Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “FERROMAGNETISM”

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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Robust Ferromagnetism in Highly Strained SrCoO 3 Thin Films

Epitaxial strain provides important pathways to control the magnetic and electronic states in transition-metal oxides. However, the large strain is usually accompanied by a strong reduction of the oxygen-vacancy formation energy, which hinders the direct manipulation of their intrinsic properties. Here, using a postdeposition ozone annealing method, we obtain a series of oxygen stoichiometric SrCoO 3 thin films with the tensile strain up to 3.0%. We observe a robust ferromagnetic ground state in all strained thin films, while interestingly the tensile strain triggers a distinct metal-to-insulator transition along with the increase of the tensile strain. The persistent ferromagnetic state across the electrical transition therefore suggests that the magnetic state is directly correlated with the localized electrons, rather than the itinerant ones, which then calls for further investigation of the intrinsic mechanism of this magnetic compound beyond the double-exchange mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Charge Density Wave and Ferromagnetism in Intercalated CrSBr

In materials with 1D electronic bands, electron–electron interactions can produce intriguing quantum phenomena, including spin-charge separation and charge density waves (CDW). Most of these systems, however, are non-magnetic, motivating a search for anisotropic materials where the coupling of charge and spin may affect emergent quantum states. Here, in this study, chemical intercalation of the van der Waals magnetic semiconductor CrSBr yields Li 0.17(2) (tetrahydrofuran) 0.26(3) CrSBr, which possesses an electronically driven quasi-1D CDW with an onset temperature above room temperature. Concurrently, electron doping increases the magnetic ordering temperature from 132 to 200 K and switches its interlayer magnetic coupling from antiferromagnetic to ferromagnetic. The spin-polarized nature of the anisotropic bands that give rise to this CDW enforces an intrinsic coupling of charge and spin. The coexistence and interplay of ferromagnetism and charge modulation in this exfoliatable material provide a promising platform for studying tunable quantum phenomena across a range of temperatures and thicknesses.

2D magnets↗
DOE OSTI2023

Controllable Skyrmionic Phase Transition between Néel Skyrmions and Bloch Skyrmionic Bubbles in van der Waals Ferromagnet Fe 3-δ GeTe 2

The van der Waals (vdW) ferromagnet Fe 3-δ GeTe 2 has garnered significant research interest as a platform for skyrmionic spin configurations, that is, skyrmions and skyrmionic bubbles. However, despite extensive efforts, the origin of the Dzyaloshinskii–Moriya interaction (DMI) in Fe 3-δ GeTe 2 remains elusive, making it challenging to acquire these skyrmionic phases in a controlled manner. In this study, it is demonstrated that the Fe content in Fe 3-δ GeTe 2 has a profound effect on the crystal structure, DMI, and skyrmionic phase. For the first time, a marked increase in Fe atom displacement with decreasing Fe content is observed, transforming the original centrosymmetric crystal structure into a non-centrosymmetric symmetry, leading to a considerable DMI. Additionally, by varying the Fe content and sample thickness, a controllable transition between Néel-type skyrmions and Bloch-type skyrmionic bubbles is achieved, governed by a delicate interplay between dipole–dipole interaction and the DMI. The findings offer novel insights into the variable skyrmionic phases in Fe 3-δ GeTe 2 and provide the impetus for developing vdW ferromagnet-based spintronic devices.

2D ferromagnet Fe3-δGeTe2↗
DOE OSTI2024

Highly Efficient Room‐Temperature Spin‐Orbit‐Torque Switching in a Van der Waals Heterostructure of Topological Insulator and Ferromagnet

Abstract All‐Van der Waals (vdW)‐material‐based heterostructures with atomically sharp interfaces offer a versatile platform for high‐performing spintronic functionalities at room temperature. One of the key components is vdW topological insulators (TIs), which can produce a strong spin‐orbit‐torque (SOT) through the spin‐momentum locking of their topological surface state (TSS). However, the relatively low conductance of the TSS introduces a current leakage problem through the bulk states of the TI or the adjacent ferromagnetic metal layers, reducing the interfacial charge‐to‐spin conversion efficiency ( q ICS ). Here, a vdW heterostructure is used consisting of atomically‐thin layers of a bulk‐insulating TI Sn‐doped Bi 1.1 Sb 0.9 Te 2 S 1 and a room‐temperature ferromagnet Fe 3 GaTe 2, to enhance the relative current ratio on the TSS up to ≈20%. The resulting q ICS reaches ≈1.65 nm −1 and the critical current density J c ≈0.9 × 10 6 Acm −2 at 300 K, surpassing the performance of TI‐based and heavy‐metal‐based SOT devices. These findings demonstrate that an all‐vdW heterostructure with thickness optimization offers a promising platform for efficient current‐controlled magnetization switching at room temperature.

2D ferromagnet↗
DOE OSTI2024

Tunable Anomalous Hall Effect in a Kagomé Ferromagnetic Weyl Semimetal

Emerging from the intricate interplay of topology and magnetism, the giant anomalous Hall effect (AHE) is the most known topological property of the recently discovered kagomé ferromagnetic Weyl semimetal Co 3 Sn 2 S 2 with the magnetic Co atoms arranged on a kagomé lattice. Here it is reported that the AHE in Co 3 Sn 2 S 2 can be fine-tuned by an applied magnetic field orientated within ≈2° of the kagomé plane, while beyond this regime, it stays unchanged. Particularly, it can vanish in magnetic fields parallel to the kagomé plane and even decrease in magnetic fields collinear with the spin direction. This tunable AHE can be attributed to local spin switching enabled by the geometrical frustration of the magnetic kagomé lattice, revealing that spins in a kagomé ferromagnet change their switching behavior as the magnetic field approaches the kagomé plane. Furthermore, these results also suggest a versatile way to tune the properties of a kagomé magnet.

anomalous Hall effect↗
DOE OSTI2017

Group of Quantum Bits Acting as a Bit Using a Single-Domain Ferromagnet of Uniaxial Magnetic Ions

Read/write operations with individual quantum bits (i.e., qbits) are a demanding concern to solve in quantum computing. To alleviate this difficulty, we considered the possibility of using a group of qbits that act collectively as a bit (hereafter, a group bit or a gbit, in short). A promising candidate for a gbit is a single-domain ferromagnet (SDF) independent of its size, which can be prepared as a magnet of well-separated uniaxial magnetic ions (UMIs) at sites of no electric dipole moment with their uniaxial axes aligned along one common direction. When magnetized, the UMIs of such a magnet have a ferromagnetic (FM) arrangement and the resulting SDF becomes a gbit with its two opposite moment orientations representing the |0⟩ and |1⟩ states of a bit. Here, we probed the requirements for such magnets and identified several 2H-perovskites as materials satisfying these requirements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Discovery of a Ferromagnetic Nickel Chalcogenide Nanocluster Ni 3 S 3 H(PEt 3 ) 5

Atomically precise ligated nanoclusters (NC) are promising cluster-based materials with novel molecular architectures and tunable magnetic properties. Herein, the synthesis and characterization of a nickel sulfide NC Ni 3 S 3 H(PEt 3 ) 5 (PEt 3 = triethylphosphine) with distinct magnetic properties are reported. Magnetization measurements reveal its magnetic moment of 1.5 µ B in the solid phase, consistent with the existence of one unpaired electron predicted by density functional theory (DFT) calculations. Additionally, experimental measurements indicate the presence of ferromagnetic ordering within each Ni 3 S 3 H(PEt 3 ) 5 NC and strong coercivity at temperatures below 20 K. Ion mobility-mass spectrometry is employed in conjunction with DFT calculations and collision cross-section simulations to investigate the structure of the isolated Ni 3 S 3 H(PEt 3 ) 5 . Theoretical studies show that [Ni 3 S 3 H(PEt 3 ) 5 ] + has a planar Ni 3 S 3 core where three Ni atoms are arranged in a triangle with three bridging S atoms residing in the same plane. This structure is preserved in both solution and solid phases, which is confirmed by spectroscopic studies of Ni 3 S 3 H(PEt 3 ) 5 . Additionally, DFT calculations indicate that all spins at the Ni sites are aligned parallel, confirming the presence of ferromagnetic coupling. Overall, this study provides key insights into the structure and magnetic properties of Ni 3 S 3 H(PEt 3 ) 5 , which will facilitate the design of new NC-based magnetic materials.

Nickel sulfide nanocluster↗
DOE OSTI2018

Electronic Structures of Several New Rare-Earth Half-Metallic Ferromagnets SmX (X = O, S, Se, and Te)

Several new rare-earth half-metallic ferromagnets with the NaCl structure, namely SmX (X = O, S, Se, and Te), are found based on the first-principle calculations (LSDA + U). These materials only have spin-up subbands at the Fermi level and their net crystal cell magnetic moments are all 6.00 µ{sub B} per unit cell, which shows that SmX are potential half-metallic ferromagnets. They have high Curie temperatures (above 1000 K) and stable half-metallicity. The magnetic moments, the electrical conductivity, and the half-metallicity of SmX mainly originate from the spin-polarization of Sm-4f orbitals, which are induced by the strong octahedral crystal field in the ligand complex ML{sub 6} consisting of the Sm ion and its six X ion ligands. Six 4f electrons occupy six 4f orbitals of the Sm ion in the high-spin sequence. The main reason is that the splitting energy is lower than the pairing energy of 4f electrons because the 4f orbitals are partly electrostaticly shielded by other electrons outside the 4f orbitals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The First-Principle Study of the Electronic Structure, Ferromagnetic and Thermoelectric Properties of Spinel Alloy FeAl{sub 2}O{sub 4} Using mBJ Functional Approach

In this research work, the modified Becke and Johnson potential has been used to realize the actual electronic states and band gap properties of FeAl{sub 2}O{sub 4}. Ferromagnetism is illustrated in terms of John-Teller energy and exchange energies involved in the system due to electron spin. Moreover, the exchange constants also support the ferromagnetism in the studied compound. The reduction of the magnetic moment of Fe from its free space value and the shifting of the magnetic moment to nonmagnetic sites are the consequence of strong magnetization. In the end, the electrical conductivity and Seebeck coefficient incorporated to give a high value of the power factor and thermal efficiency for energy renewable devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Transition of Magnetic Characteristics from Paramagnetic State to Ferromagnetic Phase in Ce{sub 1−x}Ni{sub x}O{sub 2} Nanoparticles

Nowadays, oxide-based diluted magnetic semiconductor nanoparticles are the most reliable compounds, wherein they accommodate both spin as well as charge of the electron in single domain, means most preferable for the fabrication of spintronic devices. In this view, we report on new Ce{sub 1−x}Ni{sub x}O{sub 2} (x = 0.00, 0.02, 0.04, 0.06, and 0.08) nanoparticles prepared by precipitation method via polyethylene glycol as a surfactant. XRD analysis revealed that all the synthesized nanoparticles were crystallized in distinct FCC fluorite structure as that of CeO{sub 2} host lattice. Transmission electron microscopy analysis confirmed that all the synthesized samples were in spherical shape with average particle size of 8–10 nm, which is well concord with the grain size estimated from the Scherrer formula. The vibrating sample magnetometer evaluations suggested that pristine host lattice shows signals of paramagnetism; meanwhile, Ni substitution CeO{sub 2} nanoparticles exhibits strong ferromagnetism at room temperature. Particularly, 4% Ni-doped CeO{sub 2} samples shows enhanced ferromagnetism and which is suppressed with raising dopant concentration. The perceived magnetization with respect to the Ni dopant concentration is well anticipated by F-center exchange mechanism. We expect that the observations in this research suggest suitable path for preparing of various oxide-based diluted magnetic semiconductor nanoparticles and their applications in fabrication of spintronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Half-metallic Ferromagnetism in Novel Rh{sub 2}-based Full-Heusler Alloys Rh{sub 2}FeZ (Z = Ga and In)

In this approach, we have employed the ab initio method of full-potential linearized plane waves plus local orbital based on the framework of density functional theory, within the spin generalized gradient approximation plus U (GGA+U), where U is the Hubbard correlation term for exchange-correlation potential. This method is used to predict the equilibrium structural parameters, the electronic structure, and the magnetic properties of Rh{sub 2}FeGa and Rh{sub 2}FeIn full-Heusler alloys. The structural properties result show that both Rh{sub 2}FeGa and Rh{sub 2}FeIn compounds are stable in ferromagnetic states. The spin-polarized electronic structure demonstrate that both full-Heusler compounds are half-metals with half-metallic band gap (E{sub HM}) of 0.326 eV for Rh{sub 2}FeGa alloy and 0.245 eV for Rh{sub 2}FeIn alloy, where the apparition of an indirect gap from Γ to X in minority spin is shown by these Heusler alloys. Furthermore, calculations of total magnetic moment give the value of 5 µ{sub B}, which agrees with Slater-Pauling rule; also, the atomic magnetic moment of both Rh and Fe transition metals have the same sign which depicts the ferromagnetic behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Tunable Optical Behaviour and Room Temperature Ferromagnetism of Cobalt-Doped BaSnO{sub 3} Nanostructures

In this work, the effect of Co doping on the structural, vibrational, morphological, optical and magnetic behaviour of BaSnO{sub 3} nanostructures is reported. Pure and Co (1,3, and 5%)-doped barium stannate (BSO) nanostructures were prepared by conventional hydrothermal technique followed by calcination at 900 °C for 5 h. The single crystalline cubic phase was identified by XRD analysis and structural distortions associated with Co doping were evidenced by variation in microstarin and crystallite size. FTIR and Raman studies further confirm the structural quality of the prepared samples. FESEM analysis revealed the mixed morphology of prepared samples, and the chemical compositions of all the samples were analysed using EDAX studies. The absorption studies revealed the incorporation of dopant ions and their effect on the bandgap subsequently in samples. The presence of defects and paramagnetic centres in the samples were confirmed by PL and EPR analyses. Magnetization studies demonstrated that pure BSO exhibits characteristic diamagnetism at room temperature and the addition of Co into Ba–Sn–O lattice drives the F-centre exchange interactions which results in the ferromagnetic behaviour. Hence, the occurrence of diamagnetic to ferromagnetic transition at room temperature with addition of Co as a dopant was identified.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Possible Origin of Ferromagnetism in Transition Metal Doped Zirconia

We have studied the electronic structure and magnetic properties of cubic zirconia (c-ZrO{sub 2}) with cobalt (Co) or nickel (Ni) doping using density functional theory (DFT) calculations. The pure c-ZrO{sub 2} is a nonmagnetic insulator with a wide bandgap. The calculated results reveal that isolated Co or Ni atom can both produce the local magnetic moment in c-ZrO{sub 2}. And the isolated Co atom can introduce a magnetic moment of about 0.98 μ{sub B}, while the Ni atom is 2.85 μ{sub B}. The impurity peaks can be formed in the bandgap. Our studies show that the magnetic moments mainly result from d orbitals of the impurity atoms. And the spin-up electrons will be arranged in t{sub 2g} orbitals under the ligand field of O{sub h} group in Co- or Ni-doped c-ZrO{sub 2}. Obviously, this will lead to a high-spin state (S = 1/2 or 1). The studies of magnetic coupling reveal that the two Co atoms in c-ZrO{sub 2} are not always coupled ferromagnetically at different distances. And the system will be in a spin singlet state (S = 0) when the distance is 6.209 or 7.170 Å between two Co atoms. However, the two Ni atoms in c-ZrO{sub 2} are always coupled ferromagnetically at all distances. So we can conclude that the Ni-doped c-ZrO{sub 2} is more suitable for spintronic material than Co doping. These results are significant for spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

First-Principle Study on the Origin of Ferromagnetism in Non-magnetic Halide Perovskite CsCdM{sub 3} (M = Cl and Br) Doped with B, C, and N

Based on the density functional theory (DFT), we elucidate the origin of magnetization in non-magnetic cubic halide perovskite CsCdM{sub 3} (M = Cl and Br) induced by substitution of non-magnetic 2p-impurities (B, C, and N) substitution. The calculations were done within the generalized gradient approximation (GGA) and GGA plus-modified Becke and Johnson (mBJ-GGA) as the exchange correlation. The results reveal that half-metallic ferromagnetism can be obtained for C- and N-dopings with the integer magnetic moment of 3.00 and 2.00 µ{sub B} per cell. However, B substitution does not induce magnetism in both CsCdCl{sub 3} and CsCdBr{sub 3} systems. The localized magnetic moments substantially come from impurity atoms. The origin of ferromagnetism can be attributed to the p - p hybridization between 2p-impurities and its surrounding halide atoms. Our results show that doped perovskites could provide a new promising class of materials for future spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Improved Ferroelectric and Ferromagnetic Properties of 1 − xBiFeO{sub 3}-xBaTiO{sub 3} Ceramics

This paper introduces the solid-phase preparation of bismuth ferrite-based multiferroic ceramics (1 − x BiFeO{sub 3}-x BaTiO{sub 3}). After the Ba and Ti doping, it can be observed from the XRD pattern that the crystal structure of the sample changes obviously. From the picture obtained from the SEM test, the grain size of the doped samples was significantly reduced. Pure BiFeO{sub 3} (BFO) showed a large leakage current, and in the leakage current test, we found that the leakage current of Ba, Ti-doped samples decreased significantly, which may be related to doping, leading to oxygen vacancy reduction. From the magnetization hysteresis loops, we can see that the ferromagnetism of the doped samples was significantly improved compared to pure BFO, because Ba, Ti doping destroys the G-type antiferromagnetic sequence of pure BFO, thereby enhancing the ferromagnetic properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Investigation of the Substituting Effect of Chromium on the Electronic Structures and the Half-Metallic Ferromagnetic Properties of BaO

The first-principle methods of density functional theory were used to investigate the doping effect of 3d chromium (Cr) impurities on the electronic properties and the ferromagnetic arrangement of (BaO) barium oxide such as Ba{sub 1−x}Cr{sub x}O compounds at concentrations x = 0.25, 0.5, and 0.75. The p–d exchange coupling between 2p states of oxygen (O) and 3d (Cr) partially filled levels induces magnetism in the Ba{sub 1−x}Cr{sub x}O compounds. The majority- and minority-spin states exhibit respectively metallic and semiconducting features, leading to a half-metallic (HM) character with 100% spin polarization for all concentrations. The Ba{sub 0.75}Cr{sub 0.25}O, Ba{sub 0.5}Cr{sub 0.5}O, and Ba{sub 0.25}Cr{sub 0.75}O compounds have integral total magnetic moments of 4 μ{sub B} per Cr atom with HM gaps of 0.055, 0.218, and 0.308 eV, respectively. These behaviors form accurate half-metallic ferromagnets and make Ba{sub 1−x}Cr{sub x}O as potential materials for possible spintronics applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Half-Metallic Ferromagnetism Character in Cr-Doped CaS Diluted Magnetic Insulator and Semiconductor: an Ab Initio Study

The overall aim of this study is to investigate theoretically the structural, electronic, and magnetic properties of calcium sulfide (CaS) doped with chromium (Cr) impurity, in order to conduct a new search dilute magnetic semiconductors (DMS) suitable for different applications in electronics and spintronics. For measuring, the physical property of this compound is implemented using the first principles approach employed in WIEN2K code. The structural characteristics are optimized using the Generalized Gradient Approximation established by Perdew-Burk-Ernzerhof (PBE-GGA). We calculate and minimize the total energy of the three ternary compounds (Ca{sub 0.75}Cr{sub 0.25}S, Ca{sub 0.50}Cr{sub 0.50}S, and Ca{sub 0.25}Cr{sub 0.75}S) in the paramagnetic (PM), ferromagnetic (FM), and antiferromagnetic (AFM) phase. We find all compounds stable in (FM) structure, whereas the modified Becke and Johnson local density approximation (mBJ-LDA) functional has been employed to evaluate the electronic and magnetic properties. Based on our findings, indicate that this system revealed a half-metallic ferromagnetic behavior with half-metallic gap (HM) and 100% spin-polarized at the fermi level for all chromium (Cr) concentrations. This advantageous set of properties is due to the half-metallic behavior, where the majority spin and minority spin exhibit metallic and semiconducting behaviors respectively. The chromium atom is the most important source of the total magnetic moment in these compounds (4 μβ) by comparison with magnetic moments produced by Ca and S atoms, which have minor contribution. Finally, our prediction results require an experimental confirmation in the future.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Oxygen Vacancy-Induced Room Temperature Ferromagnetism in Rutile TiO{sub 2}

As oxygen vacancies play an important role in ferromagnetism of rutile TiO{sub 2}, a method of γ-ray irradiates rutile TiO{sub 2} single crystals was subtly proposed to study the effect of oxygen vacancies on magnetic properties. Remarkably, room temperature ferromagnetism was observed in γ-ray irradiated rutile TiO{sub 2} single crystals, and the saturation magnetization is the strongest when dose is 4 × 10{sup 4} Gy which assigned to ESR results. Since the displacement threshold energy of Ti atom is much bigger than that of O atom, the defects produced by γ-irradiation are mainly oxygen vacancies. After irradiation, XPS, PL spectra indicate the presence of oxygen vacancies(V{sub O}), Ti{sup 3+}, and V{sub O}-Ti{sup 3+} composite defects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗