Search NASA⌕ Search

SEARCH · Search NASA

Results for “FERROMAGNETIC MATERIALS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Computational discovery of ferromagnetic semiconducting single-layer CrSnTe 3

Despite many single-layer materials being reported in the past decade, few of them exhibit magnetism. Here we perform first-principles calculations using accurate hybrid density functional methods (HSE06) to predict that single-layer CrSnTe 3 (CST) is a ferromagnetic semiconductor, with band gaps of 0.9 and 1.2 eV for the majority and minority spin channels, respectively. We determine the Curie temperature as 170 K, significantly higher than that of single-layer CrSiTe 3 (90K) and CrGeTe 3 (130 K). This is due to the enhanced ionicity of the Sn-Te bond, which in turn increases the superexchange coupling between the magnetic Cr atoms. We further explore the mechanical and dynamical stability and strain response of this single-layer material for possible epitaxial growth. Lastly, our study provides an intuitive approach to understand and design novel single-layer magnetic semiconductors for a wide range of spintronics and energy applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Magnetic ordering through itinerant ferromagnetism in a metal-organic framework

In this report, the materials that combine magnetic order with other desirable physical attributes could find transformative applications in spintronics, quantum sensing, low-density magnets and gas separations. Among potential multifunctional magnetic materials, metal-organic frameworks, in particular, bear structures that offer intrinsic porosity, vast chemical and structural programmability, and the tunability of electronic properties. Nevertheless, magnetic order within metal-organic frameworks has generally been limited to low temperatures, owing largely to challenges in creating a strong magnetic exchange. Here we employ the phenomenon of itinerant ferromagnetism to realize magnetic ordering at T C = 225 K in a mixed-valence chromium(II/III) triazolate compound, which represents the highest ferromagnetic ordering temperature yet observed in a metal-organic framework. The itinerant ferromagnetism proceeds through a double-exchange mechanism, which results in a barrierless charge transport below the Curie temperature and a large negative magnetoresistance of 23% at 5 K. These observations suggest applications for double-exchange-based coordination solids in the emergent fields of magnetoelectrics and spintronics.

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

Ingeniously enhanced ferromagnetism in chemically-reduced 2D Ti 3 C 2 T X MXene

Chemical reduction is a facile and cost-effective technique for the modulation of the physical and chemical properties of nanomaterials. In this work, we demonstrate an enhancement of the magnetic behavior of Ti 3 C 2 T x MXene after its chemical reduction via l-ascorbic acid treatment. Small ferromagnetic loops have been observed below 50 K for Ti 3 C 2 T x prepared by hydrofluoric acid (HF) etching of Al layers from Ti 3 AlC 2 . Such a ferromagnetic ordering of spins was significantly enhanced via a chemical reduction of Ti 3 C 2 T x with l-ascorbic acid. Ferromagnetic hysteresis loops were observed for reduced Ti 3 C 2 T x (r-Ti 3 C 2 T x ) up to 150 K indicating a significant upshift of the paramagnetic to the ferromagnetic transition temperature, pushing towards room temperature. The enhancement of ferromagnetism and upshift of the ferromagnetic transition temperature could be attributed to the localized unpaired electron in Ti-3d orbital of the r-Ti 3 C 2 T x crystal and increase in the number of unsaturated Ti atoms upon l-ascorbic acid treatment. Chemical reduction via l-ascorbic acid treatment shows a promising pathway towards the modulation and enhancement of magnetism in various MXene materials for the development of 2D metallic soft ferromagnets and spintronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Preference of the Ferromagnetic Ordering for the Novel Heusler Rh{sub 2}MnTi Compound

Rh{sub 2}MnTi is a novel magnetic material at potentially high speed in modern technologies. Rh{sub 2}MnTi is susceptible to structural distortion of the ferromagnetic tetragonal Heusler. We tried to provide additional information on the magnetic order for this material through a study by means of first-principle calculations. The numerical work on the electronic and magnetic structural parameters of Rh{sub 2}MnTi crystal was carried out within the density functional theory level as implemented in all-electron full-potential linearized augmented plane wave (FP-LAPW) method. The dependence of the elastic constants C{sub ij} for cubic structure, the aggregate elastic moduli B and G, and the related mechanical properties are investigated. The calculated density of states (DOS) and band structure for Rh{sub 2}MnTi show the absence of energy band gap in their minority-spin channel which moves away half-metallic character, the magnetic moments, and Curie temperature in both the ferromagnetic and antiferromagnetic ordering are also investigated. The dependence of Seebeck coefficient, electrical conductivity, and power factor on the Fermi level are investigated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Ferromagnetism in half-metallic quaternary FeVTiAl Heusler compound

The electronic structure and magnetic properties of FeVTiAl quaternary Heusler alloy have been investigated within the density functional theory framework. The material was found completely spin-polarized half-metallic Ferromagnet in the ground state with F-43m structure. The structural stability was further confirmed by calculating different elastic constants in the cubic phase. Present study predicts an energy band gap of 0.72 eV calculated in localized minority spin channel at an equilibrium lattice parameter of 6.0Å. The calculated total spin magnetic moment of 2 µ{sub B}/f.u. is in agreement with the Slater-Pauling rule for full Heusler alloys.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Tuning Noncollinear Spin Structure and Anisotropy in Ferromagnetic Nitride MXenes

Recent experimental success in the realization of two-dimensional magnetism has invigorated the search for low-dimensional material systems with tunable magnetic anisotropy that exhibit intrinsic long-range ferromagnetic order. Here in this paper, we report that modifying the surface termination and transition metal in monolayer M 2 NT x nitride MXenes gives rise to a rich diversity of noncollinear spin structures and finely tunable magnetocrystalline anisotropy. Based on first-principles simulations, we predict that manipulating the strength of the spin–orbit interaction and electron localization via the chemical degrees of freedom can induce sufficient anisotropy to counteract thermal fluctuations that suppress long-range magnetic order. We find that Ti 2 NO 2 and Mn 2 NF 2 MXenes have continuous O(3) and O(2) spin symmetries, respectively, that may be broken by an applied field, while Cr 2 NO 2 and Mn 2 NO 2 are intrinsic Ising ferromagnets with out-of-plane easy axes and magnetic anisotropy energies up to 63 μeV/atom. These systems also exhibit both gapped and gapless Dirac points near the Fermi level. Our study suggests that nitride MXenes offer a promising avenue for achieving both practical spintronic devices and investigating fundamental spin processes in two-dimensional materials.

2D materials↗
DOE OSTI2014

Large anomalous Hall effect in ferromagnetic insulator-topological insulator heterostructures

We demonstrate the van der Waals epitaxy of the topological insulator compound Bi{sub 2}Te{sub 3} on the ferromagnetic insulator Cr{sub 2}Ge{sub 2}Te{sub 6}. The layers are oriented with (001)Bi{sub 2}Te{sub 3}||(001)Cr{sub 2}Ge{sub 2}Te{sub 6} and (110)Bi{sub 2}Te{sub 3}||(100)Cr{sub 2}Ge{sub 2}Te{sub 6}. Cross-sectional transmission electron microscopy indicates the formation of a sharp interface. At low temperatures, bilayers consisting of Bi{sub 2}Te{sub 3} on Cr{sub 2}Ge{sub 2}Te{sub 6} exhibit a large anomalous Hall effect (AHE). Tilted field studies of the AHE indicate that the easy axis lies along the c-axis of the heterostructure, consistent with magnetization measurements in bulk Cr{sub 2}Ge{sub 2}Te{sub 6}. The 61 K Curie temperature of Cr{sub 2}Ge{sub 2}Te{sub 6} and the use of near-stoichiometric materials may lead to the development of spintronic devices based on the AHE.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Exploring Electric Polarization Mechanisms in Multiferroic Oxides

Multiferroic oxides are a class of systems which exhibit coupling between the electrical polarization and the magnetization. These materials show promise to lead to devices in which ferromagnetic memory can be written with magnetic fields or magnetic bits can be written by an electric field. The work conducted in our research focuses on single phase materials. We studied the detailed coupling of the spin and lattice correlations in these systems. In the first phase of the proposal, we explored the complex spin spiral systems and low temperature behavior of hexagonal layered REMnO 3 (RE= rare earth, Y and Sc) system following the detailed structural changes which occurred on crossing into the magnetic states. The techniques were applied to other layered materials such as superconductors and thermoelectric where the same layered motif exists. The second phase of the proposal focused on understanding the mechanisms involved in the onset high temperature ferroelectricity ion hexagonal REMnO 3 and at low temperature in E-Type magnetic ordered perovskite REMnO 3 . We wsynthesized preovskite small A site multiferroics by high pressure and high temperature methods. Detailed measurement of the structural properties and dynamics were conducted over a range of length scales from atomic to mesoscopic scale using, x-ray absorption spectroscopy, x-ray diffuse scattering, x-ray and neutron pair distribution analysis and high resolution x-ray diffraction. Changes in vibration modes which occur with the onset of polarization were probed with temperature and pressure dependent infrared absorption spectroscopy. In addition the orthorhombic system (small radius RE ions) which is believed to exhibit electronically driven ferroelectricity and is also not understood was examined. The multiple length scale synchrotron based measurements may assist in developing more detailed models of these materials and possibly lead to device applications. The experimental work was complemented by density functional methods to determine the magnetic ground states and ab initio molecular dynamics methods (AIMD) to determine the high temperature structures. Simulation were carried out on supercomputers at the National Energy Research Scientific Computing Center (NERSC). An important contribution of this work was the training of graduate students and postdoctoral researchers in materials synthesis, high pressure methods and synchrotron based spectroscopy and x-ray scattering techniques.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Strong spin-lattice coupling in CrSiTe{sub 3}

CrSiTe{sub 3} has attracted recent interest as a candidate single-layer ferromagnetic semiconductor, but relatively little is known about the bulk properties of this material. Here, we report single-crystal X-ray diffraction, magnetic properties, thermal conductivity, vibrational, and optical spectroscopies and compare our findings with complementary electronic structure and lattice dynamics principles calculations. The high temperature paramagnetic phase is characterized by strong spin-lattice interactions that give rise to glassy behavior, negative thermal expansion, and an optical response that reveals that CrSiTe{sub 3} is an indirect gap semiconductor with indirect and direct band gaps at 0.4 and 1.2 eV, respectively. Measurements of the phonons across the 33 K ferromagnetic transition provide additional evidence for strong coupling between the magnetic and lattice degrees of freedom. The Si-Te stretching and Te displacement modes are sensitive to the magnetic ordering transition, a finding that we discuss in terms of the superexchange mechanism. Spin-lattice coupling constants are also extracted.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Determination of the Transition Temperature of a Weak Ferromagnetic Thin Film by Means of an Evolution of the Method Based on the Arrott Plots

The ferromagnetic transition temperature (T{sub c}) of a weak ferromagnetic thin film Cu{sub 0.38}Ni{sub 0.62} has been estimated by using an evolution of the Belov, Goriaga, and Arrott (BGA) model. In fact, the typically used measurements of the zero-field-cooled-field-cooled magnetic moment (m) as a function of temperature (T), the magnetic hysteresis loops (m(H)) as a function of field, and the temperature dependence of the remanent magnetic moment, performed on our sample, did not allow us to individuate precisely the value of T{sub c}, mainly due to the influence of thermal effects and noise on the weak ferromagnetic response of the sample, resulting in a large uncertainty in the estimation of T{sub c}. On the other hand, also the commonly used method of determining the T{sub c} by means of a linear extrapolation of the high-field region of m{sup 2} as a function of the normalized magnetic field (H/m) at different temperatures (Arrott curves), working though for our analyzed material, could not completely fulfill the basic assumptions of the BGA model in general. For these reasons, we have considered the analysis of the derivatives of the Arrott curves, starting from observing that the T{sub c} of the sample corresponds to the temperature where the curvature of the Arrott curves at low fields inverts. In this way, the sensitivity in the determination of the Curie point from the inductive measurements of the magnetic moment is improved while the correct assumptions of the Arrott model are also fully respected.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Field-free deterministic switching of all–van der Waals spin-orbit torque system above room temperature

Two-dimensional van der Waals (vdW) magnetic materials hold promise for the development of high-density, energy-efficient spintronic devices for memory and computation. Recent breakthroughs in material discoveries and spin-orbit torque control of vdW ferromagnets have opened a path for integration of vdW magnets in commercial spintronic devices. However, a solution for field-free electric control of perpendicular magnetic anisotropy (PMA) vdW magnets at room temperatures, essential for building compact and thermally stable spintronic devices, is still missing. Here, we report a solution for the field-free, deterministic, and nonvolatile switching of a PMA vdW ferromagnet, Fe 3 GaTe 2 , above room temperature (up to 320 K). We use the unconventional out-of-plane anti-damping torque from an adjacent WTe 2 layer to enable such switching with a low current density of 2.23 × 10 6 A cm –2 . This study exemplifies the efficacy of low-symmetry vdW materials for spin-orbit torque control of vdW ferromagnets and provides an all-vdW solution for the next generation of scalable and energy-efficient spintronic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Microscopic subsurface characterization of layered magnetic materials using magnetic resonance force microscopy

This project resulted in the following accomplishments: 1) The invention of scanned probe ferromagnetic resonance microscopy. Upon implementation and refinement this approach was used to measure static and dynamic magnetic resonance properties of ferromagnets with an unprecedented combination of spectral and spatial resolution. 2) Demonstration and study of spin pumping in a pristine ferromagnet across a boundary defined entirely by a magnetic field gradient, and so free of materials discontinuities. 3) First demonstrated highly efficient dynamic spin injection from Y 3 Fe 5 O 12 (YIG) into NiO, an antiferromagnetic (AF) insulator and robust spin propagation in AF NiO over distances up to 100-nm thickness; both spin injection and spin transport are mediated by the AF spin correlations. 4) Demonstration of exceptionally high efficiency conversion of spin current to charge current achieved in spin pumping from the dynamic magnetization of a ferromagnetic insulator into a variety of adjacent metal films. 5) Seminal study of the nature of spin-orbit coupling in d-electron metals that revealed the dominant sensitivity of the d-orbital moment to the d-electron count and revealing the important roles of both d-electron configuration and atomic number in the physics of the spin Hall effect. 6) Demonstration of observation of FMR by means of optically-detected NV diamond relaxometry that provided a highly sensitive, spatially resolved FMR detection method and revealed spin pumping across 100-nm length scales by means of dipolar coupling. 7) Using magnetic field localization, developed for FMR imaging, demonstrated a novel approach to discretizing spin wave modes to improve the characteristics of auto-oscillators driven by pure spin currents produced by the spin Hall effect. 8) We demonstrated large spin pumping signals from propagating high wavevector spinwaves in thin film YIG find that the spin pumping efficiency was insensitive to wavevector thus emphasizing the promise of thin YIG films for spinwave-based spintronics by allowing for predictable down-scaling of device dimensions and enabling a broad range of operational frequencies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Mn-substituted cerium oxide nanostructures and their magnetic properties

Highlights: • Mn{sub x}Ce{sub 1-x}O{sub 2} (0.1 ≤ x ≤ 0.5) nanostructures were prepared by one step microwave refluxing method. • The saturation magnetization values for the samples rose with increased Mn content. • The oxygen vacancies inherently played crucial role in increasing the magnetization values. - Abstract: In this study, we report the magnetic properties of nanostructured Mn{sub x}Ce{sub 1-x}O{sub 2} (0 0.1 ≤ x ≤ 0.5) materials, synthesized via microwave refluxing technique. Phase purity of the samples was investigated using the structural characterization techniques such as X-ray diffraction (XRD) and transmission electron microscopy (TEM). These analyses indicated the substitution of Ce-ions with Mn-ions in the lattice. The progressive increase in the oxygen vacancies with increased dopant concentration was demonstrated by Raman, UV–vis and photoluminescence spectroscopic studies. X-ray photoelectron spectroscopy analysis further supported the presence of Mn{sup 2+}, Ce{sup 3+} and Ce{sup 4+} ions as well as oxygen vacancies in the samples. The Mn substituted CeO{sub 2} nanostructures were found to exhibit room temperature ferromagnetism (RTFM). There was a continuous improvement in the saturation magnetization (M{sub S}) values with increased Mn concentration. This might be due to the prevalence of surface oxygen vacancies and the systematic rise in their concentration with increased dopant content.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

The Electronic Structures and Ferromagnetism of Cu-Doped ZnO: the First-Principle Calculation Study

We have carried out first-principle spin-polarized calculations to investigate the electronic structures and the magnetic properties of Cu-doped wurtzite ZnO. It was found that the Cu{sub Zn} substitution can introduce 1 μ{sub B} local magnetic moment into the doped system, whereas the ferromagnetic coupling between Cu{sub Zn}s is so weak that the system cannot keep ferromagnetism at higher temperature. In Zn vacancy (V{sub Zn}) and Cu{sub Zn} coexisted system, Cu is in the Cu {sup 2+}/Cu {sup 3+} mixed valence under the influence of acceptor defect V{sub Zn}. Cu-3d electrons couple with O(around V{sub Zn})-sp electrons and then form Cu{sup 2+} −V{sub Zn} −Cu{sup 2+} or Cu{sup 2+} −VZn−−Cu{sup 3+} bound magnetic polaron (BMP) in the range of 1.27 ∼ 1.90 nm. The overlapping between BMPs is the main ferromagnetism origin of ZnO/Cu. According to our analysis, we thought that ZnO/Cu system will display stronger ferromagnetism when the Cu concentration attains 3% in atomic percentage. The calculated results and analysis will shed light on the origin of ferromagnetism in ZnO/Cu.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Emergent Spin Dynamics Enabled by Lattice Interactions in a Bicomponent Artificial Spin Ice

Artificial spin ice (ASI) are arrays of nanoscaled magnets that can serve both as models for frustration in atomic spin ice as well as for exploring new spin-wave-based strategies to transmit, process, and store information. Here, we exploit the intricate interplay of the magnetization dynamics of two dissimilar ferromagnetic metals arranged on complimentary lattice sites in a square ASI to modulate the spin-wave properties effectively. We show that the interaction between the two sublattices results in unique spectra attributed to each sublattice, and we observe inter- and intra-lattice dynamics facilitated by the distinct magnetization properties of the two materials. The dynamic properties are systematically studied by angular-dependent broadband ferromagnetic resonance and confirmed by micromagnetic simulations. Here, we show that combining materials with dissimilar magnetic properties enables the realization of a wide range of two-dimensional structures, potentially opening the door to new concepts in nanomagnonics.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Analytical theory and possible detection of the ac quantum spin Hall effect

Here, we develop an analytical theory of the low-frequency ac quantum spin Hall (QSH) effect based upon the scattering matrix formalism. It is shown that the ac QSH effect can be interpreted as a bulk quantum pumping effect. When the electron spin is conserved, the integer-quantized ac spin Hall conductivity can be linked to the winding numbers of the reflection matrices in the electrodes, which also equal to the bulk spin Chern numbers of the QSH material. Furthermore, a possible experimental scheme by using ferromagnetic metals as electrodes is proposed to detect the topological ac spin current by electrical means.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Polaronic Conductivity in Cr 2 Ge 2 Te 6 Single Crystals

We report that intrinsic 2D ferromagnetic semiconductors are an important class of materials for spin-charge conversion applications. Cr 2 Ge 2 Te 6 retains long-range magnetic order in the bilayer at cryogenic temperatures and shows complex magnetic interactions with considerable magnetic anisotropy. Here, a series of structural, magnetic, X-ray scattering, electronic, thermal transport and first-principles calculation studies are performed, which reveal that localized electronic charge carriers in Cr 2 Ge 2 Te 6 are dressed by the surrounding lattice and are involved in polaronic transport via hopping that is observed via magnetocrystalline anisotropy. This opens the possibility for manipulation of charge transport in Cr 2 Ge 2 Te 6 —based devices by electron–phonon- and spin–orbit coupling-based tailoring of polaron properties.

2D materials↗
DOE OSTI2019

Magnetic Relaxation Experiments in CNT-Based Magnetic Nanocomposite

In this work, we discuss the relaxation of the magnetic moments in a novel carbon nanotube (CNT)-based nanocomposite synthesized by using chemical vapor deposition process. The material consists of a matrix of CNT filled by Fe-based nanoparticles. This structure is seen clearly by scanning and transmission. X-ray diffraction and Raman spectroscopy are used to detect the predominant Fe{sub 3}C phase and the CNT presence in the sample, respectively. The results obtained from both hysteresis cycles, M(H), and zero field cooled-field cooled (ZFC-FC) measurements confirm that the material is characterized by both a strong ferromagnetic exchange and random magnetic anisotropy. For the first time, we have been able to fit the magnetic relaxation data, M(t), by using both the two distributions of nanoparticles data deduced from the ZFC-FC data and the temperature dependence of the magnetic anisotropy obtained from the law of approach to saturation in random magnets. .

77 NANOSCIENCE AND NANOTECHNOLOGY↗