Coexistence Of Magnetic Order Research Articles

Complex magnetic ordering in the noncentrosymmetric metal PrCuGe3

We report on the successful synthesis of PrCuGe3 which crystallizes in the tetragonal BaNiSn3-type structure (space group: I4mm) with lattice parameters, a = 4.1470(2) Å and c = 10.185(3) Å. The material is characterized using dc magnetic susceptibility χ(T), ac magnetic susceptibility χac(T), isothermal magnetization M(B), specific heat Cp(T), and electrical resistivity ρ(T) measurements. PrCuGe3 undergoes a long-range ferromagnetic ordering at TC = 23 K, which is followed by another transition below Ttr = 17 K. TC has a quite small anomaly in Cp(T) and ρ(T) despite displaying large associated anomalies in both χ(T) and χac(T) and a sizable ferromagnetic ordered moment. Instead the transition at Ttr has a much larger anomaly in Cp(T) and ρ(T) but essentially no signal in χ(T) and χac(T). Such observations in PrCuGe3 are nontrivial. A Sommerfeld coefficient γ = 375 mJ/(mol K2) is extracted from specific heat which indicates a significant enhancement of the quasi-particle mass at low temperature. Hence, PrCuGe3 exemplifies a system with the coexistence of complex magnetic ordering and a putative heavy-fermion state.

Jahn–Teller effect driven dielectric anomaly and intrinsic magnetodielectric behaviors in nickel chromate

Some spinel chromium oxides with the chemical formula ACr2O4 exhibit magnetic-induced multiferroicity due to the special spiral spin order. However, because of the relatively low temperature of the ordered spiral phase, this kind of multiferroicity generally displays a limited coexistence of magnetic and ferroelectric orders in a narrow temperature range. The Jahn–Teller (JT) effect, serving as a crucial link between charge and orbit degrees of freedom, can facilitate efficient modulation of multiferroic properties. In this work, Ni1−xCuxCr2O4 (0 ≤ x ≤ 0.2) series are synthesized by occupying the same Wyckoff site with two kinds of JT ions. The microstructure and JT distortion can be distinctly influenced by varying the doping level of Cu2+ ions. Particularly, Ni0.85Cu0.15Cr2O4 (x = 0.15) presents the pronounced JT distortion, accompanied by observation of dielectric anomaly at ∼78 K, resulting from spin–orbit coupling. This implies that the JT effect can significantly promote the contribution of spin–orbit coupling in magnetoelectric correlation. Moreover, the magnetodielectric effect induced by intrinsic magnetoelectric coupling is confirmed in Ni0.85Cu0.15Cr2O4 over a wide temperature range of 10–200 K, which is much higher than the Néel temperature of ∼85 K. It indicates that spin–orbit coupling based on the JT effect could overcome the constraint of magnetic order to achieve effective control on electric polarization performance under an applied magnetic field, thereby showing broad application prospects.

Chiral multiferroicity in two-dimensional hybrid organic-inorganic perovskites.

Chiral multiferroics offer remarkable capabilities for controlling quantum devices at multiple levels. However, these materials are rare due to the competing requirements of long-range orders and strict symmetry constraints. In this study, we present experimental evidence that the coexistence of ferroelectric, magnetic orders, and crystallographic chirality is achievable in hybrid organic-inorganic perovskites [(R/S)-β-methylphenethylamine]2CuCl4. By employing Landau symmetry mode analysis, we investigate the interplay between chirality and ferroic orders and propose a novel mechanism for chirality transfer in hybrid systems. This mechanism involves the coupling of non-chiral distortions, characterized by defining a pseudo-scalar quantity, ( represents the ferroelectric displacement vector and denotes the ferro-rotational vector), which distinguishes between (R)- and (S)-chirality based on its sign. Moreover, the reversal of this descriptor's sign can be associated with coordinated transitions in ferroelectric distortions, Jahn-Teller antiferro-distortions, and Dzyaloshinskii-Moriya vectors, indicating the mediating role of crystallographic chirality in magnetoelectric correlations.

Coexistence of Long-Range Magnetic Order and Magnetic Frustration of a Novel Two-Dimensional S = 1/2 Structure: Na2Cu3(SeO3)4

Novel quantum materials offer the opportunity to expand next-generation computers, high-precision sensors, and new energy technologies. Among the most important factors influencing the development of quantum materials research is the ability of inorganic and materials chemists to grow high-quality single crystals. Here, the synthesis, structure characterization and magnetic properties of Na2Cu3(SeO3)4 are reported. It exhibits a novel two-dimensional (2D) structure with isolated layers of Cu nets. Single crystals of Na2Cu3(SeO3)4 were grown using a low-temperature hydrothermal method. Single-crystal X-ray diffraction reveals that Na2Cu3(SeO3)4 crystallizes in the monoclinic crystal system and has space group symmetry of P21/n (No.14) with a unit cell of a = 8.1704(4) Å, b = 5.1659(2) Å, c = 14.7406(6) Å, β = 100.86(2), V = 611.01(5) Å3 and Z = 2. Na2Cu3(SeO3)4 comprises a 2D Cu-O-Cu lattice containing two unique copper sites, a CuO6 octahedra and a CuO5 square pyramid. The SeO3 groups bridge the 2D Cu-O-Cu layers isolating the neighboring Cu-O-Cu layers, thereby enhancing their 2D nature. Magnetic properties were determined by measuring the magnetic susceptibility of an array of randomly oriented single crystals of Na2Cu3(SeO3)4. The temperature-dependent magnetic measurement shows an antiferromagnetic transition at TN = 4 K. These results suggest the fruitfulness of hydrothermal synthesis in achieving novel quantum materials and encourage future work on the chemistry of transition metal selenite.

A possible coexistence of spontaneous magnetic order and thermal entanglement in a spin-1/2 Ising–Heisenberg diamond-decorated square lattice

The spin-1/2 Ising–Heisenberg model on a diamond-decorated square lattice is exactly solved by the decoration-iteration transformation, which establishes an exact mapping correspondence with the spin-1/2 Ising model on a square lattice with an effective temperature-dependent interaction between the nearest-neighbor spins. Exact results for the pair correlation function and spontaneous magnetization of the Heisenberg spins gained from the exact mapping equivalence allow a straightforward implementation of the concurrence, which may serve as a measure of the bipartite entanglement within decorating Heisenberg spin pairs. It is evidenced that the concurrence gradually diminishes upon increase of temperature above a disordered monomer-dimer ground state until it completely vanishes at a threshold temperature, while the concurrence is either always zero above a spontaneously ordered ferrimagnetic ground state or it shows a peculiar thermally assisted reentrance accompanied with a mutual coexistence of the spontaneous ferrimagnetic long-range order and the thermal entanglement.

Coexistence of magnetic ordering and ferroelectricity in a Dy-nitronyl nitroxide chain

A new nitronyl nitroxide Dy-radical chain displays the coexistence of magnetic ordering and ferroelectricity.

Mapping the phase-separated state in a 2D magnet.

Intrinsic 2D magnets have recently been established as a playground for studies on fundamentals of magnetism, quantum phases, and spintronic applications. The inherent instability at low dimensionality often results in coexistence and/or competition of different magnetic orders. Such instability of magnetic ordering may manifest itself as phase-separated states. In 4f 2D materials, magnetic phase separation is expressed in various experiments; however, the experimental evidence is circumstantial. Here, we employ a high-sensitivity MFM technique to probe the spatial distribution of magnetic states in the paradigmatic 4f 2D ferromagnet EuGe2. Below the ferromagnetic transition temperature, we discover the phase-separated state and follow its evolution with temperature and magnetic field. The characteristic length-scale of magnetic domains amounts to hundreds of nanometers. These observations strongly shape our understanding of the magnetic states in 2D materials at the monolayer limit and contribute to engineering of ultra-compact spintronics.

First-Principles Approaches to Magnetoelectric Multiferroics

Magnetoelectric multiferroics, which display both ferroelectric and magnetic orders, are appealing because of their rich fundamental physics and promising technological applications. The revival of multiferroics since 2003 led to a comprehensive understanding of the mechanisms that facilitate the coexistence of electric and magnetic orders and conceptually new design strategies for device architectures, which brought us an important step closer to multiferroic-based technology. In the past thirty years, first-principles calculations based on the laws of quantum mechanics played a crucial role in understanding the electronic, magnetic, and structural properties of multiferroics and guided the design of new multiferroics with improved properties. In this review, we provide a comprehensive overview of first-principles approaches to magnetoelectric multiferroics, especially in low-dimensional forms. In particular, we discuss methods to build an effective Hamiltonian from first principles for magnets, ferroelectrics, and multiferroics. The recently developed machine learning potential approach for multiferroics is also outlined. Furthermore, we present the unified model for spin-induced ferroelectricity and methods for computing the linear magnetoelectric coupling tensor. Finally, recent progress in multiferroic systems and the applications of first-principles approaches to these systems are reviewed.

Unusual magnetic properties of (Sr, Mn)-substituted BiFeO3 near the polar/antipolar phase boundary

Investigations of the crystal structure and magnetic properties of the Bi0.85Sr0.15Fe1-xMnxO3 (0.1 ≤ x ≤ 0.5) ferromanganites were carried out. The materials maintain the single-phase polar R3c structure of the pure bismuth ferrite up to x = 0.35 (a further increase in the Mn content stabilizes the antipolar Pnam phase), thus exhibiting the coexistence of spontaneous polarization and magnetic order over a wide range of Mn concentrations, sufficient to influence the cycloidal antiferromagnetic arrangement typical of the parent compound and contribute to the canted antiferromagnetic phase formation (at room temperature). A complex magnetic behaviour with irregular changes in remanent magnetization and coercive field suggesting the temperature-driven modification of the canted antiferromagnetic structure near the polar/antipolar phase boundary has also been found.

The Study of Interplay of Singlet Superconductivity and Ferromagnetism in Superconducting HoMo6Se8

This article reports the effect of magnetic ordering and superconducting order parameter on superconducting and magnetic transition temperatures of interacting singlet superconductivity and ferromagnetism in HoMo6Se8 material. The basic superconducting parameters were calculated starting with the BCS type model Hamiltonian and using the double time temperature dependent Green function formalisms. Results showed that the superconducting critical temperature decreases with enhancement of superconducting order parameter and vice versa. This is perhaps due to the weakening of the binding energy as the temperature approaches its critical value. On the other hand, the superconducting critical temperature demonstrates attenuation with increasing magnetic order parameters . It was also observed that the enhancement of magnetic transition temperature with the increase of the magnetic order parameter demonstrates variation with the alteration of the superconducting order parameter. Moreover, the calculations revealed that there is a temperature region where both superconductivity and magnetic order coexist. Furthermore, the present theoretical analysis is broadly in agreement with existing experimental findings.

Symmetry-broken Josephson junctions and superconducting diodes in magic-angle twisted bilayer graphene

The coexistence of gate-tunable superconducting, magnetic and topological orders in magic-angle twisted bilayer graphene provides opportunities for the creation of hybrid Josephson junctions. Here we report the fabrication of gate-defined symmetry-broken Josephson junctions in magic-angle twisted bilayer graphene, where the weak link is gate-tuned close to the correlated insulator state with a moiré filling factor of υ = −2. We observe a phase-shifted and asymmetric Fraunhofer pattern with a pronounced magnetic hysteresis. Our theoretical calculations of the junction weak link—with valley polarization and orbital magnetization—explain most of these unconventional features. The effects persist up to the critical temperature of 3.5 K, with magnetic hysteresis observed below 800 mK. We show how the combination of magnetization and its current-induced magnetization switching allows us to realise a programmable zero-field superconducting diode. Our results represent a major advance towards the creation of future superconducting quantum electronic devices.

Electric-field control of magnetization reversal at room temperature in SmFeO3 single-phase multiferroic thin film

Rare-earth orthoferrite SmFeO3 (SFO) is a promising single-phase multiferroic material because of simultaneous coexistence of magnetic and ferroelectric orders at room temperature (RT). However, the spin structures within this bulk material are antiferromagnetic arrangements, and the magnetoelectric (ME) coupling effect is weak. Thus, the realization of electric control of magnetization reversal at RT remains challenging. In this work, SFO thin films with different thicknesses of 30 nm, 60 nm and 90 nm were constructed onto LaNiO3 (LNO)-buffered LaAlO3 (LAO) substrates by pulsed laser deposition (PLD) method. The X-ray diffraction (XRD) θ-2θ scans and reflection high-energy electron diffraction (RHEED) patterns demonstrate the SFO is perfect growth along the LAO (00 l) direction. Besides, the magnetic measurement results indicate that all the thin films are induced obvious RT ferromagnetism by compressive strain of substrates. More importantly, when providing a pair of opposite polarization voltages of± 2.5 V for the 90 nm thin film, the ferroelectric and induced ferromagnetic domains at the same local area can realize synchronous reversal, which shows that the SFO thin film under compressive strain is a rare ferromagnetic-based ME multiferroic material at RT. This kind of material will produce wide application prospect in future electric-write magnetic-read high-density memories and other spintronics devices.

Double glassy states and large spontaneous and conventional exchange bias in La1.5Ca0.5CoFeO6 ferrimagnetic double perovskite

The structural and magnetic properties of hole doped double perovskite La1.5Ca0.5CoFeO6 have been investigated by measuring x-ray photoemission spectroscopy, neutron powder diffraction and magnetization. A ferrimagnetic transition is observed at T C∼ 167 K. The presence of anti-site disorder (ASD) in La1.5Ca0.5CoFeO6 has also been demonstrated. Double re-entrant cluster glass transitions (T 1∼ 11 K and TS ∼ 35 K) were observed which has been attributed to the ASD effect. The presence of both large spontaneous exchange bias H SEB ∼ 2.106 kOe and giant conventional exchange bias H CEB ∼ 1.56 T at 5 K has also been observed which can be attributed to the coexistence of long range magnetic ordering and glassy state. The experimental observations were explained with the results obtained by the density functional theory calculation. The presence of double glassy states, large exchange-bias effect and different magnetic phases make this system a potential candidate for spintronic applications.

Pressure engineering of intertwined phase transitions in lanthanide monopnictide NdSb

Coexistence of non-trivial band topology and intrinsic magnetic order not only leads to emergent phenomena but also allows for the tunability of the exotic properties from different degrees of freedom. By performing transport measurements at synergetic extreme conditions, here we report on pressure engineering of intertwined structural, magnetic, and topological phase transitions in an antiferromagnetic Dirac semimetal NdSb. We show that the original antiferromagnetic state is strengthened in the low-pressure region while destabilized upon further compression close to the critical pressure where a structural transition from Fm-3m phase to P4/mmm phase takes place at PC∼18 GPa, forming a yurt-shaped evolution in response to magnetic field, pressure and temperature. Concomitant with the structural transition, NdSb simultaneously carries on a magnetic transition to the ferromagnetic state. Moreover, theoretical calculations unravel that the ferromagnetic tetragonal phase presents nontrivial features of Weyl fermions. These findings offer new important insight into the microscopic interplay among lattice, spin, and relativistic fermions in lanthanide monopnictides.

Successive Phase Transitions and Multiferroicity in Deformed Triangular-Lattice Antiferromagnets Ca3MNb2O9 (M=Co, Ni) with Spatial Anisotropy

We constructed the magnetic field-temperature phase diagrams of new quasi-two-dimensional isosceles triangular lattice antiferromagnets (TLAF) Ca3MNb2O9 (M=Co, Ni) from dc and ac magnetic susceptibilities, specific heat, dielectric constant, and electric polarization measurements on single crystalline samples. Ca3CoNb2O9 with effective spin-1/2 Co2+ ions undergoes a two-step antiferromagnetic phase transition at T N1 = 1.3 K and T N2 = 1.5 K and enters a stripe ordered state at zero magnetic field. With increasing field, successive magnetic phase transitions, reminiscent of the up-up-down (uud) and the oblique phases, are observed. The dielectric constant of Ca3CoNb2O9 shows anomalies related to the magnetic phase transitions, but clear evidence of ferroelectricity is absent. Meanwhile, Ca3NiNb2O9 with spin-1 Ni2+ ions also shows a two-step antiferromagnetic transition at T N1 = 3.8 K and T N2 = 4.2 K at zero field. For Ca3NiNb2O9, the electric polarization in the magnetic ordered phases was clearly observed from the pyroelectric current measurements, which indicates its coexistence of magnetic ordering and ferroelectricity.

Frustrations on Decorated Planar Lattices in Ising Model

We study the frustration properties of the Ising model on several decorated lattices with arbitrary numbers of decorating spins on all bonds of the lattice within an exact analytical approach based on the Kramers--Wannier transfer-matrix technique. The existence of magnetic frustrations in such situations and their influence on the behavior of the thermodynamic functions of systems is shown. The most important result of our study is related to the description of the possible coexistence of frustrations and long-range magnetic order in partially ordered spin systems.

Coexistence of non-Abelian chiral spin liquid and magnetic order in a spin-1 antiferromagnet

We study the ground-state properties of a spin-1 Heisenberg model on a square lattice with the first- and second-nearest-neighbor antiferromagnetic couplings $J_1$ and $J_2$ and a three-spin scalar chirality term $J_\chi$. Using the density matrix renormalization group calculation, we map out a global phase diagram including various magnetic order phases and an emergent quantum spin liquid phase. The nature of the spin liquid is identified as a bosonic non-Abelian Moore-Read state from the fingerprint of the entanglement spectra and identification of a full set of topological sectors. We further unveil a stripe magnetic order coexisting with this spin liquid. Our results not only establish a rare example of non-Abelian spin liquids in simple spin systems but also demonstrate the coexistence of fractionalized excitations and magnetic order beyond mean-field descriptions.

Janus 2H-VSSe monolayer: two-dimensional valleytronic semiconductor with nonvolatile valley polarization

Valleytronic as a hot topic in recent years focuses on electrons’ valley degree of freedom as a quantum information carrier. Here, by combining two-band k.p model with high-throughput density functional theory (DFT) calculations, the valley states of Janus 2H-VSSe monolayer are studied which have spontaneous polarization. Nonvolatile valley polarization state is mainly arises from intrinsic ferromagnetism contributed by V-3d electronic configuration and not the spontaneous out-of-plane dipole moment of VSSe monolayer. The effective Hamiltonian model and DFT calculations both showed that the valley splitting mainly originates from the smaller spin splitting coming from the spin–orbit coupling effect rather than the spin splitting of magnetic exchange field. By using the effective Dirac Hamiltonian and Kubo formula, we further calculated the longitudinal and transversal conductivities and absorption spectra of VSSe monolayer which exhibits an anomalous valley Hall effect and clear valley-selective circular dichroism. Our calculations indicate that the modification of valley and spin splitting related to Berry curvature by applying an external strain is more noticeable than by the change of the magnetic moment orientation and electric field. We found that carriers accumulation with particular spin and valley label can be manipulated by tuning effective Hamiltonian parameters. The coexistence of robust in-plane magnetic ordering and spontaneous valley polarization of 2H-VSSe monolayer supports the possibility of applications in spintronics, valleytronics and optoelectronics devices.

Microscopic origin of multiferroic order in monolayer NiI2

The discovery of multiferroic behavior in monolayer NiI2 provides a new symmetry-broken state in van der Waals monolayers, featuring the simultaneous emergence of helimagnetic order and ferroelectric order at a critical temperature of T = 21 K. However, the microscopic origin of multiferroic order in NiI2 monolayer has not been established, and in particular, the role of non-collinear magnetism and spin–orbit coupling in this compound remains an open problem. Here we reveal the origin of the two-dimensional multiferroicity in NiI2 using first-principles electronic structure methods. We show that the helimagnetic state appears as a consequence of the long-range magnetic exchange interactions, featuring sizable magnetic moments in the iodine atoms. We demonstrate that the electronic density reconstruction accounting for the ferroelectric order emerges from the interplay of non-collinear magnetism and spin–orbit coupling. We demonstrate that the ferroelectric order is controlled by the iodine spin–orbit coupling, and leads to an associated electronically-driven distortion in the lattice. Our results establish the microscopic origin of the multiferroic behavior in monolayer NiI2, putting forward the coexistence of helical magnetic order and ligand spin–orbit coupling as driving forces for multiferroic behavior in two-dimensional materials.

Coexistence of spontaneous dimerization and magnetic order in a transverse-field Ising ladder with four-spin interactions

The spin-1/2 transverse field two-leg Ising ladder with nearest-neighbor exchange and plaquette four-spin interaction ${J}_{4}$ is studied analytically and numerically with the density matrix renormalization group approach. The quantum phase diagram in the transverse field $B$ versus ${J}_{4}$ plane has been obtained. There are three different phases: a paramagnetic (PM) phase for high values of the transverse field and, for low values of $B$, a ferromagnetic (FM) ordered phase for small ${J}_{4}$, and a dimerized-rung (DR) phase for large negative values of ${J}_{4}$. All phases are separated by quantum phase transition lines meeting at a multicritical point. The critical lines have been obtained by exploring the entanglement entropy. The results show that along the critical lines the central charge is $c=1/2$, while at the multicritical point one has $c=1$. The scaling dimension of the energy operator is ${X}_{\ensuremath{\epsilon}}=1$, in agreement with the universality class of the critical behavior of the quantum Ising chain. An effective field theory for the multicritical point is also discussed. The FM and the DR order parameters have also been computed and we found a region where the FM and the DR phases coexist.