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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Chemical Design of Spin Frustration to Realize Topological Spin Glasses

Patterning spins to generate collective behavior is at the core of condensed matter physics. Physicists develop techniques, including the fabrication of magnetic nanostructures and precision layering of materials specifically to engender frustrated lattices. As chemists, we can access such exotic materials through targeted chemical synthesis and create new lattice types by chemical design. Here, in this study, we introduce a new approach to induce magnetic frustration on a modified honeycomb lattice through a competition of alternating antiferromagnetic (AFM) and ferromagnetic (FM) nearest-neighbor interactions. By subtly modulating these two types of interactions through facile synthetic modifications, we created two systems: (1) a topological spin glass and (2) a frustrated spin-canted magnet with low-temperature exchange bias. To design this unconventional magnetic lattice, we used a metal–organic framework (MOF) platform, Ni 3 (pymca) 3 X 3 (NipymcaX where pymca = pyrimidine-2-carboxylato and X = Cl, Br). We isolated two MOFs, NipymcaCl and NipymcaBr, featuring canted Ni 2+ -based moments. Despite this similarity, differences in the single-ion anisotropies of the Ni 2+ spins result in distinct magnetic properties for each material. NipymcaCl is a topological spin glass, while NipymcaBr is a rare frustrated magnet with low-temperature exchange bias. Density functional theory calculations and Monte Carlo simulations on the NipymcaX lattice support the presence of magnetic frustration as a result of alternating AFM and FM interactions. Our calculations enabled us to determine the ground-state spin configuration and the distribution of spin–spin correlations relative to paradigmatic kagomé and triangular lattices. This modified honeycomb lattice is similar to the electronic Kekulé-O phase in graphene and provides a highly tunable platform to realize unconventional spin physics.

Exchange bias↗
DOE OSTI2025

Spin Frustration and Unconventional Surface Spin Canting State in Van der Waals Ferromagnet/Antiferromagnet Heterostructures

Atomically flat surfaces of van der Waals (vdW) materials pave an avenue for addressing a long-standing fundamental issue of how a compensated antiferromagnet (AFM) surface frustrates a ferromagnetic (FM) overlayer in FM/AFM heterostructures. We investigate Fe5GeTe2/NiPS3 vdW heterostructures by characterizing AFM and FM spins separately. We find that in-plane zig-zag AFM NiPS3 develops three equivalent AFM domains, which are robust against external magnetic field and magnetic coupling with Fe5GeTe2. Moreover, evidence is provided of in-plane-AFM-induced perpendicular magnetic anisotropy (PMA) in adjacent Fe5GeTe2, and an unconventional out-of-plane surface spin canting state with the Fe5GeTe2 spins spatially turn from out-of-plane direction near the interface to in-plane direction away from the interface in Fe5GeTe2/NiPS3. The out-of-plane surface spin canting is a unique property of spin frustration in vdW magnetic heterostructures.

Wang, Tianye↗
DOE OSTI2020

Emergent spin-1 Haldane gap and ferroelectricity in a frustrated spin- 1 2 ladder

We report experimental and theoretical evidence that Rb 2 Cu 2 Mo 3 O 12 has a nonmagnetic tetramer ground state of a two-leg ladder comprising antiferromagnetically coupled frustrated spin-12 chains and exhibits a Haldane spin gap of emergent spin-1 pairs. Three spin excitations split from the spin-1 triplet by a Dzyaloshinskii-Moriya interaction are identified in inelastic neutron-scattering and electron spin resonance spectra. A tiny magnetic field generates ferroelectricity without closing the spin gap, indicating a unique class of ferroelectricity induced by a vector spin chirality order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Quantum order by disorder in frustrated spin nanotubes

Here we investigate quantum order by disorder in a frustrated spin nanotube formed by wrapping a J1–J2 Heisenberg model at 45° around a cylinder. Using Schwinger boson theory and density matrix renormalization group (DMRG), we have computed the ground-state phase diagram to reveal a Z2 phase in which collinear spin stripes form a right- or left-handed helix around the nanotube. We have derived an analytic estimate for the critical η c = J 1 /2J 2 of the Z 2 -helical phase transition, which is in agreement with the DMRG results. By evaluating the entanglement spectrum and nonlocal string order parameters we discuss the topology of the Z 2 -helical phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1989

Phase diagram of the frustrated spin-1/2 Heisenberg antiferromagnet in two dimensions

A Lanczos technique is used to study the frustrated spin-1/2 Heisenberg model on square lattices of 16 and 20 sites. Frustration is introduced by an interaction along the diagonals of the plaquettes with coupling J2 greater than or equal to 0. For large J2, the ground state breaks (spontaneously) the lattice rotational symmetry. For intermediate values of J2, the squares of order parameters associated with spin-Peierls and 'twisted'states have a peak, while a similar quantity for a chiral state shows no interesting structure.

Dagotto, Elbio↗
DOE OSTI2024

Spin frustration and an exotic critical point in ferromagnets from nonuniform opposite g factors

Here, it is demonstrated that novel spin frustration can be induced in ferromagnets with nonuniform opposite Landé g-factors. The frustrated state is characterized by a mutual interplay of typical ferromagnetic (FM) and antiferromagnetic (AF) features, such as the zero-field susceptibility being FM-like at low temperatures but AF-like at high temperatures. It is also found to contain an exotic zero-temperature 'half fire, half ice' critical point at which the spins on one sublattice are fully disordered and on the other one are fully ordered. We suggest that such frustration may occur in a number of copper-iridium oxides such as Sr 3 CuIrO 6 . We also anticipate a realization of the frustration and 'partial fire, partial ice' states in certain antiferromagnets, lattice gas, and neuron systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Structural and double magnetic transitions in the frustrated spin- 1 2 capped-kagome antiferromagnet ( RbCl ) Cu 5 P 2 O 10

The structural and magnetic properties of the geometrically frustrated spin- 1 2 capped-kagome antiferromagnet (RbCl) Cu 5 P 2 O 10 are investigated via temperature-dependent x-ray diffraction, magnetization, heat capacity, and 31 P NMR experiments on a polycrystalline sample. It undergoes a structural transition at around T t ≃ 310 K from a high-temperature trigonal (P ¯3m1) to a low-temperature monoclinic (C2/c) unit cell, where the low-temperature structure features the capped-kagome geometry of Cu 2+ ions. Interestingly, it shows the onset of two successive magnetic transitions at T N1 ≃ 20 K and T N2 ≃ 7 K. The shape of the 31 P NMR spectra unfolds the possible nature of the transitions below T N1 and T N2 to be of incommensurate and commensurate antiferromagnetic type, respectively. A large value of the Curie-Weiss temperature as compared to T N1 sets the frustration parameter f ≃ 8, ensuring strong magnetic frustration in the compound. From the 31 P NMR spin-lattice relaxation rate, the leading antiferromagnetic exchange coupling is estimated to be J/k B ≃ 117 K. Furthermore, these unusual double magnetic transitions make this compound beguiling for further investigations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Dzyaloshinskii-Moriya interaction induced magnetoelectric coupling in a tetrahedral molecular spin-frustrated system

We have investigated magnetoelectric (ME) coupling in the single-molecule magnet Mn 4 Te 4 (PEt 3 ) 4 with tetrahedral spin frustration. Our density functional studies found that an electric dipole moment can emerge with various noncollinear spin orderings. The forms of spin-dependent dipole are determined and consistent with that in noncentrosymmetric magnets driven by the Dzyaloshinskii-Moriya interaction. Writing a parameterized spin Hamiltonian, after solving for eigenvalues and eigenstates, we quantified the ME coupling by calculating the thermal average of the electric and magnetic susceptibilities, which can be influenced by external magnetic and electric fields, respectively. The quadratic relations are expected to be observable in experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Helimagnetism in MnBi 2 Se 4 Driven by Spin-Frustrating Interactions Between Antiferromagnetic Chains

We report the magnetic properties and magnetic structure determination for a linear-chain antiferromagnet, MnBi 2 Se 4 . The crystal structure of this material contains chains of edge-sharing MnSe 6 octahedra separated by Bi atoms. The magnetic behavior is dominated by intrachain antiferromagnetic (AFM) interactions, as demonstrated by the negative Weiss constant of –74 K obtained by the Curie–Weiss fit of the paramagnetic susceptibility measured along the easy-axis magnetization direction. The relative shift of adjacent chains by one-half of the chain period causes spin frustration due to interchain AFM coupling, which leads to AFM ordering at TN = 15 K. Neutron diffraction studies reveal that the AFM ordered state exhibits an incommensurate helimagnetic structure with the propagation vector k = (0, 0.356, 0). The Mn moments are arranged perpendicular to the chain propagation direction (the crystallographic b axis), and the turn angle around the helix is 128°. The magnetic properties of MnBi2Se4 are discussed in comparison to other linear-chain antiferromagnets based on ternary mixed-metal halides and chalcogenides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Analysis of spin frustration in an Fe III 7 cluster using a combination of computational, experimental, and magnetostructural correlation methods

The synthesis, structure, and magnetic properties are reported for [Fe 7 O 3 (O 2 C t Bu) 9 (mda) 3 (H 2 O) 3 ] ( 1 ), where mdaH 2 is N -methyldiethanolamine. 1 was prepared from the reaction of [Fe 3 O(O 2 C t Bu) 6 (H 2 O) 3 ](NO 3 ) with mdaH 2 in a 1:~3 ratio in MeCN. The core of 1 consists of a central octahedral Fe III ion held within a non-planar Fe 6 loop by three μ 3 -O 2- and three μ 2 -RO - arms from the three mda 2- chelates. Variable-temperature dc and ac magnetic susceptibility studies revealed dominant antiferromagnetic coupling, leading to a ground state spin of S = 5 / 2 . The ground state was confirmed by a fit of magnetization data collected in the 0.1–7.0 T and 1.8–10.0 K ranges. The four Fe 2 pairwise exchange parameters ( J 1 - J 4 ) were estimated by independent methods: theoretical calculations using either broken symmetry energy differences (-46.3, -16.2, -3.9, and - 28.1 cm -1 , respectively) or Green’s function approximation methods (-41.4, -14.8, -13.2, and - 24.7 cm -1 ), and a magnetostructural correlation (MSC) previously developed for high nuclearity Fe III /O complexes (-39.5, -13.8, -6.7, and - 23.5 cm -1 ). Additionally, the J 1 - J 4 obtained from the MSC and theoretical methods were used with the program PHI to both simulate χ M T vs T as well as to serve as reasonable input values to fit the experimental data (-41.0, -11.4, -5.0, and - 27.3 cm -1 ). Analysis of the J ij led to identification of the spin frustration effects operative and the resultant spin vector alignments at each Fe III ion, thus allowing for the rationalization of the experimental ground state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Some exactly solvable and tunable frustrated spin models

In this report we discuss three exactly solvable spin models of geometric frustration. First, we discuss a 1-parameter subfamily of the 16 vertex model, which can be mapped to a planar Ising model and solved via Fisher-Dubedát decorations. We then consider a 1-parameter family generalization of the Villain’s fully frustrated model, which interpolates between Onsager’s 2D Ising model and the Villain one. We then discuss spin ice models on a tree, which can be solved exactly using recursions a lá Bethe.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Three-state Potts nematic order in stacked frustrated spin models with SO(3) symmetry

Here, we propose stacked two-dimensional lattice designs of frustrated and SO(3) symmetric spin models consisting of antiferromagnetic (AF) triangular and ferromagnetic (FM) sixfold symmetric sublattices that realize emergent $\mathbb{Z}_{3}$ Potts nematic order. Considering bilinear-biquadratic spin interactions, our models describe an SO(3)-symmetric triangular lattice AF subject to a fluctuating magnetization arising from the FM coupled sublattice. We focus on the classical AFM-FM windmill model and map out the zero- and finite-temperature phase diagram using Monte Carlo simulations and analytical calculations. We discover a state with composite Potts nematic order above the ferrimagnetic three-sublattice up-up-down ground state and relate it to Potts phases in SO(3)-broken Heisenberg and Ising AFMs in external magnetic fields. Finally, we show that the biquadratic exchange in our model is automatically induced by thermal and quantum fluctuations in the purely bilinear Heisenberg model, easing the requirements for realizing these lattice designs experimentally.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Non-equilibrium dynamics in geometrically frustrated spin glass Bi 2 Fe 3 GaO 9 with a Cairo lattice

We have explored the magnetic relaxation of the spin glass phase in Bi 2 Fe 3 GaO 9 , a geometrically frustrated magnet with a unique Cairo lattice made of pentagonal building blocks. Using dc magnetization measurements, we find the relaxation behavior in single crystals follows the Arrhenius law as a function of temperature but remains relatively constant under different magnetic fields. Through a carefully designed protocol, we observe significant rejuvenation and memory effects, reminiscent of classical dilute spin glasses rather than spin jamming systems. Our finding suggests that Bi 2 Fe 3 GaO 9 is probably located in the crossover between conventional spin glass and perfect spin jam and thus provides an excellent platform for investigating the evolution of underlying magnetic structure, paving the way for further neutron scattering research.

aging↗
DOE OSTI2022

Circuit Quantum Electrodynamics in Hyperbolic Space: From Photon Bound States to Frustrated Spin Models

Circuit quantum electrodynamics is one of the most promising platforms for efficient quantum simulation and computation. In recent groundbreaking experiments, the immense flexibility of superconducting microwave resonators was utilized to realize hyperbolic lattices that emulate quantum physics in negatively curved space. Here we investigate experimentally feasible settings in which a few superconducting qubits are coupled to a bath of photons evolving on the hyperbolic lattice. We compare our numerical results for finite lattices with analytical results for continuous hyperbolic space on the Poincaré disk. We find good agreement between the two descriptions in the long-wavelength regime. We show that photon-qubit bound states have a curvature-limited size. We propose to use a qubit as a local probe of the hyperbolic bath, for example, by measuring the relaxation dynamics of the qubit. We find that, although the boundary effects strongly impact the photonic density of states, the spectral density is well described by the continuum theory. We show that interactions between qubits are mediated by photons propagating along geodesics. We demonstrate that the photonic bath can give rise to geometrically frustrated hyperbolic quantum spin models with finite-range or exponentially decaying interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Frustrated spin-1/2 dimer compound K 2 Co 2 ( Se O 3 ) 3 with easy-axis anisotropy

Magnetic susceptibility, magnetization, and specific-heat measurements under both in-plane and out-of-plane field on K 2 Co 2 (SeO 3 ) 3 single crystals are reported. The Co dimers in this compound, which are made from face-sharing effective spin-1/2 CoO 6 octahedra, sit on the corners of a geometrically frustrating triangular planar lattice. No long-range magnetic ordering is found down to 0.35 K, which, together with the large negative Curie-Weiss temperature obtained from fitting the temperature-dependent magnetic susceptibility, indicates that the system is magnetically frustrated. Analysis of the field and orientation dependence of the magnetic and thermodynamic properties suggests the presence of an easy-axis anisotropy. Furthermore, the magnetic fluctuations present due to geometric frustration are more resistant to an in-plane field than a perpendicular-to-plane field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

High-temperature anomalous Hall effect driven by frustrated spin fluctuations in the antiferromagnetic delafossite metal PdCrO 2

Metallic delafossite oxides are of exceptional interest due to their ultraclean metallic transport. In the case of PdCrO 2 , this arises in a triangular-lattice antiferromagnet, creating a unique opportunity to study frustrated magnetism in a very clean metal. Here, we combine a chemical vapor transport crystal growth approach with magnetic, thermodynamic, magnetotransport, and neutron scattering measurements to elucidate the striking anomalous Hall effect (AHE) in antiferromagnetic PdCrO 2 . The unconventional AHE (with anomalous Hall conductivity ~10 5 Ω −1 cm −1 ) and a large positive magnetoresistance effect (>1,000%) are shown to exhibit complex temperature dependencies, persisting to almost seven times the Néel temperature (~250 K). These effects are directly compared to elastic neutron scattering, inelastic neutron scattering, and neutron magnetic pair distribution function data, establishing unambiguous links between anomalous magnetotransport properties and directly probed short-range spin fluctuations. The latter occur over a notably broad temperature range due to geometrical magnetic frustration. Connecting to recent experimental and theoretical developments, these findings are discussed in terms of a temperature-dependent interplay between chiral spin order and chiral spin fluctuations, significantly elucidating the high-temperature anomalous magnetotransport in such compounds.

anomalous Hall effect↗
DOE OSTI2024

Magnetic properties of the frustrated spin-$\frac{1}{2}$ capped-kagome antiferromagnet (CsBr)Cu 5 V 2 O 10

Here, the structural and magnetic properties of a spin-$\frac{1}{2}$ averievite (CsBr)⁢Cu 5⁢ V 2 ⁢O 10 are investigated by means of temperature-dependent x-ray diffraction, magnetization, heat capacity, and 51 V nuclear magnetic resonance (NMR) measurements. The crystal structure (trigonal, $P\bar{3}$) features a frustrated capped-kagome lattice of the magnetic Cu 2+ ions. Magnetic susceptibility analysis indicates a large Curie-Weiss temperature of $\theta$ CW ≃ -175K. Heat capacity signals the onset of a magnetic long-range-order (LRO) at T N ≃21.5K at zero magnetic field due to the presence of significant inter-planer coupling in this system. The magnetic LRO below 27 K is further evident from the drastic change in the 51 V NMR signal intensity and rapid enhancement in the 51 V spin-lattice relaxation rate in a magnetic field of 6.3 T. The frustration index ƒ=|⁢$\theta$ CW ⁢|/⁢T N ≃ 8 ascertains strong magnetic frustration in this compound. From the high-temperature value of the 51 V NMR spin-lattice relaxation rate, the leading antiferromagnetic exchange interaction between the Cu 2+ ions is calculated to be J/k B ≃ 136K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Interplay between defect transport and cation spin frustration in corundum-structured oxides

Despite the fundamental importance of mass transport, there is still a lack of knowledge regarding the mechanisms in many materials. In particular, how the magnetic spin structure interacts with migrating defects is unclear. In this work, using density functional theory to examine cation interstitial transport in antiferromagnetic corundum-structured oxides, we reveal an interplay between the migration of the interstitial and the magnetic structure of the oxide. The magnetic spin configuration impacts the migration energy of the migrating defect but, critically, the defect modifies the spin configuration. Thus, the two aspects change in concert to modify one another. This has profound implications for mass transport in magnetic materials.

36 MATERIALS SCIENCE↗