Ba6RE2Ti4O17 (RE = Nd, Sm, Gd, Dy-Yb): A Family of Rare-Earth-Based Layered Triangular Lattice Magnets.

The exploration of new rare-earth (RE)-based triangular-lattice materials plays a significant role in motivating the discovery of exotic magnetic states. Herein, we report a family of hexagonal perovskite compounds Ba6RE2Ti4O17 (RE = Nd, Sm, Gd, Dy-Yb) with a space group of P63/mmc, where magnetic RE3+ ions are distributed on the parallel triangular-lattice layers within the ab-plane and stacked in an 'AA'-type fashion along the c-axis. The low-temperature magnetic characterizations indicate that all synthesized Ba6RE2Ti4O17 compounds exhibit dominant antiferromagnetic (AFM) interactions and the absence of magnetic order down to 1.8 K. The isothermal magnetization and electron spin resonance results reveal the distinct magnetic anisotropy for the compounds with different RE ions. Moreover, the as-grown Ba6Nd2Ti4O17 single crystals exhibit Ising-like magnetic anisotropy with a magnetic easy-axis perpendicular to the triangle-lattice plane and no long-range magnetic order down to 80 mK, as the quantum spin liquid candidate with dominant Ising-type interactions.

Ba9RE2(SiO4)6 (RE = Ho-Yb): A Family of Rare-Earth-Based Honeycomb-Lattice Magnets.

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 R3̅. 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.

Transient Magnetoelectric Coupling Induced by the Dynamic Intertwinement between Exchange Striction and Compensation in GdFeO3.

In this study, we investigate the dynamic magnetoelectric (ME) coupling behaviors of GdFeO3 under pulsed magnetic fields. When a magnetic field is applied along the c-axis, and the temperature is near the compensation temperature (Tcomp = 3.5 K), we observe a subtle transition involving the reversal of Fe3+ moments at approximately 0.8 T in magnetization (M) measurements. This transition induces a corresponding jump in electrical polarization (P), which is not present in the static field measurements. The dynamic intertwining between M and P signifies a competition between antiferromagnetic (AFM) coupling between Gd3+ and Fe3+ moments and their Zeeman energies. The robust AFM coupling leads to the reversal of Fe3+ moments near Tcomp, triggering the abrupt change in P. Based on the exchange striction mechanism in the ferrimagnetic GdFeO3, we propose the possibility of achieving highly magnetic field sensitive ME coupling near the compensation temperature in ferrimagnetic multiferroic orthoferrites.

Anisotropic magnetic property, magnetostriction, and giant magnetocaloric effect with plateau behavior in TbMn2Ge2 single crystal.

The ternary RMn2Ge2 (R = rare earth) intermetallic compounds have attracted great attention due to their interesting magnetic behaviors and magnetotransport responses. Here, we reported our observation of anisotropic magnetic property, magnetostriction, and magnetocaloric effect (MCE) in TbMn2Ge2 single crystal. Below the transition temperature of Tb magnetic sublattices ([Formula: see text] ~ 95 K), strong Ising-like magnetocrystalline anisotropy is observed with an out-of-plane ferromagnetic moments 5.98 µB/f.u. along the easy c axis, which is two orders of magnitude larger than that of field along a axis. Above [Formula: see text], a field-induced metamagnetic transition is observed from the spin-flip of Mn sublattices. During this transition, remarkable magnetostriction effect is observed, indicating of strong spin-lattice coupling. The responses of Tb and Mn sublattices to the magnetic field generate a giant magnetic entropy change ([Formula: see text]) and large values of relative cooling power (RCP) and temperature-averaged entropy change (TEC). The calculated maximum magnetic entropy change ([Formula: see text]), RCP, and TEC(10) with magnetic field change of 7 T along c axis reach 24.02 J kg-1 K-1, 378.4 J kg-1, and 21.39 J kg-1 K-1 near [Formula: see text], which is the largest among RMn2Ge2 families. More importantly, this giant MCE shows plateau behavior with wide window temperatures from 93 to 108 K, making it be an attractive candidate for magnetic refrigeration applications.

Shubnikov-de Haas oscillations and nontrivial topological states in Weyl semimetal candidate SmAlSi.

The RAlX (R = Light rare earth; X = Ge, Si) compounds, as a family of magnetic Weyl semimetal, have recently attracted growing attention due to the tunability of Weyl nodes and its interactions with diverse magnetism by rare-earth atoms. Here, we report the magnetotransport evidence and electronic structure calculations on nontrivial band topology of SmAlSi, a new member of this family. At low temperatures, SmAlSi exhibits large non-saturated magnetoresistance (MR) (as large as ∼5500% at 2 K and 48 T) and distinct Shubnikov-de Haas (SdH) oscillations. The field dependent MRs at 2 K deviate from the semiclassical (µ0H)2variation but follow the power-law relation MR∝(µ0H)mwith a crossover fromm∼ 1.52 at low fields (µ0H< 15 T) tom∼ 1 under high fields (µ0H> 18 T), which is attributed to the existence of Weyl points and electron-hole compensated characteristics with high mobility. From the analysis of SdH oscillations, two fundamental frequencies originating from the Fermi surface pockets with non-trivialπBerry phases and small cyclotron mass can be identified, this feature is supported by the calculated electronic band structures with two Weyl pockets near the Fermi level. Our study establishes SmAlSi as a paradigm for researching the novel topological states of RAlX family.

Structure and Magnetic Properties of Melilite-Type Compounds RE2Be2GeO7 (RE = Pr, Nd, Gd-Yb) with Rare-Earth Ions on Shastry-Sutherland Lattice.

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 P4̅21m 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 ∼ 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.

A comparative study on magnetic order and field-induced magnetic transition in double perovskite iridates: RE2ZnIrO6 and RE2MgIrO6 (RE = Pr, Nd, Sm, Eu, Gd).

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 ∼330 meV to ∼560 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.

A New Family of Disorder-Free Rare-Earth-Based Kagome Lattice Magnets: Structure and Magnetic Characterizations of RE3BWO9 (RE = Pr, Nd, Gd-Ho) Boratotungstates.

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.

The effect of carrier doping on magnetism and electronic behavior in double perovskite La2ZnIrO6.

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-y Ga y IrO6 (0 ⩽ y  ⩽ 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.

Strain-induced spontaneous Hall effect in an epitaxial thin film of a Luttinger semimetal.

Pyrochlore iridates have provided a plethora of novel phenomena owing to the combination of topology and correlation. Among them, much attention has been paid to [Formula: see text], as it is known as a Luttinger semimetal characterized by quadratic band touching at the Brillouin zone center, suggesting that the topology of its electronic states can be tuned by a moderate lattice strain and external magnetic field. Here, we report that our epitaxial [Formula: see text] thin films grown by solid-state epitaxy exhibit a spontaneous Hall effect that persists up to 50 K without having spontaneous magnetization within our experimental accuracy. This indicates that the system breaks the time reversal symmetry at a temperature scale that is too high for the magnetism to be due to Pr 4f moments and must be related to magnetic order of the iridium 5d electrons. Moreover, our analysis finds that the chiral anomaly induces the negative contribution to the magnetoresistance only when a magnetic field and the electric current are parallel to each other. Our results indicate that the strained part of the thin film forms a magnetic Weyl semimetal state.

Magnetic Excitations across the Metal-Insulator Transition in the Pyrochlore Iridate Eu_{2}Ir_{2}O_{7}.

We report a resonant inelastic x-ray scattering study of the magnetic excitation spectrum in a highly insulating Eu_{2}Ir_{2}O_{7} single crystal that exhibits a metal-insulator transition at T_{MI}=111(7) K. A propagating magnon mode with a 20 meV bandwidth and a 28 meV magnon gap is found in the excitation spectrum at 7 K, which is expected in the all-in-all-out magnetically ordered state. This magnetic excitation exhibits substantial softening as the temperature is raised towards T_{MI} and turns into a highly damped excitation in the paramagnetic phase. Remarkably, the softening occurs throughout the whole Brillouin zone including the zone boundary. This observation is inconsistent with the magnon renormalization expected in a local moment system and indicates that the strength of the electron correlation in Eu_{2}Ir_{2}O_{7} is only moderate, so that electron itinerancy should be taken into account in describing its magnetism.

Polarization enhancement and ferroelectric switching enabled by interacting magnetic structures in DyMnO3 thin films.

The mutual controls of ferroelectricity and magnetism are stepping towards practical applications proposed for quite a few promising devices in which multiferroic thin films are involved. Although ferroelectricity stemming from specific spiral spin ordering has been reported in highly distorted bulk perovskite manganites, the existence of magnetically induced ferroelectricity in the corresponding thin films remains an unresolved issue, which unfortunately halts this step. In this work, we report magnetically induced electric polarization and its remarkable response to magnetic field (an enhancement of ~800% upon a field of 2 Tesla at 2 K) in DyMnO3 thin films grown on Nb-SrTiO3 substrates. Accompanying with the large polarization enhancement, the ferroelectric coercivity corresponding to the magnetic chirality switching field is significantly increased. A picture based on coupled multicomponent magnetic structures is proposed to understand these features. Moreover, different magnetic anisotropy related to strain-suppressed GdFeO3-type distortion and Jahn-Teller effect is identified in the films.