Coexistence Of Antiferromagnetism Research Articles

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.

Structural evolution and coexistence of ferroelectricity and antiferromagnetism in Fe, Nb co-doped BaTiO3 ceramics

Multiferroics are materials that exhibit two or more primary ferroic properties within the same phase and have potential applications in sensors, spintronics and memory devices. Here, the dielectric, ferroelectric and magnetic properties of novel multiferroics derived from BaTi1−x(Fe0.5Nb0.5)xO3 (BTFN, 0.01 ≤ x ≤ 0.10) ceramics are investigated. Multiferroism in these ceramics is manifested by the coexistence of ferroelectric long-range ordering and antiferromagnetism. With increasing x-value, there is a structural evolution from a tetragonal perovskite to a mixture of tetragonal and cubic phases, accompanied by a decrease in the temperature of maximum permittivity. At room temperature, ferroelectric behaviour is evidenced by the presence of current peaks corresponding to domain switching in the current-electric field loops, while the observation of non-linear narrow magnetic hysteresis loops suggests dilute magnetism. The results indicate that in the x = 0.07 composition the antiferromagnetic order is established through an indirect super-exchange interaction between adjacent Fe ions.

Terahertz Spin Current Pulses in Antiferromagnetic Oxide: The Role of Vacancy‐Induced Ferromagnetism

Antiferromagnetic oxides have attracted increasing attention for their outstanding peculiarities in spintronics. Crystal lattice defects that are present in antiferromagnetic oxides can influence their physical properties, such as vacancy‐induced ferromagnetism. Meanwhile, the generation and manipulation of ultrafast spin currents of antiferromagnetic insulators are highly desired. Although the generation and detection of terahertz spin current pulses in antiferromagnetic oxides have been realized, the effect of vacancy‐induced ferromagnetism on spin current in antiferromagnetic oxides is not yet known. Herein, the role of vacancy‐induced ferromagnetism on the terahertz spin current in antiferromagnetic nickel oxide thin films is reported. Structural and magnetic characterizations reveal that nickel vacancies effectively break the strong antiferromagnetic exchange coupling, giving rise to the coexistence of antiferromagnetism and ferromagnetism in NiO thin films. Notably, the enhancement of terahertz radiation associated with the photo‐induced ultrafast spin current of NiO thin film with the strongest ferromagnetism is the most significant. Besides, the nonlinear susceptibility tensor parameters related to the antiferromagnetic property of NiO thin films also change distinctly. The findings indicate that the defects of antiferromagnetic materials play a decisive role in the application of antiferromagnetic spintronics in the terahertz field.

Excitonic Order in Strongly Correlated Systems with the Spin Crossover

Features of the formation of the magnetic structure and the exciton Bose–Einstein condensate phase of magnetic excitons in strongly correlated systems near the spin crossover have been considered with the effective Hamiltonian obtained from the two-band Hubbard–Kanamori model. The coexistence of antiferromagnetism and exciton condensate, as well as the appearance of the long-range excitonic antiferromagnetic order even in the absence of the interatomic exchange interaction, has been revealed. The role of the electron–phonon coupling has been considered.

Terahertz Spin Current Dynamics in Antiferromagnetic Hematite.

An important vision of modern magnetic research is to use antiferromagnets (AFMs) as controllable and active ultrafast components in spintronic devices. Hematite (α-Fe2 O3 ) is a promising model material in this respect because its pronounced Dzyaloshinskii-Moriya interaction leads to the coexistence of antiferromagnetism and weak ferromagnetism. Here, femtosecond laser pulses are used to drive terahertz (THz) spin currents from α-Fe2 O3 into an adjacent Pt layer. Two contributions to the generation of the spin current with distinctly different dynamics are found: the impulsive stimulated Raman scatting that relies on the AFM order and the ultrafast spin Seebeck effect that relies on the net magnetization. The total THz spin current dynamics can be manipulated by a medium-strength magnetic field below 1 T. The control of the THz spin current achieved in α-Fe2 O3 opens the pathway toward tailoring the exact spin current dynamics from ultrafast AFM spin sources.

Magnetism and Transport Properties of EuCdBi2 with Bi Square Net

We report a possible coexistence of nontrivial topology and antiferromagnetism in the newly discovered compounds EuCdBi2, with magnetic Eu layer locating above and below Bi square net. The X-ray diffraction on single crystals and powder indicats that this 112-type material crystalizes in space group of I4/mmm, the same as SrMnBi2 and EuMnBi2. Our combined measurements of magnetization, electrical transport and specific heat consistently reveal antiferromagnetic (AFM) transition of Eu2+ moments at TN = 20 K. The Eu moments are not saturated under a field of 7 T at 1.8 K. The anisotropic susceptibility suggests the Eu moments lie in the ab plane, and a metamagnetic (MM) transition is observed near 1 T below TN. Large positive magnetoresistance (MR) present for both H ‖ ab and H ‖ c, which are considered to contain part contributions from Dirac bands. Hall measurements show the electron-hole compensation effect is prominent above 100 K, with a crossover of Hall resistance from negative to positive values at ∼150 K. The fitted mobility of electrons is as high as 3250 cm2 V−1 S−1 at 1.8 K. Interestingly, the rapid increase of carrier density and suppression of mobility appear at around TN, indicating non-negligible interaction between Eu moments and electron/hole bands. EuCdBi2 may provide a new platform to investigate the interplay of topological bands and antiferromagnetic order.

Magnetic and Electrical Properties of Ni3Te2 Single Crystals Grown by Physical Vapor Transport Technique

The transition metal tellurides (TMTs) have attracted much attention due to their rich properties in both fundamental research and applications. Among all the TMTs, the study of Ni3Te2 large single crystals is rare. By using the physical vapor transport technique, Zhe Li, Jun-Yi Ge, and co-workers have successfully grown Ni3Te2 single crystals with unique hexagonal cross section and a tubular shape (see article number 2200037). The crystal structure, the electrical transport and magnetic properties, and band structures are investigated in detail. It is revealed that Ni3Te2 exhibits a metallic behavior with the coexistence of ferromagnetism and antiferromagnetism.

Density of states in antiferromagnetic nanowire superconductors

The coexistence of different order parameters and the pairing symmetry is the major issue in the study of one dimensional wires. We adopt a tight-binding model, for the coexistence of superconductivity and antiferromagnetism in s-wave pairing symmetry, which is consistent and most favourable for the nearest-neighbour pairing interaction, and derive a set of gap equations which are solved numerically and self-consistently. The effects of the order parameters on one another are studied. We have also calculated the density of states and band energies. The density of states shows the defined interference peaks on either side of the Fermi level corresponding to the order parameters with van Hove singularities.

Magnetic and Electrical Properties of Ni3Te2 Single Crystals Grown by Physical Vapor Transport Technique

High‐quality single crystals with length up to 6 mm are successfully grown by the physical vapor transport (PVT) technique. The crystals exhibit unique tubular structures with a hexagonal cross section. The high‐quality crystal is studied by a series of structural and morphological characterization. The physical properties including both magnetization and electrical transport are studied in detail. It is found that there exists a coexistence of weak ferromagnetism and antiferromagnetism at low temperatures. In the measured temperature range of 2–300 K, shows a typical metallic behavior, and the temperature dependence of the resistivity ρ x x (T) can be well fitted by the parallel‐resistor model.

Coexistence of antiferromagnetism and superconductivity in Mn/Nb(110)

We report on the structural and magnetic properties of single and double atomic layers of Mn on a clean and unreconstructed Nb(110) substrate. Low-temperature scanning tunneling spectroscopy measurements reveal a proximity-induced superconducting state in the Mn thin films, which are found to grow pseudomorphically on the Nb surface. Spin-polarized scanning tunneling microscopy measurements reveal a c(2x2) antiferromagnetic order in the Mn layers, with an out-of-plane spin-orientation. First-principles density functional theory calculations confirm the experimentally observed magnetic state, which is understood as the consequence of a strong intra- and inter-layer nearest-neighbor antiferromagnetic exchange coupling. These results are expected to be of importance for the design and the investigation of novel superconducting antiferromagnetic spintronic systems.

Seebeck coefficient of Cr100−zOsz alloy system

The magnetic phase diagram of the Cr100−zOsz alloy system exhibits possible quantum critical behavior (QCB), with commensurate spin-density-wave to paramagnetic (CSDW-PM) phase line terminating at z ≈ 14, in a superconducting dome at z ≈ 12. Also indicated is the co-existence of SDW antiferromagnetism (AFM) and superconductivity (SC) for the z = 12.2 sample with a bcc structure. Considering the unique behaviour in the Cr100−zOsz system, this study reports on an investigation into the temperature dependence of the thermoelectric power or Seebeck coefficient, ST. With S(T) sensitive to the electronic structure and scattering mechanisms it is used here in order to investigate the unique magnetic behaviour observed in this alloy. ST measurements were performed on polycrystalline Cr100−zOsz (2.1 ≤ z ≤ 14.1) samples, as confirmed by XRD to be in a single bcc phase. The low-temperature S(T) behaviour is expressed in the form S = aT + bT3, where a and b are constants that were determined to discuss the possible contributions of phonon and/or magnon drag to S. Resulting a(z) and b(z) behaviour indicate anomalies that can be associated with three crucial points in the Cr100−zOsz magnetic phase diagram: (i) at z ≈ 8 is associated with the destabilization of the CSDW phase with the continual addition of Os into the system, (ii) at z ≈ 12 where the SC properties manifest and (iii) at z ≈ 13 associated with quantum critical behaviour this the system. Considering dS/dT where T approaches 0 K, as function of z, clear anomalies are observed at z ≈ 12 and 13, which, are associated with the onset of SC and QCB in this system. The present results suggest that S is a decisive experimental parameter in characterizing anomalous behaviour reflected in the magnetic phase diagram of Cr100−zOsz.

Coexistence of antiferromagnetism, ferromagnetism and superconductivity in Iron based superconductors

Although the coexistence of Superconductivity (SC) and magnetism in one compound is rare as both phenomena are antagonistic to each other but many examples of such materials like high Tc cuprates, heavy fermion materials and Uranium based compounds are also known to exist. The study of this interplay of SC and magnetism might be very important as high Tc cuprates are antiferromagnetic insulators in its pristine form and upon doping, theirs transition temperature (Tc) could enhance up to 183 K in Hg based cuprates at high pressure. Iron based Superconductors (IBSCs) are also showing magnetic ground state and doping with rare earth ions change its state and it starts superconducting. In this paper, I have theoretically studied the Hamiltonian of Iron based superconductors especially Eu1-xLaxFeAs2 having superconducting, antiferromagnetic and ferromagnetic interactions. I have also tried to find the exact mechanism responsible for Cooper pairing in these compounds by finding superconducting order parameter (Δ), ferromagnetic (∅↑↑) and antiferromagnetic (∅↑↓) order parameters. In the pretext of this finding, we would able to find many Fe based materials which could super conduct even at room temperature.

Role of Three Bands on Coexistence of Superconductivity and Antiferromagnetism in Samarium Iron Pnictide Superconductor

Role of Three Bands on Coexistence of Superconductivity and Antiferromagnetism in Samarium Iron Pnictide Superconductor

Exchange Bias Effect in NiMnSbB Ferromagnetic Shape Memory Alloys Depending on Mn Content

In this study, exchange bias effect was investigated in boron added NiMnSb Heusler alloys. The samples were fabricated by arc melting method with Ni49Mn37,5Sb13,5+Bx, Ni49Mn37,7Sb13,3+Bx and Ni49Mn37,9Sb13,1+Bx nominal compositions. XRD analyzes showed that the samples were in L21 crystal structure at room temperature. While the martensitic phase transition temperatures increased, the magnetic moment value decreased with the increase in Mn content. The decrease in magnetization is owing to the increase in antiferromagnetic interactions with the increase of Mn content. Under low field and zero field cooling M-T measurements revealed that antiferromagnetic interactions were more dominant at low temperature but ferromagnetic behavior was more effective in the system at high temperature region. The coexistence of ferromagnetism and antiferromagnetism in a magnetic material can cause the exchange bias effect. Therefore, the hysteresis loops were examined at 5 K of the samples cooled under 50 kOe magnetic field. The shift at the origin of the magnetization curve, which is attributed to the exchange bias effect, increased with increasing Mn amount.

Magnetization and thermal expansion measurements on the Ising magnet SmPt2Si2 : Potential coexistence of spin glass and antiferromagnetic states

The Ising magnet $\mathrm{Sm}{\mathrm{Pt}}_{2}{\mathrm{Si}}_{2}$ undergoes an antiferromagnetic (AFM) transition at ${T}_{\mathrm{N}1}$ = 5.6 K, but the magnetic moments of some Sm ions remain disordered even below ${T}_{\mathrm{N}1}$. Here, we report the results of measurements of thermal expansion, magnetostriction, and dc magnetization of $\mathrm{Sm}{\mathrm{Pt}}_{2}{\mathrm{Si}}_{2}$ in the temperature range from 0.26 to 7 K. The magnetization and thermal expansion results show clear irreversible phenomena at temperatures below ${T}_{\mathrm{g}}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}$ 2.4 K. These results suggest that the partially disordered state of the Sm ions becomes a cluster spin glass below ${T}_{\mathrm{g}}$ and coexists with the AFM long-range order. However, unlike the conventional coexistence of spin glass and antiferromagnetism, the isothermal magnetization process at 0.26 K shows a hysteresis curve with almost no remanent magnetization. This observation suggests that the cluster spin glass state is an unusual state with a short relaxation time at zero field.

Antiferromagnetic ordering and excitonic pairing in AA-stacked bilayer graphene

In this paper, we describe the antiferromagnetic and excitonic correlations in the AA-stacked bilayer graphene. We consider the applied external electric field potential to the structure which leads to the electronic charge imbalance between the layers in the system. By using the generalized two-layer Hubbard Hamiltonian, we consider different particle-filling regimes in the layers. We calculate the important energy scales in the system and we establish the conditions for the appearance of the antiferromagnetic order in the system. We consider both large and small Coulomb interaction limits in the layers and the effect of the electric field potential on the calculated order parameters. We discuss the coexistence of antiferromagnetism and excitonic phases and we show that they can coexist only in the regime away from half-filling. In the case away from the half-filling, we show the existence of a critical value ${U}_{\mathrm{C}}$ of the Coulomb interaction potential at which we establish the transition from the single-valued to the triple-valued excitonic states, governed by the strong electronic reconfiguration, in the system. The zero-temperature limit is considered in the problem.

Emergence of exchange bias field in FeS superconductor with cobalt-doping

Among all the iron-based superconductors, the 11 series has the simplest layered structure but exhibits rich physical phenomenon. In this work, we have synthesized Fe1−x Co x S single crystals with tetragonal structure and studied their structure and magnetic properties. Magnetic susceptibility measurements indicate that the cobalt doping would suppress superconductivity and even introduce weak ferromagnetism besides antiferromagnetism. Scanning electron microscopy study reveals that the Co-doped samples exhibit intrinsic phase separation. Moreover, magnetic force microscopy measurement shows no magnetic domain in Fe1−x Co x S, indicating that neither phase is pure ferromagnetic. The coexistence of ferromagnetism and antiferromagnetism leads to the relatively large exchange bias field. Since the exchange bias effect has been widely used in the field of information storage, spin-valves, and magnetic tunnel junctions, our study provides another option for further application.

Crystal structure and physical properties of Ba2Nb3S8I: A new misfit-layered transition-metal dichalcogenide superconductor

Single crystals of Ba2Nb3S8I have been grown using iodine-vapor transport in fused-quartz tubes. The crystals form as flakes with typical areas of 5–10 mm2 and thicknesses of 5–11 μm. The crystal structure was determined using single-crystal x-ray diffraction with the aid of an APEX II CCD diffractometer. The structure shows trigonal symmetry with space group P31c and lattice parameters a = b = 10.0156(5) Å and c = 25.1414(15) Å. Compositional analysis via x-ray spectroscopy confirms the presence of iodine. Superlattice reflections are evident in x-ray precession images. Measurements of the electrical resistivity reveal a metallic temperature dependence and superconductivity near 1 K. Polycrystalline samples of Ba2Nb3S8I were made in order to have samples large enough for other bulk physical properties measurements. Magnetic susceptibility reveals antiferromagnetism below 275 K. The coexistence of antiferromagnetism and superconductivity is surprising. Specific heat measurements reveal the electronic coefficient γ = 3.95(66) mJ/mol K2. The jump in the specific heat at the superconducting transition temperature Tc (ΔC/γTc = 1.4(2)) and the energy gap associated with the superconducting state (Eg = 0.405(17) meV) agree well with BCS theory.

Competing order parameters of SC and AFM in bilayer cuprate superconductors

Antiferromagnetism and d-wave superconductivity are the most important competing ground-state phases of cuprate superconductors. In this regard, we have proposed a model Hamiltonian describing the interlayer tunnelling in d-wave bilayer cuprate superconductors in the coexistence of superconductivity and antiferromagnetism. The Hamiltonian model is solved for the quasiparticle energy bands, the superconducting and the antiferromagnetic gap parameters by using Zubarev’s technique of double time electron Green’s functions. The effects of interlayer tunnelling are studied for superconducting and antiferromagnetic gap parameters.

Temperature dependence of the effective Gilbert damping constant of FeRh thin films

Antiferromagnetic (AFM) materials have attracted attention for device applications due to the absence of the stray field and high-frequency response. To integrate AFM materials into magnetic devices, the understanding of the interfacial effect between AFM and ferromagnetic (FM) materials is required. In particular, magnetization dynamics and magnetic damping are critical phenomena to be elucidated since they govern magnetization switching, spin-wave propagation, etc. Although a conventional method for studying the interfacial effects is stacking materials, the approach may cause unfavorable factors. To get insight into the dynamic properties at the AFM and FM interfaces, we have focused on B2-ordered FeRh, showing the first-order phase transition from the AFM to FM states, since the coexistence of AFM and FM domains occurs during transitions, which is an ideal platform for studying interfacial effects. For this study, we have studied ferromagnetic resonance (FMR) of FeRh thin films during the AFM–FM phase transition as a function of temperature. From the FMR measurements, we characterize the temperature dependence of the effective Gilbert damping constant αeff. We find that αeff decreases with increasing temperature, indicating that the temperature variation of the effective Gilbert damping constant originates from the exchange interaction between the AFM and FM domains in the film and/or AFM domains as a spin sink.