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At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Magnetosynthesis effect on magnetic order, phonons, and magnons in single-crystal Sr 2 ⁢ IrO 4

It was shown earlier that applying a magnetic field during the growth of Sr 2 IrO 4 , also known as “field-alteration”, induces significant changes to its structural, magnetic, and transport properties. However, the microscopic nature of these changes is enigmatic. Here, in this study, we employed resonant elastic and inelastic x-ray scattering, as well as Raman scattering, to investigate samples from two batches of Sr 2 IrO 4 grown in magnetic fields of different strengths. Our findings reveal that samples grown in a weaker magnetic field have similar magnetic order to non-altered samples, whereas those grown in a stronger field show a different stacking of weak in-plane ferromagnetic moments. Additionally, we observed significant softening and broadening of select Raman-active phonons in the field altered samples, with a stronger effect in the samples grown in the stronger field. We discuss insights that our results provide into the microscopic nature of field-alteration in Sr 2 IrO 4 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nonlinear coupling of whistler waves to oblique electrostatic turbulence enabled by cold plasma

Kinetic simulations and theory demonstrate that whistler waves can excite oblique, short-wavelength fluctuations through secondary drift instabilities if a population of sufficiently cold plasma is present. The excited modes lead to heating of the cold populations and damping of the primary whistler waves. The instability threshold depends on the density and temperature of the cold population and can be relatively small if the temperature of the cold population is sufficiently low. Furthermore, this mechanism may thus play a significant role in controlling amplitude of whistlers in the regions of the Earth's magnetosphere where cold background plasma of sufficient density is present.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Hardware, methodology and applications of 2 + D backscatter Mössbauer spectroscopy with simultaneous x-ray and γ-ray detection

Abstract A unique method is presented for the acquisition and analysis of 57 Fe backscatter Mössbauer spectra with simultaneous detection of the resonant 14.4 keV γ -rays and the characteristic 6.4 keV x-rays, using a custom-built multi-parameter analyser constructed on the basis of commercial analogue to digital converters and high-speed digital latches. The system allows for the simultaneous registration of Doppler-modulation velocities and photon energies, with up to 4096 and 8192 digital channels respectively. This arrangement is in contrast to most related systems, which detect at a single narrow energy window per detector. Samples of arbitrary atomic structure, morphology and surface topography can be studied without altering the setup or the analysis procedure, provided that the samples are at least micrometre sized. The hardware and software that are used to acquire data with minimal dead time are described and the custom and self-contained methods for post-measurement energy discrimination, background correction and velocity-axis folding are discussed. The data are fit using a general Hamiltonian model for the nuclear energy levels of 57 Fe and a quantum mechanical description of the angular momentum coupling is utilised, with consideration of the crystalline and chemical disorder of the sample under examination. Three examples of distinct magnetic systems, with thicknesses ranging from 5 μ m to 6 mm, that were studied using this method are presented, these are: an amorphous CoFeB-based ribbon with ultra-soft coercivity for high-frequency applications, magnetically hard Nd-Fe-B thick films on Si substrates, examined in both as-deposited and annealed states, and a sample from the nickel-rich iron meteorite NWA 6259 that contains the atomically ordered, elevated coercivity, L 1 0 phase of FeNi, tetrataenite. The wide applicability and usefulness of this method is thus demonstrated on three distinct sample morphologies that required little to no surface preparation prior to examination.

Engineering↗
DOE OSTI2016

An integrated spectroscopic and wet chemical approach to investigate grass litter decomposition chemistry

The chemical transformations that occur during litter decomposition are key processes for soil organic matter formation and terrestrial biogeochemistry; yet we still lack complete understanding of these chemical processes. Thus, we monitored the chemical composition of Andropogon gerardii (big bluestem grass) litter residue over a 36 month decomposition experiment in a prairie ecosystem using: traditional wet chemical fractionation based upon digestibility, solid state 13 C nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The goals of this study were to (1) determine the chemical changes occurring during A. gerardii litter decomposition, and (2) compare the information obtained from each method to assess agreement. Overall, we observed a 97 % mass loss of the original litter, through a two-stage decomposition process. In the first stage, within 12 months, non-structural, cellulose and hemicellulose fractions not encrusted in lignin were preferentially and rapidly lost, while the acid unhydrolyzable residue (AUR) and microbial components increased. During the second stage, 12–36 months, all wet chemical fraction masses decreased equivalently and slowly with time, and the AUR and the lignin-encrusted cellulose fractions decomposition rates were comparable to each other. Method comparisons revealed that wet chemical fractionation did not accurately follow the initial litter structures, particularly lignin, likely because of chemical transformations and accumulation of microbial biomass. FTIR and NMR were able to determine bulk structural characteristics, and aid in elucidating chemical transformations but lacked the ability to measure absolute quantities of structural groups. As a result, we warn from the sole use of wet chemical methods, and strongly encourage coupling them with spectroscopic methods. Our results overall support the traditional chemical model of selective preservation of lignin, but shows that this is limited to the early stages of decomposition, while lignin is not selectively preserved at subsequent stages. Finally, our study also provides important evidence regarding the impact of chemically different litter structures on decomposition rates and pathways.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

T 1 Anisotropy Elucidates Spin Relaxation Mechanisms in an S = 1 Cr(IV) Optically Addressable Molecular Qubit

Paramagnetic molecules offer unique advantages for quantum information science owing to their spatial compactness, synthetic tunability, room-temperature quantum coherence, and potential for optical state initialization and readout. However, current optically addressable molecular qubits are hampered by rapid spin–lattice relaxation ( T 1 ) even at sub-liquid nitrogen temperatures. Here, we use temperature- and orientation-dependent pulsed electron paramagnetic resonance (EPR) to elucidate the negative sign of the ground state zero-field splitting (ZFS) and assign T 1 anisotropy to specific types of motion in an optically addressable S = 1 Cr(o-tolyl) 4 molecular qubit. The anisotropy displays a distinct sin 2 (2θ) functional form that is not observed in S = 1/2 Cu(acac) 2 or other Cu(II)/V(IV) microwave addressable molecular qubits. The Cr(o-tolyl) 4 T 1 anisotropy is ascribed to couplings between electron spins and rotational motion in low-energy acoustic or pseudoacoustic phonons. Our findings suggest that rotational degrees of freedom should be suppressed to maximize the coherence temperature of optically addressable qubits.

magnetic properties↗
DOE OSTI2014

Hybrid Pd/Fe{sub 3}O{sub 4} nanowires: Fabrication, characterization, optical properties and application as magnetically reusable catalyst for the synthesis of N-monosubstituted ureas under ligand-free conditions

Highlights: • Preparation of Pd/Fe{sub 3}O{sub 4} nanowires as magnetically reusable catalysts. • The optical properties of the catalyst were studied using Gans theory. • N-arylation of benzylurea and in situ hydrogenolysis of 1-benzyl-3-arylureas. - Abstract: This paper reports the synthesis and use of Pd/Fe{sub 3}O{sub 4} nanowires, as magnetically separable catalysts for ligand-free amidation coupling reactions of aryl halides with benzylurea under microwave irradiation. Then, the in situ hydrogenolysis of the products was performed to afford the N-monosubstituted ureas from good to excellent yields. This method has the advantages of high yields, simple methodology and easy work up. The catalyst can be recovered by using a magnet and reused several times without significant loss of its catalytic activity. The catalyst was characterized using the powder XRD, SEM, EDS and UV–vis spectroscopy. Experimental absorbance spectra was compared with results from the Gans theory.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Magnetic and EPR Spectroscopic Studies of Thiolate Bridged Divalent Ni, Pd, and Pt Ions Capped with VO(N 2 S 2 ) Metalloligands

Reactions of the metallodithiolate complex VO(bme-dach) (hereafter abbreviated as V, where bme-dach = N,N ′-bis(2-mercaptoethyl)-1,4-diazacycloheptane) with [Pd II (CH 3 CN) 4 ](BF 4 ) 2 and [Pt II (CH 3 CN) 4 ](BF 4 ) 2 yield the V–M–V trimetallic compounds [VPdV](BF 4 ) 2 (2) and [VPtV](BF 4 ) 2 (3). Reaction of a similar metalloligand, VO(bme-daco) (hereafter abbreviated as V′ where bme-daco = N,N′-bis(2-mercaptoethyl)-1,5-diazacyclooctane) with [Ni II (CH 3 CN) 6 ](BF 4 ) 2 afforded the related salt [V′NiV′](BF 4 ) 2 (1). X-ray structural analyses revealed that cations in 1, 2, and 3 adopt a stairstep C 2h structure consisting of two terminal VO(N 2 S 2 ) moieties bridged via thiolate sulfur to the group 10 metal ions. Weak ferromagnetic superexchange coupling (J = 0.282 cm –1 for 1, 0.954 cm –1 for 2, and 1.372 cm –1 for 3) was observed between the two S = 1/2 V IV centers separated by distances in the range of 5.9–6.3 Å, with J values varying following the order Ni < Pd < Pt. Frozen-solution EPR spectra measured on the more soluble [BArF 24 ] − (BArF 24 – = tetrakis((3,5-trifluoromethyl)phenyl)borate) analogues revealed that the [VPtV] 2+ cation exhibits a 15-line hyperfine splitting of 225 MHz at g = 4 in parallel mode, confirming exchange coupling between the two 51 V, I = 7/2 nuclei. Density-functional theory (DFT) calculations indicate an S = 1 ground state for 1–3. These results demonstrate that the choice of paramagnetic metallodithiolate ligand and diamagnetic bridge in such trimetallic species influences the sign and magnitude of magnetic interactions.

anions↗
DOE OSTI2023

Antiferromagnetic Fe Te 2 1 T - phase formation at the Sb 2 Te 3 / Ni 80 Fe 20 interface

Bilayer topological insulator/ferromagnet (TI/FM) heterostructures are promising for spintronic applications due to their low switching energy and therefore power efficiency. Until recently, the reactivity of TI with FM films was overlooked in the spin orbit-torque literature, even though there are reports that it is energetically favorable for TIs to react with transition metals and form interfacial layers. Here, in this study we fabricated a TI/FM heterostructure comprised of molecular beam epitaxy grown Sb 2 Te 3 and DC sputtered Ni 80 Fe 20 . Broadband ferromagnetic resonance revealed spin-pumping evident by the significant enhancement in Gilbert damping, which is likely a signature of the topological surface states or the presence of large spin-orbit-coupling in the adjacent Sb 2 Te 3 . With low-temperature magnetometry, an exchange bias is observed which indicates an exchange interaction between an antiferromagnet (AFM) and an adjacent FM. Cross-section high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) characterization of the Sb 2 Te 3 - Ni 80 Fe 20 bilayer revealed a complex interface showing diffusion of Fe and Ni into the Sb 2 Te 3 film yielding the formation of a FeTe 2 1T-type structural phase. Furthermore, density functional theory calculations revealed that the FeTe 2 1T-phase has an AFM ground state. Due to experimental limitations in the electron energy loss spectroscopy measurements precise chemistry of the interfacial phase could not be determined, therefore it is possible that the FeTe 2 1T and/or an intermixed (Fe 1-x Ni x )Te 2 1T is the AFM interfacial phase contributing to exchange bias in the system. This work emphasizes the chemical complexity of TI/FM interfaces that host novel, metastable magnetic topological phases and require more in-depth studies of other similar interfaces.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Perspectives on the Dynamic Nuclear Polarization Mechanisms of Monoradicals: Overhauser Effect or Thermal Mixing?

This mini-review summarizes the evolving debate regarding the origins of the absorptive features seen in the dynamic nuclear polarization (DNP) spectra of certain monoradicals when they are irradiated at their electron Larmor frequency. This feature has drawn attention due to its reverse scaling with respect to the magnetic field strength and potential for high-field DNP. Two competing hypotheses have been introduced to explain the DNP feature based on (1) the Overhauser effect and low-temperature molecular dynamics and (2) radical clustering and a thermal mixing mechanism. Since the original discovery, a large number of experimental observations have been made in attempts to understand and ultimately leverage the mechanism. We summarize these observations and provide critical assessments of how the competing hypotheses approach them.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2003

Differences in the hemodynamic response to event-related motor and visual paradigms as measured by near-infrared spectroscopy

Several current brain imaging techniques rest on the assumption of a tight coupling between neural activity and hemodynamic response. The nature of this neurovascular coupling, however, is not completely understood. There is some evidence for a decoupling of these processes at the onset of neural activity, which manifests itself as a momentary increase in the relative concentration of deoxyhemoglobin (HbR). The existence of this early component of the hemodynamic response function, however, is controversial, as it is inconsistently found. Near infrared spectroscopy (NIRS) allows quantification of levels of oxyhemoglobin (HbO(2)) and HbR during task performance in humans. We acquired NIRS data during performance of simple motor and visual tasks, using rapid-presentation event-related paradigms. Our results demonstrate that rapid, event-related NIRS can provide robust estimates of the hemodynamic response without artifacts due to low-frequency signal components, unlike data from blocked designs. In both the motor and visual data the onset of the increase in HbO(2) occurs before HbR decreases, and there is a poststimulus undershoot. Our results also show that total blood volume (HbT) drops before HbO(2) and undershoots baseline, raising a new issue for neurovascular models. We did not find early deoxygenation in the motor data using physiologically plausible values for the differential pathlength factor, but did find one in the visual data. We suggest that this difference, which is consistent with functional magnetic resonance imaging (fMRI) data, may be attributable to different capillary transit times in these cortices.

NASA Program Biomedical Research and Countermeasur↗
DOE OSTI2013

On the toroidal plasma rotations induced by lower hybrid waves

A theoretical model is developed to explain the plasma rotations induced by lower hybrid waves in Alcator C-Mod. In this model, torodial rotations are driven by the Lorentz force on the bulk-electron flow across flux surfaces, which is a response of the plasma to the resonant-electron flow across flux surfaces induced by the lower hybrid waves. The flow across flux surfaces of the resonant electrons and the bulk electrons are coupled through the radial electric field initiated by the resonant electrons, and the friction between ions and electrons transfers the toroidal momentum to ions from electrons. An improved quasilinear theory with gyrophase dependent distribution function is developed to calculate the perpendicular resonant-electron flow. Toroidal rotations are determined using a set of fluid equations for bulk electrons and ions, which are solved numerically by a finite-difference method. Numerical results agree well with the experimental observations in terms of flow profile and amplitude. The model explains the strong correlation between torodial flow and internal inductance observed experimentally, and predicts both counter-current and co-current flows, depending on the perpendicular wave vectors of the lower hybrid waves.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2018

Ultralow Frequency Waves as an Intermediary for Solar Wind Energy Input Into the Radiation Belts

Enhancements of electron fluxes in the outer radiation belt have been closely linked to increases in solar wind speed and density as well as to prolonged intervals of southward interplanetary magnetic field. Periodic oscillations in the Earth's magnetic field with frequencies in the range of a few millihertz (ultralow frequency or ultralow frequency waves) may be an intermediary through which these solar wind drivers influence radiation belt dynamics due to their potential for resonant interactions with energetic electrons causing the radial migration of resonant electrons. Using data from more than 180 ground magnetometers contributing to the worldwide SuperMAG collaboration, we explore possible relationships between relativistic electron flux variations and the spatial and temporal profiles of ultralow frequency wave power contained in the Pc5 frequency band (2–7 mHz). During 19 geomagnetic storms marked by relativistic (1.5 MeV < E < 6 MeV) electron flux enhancements and 19 storms that led to prolonged electron flux depletions, Pc5 wave power is found penetrating to L shells as low as 2–3. The enhancement of Pc5 wave power starts almost simultaneously with the storm onset. The depth of wave activity penetration was found associated with the strength of geomagnetic activity (Spearman's ρ = 0.54), which is also related to the location of electron flux maximum observed in the recovery phase. Pc5 wave activity persists longer (for up to ≈62 hr) for those storms that produced relativistic electrons. We also investigate the combination of interplanetary conditions necessary to differentiate the response of relativistic electron fluxes to geomagnetic storms. A coupling function that captures the increased reconnection rate at the dayside magnetopause affecting magnetospheric processes which may produce Pc5 wave power offers an additional key to further understanding the outer belt dynamics.

Georgiou, M.↗
DOE OSTI2018

Mn{sub Ga} Acceptor Center in GaAs (Review)

The model of the Mn{sub Ga} acceptor in GaAs in which initial ground state of a coupled hole Γ{sub 8} is changed due to the antiferromagnetic exchange interaction with five 3d electrons of the Mn core is described. The acceptor energy spectrum and the wave functions of its states and also their changes under action of deformations, electric and magnetic fields are considered. Expressions are presented for the description of various properties of isolated Mn{sub Ga} acceptors in GaAs, and the data of some experiments (changes in the Mn{sub Ga}{sup 0} luminescence and absorption spectra and polarization under uniaxial pressures and in magnetic field, EPR spectra, temperature dependence of the magnetic susceptibility, circular polarization of photoluminescence during excitation by polarized light in magnetic field, etc.) are analyzed. It is demonstrated that, in some cases, it is necessary to take into account the existence of random electric and strain fields splitting the acceptor states in the crystal. The analysis results show that this model agrees well with most of the experimental results. The exchange interaction constant is in the range of 3–5 meV.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Structural connectivity in schizophrenia and its impact on the dynamics of spontaneous functional networks

The neuropathology of schizophrenia remains unclear. Some insight has come from modern neuroimaging techniques, which offer an unparalleled opportunity to explore in vivo the structure and function of the brain. Using functional magnetic resonance imaging, it has been found that the large-scale resting-state functional connectivity (rsFC) in schizophrenia — measured as the temporal correlations of the blood-oxygen-level-dependent (BOLD) signal — exhibit altered network topology, with lower small-world index. The origin of these rsFC alterations and link with the underlying structural connectivity remain unclear. In this work, we used a computational model of spontaneous large-scale brain activity to explore the role of the structural connectivity in the large-scale dynamics of the brain in health and schizophrenia. The structural connectomes from 15 adolescent patients with early-onset schizophrenia and 15 age- and gender-matched controls were built from diffusion tensor imaging data to detect the white matter tracts between 90 brain areas. Brain areas, simulated using a reduced dynamic mean-field model, receive excitatory input from other areas in proportion to the number of fibre tracts between them. The simulated mean field activity was transformed into BOLD signal, and the properties of the simulated functional networks were analyzed. Our results suggest that the functional alterations observed in schizophrenia are not directly linked to alterations in the structural topology. Instead, subtly randomized and less small-world functional networks appear when the brain operates with lower global coupling, which shifts the dynamics from the optimal healthy regime.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Spectroscopic studies on two mono nuclear iron (III) complexes derived from a schiff base and an azodye

Two new mono nuclear Fe(III) complexes of an azodye (ANSN) and a Schiff base (FAHP) are reported. The azodye is prepared by coupling diazotized 1-amino-2-naphthol-4-sulphonicacid with 2-naphthol and the Schiff base is prepared by condensing 2-amino-3-hydroxy pyridine with furfural. The complexes were synthesized by the reaction of FeCl{sub 3}Ðœ‡2H{sub 2}O with respective ligands. They were characterized on the basis of elemental analysis and spectral studies like IR, NMR, Electronic and M.ssbauer. Magnetic susceptibility and Molar conductance of complexes at room temperature were studied. Based on the spectroscopic evidences and other analytical data the complexes are formulated as[Fe(ANSN)Cl(H{sub 2}O){sub 2}] and [Fe(FAHP)Cl{sub 2}(H{sub 2}O){sub 2}].

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Investigation of dynamics of ELM crashes and their mitigation techniques

The accurate prediction of H-mode pedestal dynamics is critical for planning experiments in existing tokamaks and in the design of future tokamaks such as ITER and DEMO. The main objective of the proposed research is to advance the understanding of the physics of H-mode pedestal. Through advances in coupled kinetic-MHD simulations, a new model for H-mode pedestal and ELM crashes as well as an improved model for the bootstrap current will be developed. ELMmitigation techniques will also be investigated. The proposed research will help design efficient confinement scenarios and reduce transient heat loads on the divertor and plasma facing components. During the last two years, the principal investigator (PI) of this proposal actively participated in physics studies related to the DOE Joint Research Targets. These studies include the modeling of divertor heat load in the DIII-D, Alcator C-Mod, and NSTX tokamaks in 2010, and the modeling of H-mode pedestal structure in the DIII-D tokamak in 2011. It is proposed that this close collaboration with experimentalists from major US tokamaks continue during the next funding period. Verification and validation will be a strong component of the proposed research. During the course of the project, advances will be made in the following areas; Dynamics of the H-mode pedestal buildup and recovery after ELM crashes – The effects of neutral fueling, particle and thermal pinches will be explored; Dynamics of ELM crashes in realistic tokamak geometries – Heat loads associated with ELM crashes will be validated against experimental measurements. An improved model for ELM crashes will be developed; ELM mitigation – The effect of resonant magnetic perturbations on ELMs stability and their evolution will be investigated; Development of a new bootstrap current model – A reduced model for will be developed through careful verification of existing models for bootstrap current against first-principle kinetic neoclassical simulations. The primary focus here will be on plasma regimes where the existing reduced models deviate from each other, such as high-beta and low aspect ratio plasmas; and Results will be verified against analytical models and simulation results from other codes. Simulation results will be compared with diagnostic experimental data such as Thomson measurements (HRTC) or flux measurements if available. We have arrangements with experimentalists from DIII-D and JET to use diagnostic edge data for this validation. In summary, we propose to study the H-mode pedestal buildup, the stability and evolution of ELMs using a model that will account for dynamically evolving neoclassical sources.

42 ENGINEERING↗
DOE OSTI2015

Modeling of EAST ICRF antenna performance using the full-wave code TORIC

Access to advanced operating regimes in the EAST tokamak will require a combination of electron-cyclotron resonance heating (ECRH), neutral beam injection (NBI) and ion cyclotron range frequency heating (ICRF), with the addition of lower-hybrid current drive (LHCD) for current profile control. Prior experiments at the EAST tokamak facility have shown relatively weak response of the plasma temperature to application of ICRF heating, with typical coupled power about 2 MW out of 12 MW source. The launched spectrum, at n{sub φ} = 34 for 0-π -0-π phasing and 27 MHz, is largely inaccessible at line-averaged densities of approximately 2 × 10{sup 19} m{sup −3}. However, with variable antenna phasing and frequency, this system has considerable latitude to explore different heating schemes. To develop an ICRF actuator control model, we have used the full-wave code TORIC to explore the physics of ICRF wave propagation in EAST. The results presented from this study use a spectrum analysis using a superposition of n{sub φ} spanning −50 to +50. The low density regime typical of EAST plasmas results in a perpendicular wavelength comparable to the minor radius which results in global cavity resonance effects and eigenmode formation when the single-pass absorption is low. This behavior indicates that improved performance can be attained by lowering the peak of the k{sub ||} spectrum by using π/3 phasing of the 4-strap antenna. Based on prior studies conducted at Alcator C-Mod, this phasing is also expected to have the advantage of nearly divergence-free box currents, which should result in reduced levels of impurity production. Significant enhancements of the loading resistance may be achieved by using low k{sub ||} phasing and a combination of magnetic field and frequency to vary the location of the resonance and mode conversion regions. TORIC calculations indicate that the significant power may be channeled to the electrons and deuterium majority. We expect that implementation of these recommendations in EAST will yield substantial improvements in the net absorbed power that will greatly assist in the attempt to access advanced tokamak operating regimes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Charge Condensation and Lattice Coupling Drives Stripe Formation in Nickelates

Revealing the predominant driving force behind symmetry breaking in correlated materials is sometimes a formidable task due to the intertwined nature of different degrees of freedom. This is the case for La 2–x Sr x NiO 4+δ , in which coupled incommensurate charge and spin stripes form at low temperatures. Here, we use resonant x-ray photon correlation spectroscopy to study the temporal stability and domain memory of the charge and spin stripes in La 2–x Sr x NiO 4+δ . Although spin stripes are more spatially correlated, charge stripes maintain a better temporal stability against temperature change. More intriguingly, charge order shows robust domain memory with thermal cycling up to 250 K, far above the ordering temperature. Furthermore, these results demonstrate the pinning of charge stripes to the lattice and that charge condensation is the predominant factor in the formation of stripe orders in nickelates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗