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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Order–Disorder Phase Stabilization by Pressure‐Induced Charge Transfer Enhances the Ferroelectric Photovoltaic Effect in Multiferroic BaFe 4 O 7

Abstract Multiferroic ferroelectric photovoltaic (FPV) materials, combining magnetic and ferroelectric properties, are of paramount importance for optoelectronic and photovoltaic applications. However, optimizing both the remanent polarization and the optical bandgap—key factors for enhanced FPV performance—presents a significant challenge due to their trade‐off. This work shows that pressure‐induced charge transfer between different metal sites can break this trade‐off. Above ≈20 GPa, charge transfer between different trivalent iron (Fe) sites in the multiferroic material BaFe 4 O 7 leads to Fe valence disproportionation, FeO 4 tetrahedra disorder, and Jahn–Teller distortion of FeO 6 octahedra. These changes reduce the bandgap, lower resistivity, and enhance ferroelectric polarization, resulting in a 2.5‐fold increase in photocurrent. Upon decompression, BaFe 4 O 7 retains an order–disorder structure, optimal ferroelectric and optical properties at ambient conditions. This work provides a novel pathway to simultaneously optimizing ferroelectricity and bandgap via pressure‐induced charge transfer, overcoming the traditional trade‐off in FPV materials, and offers a promising approach for developing high polarization performance, narrow‐bandgap FPV materials.

Chemistry↗
DOE OSTI2016

Spin liquid and quantum phase transition without symmetry breaking in a frustrated three-dimensional Ising model

We show that the highly frustrated transverse-field Ising model on the three-dimensional pyrochlore lattice realizes a first-order phase transition without symmetry breaking between the low-field Coulomb quantum spin liquid and the high-field polarized phase. The quantum phase transition is located quantitatively by comparing low- and high-field series expansions. Furthermore, the intriguing properties of the elementary excitations in the polarized phase are investigated. We argue that this model can be achieved experimentally by applying mechanical strain to a classical spin-ice material composed of non-Kramers spins such as Ho 2 Ti 2 O 7 . Taken together with our results, this provides an experimental platform to study quantum spin liquid physics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Ice rule for a ferromagnetic nanosite network on the face-centered cubic lattice

The magnetic properties of an inverse opal-like cobalt-based structure having the symmetry of the face-centered cubic lattice are studied. The magnetization reversal of the structure in a magnetic field applied along the [11̄0] axis is described using a phenomenological model, which uses the ice rule for the local magnetization of nanostructure elements. This description predicts the absence of a long-range magnetic order in two <111> directions that are normal to the magnetic field. The magnetic structure is analyzed by smallangle neutron diffraction. Neutron diffraction patterns are measured in an external magnetic field varying from −1.2 to 1.2 T and applied along the crystallographic [11̄0] direction. A magnetic contribution to the neutron scattering intensity is extracted. It is shown that this contribution is close to zero over the entire applied magnetic field range for all scattering planes that are normal to the field, which agrees well with the proposed model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Local cation order and ferrimagnetism in compositionally complex spinel ferrites

We present an exploration of a family of compositionally complex cubic spinel ferrites featuring combinations of Mg, Fe, Co, Ni, Cu, Mn, and Zn cations, systematically investigating the average and local atomic structures, chemical short-range order, magnetic spin configurations, and magnetic properties. All compositions result in ferrimagnetic average structures with extremely similar local bonding environments; however, the samples display varying degrees of cation inversion and, therefore, differing apparent bulk magnetization. Additionally, first-order reversal curve analysis of the magnetic reversal behavior indicates varying degrees of magnetic ordering and interactions, including potentially local frustration. Finally, reverse Monte Carlo modeling of the spin orientation demonstrates a relationship between the degree of cation inversion and the spin collinearity. Collectively, these observations correlate with differences in synthesis procedures. This work provides a framework for understanding magnetic behavior reported for “high-entropy spinels,” revealing many are likely compositionally complex oxides with differing degrees of chemical short-range order—not meeting the community established criteria for high or medium entropy compounds. Moreover, this work highlights the importance of reporting complete sample processing histories and investigating local to long-range atomic arrangements when evaluating potential entropic mixing effects and assumed property correlations in high entropy materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Geometrical Structures and Magnetic Properties of Charged Aluminum-Doped Platinum Clusters: Aluminum Occupied High Coordination Site

The most stable states of neutral and charged Pt{sub n}Al (n = 1 − 8) clusters have been performed using DFT methods. All the most stable structures of neutral and charged Pt{sub n}Al clusters can be obtained by substituting a Pt atom with an Al atom except Pt{sub 7}Al and the Al atom occupies the vertex position with lager coordination number. The Pt{sub 5}, Pt{sub 4,6}Al, Pt{sub 3}Al{sup +}, and Pt{sub 6}Al{sup −} clusters have higher local relative stability and can be seen as “magic clusters.” The fragmentation energy is the largest when a Pt atom is bonded with an Al atom. The average magnetic moments of Pt{sub n+ 1} cluster reduce due to the addition of Al atoms. The static polarizability has been studied in this paper.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Epitaxial Ni-Mn-Ga-Co thin films on PMN-PT substrates for multicaloric applications

Multicaloric stacks consisting of a magnetocaloric film on a piezoelectric substrate promise improved caloric properties as the transition temperature can be controlled by both magnetic and electric fields. We present epitaxially grown magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg{sub 1/3}Nb{sub 2/3}){sub 0.72}Ti{sub 0.28}O{sub 3} substrates. Structure and microstructure of two samples, being in the austenitic and martensitic state at room temperature, are investigated by X-ray diffraction in two- and four-circle geometry and by atomic force microscopy. In addition, high temperature magnetometry was performed on the latter sample. The combination of these methods allows separating the influence of epitaxial growth and martensitic transformation. A preferential alignment of twin boundaries is observed already in the as-deposited state, which indicates the presence of prestress, without applying an electric field to the substrate. A temperature-magnetic field phase diagram is presented, which demonstrates the inverse magnetocaloric effect of the epitaxial Ni-Mn-Ga-Co film.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Effect of heterovalent substitutions in yttrium chromite on the hyperfine interactions of {sup 119}Sn{sup 4+} studied by Mössbauer spectroscopy

In order to develop the {sup 119}Sn Mössbauer spectroscopic probe technique to study magnetically ordered materials, three Ca-substituted yttrium chromites, i.e. Y{sub 0.9}Ca{sub 0.1}CrO{sub 3}, Y{sub 0.9}Ca{sub 0.1}Cr{sub 0.9}Ti{sub 0.1}O{sub 3} and Y{sub 0.8}Ca{sub 0.2}Cr{sub 0.8}Ti{sub 0.2}O{sub 3}, doped with 0.3 atom-% Sn{sup 4+}, were for the first time investigated. {sup 119}Sn Mössbauer spectra, recorded at 4.2 K, have allowed, through analysis of the magnetic hyperfine field values, probed by {sup 119}Sn nuclei, to gain insight into the local magnetically active surrounding of different Sn{sup 4+} ions. In all of these compounds, partial segregation of Sn{sup 4+} ions is revealed. In the case of Y{sub 0.9}Ca{sub 0.1}CrO{sub 3}, neither highly oxidized Cr{sup 4+} nor Cr{sup 6+} species, expected to compensate for the Ca{sup 2+} positive charge deficit, is found in the vicinity of the {sup 119}Sn{sup 4+} probe. In the case of both studied Ti-containing chromites, {sup 119}Sn Mössbauer spectra have provided the original indirect evidence for the statistical distribution of Cr{sup 3+} and Ti{sup 4+} ions over the octahedral sites and permitted characterization of the occurring associates of Sn{sup 4+}. - Graphical abstract: Two kinds of Sn{sup 4+} associates allowing {sup 119}Sn Mössbauer spectra of tin-doped Y{sub 0.9}Ca{sub 0.1}Cr{sub 0.9}Ti{sub 0.1}O{sub 3} and Y{sub 0.8}Ca{sub 0.2}Cr{sub 0.8}Ti{sub 0.2}O{sub 3} to be accounted for. - Highlights: • {sup 119}Sn probe is tested as a source of information on the B-sublattice of AF perovskites. • Neither Cr{sup 3+} nor Cr{sup 6+} is detected nearby {sup 119}Sn{sup 4+} ions in Y{sub 0.9}Ca{sub 0.1}CrO{sub 3}. • Cr{sup 3+} and Ti{sup 4+} are found to be randomly distributed in Y{sub 1−x}Ca{sub x}Cr{sub 1−x}Ti{sub x}O{sub 3} (x=0.1 or 0.2). • Sn{sup 4+} dopant segregations are revealed in all of the studied materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Anisotropic magnetodielectric coupling behavior of Ca{sub 3}Co{sub 1.4}Rh{sub 0.6}O{sub 6} due to geometrically frustrated magnetism

We have investigated the magnetic, dielectric, and magnetodielectric (MDE) behavior of a geometrically frustrated spin-chain system, Ca{sub 3}Co{sub 1.4}Rh{sub 0.6}O{sub 6} (related to Ca{sub 3}CoRhO{sub 6}), in the single crystalline form for different orientations. The results bring out that the magnetic behavior of this compound is by itself interesting in the sense that this compound exhibits an anisotropic glassy-like magnetic behavior with a huge frequency (ν) dependence of ac susceptibility (χ) peak for an orientation along the spin-chain in the range of 30–60 K; this behavior is robust to applications of large external magnetic fields (H) unlike in canonical spin-glasses. The temperature dependence of dielectric constant also shows strong ν-dependence with similar robustness to H. The isothermal H-dependent dielectric results at low temperatures establish anisotropic MDE coupling. It is intriguing to note that there is a “step” roughly at one-third of saturation values as in the case of isothermal magnetization curves for same temperatures (for orientation along spin-chain), a correlation hitherto unrealized for geometrically frustrated systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Exploiting Spin Fluctuations for Enhanced Pure Spin Current

We demonstrate the interplay of pure spin current, spin-polarized current, and spin fluctuation in 3d Ni x Cu 1–x . By tuning the compositions of the Ni x Cu 1–x alloys, we separate the effects due to the pure spin current and spin-polarized current. By exploiting the interaction of spin current with spin fluctuation in suitable Ni-Cu alloys, we obtain an unprecedentedly high spin Hall angle of 46%, about 5 times larger than that in Pt, at room temperature. Furthermore, we show that spin-dependent thermal transport via anomalous Nernst effect can serve as a sensitive magnetometer to electrically probe the magnetic phase transitions in thin films with in-plane anisotropy. As a result, the enhancement of spin Hall angle by exploiting spin current fluctuation via composition control makes 3d magnets functional materials in charge-to-spin conversion for spintronic application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Comparison of the order of magnetic phase transitions in several magnetocaloric materials using the rescaled universal curve, Banerjee and mean field theory criteria

Magnetocaloric materials with second order phase transition near the Curie temperature can be described by critical phenomena theory. In this theory, scaling, universality, and renormalization are key concepts from which several phase transition order criteria are derived. In this work, the rescaled universal curve, Banerjee and mean field theory criteria were used to make a comparison for several magnetocaloric materials including pure Gd, SmCo{sub 1.8}Fe{sub 0.2}, MnFeP{sub 0.46}As{sub 0.54}, and La{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3}. Pure Gd, SmCo{sub 1.8}Fe{sub 0.2}, and La{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3} present a collapse of the rescaled magnetic entropy change curves into a universal curve, which indicates a second order phase transition; applying Banerjee criterion to H/σ vs σ{sup 2} Arrot plots and the mean field theory relation |ΔS{sub M}| ∝ (μ{sub 0}H/T{sub c}){sup 2/3} for the same materials also determines a second order phase transition. However, in the MnFeP{sub 0.46}As{sub 0.54} sample, the Banerjee criterion applied to the H/σ vs σ{sup 2} Arrot plot indicates a first order magnetic phase transition, while the mean field theory prediction for a second order phase transition, |ΔS{sub M}| ∝ (μ{sub 0}H/T{sub c}){sup 2/3}, describes a second order behavior. Also, a mixture of first and second order behavior was indicated by the rescaled universal curve criterion. The diverse results obtained for each criterion in MnFeP{sub 0.46}As{sub 0.54} are apparently related to the magnetoelastic effect and to the simultaneous presence of weak and strong magnetism in Fe (3f) and Mn (3g) alternate atomic layers, respectively. The simultaneous application of the universal curve, the Banerjee and the mean field theory criteria has allowed a better understanding about the nature of the order of the phase transitions in different magnetocaloric materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Magnetoelectric effect in La{sub 0.7}Sr{sub 0.3}MnO{sub 3}–BaTiO{sub 3} core–shell nanocomposite

Highlights: ► The BaTiO{sub 3} in the core–shell structure undergoes large compressive strain. ► The LSMO in the core–shell structure exhibits enhanced magnetic moment. ► The anomaly in magnetization data indicates inherent magnetoelectric coupling. ► Overall the nanocomposite shows good magnetoelectric voltage coefficient value. - Abstract: We report the magnetoelectric properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3}–BaTiO{sub 3} core–shell nanostructure synthesized by sol–gel method. X-ray diffraction analysis suggests that the BaTiO{sub 3} undergoes large strain in the core–shell structure which can be attributed to lattice induced strain. Interestingly, the core–shell nanoparticle exhibits enhanced magnetization (143 emu/g) compared to the ferromagnetic La{sub 0.7}Sr{sub 0.3}MnO{sub 3} bare core (20 emu/g). The core–shell structure also exhibits inherent magnetoelectric coupling which is reflected as an anomaly at the ferroelectric transition in the magnetization measurement. The direct magnetoelectric measurement on La{sub 0.7}Sr{sub 0.3}MnO{sub 3}–BaTiO{sub 3} nanocomposite revealed the magnetoelectric voltage coefficient value as 54.5 mV/cm Oe at 1 kOe, which is a promising result compared to the other perovskite based nanocomposites.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Light induced electron spin resonance properties of van der Waals CrX 3 (X = Cl, I) crystals

The research on layered van der Waals (vdW) magnets is rapidly progressing owing to exciting fundamental science and potential applications. In bulk crystal form, CrCl 3 is a vdW antiferromagnet with in-plane ferromagnetic ordering below 17 K, and CrI 3 is a vdW ferromagnet below 61 K. In this paper, we report on the electron spin resonance (ESR) properties of CrCl 3 and CrI 3 single crystals upon photo-excitation in the visible range. We noticed remarkable changes in the ESR spectra upon illumination. In the case of CrCl 3 , at 10 K, the ESR signal is shifted from g = 1.492 (dark) to 1.661 (light), the linewidth increased from 376 to 506 Oe, and the signal intensity is reduced by 1.5 times. Most interestingly, the observed change in the signal intensity is reversible when the light is cycled on/off. We observed almost no change in the ESR spectral parameters in the paramagnetic phase (>20 K) upon illumination. Upon photo-excitation of CrI 3 , the ESR signal intensity is reduced by 1.9 times; the g-value increased from 1.956 to 1.990; the linewidth increased from 1170 to 1260 Oe at 60 K. These findings are discussed by taking into account the skin depth, the slow relaxation mechanism, and the appearance of low-symmetry fields at the photo-generated Cr 2+ Jahn–Teller centers. Such an increase in the g-value as a result of photo-generated Cr 2+ ions is further supported by our many-body wavefunction calculations. This work has the potential to extend to monolayer vdWs magnets by combining ESR spectroscopy with optical excitation and detection.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

First-principles study on the magnetic properties in Mg doped BiFeO{sub 3} with and without oxygen vacancies

The magnetic properties of Mg-doped BiFeO{sub 3} (BFO) with and without oxygen vacancies are studied through first-principles calculations. The Mg-doping prefers to occupy the ferromagnetic planes and produces an obvious improved magnetization, and the magnetization is linearly enhanced with increasing Mg-doped content, which is consistent with the trend reported in experiment. However, our calculated result is significantly larger than the experimental one, and the reason is revealed that the relative energy differences of various spin-ordering configurations are small. Furthermore, oxygen vacancy in Mg-doped BFO can further enhance the magnetization, while keeping the insulating band gap character. The calculated results imply that the oxygen vacancy in Mg-doped BFO would be an effective way to improve the multiferroicity of BFO.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Quantum Materials at the Nanoscale - Final Report

The central aim of the Quantum Materials at the Nanoscale (QMN) cluster was to understand and control collective behavior involving the interplay of spins, orbitals, and charges, which governs many scientifically interesting and technologically important phenomena in numerous complex materials. Because these phenomena involve various competing interactions, and influence properties on many different length and energy scales in complex materials, tackling this important area of study motivated a collaborative effort that combined the diverse capabilities of QMN cluster experimentalists, the essential theoretical analysis provided by QMN cluster theorists, and the outstanding facilities and staff of the FSMRL. During the funding period 2007-2014, the DOE cluster grant for the Quantum Materials at the Nanoscale (QMN) cluster supported, at various times, 15 different faculty members (14 in Physics and 1 in Materials Science and Engineering), 7 postdoctoral research associates, and 57 physics and materials science PhD students. 41 of these PhD students have since graduated and have gone on to a variety of advanced technical positions at universities, industries, and national labs: 25 obtained postdoctoral positions at universities (14), industrial labs (2 at IBM), DOE national facilities (3 at Argonne National Laboratory, 1 at Brookhaven National Lab, 1 at Lawrence Berkeley National Lab, and 1 at Sandia National Lab), and other federal facilities (2 at NIST); 13 took various industrial positions, including positions at Intel (5), Quantum Design (1), Lasque Industries (1), Amazon (1), Bloomberg (1), and J.P. Morgan (1). Thus, the QMN grant provided the essential support for training a large number of technically advanced personnel who have now entered key national facilities, industries, and institutions. Additionally, during the period 2007-2015, the QMN cluster produced 159 publications (see pages 14-23), including 23 papers published in Physical Review Letters; 16 papers in Nature, Nature Physics, Nature Materials, or Nature Communications; 4 papers in Science, and 8 papers in Applied Physics Letters. In this report, we provide some key highlights of the collaborative projects in which the QMN cluster members have been involved since 2007.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Phase relationships in the CeFe 8 Co 3 Ti 1 - y Si y system

We investigated the phase formation behavior of the nominal CeFe 8 Co 3 Ti 1-y Si y system for 0 ≤ y ≤ 0.6 by powder x-ray diffraction and scanning electron microscopy with energy dispersive x-ray spectroscopy for ingots formed by arc-melting then annealing at 1000 °C and quenching to room temperature. The ingots are seen to nearly single phase for y ≤ 0.4 and are multi-phase for y ≥ 0.5 though a compound of the ThMn 12 type does indeed form for all values of y. We also measured the saturation magnetizations (M s ), Curie temperatures (T C ), and magnetic anisotropy fields (H a ) for the y ≤ 0.4 samples and the values of Ms and Ha appear to be nearly identical for all y 0.4. TC, but, is seen to increase about 20 °C in this range for increasing y.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Superparamagnetic behavior of Fe-doped SnO{sub 2} nanoparticles

SnO{sub 2} is an n-type semiconductor with a wide band gap of 3.62 eV, and SnO{sub 2} nanoparticles doped with magnetic ions are expected to realized new diluted magnetic semiconductors (DMSs). Realizing ferromagnetism at room temperature is important for spintronics device applications, and it is interesting that the magnetic properties of these DMS systems can be varied significantly by modifying the preparation methods or conditions. In this study, the magnetic properties of Fe-doped (3% and 5%) SnO{sub 2} nanoparticles, prepared using our novel chemical preparation method and encapsulated in amorphous SiO{sub 2}, were investigated. The particle size (1.8–16.9 nm) and crystal phase were controlled by the annealing temperature. X-ray diffraction confirmed a rutile SnO{sub 2} single-phase structure for samples annealed at 1073–1373 K, and the composition was confirmed using X-ray fluorescence analysis. SQUID magnetometer measurements revealed superparamagnetic behavior of the 5%-Fe-doped sample at room temperature, although SnO{sub 2} is known to be diamagnetic. Magnetization curves at 5 K indicated that the 3%-Fe-doped has a larger magnetization than that of the 5%-Fe-doped sample. We conclude that the magnetization of the 5%-Fe-doped sample decreased at 5 K due to the superexchange interaction between the antiferromagnetic coupling in the nanoparticle system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Excess Ni-doping induced enhanced room temperature magneto-functionality in Ni-Mn-Sn based shape memory alloy

Present work reports on the observation of large magnetoresistance (∼−30% at 80 kOe) and magnetocaloric effect (∼12 J·kg{sup −1}·K{sup −1} for 0–50 kOe) near room temperature (∼290 K) on the Ni-excess ferromagnetic shape memory alloy Ni{sub 2.04}Mn{sub 1.4}Sn{sub 0.56}. The sample can be thought of being derived from the parent Ni{sub 2}Mn{sub 1.4}Sn{sub 0.6} alloy, where excess Ni was doped at the expense of Sn. Such Ni doping enhances the martensitic transition temperature and for the Ni{sub 2.04}Mn{sub 1.4}Sn{sub 0.56} it is found to be optimum (288 K). The doped alloy shows enhanced magneto-functional properties as well as reduced saturation magnetization as compared to the undoped counterpart at low temperature. A probable increment of antiferromagnetic correlation between Mn-atoms on Ni substitution can be accounted for the enhanced magneto-functional properties as well as reduction in saturation moment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗