers can be generated by the magnitude and the orientation of the magnetic field. We use the instanton method in the spin-coherent-state path-integral representation to calculate the dependence of the rate of quantum nucleation and the crossover temperature on the orientation and strength of the field for bulk solids and two-dimensional films of antiferromagnets, respectively. We find that the rate of quantum nucleation and the crossover temperature from thermal-to-quantum transitions depend on the orientation and strength of the external magnetic field distinctly, which can be tested by use of existing experimental techniques.

Al-doping-induced magnetocapacitance in the multiferroic CuCrS_2

In this paper,magnetic and dielectric properties of the quasi-two-dimensional triangular-lattice system CuCrS2 and its B-site-diluted analogs CuAl1-xCrxS2（x = 0.01 and x = 0.02） are investigated.Antiferromagnetic phase transition is observed at about 38.5 K by magnetization measurement without shift induced by a small amount of doping Al.Magnetodielectric effect is found near TN in each of the three compounds.The dielectric constant decreases and the magnetocapacitance increases with the increase of substitution of nonmagnetic Al3＋ ions for the magnetic Cr^3＋ ions.The negative magnetocapacitive effect reaches ～ 13% for CuAl0.02Cr0.98S2.

The synthesis and exchange bias effect of monodisperse NiO nanocrystals

Monodisperse NiO nanocrystals with an average particle size of 3 -h 0.4 nm are successfully synthesized by the thermal decomposition of Ni-oleylamine complex in an organic solvent under a continuous 02 flux. The crystalline structure and the morphology of the product are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Magnetization and alternating-current （ac） susceptibility measurements indicate that the structure of the particles can be considered as consisting of an antiferromagnetieally ordered core and a spin- glass-like surface shell. In addition, both the exchange bias field and the vertical magnetization shift can be observed in this system at 10 K after field cooling. This observed exchange bias effect is explained in terms of the exchange interaction between the antiferromagnetie core and the spin-glass-like shell.

A novel spin-FET based on 2D antiferromagnet

Engineering the electronic band structure of material systems enables the unprecedented exploration of new physical properties that are absent in natural or as-synthetic materials.Electronic structures of bilayer two-dimensional(2D)systems can be flexibly engineered by the external electric field.For example.

Solitons and intrinsic localized modes in a one-dimensional antiferromagnetic chain

By use of the Hartree approximation and the method of multiple scales, we investigate quantum solitons and intrinsic localized modes in a one-dimensional antiferromagnetic chain. It is shown that there exist solitons of two different quantum frequency bands： i.e., magnetic optical solitons and acoustic solitons. At the boundary of the Brillouin zone, these solitons becornc quantum intrinsic localized modes： their quantum eigenfrequencics are below the bottom of the harmonic optical frequency band and above the top of the harmonic acoustic frequency band.