Criticality of Inverter Controller Order in Power System Dynamic Studies – Case Study: Maui Island
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Kenyon, Rick Wallace↗
SEARCH · Engineering Papers
Results for “Magnetic ordering”
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Pyrochlore-type lanthanide titanates and zirconates: Synthesis, structural peculiarities, and properties
This contribution provides a thorough examination of the structural characteristics of pyrochlore-type lanthanide titanates and zirconates Ln2Ti2O7 and Ln2Zr2O7, across various length scales. This paper also examines their processing, interesting physical properties (electrical, magnetic, and thermal characteristics), and responses to high pressure and ion irradiation. Brief sections on the elemental oxides' crystal chemistry, pertinent phase diagrams, and energetics of defect formation are also provided. Pyrochlore-type Ln2Ti2O7 and Ln2Zr2O7 stand out as truly multifunctional materials. Moreover, they have emerged as fascinating materials due to magnetic geometrical frustration, arising from the ordering of magnetic Ln3+ and non-magnetic Ti4+ (or Zr4+) cations into separate, interpenetrating lattices of corner-sharing tetrahedra. This results in a diverse array of exotic magnetic ground states, such as spin-ice (e.g., Dy2Ti2O7 or Ho2Ti2O7) or quantum spin ice (e.g., Tb2Ti2O7), observed at both low and room temperatures. They also exhibit varied electrical and electrochemical characteristics. Some members such as Gd2Zr2O7, function as fast ion conductors with a conductivity (σ) of ≈10−2 S·cm−1 at 800 °C and activation energy (Ea) ranging from 0.85 to 1.52 eV, depending on the degree of structural disorder. Others, such as Gd2TiMoO7, are mixed ionic-electronic conductors with σ ≈ 25 S·cm−1 at 1000 °C, making them promising candidate materials for applications in energy conversion and storage devices and oxygen separation membranes. Their exceptionally low thermal conductivity (e.g., κ ∼ 1.1–1.7 W·m−1·K−1 between 700 and 1200 °C for Ln2Zr2O7), close to the glass-like lower limit of highly disordered solids, positions them as valuable materials for thermal barrier coatings. They can also effectively accommodate actinides (e.g., Pu, Np, Cm, Am) in solid solutions and sustain prolonged exposure to radiation due to alpha-decay events, while preserving the integrity of the periodic atomic structure. Proposed as major components in actinide-bearing ceramics, they contribute to the long-term immobilization and disposal of long-lived waste radionuclides from nuclear programs. Some of these properties are displayed simultaneously, opening avenues for new applications. Despite the wealth of data available in the literature, this review highlights the need for a better understanding of order/disorder processes in pyrochlore-type materials and the influence of the structural length scale on their physical and chemical properties. Recent experimental evidence has revealed that pyrochlore short-range structure is far more complex than originally thought. Moreover, pyrochlore local structure is now believed to include short-range, lower symmetry, ordered domains, such as the orthorhombic weberite-type of structure. Notably, short- and long-range structures appear decoupled across different length scales and temperature regimes, and these differences persist even in well-ordered samples. We believe that the pyrochlore structure offers a unique opportunity for examining the interplay between chemical composition, defect chemistry, and properties. In Memoriam: Rodney C. Ewing, Fondly Remembered.
Physics↗
Phase Diagram of the Easy-Axis Triangular-Lattice 𝐽 1 −𝐽 2 Model
Our work studies the largely unexplored phase diagram of the S = 1/2 easy-axis triangular-lattice J 1 -J 2 model, motivated by recent interest in rare-earth and transition-metal compounds that exhibit strong quantum fluctuations and broad spin excitation continua—hallmarks of spin-liquid behavior. Combining density-matrix renormalization group simulations with analytical insights, we present a comprehensive study of the model that describes these materials. Our results provide compelling evidence for a robust spin-liquid phase stabilized between the exotic supersolid Y phase and the collinear stripe phase, remarkably persistent even in the presence of symmetry-breaking anisotropy. Additionally, we analyze the supersolid Y phase, offering a quantitative characterization of its order parameters and clarifying the surprising absence of a ferromagnetic moment; both features relevant to recent experiments on Ising-like triangular-lattice magnets. Altogether, our work provides the necessary framework and important theoretical guidance to the ongoing searches of the spin liquid and other exotic states in the rare-earth and transition-metal triangular-lattice compounds, as well as for advancing the understanding of anisotropic-exchange magnets.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Frustrated mixed-spin ladders: Evidence for a bond-order wave phase between rung-singlet and Haldane phases
In frustrated spin ladders, the interplay of frustration and correlations leads to the familiar Haldane (H) and rung-singlet (RS) phases. The nature of the transition between these two phases is still under debate. In this paper we tackle this issue using tools of quantum information theory. We consider frustrated mixed-spin-(1, 1/2) ladders with antiferromagnetic leg, rung and diagonal couplings, and calculate various quantities, such as the entanglement entropy (EE), the Schmidt gap, and the level degeneracy of the entanglement spectrum (ES). We use two numerical techniques, the infinite time-evolving block decimation (iTEBD) and the density matrix renormalization group (DMRG). We demonstrate that there exists an intermediate phase in which the ES levels do not exhibit the characteristic degeneracies of the H and RS phases. To understand the underlying physics in this phase, here we investigate short-range spin correlations along legs, rungs and diagonals and show that in this intermediate phase long-wavelength modulations occur, akin to bond-order waves.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Valley magnetism, nematicity, and density wave orders in twisted bilayer graphene
We analyze density wave and Pomeranchuk orders in twisted bilayer graphene. This complements our earlier analysis of the pairing instabilities. We assume that near half filling of either conduction or valence band, the Fermi level is close to Van Hove points, where the density of states diverges, and study potential instabilities in the particle-hole channel within a patch model with two valley degrees of freedom. The hexagonal symmetry of twisted bilayer graphene allows for either six or twelve Van Hove points. We consider both cases and find the same two leading candidates for particle-hole order. One is an SU(2)-breaking spin state with ferromagnetism within a valley. A subleading intervalley hopping induces antiferromagnetism between the valleys. The same state has also been obtained in strong-coupling approaches, indicating that this order is robust. Here, the other is a mixed state with 120° complex spin order and orthogonal complex charge order. In addition, we find a weaker but still attractive interaction in nematic channels, and discuss the type of a nematic order.
36 MATERIALS SCIENCE↗
Probing the effect of magnetic field on charge order in the quasi-two-dimensional Mott insulator κ - (ET) 2 Hg(SCN) 2 Cl
Molecular-based quasi-two-dimensional charge-ordered Mott insulators can possess both spin S = 1/2 and an electric dipole degree of freedom residing on each (BEDT - TTF) 2 lattice site. There exists a theoretical proposal for a magnetoelectric effect in such a material, which can manifest itself as a sensitivity of charge distribution on (BEDT - TTF) 2 dimers to the magnetic field. Here in this work, we used Raman scattering spectroscopy in the magnetic field up to 31 T applied perpendicular to the two-dimensional triangular lattice planes to probe a magnetoelectric effect in $\kappa$ - (ET) 2 H g (SCN) 2 Cl. This is a model compound, which shows charge order and antiferromagnetic correlations at temperatures below 30 K. We discuss possible reasons for the absence of an observable magnetoelectric effect in the probed temperature and magnetic field ranges.
36 MATERIALS SCIENCE↗
Higher order topological superconductivity in magnet-superconductor hybrid systems
Abstract Quantum engineering of topological superconductors and of the ensuing Majorana zero modes might hold the key for realizing topological quantum computing and topology-based devices. Magnet-superconductor hybrid (MSH) systems have proven to be experimentally versatile platforms for the creation of topological superconductivity by custom-designing the complex structure of their magnetic layer. Here, we demonstrate that higher order topological superconductivity (HOTSC) can be realized in two-dimensional MSH systems by using stacked magnetic structures. We show that the sensitivity of the HOTSC to the particular magnetic stacking opens an intriguing ability to tune the system between trivial and topological phases using atomic manipulation techniques. We propose that the realization of HOTSC in MSH systems, and in particular the existence of the characteristic Majorana corner modes, allows for the implementation of a measurement-based protocols for topological quantum computing.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
A Polar Magnetic and Insulating Double Corundum Oxide: Mn2MnSbO6 with Ordered Mn(II) and Mn(III) Ions
A new magnetic insulator Mn2MnSbO6 with a polar crystal structure and an ordered Mn2+ and Mn3+ arrangement was synthesized under a high pressure of 7.5 GPa and 1300 degrees C. The crystal structure of Mn2MnSbO6, investigated by synchrotron powder X-ray diffraction, was found to be isomorphous with that of Ni3TeO6-type, space group R3. The non-centrosymmetric structure was confirmed by the second-harmonic generation measurements. The X-ray absorption near-edge spectroscopy measurement confirmed the nominal oxidation states of Mn22+Mn3+SbO6. Magnetic measurements indicate that Mn2MnSbO6 orders antiferromagnetically below 44 K and undergoes a field-induced spin-flop transition at 5 K. First-principles calculations indicate an antiferromagnetic ground state with up/up/up/down/down/down (uuuddd) spin configuration of the six crystallographically unique Mn ions in the c-axis doubled magnetic structure. The density functional theory calculations also substantiate the experimentally observed charge ordering of the Mn2+/Mn3+ ions and the insulating behavior due to a bandgap of 0.52 eV. To the best of our knowledge, this is the first double corundum oxide containing Jahn-Teller active Mn3+ ions.
Feng, Hai L.↗
Magnetism and quantum melting in moiré-material Wigner crystals
Recent experiments have established that semiconductor-based moir´e materials can host incompressible states at a series of fractional moir´e-miniband fillings. These states have been identified as generalized Wigner crystals in which electrons localize on a subset of the available triangular-lattice moir´e superlattice sites. In this article, we use momentum-space exact diagonalization to investigate the many-body ground state evolution at rational fillings from the weak-hopping classical lattice gas limit, in which only spin degrees-of-freedom are active at low energies, to the strong-hopping metallic regime where the Wigner crystals melt. We specifically address the nature of the magnetic ground states of the generalized Wigner crystals at fillings ν = 1/3 and ν = 2/3.
36 MATERIALS SCIENCE↗
Striped electron fluid on (111) KTaO 3
A recent study has revealed that the low carrier density electron gas (2DEG) induced at the interface of EuO and (111) KTaO 3 exhibits a broken symmetry phase with a strong in-plane anisotropy of the resistivity. We present a minimal tight-binding model of this (111) 2DEG, including the large spin-orbit coupling from the Ta ions, which reveals a hexagonal Fermi surface with a highly enhanced 2k F electronic susceptibility. We argue that repulsive electronic interactions, together with a ferromagnetic EuO substrate, favor a magnetic stripe instability leading to a partially gapped Fermi surface. Such a stripe state, or its vestigial nematicity, could explain the observed transport anisotropy. We propose a k · p theory for the low energy j = 3/2 states, which captures the key results from our tight-binding study, and further reveals the intertwined dipolar and octupolar modulations underlying this magnetic stripe order. We conclude by speculating on the relation of this stripe order to the superconductivity seen in this material.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Magnetization Process of Atacamite: A Case of Weakly Coupled S = 1/2 Sawtooth Chains
We present a combined experimental and theoretical study of the mineral atacamite Cu 2 Cl(OH) 3 . Density-functional theory yields a Hamiltonian describing anisotropic sawtooth chains with weak 3D connections. Experimentally, we fully characterize the antiferromagnetically ordered state. Here, magnetic order shows a complex evolution with the magnetic field, while, starting at 31.5 T, we observe a plateaulike magnetization at about M sat /2. Based on complementary theoretical approaches, we show that the latter is unrelated to the known magnetization plateau of a sawtooth chain. Instead, we provide evidence that the magnetization process in atacamite is a field-driven canting of a 3D network of weakly coupled sawtooth chains that form giant moments.
1-dimensional spin chains↗
Fast Ramping Accelerator Dipole Models for Fermilab’s Booster Upgrade and Muon Collider
The future discoveries in the field of High Energy Physics are led by the development of new types of accelerators. Around the world, there are a lot of researchers that are studying some possible designs for the future accelerators and some of them are considering the use of alternating current inside the superconducting magnets in order to have better efficiency. The work described in this report tries to compare some superconducting magnets made of different materials and to understand which one of them can be considered for its better performance working in a variable magnetic field. For this goal, becomes really important to control the temperature of the coil, and, as visible in the next chapter, to relate this parameter to the frequency of the magnetic field, in order to find, as will be named, the critical frequency .
43 PARTICLE ACCELERATORS↗
Magnetic and transport properties of amorphous, B 2 and L 2 1 Co 2 MnGa thin films
We have studied the magnetic and transport properties of Co 2 MnGa (CMG) thin films grown on MgO(100) substrates in terms of their chemical evolution from amorphous to ordered L 2 1 phases at the substrate temperature T s during the thin film deposition. Interestingly, the chemical order and magnetic properties sharply change depending on T s . The CMG film deposited at T s = 550 °C exhibits the L 2 1 -ordered structure and the magnetization of 3.5 μ B /f.u., while the CMG film deposited at T s = 300 °C shows a B 2-ordered structure and a relatively lower magnetization of 3 μ B /f.u., possibly due to the Mn–Mn antiferromagnetic interactions. A metallic behavior of the electrical resistivity appeared in the CMG film deposited at T s = 550 °C, whereas the semiconducting behavior appeared in the CMG films deposited at 300 °C and room temperature. Moreover, we found that the absolute value of α = d(Δ ρ )/d( T 1/2 ) in the low-temperature range below about 20 K is a measure to evaluate the degree of the chemical disorder. In a Hall effect measurement, the L 2 1 -ordered CMG film obtained at T s = 550 °C shows a sizable anomalous Hall resistivity of 15 µ Ω cm. This study unveils the relation between T s and atomic ordering, providing a new pathway for optimizing the chemical order.
36 MATERIALS SCIENCE↗
Structures and Magnetic Properties of K 2 Pd 4 U 6 S 17 , K 2 Pt 4 U 6 S 17 , Rb 2 Pt 4 U 6 S 17 , and Cs 2 Pt 4 U 6 S 17 Synthesized Using the Boron–Chalcogen Mixture Method
A series of A 2 M 4 U 6 S 17 (A = Alkali metal, M = Pd or Pt) compounds, specifically K 2 Pd 4 U 6 S 17 , K 2 Pt 4 U 6 S 17 , Rb 2 Pt 4 U 6 S 17 , and Cs 2 Pt 4 U 6 S 17 , were synthesized using the combined Boron-Chalcogen Mixture (BCM) and molten flux crystal growth methods. The formation of the Rb- and Cs- containing analogues resulted from the in-situ alkali polysulfide flux formation formed from the alkali carbonates. The successful synthesis of single crystals of the title compounds allowed for their structural characterization by single crystal X-ray diffraction. The structure determination revealed disorder of the alkali cations in Rb 2 Pt 4 U 6 S 17 , and Cs 2 Pt 4 U 6 S 17 , while the potassium cations in K 2 Pd 4 U 6 S 17 and K 2 Pt 4 U 6 S 17 were fully ordered. Here, magnetic measurements were performed on samples of K 2 Pt 4 U 6 S 17 , Rb 2 Pt 4 U 6 S 17 , and Cs 2 Pt 4 U 6 S 17 that contained small amounts of paramagnetic β-US 2 and diamagnetic PtS. Antiferromagnetic order is observed at T N = 9.1 K for K 2 Pt 4 U 6 S 17 . No long-range magnetic order was observed for Rb 2 Pt 4 U 6 S 17 and Cs 2 Pt 4 U 6 S 17 . Uranium moments of 2.5, 2.6, and 2.6 μB were measured for K 2 Pt 4 U 6 S 17 , Rb 2 Pt 4 U 6 S 17 , and Cs 2 Pt 4 U 6 S 17 , respectively.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Confinement of many-body Bethe strings
Based on the Bethe ansatz approach and inelastic neutron scattering experiments, we reveal the evolution of confinement of many-body Bethe strings in ordered regions of the quasi-one-dimensional antiferromagnet YbAlO 3 . In the antiferromagnetic phase, the spin dynamics is dominated by confined length-1 Bethe strings, whose dominancy in the high-energy branch of the excitation spectrum yields to confined length-2 Bethe strings when the material is tuned to the spin-density-wave phase. In the thermal-induced disordered region, the confinement effect disappears, and the system restores the conventional quantum integrable physics of the one-dimensional Heisenberg model. Finally, our results establish a unified picture based on a Bethe string for the spin dynamics in different magnetic phases of YbAlO 3 , and thus provide profound insight into many-body quantum magnetism.
1-dimensional spin chains↗
Ordering of room-temperature magnetic skyrmions in a polar van der Waals magnet
Abstract Control and understanding of ensembles of skyrmions is important for realization of future technologies. In particular, the order-disorder transition associated with the 2D lattice of magnetic skyrmions can have significant implications for transport and other dynamic functionalities. To date, skyrmion ensembles have been primarily studied in bulk crystals, or as isolated skyrmions in thin film devices. Here, we investigate the condensation of the skyrmion phase at room temperature and zero field in a polar, van der Waals magnet. We demonstrate that we can engineer an ordered skyrmion crystal through structural confinement on the μ m scale, showing control over this order-disorder transition on scales relevant for device applications.
36 MATERIALS SCIENCE↗
Magnetically driven short-range order can explain anomalous measurements in CrCoNi
Significance High-entropy alloys, an exciting new class of structural materials involving many concentrated elements, are generally assumed to be chemically disordered. This work reveals how magnetic interactions can drive atomic-scale ordering in a mechanically interesting system that has been widely studied as a model for many promising alloys. The formation of short-range order in this manner is used to explain experimental anomalies, suggesting that many related materials could contain similarly impactful ordering under standard conditions. This possibility offers solutions to outstanding questions concerning CrCoNi and emphasizes the importance of magnetism and short-range order in related high-entropy alloys.
36 MATERIALS SCIENCE↗
Magnetic, charge, and bond order in the two-dimensional Su-Schrieffer-Heeger-Holstein model
Most nonperturbative numerical studies of electron-phonon interactions focus on model Hamiltonians where the electrons interact with a phonon branch via a single type of microscopic mechanism. Two commonly explored couplings in this context are the Holstein and Su-Schrieffer-Heeger (SSH) interactions, which describe phonons modulating the on-site energy and intersite electron hopping, respectively. Many materials, however, have multiple phonon branches that can each interact with electronic degrees of freedom in different ways. We present here a determinant quantum Monte Carlo study of the half-filled two-dimensional (bond) SSH-Holstein Hamiltonian, where electrons couple to different phonon branches via either the Holstein or SSH mechanism. As a result, we map the model's phase diagram and determine the nature of the transitions between charge-density wave, bond-order wave, and antiferromagnetic order.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗