ABSTRACT
Rare-earth (RE)-based honeycomb-lattice materials with strong spin-orbit coupled Jeff = 1/2 moments have attracted great interest as a platform to realize the Kitaev quantum spin liquid (QSL) state. Herein, we report the discovery of a family of RE-based honeycomb-lattice magnets Ba9RE2(SiO4)6 (RE = Ho-Yb), which crystallize into the rhombohedral structure with the space group R3Ì . In these serial compounds, magnetic RE3+ ions are arranged on a perfect honeycomb lattice within the ab-plane and stacked in the "ABCABC"-type fashion along the c-axis. All synthesized Ba9RE2(SiO4)6 (RE = Ho-Yb) polycrystals exhibit the dominant antiferromagnetic interaction and absence of magnetic order down to 2 K. In combination with the magnetization and electron spin resonance results, magnetic behaviors are discussed for the compounds with different RE ions. Moreover, the as-grown Ba9Yb2(SiO4)6 single crystals show large magnetic frustration with frustration index f = θCW/TN > 8 and no long-range magnetic ordering down to 0.15 K, being a possible QSL candidate material. These series of compounds are attractive for exploring the exotic magnetic phases of Kitaev materials with 4f electrons.
ABSTRACT
Rare-earth (RE)-based frustrated magnets, such as typical systems of combining strong spin-orbit coupling (SOC), geometric frustration, and anisotropic exchange interaction, can give rise to diverse exotic magnetic ground states such as quantum spin liquid. The discovery of new RE-based frustrated materials is crucial for exploring the exotic magnetic phases. Herein, we report the synthesis, structure, and magnetic properties of a family of melilite-type RE2Be2GeO7 (RE = Pr, Nd, and Gd-Yb) compounds crystallized in a tetragonal P4Ì 21m structure, where magnetic RE3+ ions lay out on the Shastry-Sutherland lattice (SSL) within the ab plane and are well separated by nonmagnetic [GeBe2O7]6- polyhedrons along the c-axis. Temperature (T)-dependent susceptibilities χ(T) and isothermal magnetization M(H) measurements reveal that most RE2Be2GeO7 compounds except RE = Tb show no magnetic ordering down to 2 K despite the dominant antiferromagnetic (AFM) interactions, where Tb2Be2GeO7 undergoes AFM transition with Néel temperature TN â¼ 2.5 K and field-induced spin flop behaviors (T < TN). In addition, the calculated magnetic entropy change ΔSm from the isothermal M(H) curves reveals viable magnetocaloric effect for RE2Be2GeO7 (RE = Gd and Dy) in liquid helium temperature regimes; Gd2Be2GeO7 shows the maximum ΔSm up to 54.8 J K-1 kg-1 at ΔH = 7 T and Dy2Be2GeO7 has the largest value ΔSm = 16.1 J K-1 kg-1 at ΔH = 2 T in this family. More excitingly, the rich diversity of RE ions in this family enables an archetype for exploring exotic quantum magnetic phenomena with large variability of spin located on the SSL lattice.
ABSTRACT
We perform a comparative magnetic study on two series of rare-earth (RE) based double perovskite iridates RE2BIrO6 (RE = Pr, Nd, Sm-Gd; B = Zn, Mg), which show Mott insulating state with tunable charge energy gap from â¼330 meV to â¼560 meV by changing RE cations. For nonmagnetic RE = Eu cations, Eu2MgIrO6 shows antiferromagnetic (AFM) order and field-induced spin-flop transitions below Néel temperature (T N) in comparison with the ferromagnetic (FM)-like behaviors of Eu2ZnIrO6 at low temperatures. For magnetic-moment-containing RE ions, Gd2BIrO6 show contrasting magnetic behaviors with FM-like transition (B = Zn) and AFM order (B = Mg), respectively. While, for RE = Pr, Nd and Sm ions, all members show AFM ground state and field-induced spin-flop transitions below T N irrespective of B = Zn or Mg cations. Moreover, two successive field-induced metamagnetic transitions are observed for RE2ZnIrO6 (RE = Pr, Nd) in high field up to 56 T, the resultant field temperature (H-T) phase diagrams are constructed. The diverse magnetic behaviors in RE2BIrO6 reveal that the 4f-Ir exchange interactions between the RE and Ir sublattices can mediate their magnetism.
ABSTRACT
Exploration of rare-earth (RE)-based Kagomé lattice magnets with spin-orbital entangled jeff = 1/2 moments will provide a new platform for investigating the exotic magnetic phases. Here, we report a new family of RE3BWO9 (RE = Pr,Nd,Gd-Ho) boratotungstates with magnetic RE3+ ions arranged on Kagomé lattice and perform its structure and magnetic characterizations. These serial compounds crystallize in a hexagonal coordinated structure with space group P63 (no. 173), where magnetic RE3+ ions have distorted Kagomé lattice connections within the ab plane and stacked in an AB-type fashion along the c axis. The interlayer RE-RE separation is comparable with that of the intralayer distance, forming 3-dimensional (3D) exchange coupled magnetic framework of RE3+ ions. The magnetic susceptibility data of RE3BWO9 (RE = Pr, Nd, Gd-Ho) reveal dominant antiferromagnetic interactions between magnetic RE3+ ions, but without visible magnetic ordering down to 2 K. The magnetization analyses for different RE3+ ions show diverse anisotropic behaviors, making RE3BWO9 as an appealing Kagomé-lattice antiferromagnet to explore exotic magnetic phases.
ABSTRACT
Recent developments in various technologies, such as hybrid electric vehicles and pulsed power systems, have challenged researchers to discover affordable, compact, and super-functioning electric energy storage devices. Among the existing energy storage devices, polymer nanocomposite film capacitors are a preferred choice due to their high power density, fast charge and discharge speed, high operation voltage, and long service lifetime. In the past several years, they have been extensively researched worldwide, with 0D, 1D, and 2D nanofillers being incorporated into various polymer matrixes. However, 1D nanofillers appeared to be the most effective in producing large dipole moments, which leads to a considerably enhanced dielectric permittivity and energy density of the nanocomposite. As such, this Review focuses on recent advances in polymer matrix nanocomposites using various types of 1D nanofillers, i.e., linear, ferroelectric, paraelectric, and relaxor-ferroelectric for energy storage applications. Correspondingly, the latest developments in the nanocomposite dielectrics with highly oriented, surface-coated, and surface-decorated 1D nanofillers are presented. Special attention has been paid to identifying the underlying mechanisms of maximizing dielectric displacement, increasing dielectric breakdown strength, and enhancing the energy density. This Review also presents some suggestions for future research in low-loss, high energy storage devices.
ABSTRACT
Tuning of spin-orbit coupling and electron correlation effects in iridates by introducing electron or hole carriers can produce interesting physical phenomena. In this work, we experimentally investigate the electron/hole doping effect on magnetism and electrical transport in the canted antiferromagnetic (AFM) double perovskite La2ZnIrO6, where hole/electron doping are realized in two serial La2Zn1-x Li x IrO6 (0 ⩽ x ⩽ 0.35) and La2Zn1-yâGa yâIrO6 (0 ⩽ yâ ⩽ 0.3) compounds, respectively. The x-ray photoelectron spectroscopy (XPS) reveals the existence of Ir5+ and Ir3+ oxide states in the Li+ and Ga3+ doped La2ZnIrO6. The magnetic susceptibilities and electron spin resonance (ESR) results reveal different responses between the Ir5+(5d4) and Ir3+ (5d6) ions in doped La2ZnIrO6, the Ir5+ ions have Van-Vleck paramagnetic contribution contrast to the completely nonmagnetic Ir3+ ions. Moreover, the Li+ doping cause more dramatic suppression of transition temperature (T N) and net ferromagnetic (FM) moments. All the Li+/Ga3+ doped samples remain Mott insulating state well fitted by the variable-range-hopping (VRH) transport mechanism. As a comparison, hole-doping is more effective to enhance the electrical conductivity than the case of electron, suggesting possible asymmetry of density of states nearby the Fermi level.
