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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Ferromagnetic-superparamagnetic granulometry of lunar surface materials

A technique of magnetic granulometry is applied to previously reported data for the temperature dependence of isothermal remanent magnetization (IRM) in 13 lunar surface samples, including three soils. Observed increases in IRM with decreasing temperature are attributed to changes from superparamagnetic to single-domain types of behavior for fine metallic-iron particles. Based on this hypothesis, the temperature dependence of IRM in the examined samples is analyzed to obtain particle-size distributions over the range of mean diameters from 30 to 130 A. It is found that the distribution functions for the soils and a low-grade breccia vary as the inverse square of particle volume and that the distributions for recrystallized breccias and igneous rocks apparently peak about mean values.

Schwerer, F. C.↗
DOE OSTI2019

Controlling the Magnetic Anisotropy of the van der Waals Ferromagnet Fe 3 GeTe 2 through Hole Doping

Identifying material parameters affecting properties of ferromagnets is key to optimized materials that are better suited for spintronics. Magnetic anisotropy is of particular importance in van der Waals magnets, since it not only influences magnetic and spin transport properties, but also is essential to stabilizing magnetic order in the two-dimensional limit. Here, we report that hole doping effectively modulates the magnetic anisotropy of a van der Waals ferromagnet and explore the physical origin of this effect. We report Fe 3–x GeTe 2 nanoflakes show a significant suppression of the magnetic anisotropy with hole doping. Electronic structure measurements and calculations reveal that the chemical potential shift associated with hole doping is responsible for the reduced magnetic anisotropy by decreasing the energy gain from the spin–orbit induced band splitting. Our findings provide an understanding of the intricate connection between electronic structures and magnetic properties in two-dimensional magnets and propose a method to engineer magnetic properties through doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Amorphous nonstoichiometric oxides with tunable room-temperature ferromagnetism and electrical transport

Material functionalities strongly depend on the stoichiometry, crystal structure, and homogeneity. Here we demonstrate an approach of amorphous nonstoichiometric inhomogeneous oxides to realize tunable ferromagnetism and electrical transport at room temperature. In order to verify the origin of the ferromagnetism, we employed a series of structural, chemical, and electronic state characterizations. Combined with electron microscopy and transport measurements, synchrotron-based grazing incident wide angle X-ray scattering, soft X-ray absorption and circular dichroism clearly reveal that the room-temperature ferromagnetism originates from the In 0.23 Co 0.77 O 1-v amorphous phase with a large tunable range of oxygen vacancies. The room-temperature ferromagnetism is tunable from a high saturation magnetization of 500 emu cm -3 to below 25 emu cm -3 , with the evolving electrical resistivity from 5 × 10 3 μΩ cm to above 2.5 × 10 5 μΩ cm. Inhomogeneous nano-crystallization emerges with decreasing oxygen vacancies, driving the system towards non-ferromagnetism and insulating regime. Our work unfolds the novel functionalities of amorphous nonstoichiometric inhomogeneous oxides, which opens up new opportunities for developing spintronic materials with superior magnetic and transport properties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Room-Temperature Skyrmions in an Antiferromagnet-Based Heterostructure

Magnetic skyrmions as swirling spin textures with a nontrivial topology have potential applications as magnetic memory and storage devices. Since the initial discovery of skyrmions in non-centrosymmetric B20 materials, the recent effort has focused on exploring room-temperature skyrmions in heavy metal and ferromagnetic heterostructures, a material platform compatible with existing spintronic manufacturing technology. Here, we report the surprising observation that a room-temperature skyrmion phase can be stabilized in an entirely different class of systems based on antiferromagnetic (AFM) metal and ferromagnetic (FM) metal IrMn/CoFeB heterostructures. There are a number of distinct advantages of exploring skyrmions in such heterostructures including zero-field stabilization, tunable antiferromagnetic order, and sizable spin–orbit torque (SOT) for energy-efficient current manipulation. Through direct spatial imaging of individual skyrmions, quantitative evaluation of the interfacial Dzyaloshinskii–Moriya interaction, and demonstration of current-driven skyrmion motion, our findings firmly establish the AFM/FM heterostructures as a promising material platform for exploring skyrmion physics and device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Thickness-dependent magnetic order in CrI 3 single crystals

Two-dimensional (2D) materials with intrinsic ferromagnetism offers unique opportunity to engineer new functionalities in nano-spintronics. One such material is CrI 3 , showing long-range magnetic order in monolayer with the Curie temperature (T c ) of 45 K. In this work, we study detailed evolution of magnetic transition and magnetic critical properties in response to systematic reduction in crystal thickness down to 50 nm. Bulk T c of 61 K is gradually suppressed to 57 K, however, the satellite transition at T*=45 K is observed layer-independent at fixed magnetic field of 1 kOe. The origin of T* is proposed to be a crossover from pinning to depinning of magnetic domain walls. The reduction of thickness facilitates a field-driven metamagnetic transition around 20 kOe with out-of-plane field, in contrast to the continuous changes with in-plane field. The critical analysis around Tc elucidates the mean-field type interactions in microscale-thick CrI 3 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Author Correction: Thickness-dependent magnetic order in CrI3 single crystals

Two-dimensional (2D) materials with intrinsic ferromagnetism provide unique opportunity to engineer new functionalities in nano-spintronics. One such material is CrI3, showing long-range magnetic order in monolayer with the Curie temperature (Tc) of 45 K. Here we study detailed evolution of magnetic transition and magnetic critical properties in response to systematic reduction in crystal thickness down to 50 nm. Bulk Tc of 61 K is gradually suppressed to 57 K, however, the satellite transition at T * = 45 K is observed layer-independent at fixed magnetic field of 1 kOe. The origin of T * is proposed to be a crossover from pinning to depinning of magnetic domain walls. The reduction of thickness facilitates a field-driven metamagnetic transition around 20 kOe with out-of-plane field, in contrast to the continuous changes with in-plane field. The critical analysis around Tc elucidates the mean-field type interactions in microscale-thick CrI3.

36 MATERIALS SCIENCE↗
DOE OSTI2017

BaFe 4 O 7 and K 0.22 Ba 0.89 Fe 4 O 7 : Canted Antiferromagnetic Diferrites with Exceptionally High Magnetic Ordering Temperatures [BaFe 4 O 7 and K 0.22 Ba 0.89 Fe 4 O 7 – New Canted Antiferromagnetic Diferrites with Exceptionally High Magnetic Ordering Temperatures]

Here, complex iron containing oxides, typically referred to as ferrites, have been extensively studied for their electronic and magnetic properties, including magnetotransport, ferromagnetism, ferroelectricity, and a combination of the latter two, known as multiferroism. The search for materials possessing simultaneous ferromagnetic and ferroelectric behavior is of significant interest both for the advancement of fundamental science and for applications in random access memory (RAM). Despite the great technological potential of multiferroics, one or both of the ferroic ordering temperatures tend to fall below room temperature, such as in the compositions TbMnO 3 and Ni 3 V 2 O 8 , thus eliminating their practical utility for RAM applications. The scarcity of multiferroics possessing room temperature ferroic orderings continues to drive exploratory research in this field. For this reason, ferrites have garnered significant interest due to their often high ferroic ordering temperatures, for example in BiFeO 3 . Among all ferrites, hexaferrites are the most studied prototypical examples and constitute a specific subclass of ferrites that follows the stoichiometry Ba O– n Fe 2 O 3 , in which the n value dictates the nomenclature, i.e., ( n = 6) is a hexaferrite or ( n = 1) is a monoferrite. This versatile class of materials encompasses a wide range of related structures best described by Pullar, serving as the motivation for this work.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Dynamic response in a finite size composite multiferroic thin film

Composite multiferroics, heterostructures of ferromagnetic and ferroelectric materials, are characterized by a remarkable magnetoelectric effect at the interface. Previous work has supported the ferromagnetic structure with magnetic spins and the ferroelectric with pseudospins which act as electric dipoles in a microscopic model, coupled with a magnetoelectric interaction [Wang and Grimson, J. Appl. Phys. 118, 124109 (2015)]. In this work, by solving the stochastic Landau-Lifshitz-Gilbert equation, the electric-field-induced magnetization switching in a twisted boundary condition has been studied, and a behavior of domain wall in the ferromagnetic structure is discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Magnetic and electrical control of engineered materials

Methods, systems, and devices are disclosed for controlling the magnetic and electrical properties of materials. In one aspect, a multi-layer structure includes a first layer comprising a ferromagnetic or ferrimagnetic material, and a second layer positioned within the multi-layer structure such that a first surface of the first layer is in direct physical contact with a second surface of the second layer. The second layer includes a material that undergoes structural phase transitions and metal-insulator transitions upon experiencing a change in temperature. One or both of the first and second layers are structured to allow a structural phase change associated with the second layer cause a change magnetic properties of the first layer.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Synthetic magnetoelectric coupling in a nanocomposite multiferroic

Given the paucity of single phase multiferroic materials (with large ferromagnetic moment), composite systems seem an attractive solution to realize magnetoelectric coupling between ferromagnetic and ferroelectric order parameters. Despite having antiferromagnetic order, BiFeO₃ (BFO) has nevertheless been a key material due to excellent ferroelectric properties at room temperature. We studied a superlattice composed of 8 repetitions of 6 unit cells of La₀.₇Sr₀.₃MnO₃ (LSMO) grown on 5 unit cells of BFO. Significant net uncompensated magnetization in BFO, an insulating superlattice, is demonstrated using polarized neutron reflectometry. Remarkably, the magnetization enables magnetic field to change the dielectric properties of the superlattice, which we cite as an example of synthetic magnetoelectric coupling. Importantly, controlled creation of magnetic moment in BFO is a much needed path toward design and implementation of integrated oxide devices for next generation magnetoelectric data storage platforms.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The magnetic states of a van der Waals ferromagnet CrGeTe 3 probed by vector-field magnetic force microscopy

Here, we present a study on the magnetic domain configuration in the van der Waals ferromagnet CrGeTe 3 using a vector-field cryogenic magnetic force microscopy. Our investigation demonstrates the influence of magnetic fields strength and angle on the magnetic domain configuration, showing the coexistence of striped and spike-like magnetic domains. This study contributes to understanding the impact of uniaxial magnetic anisotropy on the domain configuration of van der Waals ferromagnets, offering insights into stabilizing different domain patterns.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation on Physical Properties of Sn-Modified Cubic Cu{sub 2}O Nanostructures

Cubic Cu{sub 2−x} Sn{sub x}O (0 ≤ x ≤ 0.4) nanostructures have been developed with the solvothermal method. X-ray diffraction data analysis confirms the formation of a pristine Cu{sub 2}O phase below x=0.3 Sn{sup 2+} substitution, and SnO-related phases appear in 0.3 substitute sample indicating phase segregation starts at x≥0.3. The magnetization versus applied field (M − H) curves have been determined using a vibrating sample magnetometer at 300 K which reveals that ferromagnetic behavior of synthesized nanomaterials is reliant on the substituent concentration and enhanced gradually with its addition in the material. Photoluminescence spectra show that ferromagnetism originates from the induced magnetic moment in defects created as cation vacancies in the host material. Beside these, the dielectric measurements were performed at various frequencies (20 Hz–1 MHz) and in the temperature range of 100 to 350 K.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Prediction of a new class of half-metallic ferromagnets from first principles [A new class of half-metallic ferromagnets from first principles]

Half-metallic ferromagnetism (HMFM) occurs rarely in materials and yet offers great potential for spintronic devices. Recent experiments suggest a class of compounds with the `ThCr$_{2}$Si$_{2}$' (122) structure -- isostructural and containing elements common with Fe pnictide-based superconductors -- can exhibit HMFM. Here we use $ab$ $initio$ density-functional theory calculations to understand the onset of half-metallicity in this family of materials and explain the appearance of ferromagnetism at a quantum critical point. We also predict new candidate materials with HMFM and high Curie temperatures through A-site alloying.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Morphotropic phase boundary and magnetoelastic behaviour in ferromagnetic Tb 1-x Gd x Fe 2 system

Morphotropic phase boundary (MPB), separating two ferroic phases of different crystal symmetries, has been studied extensively for its extraordinary enhancement of piezoelectricity in ferroelectrics. Based on the same mechanism, we have designed a magnetic MPB in the pseudobinary ferromagnetic system of Tb 1-x Gd x Fe 2 and the corresponding crystal structure, magnetic properties, and magnetostriction are explored. With the synchrotron x-ray diffractometry, the structure symmetry of TbFe 2 -rich compositions is detected to be rhombohedral (R) and that of GdFe 2 -rich compositions is tetragonal (T) below T c . With the change of concentration, the value of magnetostriction of the samples changes monotonously, while the MPB composition Tb 0.1 Gd 0.9 Fe 2 , which corresponds to the coexistence of R and T phases, exhibits the maximum magnetization among all available compositions and superposition of magnetostriction behaviour of R and T phases. Furthermore, our result of MPB phenomena in ferromagnets may provide an effective route to design functional magnetic materials with exotic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structure and magnetic properties of Fe doped In{sub 2}O{sub 3} thin films prepared by electron beam evaporation

Pure and Fe (7 at.%) doped In{sub 2}O{sub 3} thin films were grown onto the glass substrates by electron beam evaporation technique. The structural and magnetic properties of the pure and Fe doped In{sub 2}O{sub 3} thin films have been studied. The undoped and Fe doped In{sub 2}O{sub 3} thin films shown ferromagnetic property at room temperature. A magnetization of 24 emu/cm{sup 3} was observed for pure In{sub 2}O{sub 3} thin films. The magnetization of 38.23 emu/cm{sup 3} was observed for the Fe (7 at.%) doped In{sub 2}O{sub 3} thin films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Optimization of magneto-resistive response of ion-irradiated exchange biased films through zigzag arrangement of magnetization

Exchange coupled ferromagnetic-antiferromagnetic Ni{sub 81}Fe{sub 19}/Ir{sub 23}Mn{sub 77} films with a zigzag alignment of magnetization are prepared by local ion irradiation. The anisotropic magneto-resistive behavior of the magnetic thin film structures is correlated to the magnetic structure and modeled. A unique uniaxial field sensitivity along the net magnetization alignment is obtained through the orthogonally modulated and magnetic domain wall stabilized magnetic ground state. Controlling local thin film magnetization distributions and, thus, the overall magnetization response opens unique ways to tailor the magneto-resistive sensitivity of functional magnetic thin film devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Synthesize and microstructure characterization of Ni{sub 43}Mn{sub 41}Co{sub 5}Sn{sub 11} Heusler alloy

The ferromagnetic heusler alloys are promising materials in many technical applications due to their multifunctional properties such as shape memory effect, magnetocaloric effect, giant magnetoresistance, etc. In this work, synthesize and characterization of polycrystalline Ni{sub 43}Mn{sub 41}Co{sub 5}Sn{sub 11} (NMCS) alloy are reported. Alloy preparation was conducted by melting the constitute elements under an innert Argon (Ar) atmosphere in a vacuum mini arc-melting furnace. Homogenization of the microstructure of the as-cast ingot was obtained after annealing process at 750°C for 48 hours. It is shown that the dendrites structure has changed to equaixed grains morphology after homogenization. Microstructure characteristics of material by x-ray diffraction revealed that the alloy has a L{sub 21}-type cubic crystal structure as the main phase at room temperature. In order to induce the shape anisotropy, a forging treatment was applied to show the shape orientation of material. Various enhancements of magnetic properties in a longitudinal direction were observed at various degree of anisotropy. The microstructure changes of as-cast NMCS and effects of homogenization treatments as studied by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) are discussed in details.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Spin transport in normal metal/insulator/topological insulator coupled to ferromagnetic insulator structures

In this study, we investigate the spin transport in normal metal (NM)/insulator (I)/topological insulator (TI) coupled to ferromagnetic insulator (FI) structures. In particular, we focus on the barrier thickness dependence of the spin transport inside the bulk gap of the TI with FI. The TI with FI is described by two-dimensional (2D) Dirac Hamiltonian. The energy profile of the insulator is assumed to be a square with barrier height V and thickness d along the transport-direction. This structure behaves as a tunnel device for 2D Dirac electrons. The calculation is performed for the spin conductance with changing the barrier thickness and the components of magnetization of FI layer. It is found that the spin conductance decreases with increasing the barrier thickness. Also, the spin conductance is strongly dependent on the polar angle θ, which is defined as the angle between the axis normal to the FI and the magnetization of FI layer. These results indicate that the structures are promising candidates for novel tunneling magnetoresistance devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗