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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Topological Spin Textures in an Insulating van der Waals Ferromagnet

Generation and control of topological spin textures constitutes one of the most exciting challenges of modern spintronics given their potential applications in information storage technologies. Of particular interest are magnetic insulators, which due to low damping, absence of Joule heating and reduced dissipation can provide energy-efficient spin-textures platform. Here, it is demonstrated that the interplay between sample thickness, external magnetic fields, and optical excitations can generate a prolific paramount of spin textures, and their coexistence in insulating CrBr 3 van der Waals (vdW) ferromagnets. Using high-resolution magnetic force microscopy and large-scale micromagnetic simulation methods, the existence of a large region in T-B phase diagram is demonstrated where different stripe domains, skyrmion crystals, and magnetic domains exist and can be intrinsically selected or transformed to each-other via a phase-switch mechanism. Lorentz transmission electron microscopy unveils the mixed chirality of the magnetic textures that are of Bloch-type at given conditions but can be further manipulated into Néel-type or hybrid-type via thickness-engineering. The topological phase transformation between the different magnetic objects can be further inspected by standard photoluminescence optical probes resolved by circular polarization indicative of an existence of exciton-skyrmion coupling mechanism. The findings identify vdW magnetic insulators as a promising framework of materials for the manipulation and generation of highly ordered skyrmion lattices relevant for device integration at the atomic level.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Direct Observation of Room–Temperature Magnetic Skyrmion Motion Driven by Ultra–Low Current Density in Van Der Waals Ferromagnets

The recent discovery of room-temperature ferromagnetism in 2D van der Waals (vdW) materials, such as Fe 3 GaTe 2 (FGaT), has garnered significant interest in offering a robust platform for 2D spintronic applications. Various fundamental operations essential for the realization of 2D spintronics devices are experimentally confirmed using these materials at room temperature, such as current-induced magnetization switching or tunneling magnetoresistance. Nevertheless, the potential applications of magnetic skyrmions in FGaT systems at room temperature remain unexplored. In this work, the current-induced generation of magnetic skyrmions in FGaT flakes employing high-resolution magnetic transmission soft X-ray microscopy is introduced, supported by a feasible mechanism based on thermal effects. Furthermore, direct observation of the current-induced magnetic skyrmion motion at room temperature in FGaT flakes is presented with ultra-low threshold current density. This work highlights the potential of FGaT as a foundation for room-temperature-operating 2D skyrmion device applications.

2D ferromagnets↗
DOE OSTI2021

Epitaxial Stabilization of Metastable 3C BaRuO 3 Thin Film with Ferromagnetic Non-Fermi Liquid Phase

Thin films of perovskite ruthenates of the general formula ARuO 3 (A = Ca and Sr) are versatile electrical conductors for viable oxide electronics. They are also scientifically intriguing, as they exhibit nontrivial electromagnetic ground states depending on the A-site element. Among them, realization of the cubic perovskite (3C) BaRuO 3 in thin film form has been a challenge so far, because the 3C phase is metastable with the largest formation energy among the various polymorph phases of BaRuO 3 . In this study, 3C BaRuO 3 thin films are successfully prepared employing epitaxial stabilization. Here the 3C BaRuO 3 thin films show itinerant ferromagnetism with a transition temperature of ≈48 K and a non-Fermi liquid phase. The epitaxial stabilization of the 3C BaRuO 3 further enables to make a standard comparison of perovskite ruthenates, thereby establishing the importance of the Ru-O orbital hybridization in understanding the itinerant magnetic system.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Multiferroic and Related Hysteretic Behavior in Ferromagnetic Shape Memory Alloys

In this work, we combine a Ginzburg–Landau model for a ferroelastic transition with the theory of micromagnetism to study the magnetostructural behavior leading to multicaloric effects in ferromagnetic shape memory alloys. We analyze the ferroelastic transition under different conditions of temperature, stress and magnetic field and establish the corresponding phase diagram. On the one hand, our results show that the proper combination of both fields may be used to reduce the transition hysteresis and thus improve the reversibility of the related elastocaloric effects, superelasticity and stress-mediated magnetocaloric effects. On the other hand, the stress-free magnetic field-driven and thermally driven magnetostructural evolution provides physical insight into the low-temperature field-induced domain reorientation, from which we derive strategies to modify the operational temperature ranges and thus the corresponding (magnetic) shape-memory effect.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Separation of Artifacts from Spin–Torque Ferromagnetic Resonance Measurements of Spin–Orbit Torque for the Low–Symmetry Van der Waals Semi–Metal ZrTe 3

Spin-orbit torques generated by exfoliated layers of the low-symmetry semi-metal ZrTe 3 are measured using the spin-torque ferromagnetic resonance (ST-FMR) technique. When the ZrTe 3 has a thickness greater than about 10 nm, artifacts due to spin pumping and/or resonant heating can cause the standard ST-FMR analysis to overestimate the true magnitude of the torque efficiency by as much as a factor of 30, and to indicate incorrectly that the spin-orbit torque depends strongly on the ZrTe 3 layer thickness. Artifact-free measurements can still be achieved over a substantial thickness range by the method developed recently to detect ST-FMR signals in the Hall geometry as well as the longitudinal geometry. ZrTe 3 /Permalloy samples generate a conventional in-plane anti-damping spin torque efficiency ξ$^{FL}_{∥}$ = 0.014 ± 0.004, and an unconventional in-plane field-like torque efficiency |ξ$^{FL}_{∥}$| = 0.003 ± 0.001. As a result, the out-of-plane anti-damping torque is negligible. It is suggested that artifacts similarly interfere with the standard ST-FMR analysis for other van der Waals samples thicker than about 10 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Theoretical Investigation of Half-Metallic Ferromagnetism in Sodium-Based Fluoro-perovskite NaXF{sub 3} (X = V, Co)

We report on the structural, mechanical, magneto-electronic and thermodynamic properties of cubic sodium based fluoro-perovskite NaXF3 (X = V, Co) through density functional theory (DFT). The generalized gradient approximation of Perdew, Burke, and Ernzerh (GGA-PBE) and the Tran-Blaha modified Becke-Johnson potential (TB-mBJ) are used for modeling exchange-correlation effects. The calculated lattice parameters agree well with the experimental measurements. Elastic properties show that these compounds are mechanically stable. The results of spin-polarized band structure show a half metallic behavior of NaVF{sub 3} and NaCoF{sub 3}. The magnetic study shows that the nature of these compounds is ferromagnetic and the integer value of the total magnetic moment confirms the half metallicity for both materials. The thermodynamic characters are also investigated through quasi-harmonic approximation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Rich Soliton Structures for the Kraenkel-Manna-Merle (KMM) System in Ferromagnetic Materials

A particular attention is paid to investigate the Kraenkel-Manna-Merle (KMM) system, which can describe the nonlinear short-wave propagation in saturated ferromagnetic materials with zero-conductivity in an external field. A class of exact soliton solutions is constructed via the generalized G{sup ′}/G-expansion method. Some novel soliton structures are excited by choosing the arbitrary functions in the solution as certain specific functions. Hump-soliton, cusp-soliton, loop-soliton, and kink-soliton are observed graphically. The results reveal the system theoretically possesses extremely rich soliton structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Search for New Half-Metallic Ferromagnets in Quaternary Diamond-Like Compounds I–II{sub 2}–III–VI{sub 4} and I{sub 2}–II–IV–VI{sub 4} (I = Cu; II = Mn, Fe, Co; III = In; IV = Ge, Sn; VI = S, Se, Te)

The structural, electronic, and magnetic properties I–II{sub 2}–III–VI{sub 4} and I{sub 2}–II–IV–VI{sub 4} are investigated firstly by using the first-principles calculations. The investigation was done using the ab initio full-potential linearized augmented plane wave (FPLAPW) method where the exchange–correlation potential was calculated with the frame of GGA and GGA+U. The theoretically predicted lattice parameters for I–II{sub 2}–III–VI{sub 4} and I{sub 2}–II–IV–VI{sub 4} alloys are in good agreement with existing experimental measurements. The possibility of half-metallic ferromagnetism in I–II{sub 2}–III–VI{sub 4} and I{sub 2}–II–IV–VI{sub 4} (I = Cu; II = Mn, Fe, Co; III = In; IV = Ge, Sn; VI = S, Se, Te) was analyzed by electronic band structure and density of states calculations. We found that Cu{sub 2}CoGeS{sub 4}, Cu{sub 2}FeGeS{sub 4}, Cu{sub 2}FeSnS{sub 4}, and CuMn{sub 2}InSe{sub 4} compounds exhibit a complete half-metallic characteristic with a total spin moment of 3.00, 4.00, 4.00, and 10.00 μ{sub B} and direct band gap of (Eg ↑ = 0.63 eV), (Eg ↑ = 0.90 eV), (Eg ↑ = 0.31 eV), and (Eg ↓ = 1.10 eV), respectively. These results may be of interest for spintronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Doping Effect on Ferromagnetic Arrangement and Electronic Structure of Cubic AlAs with Low Concentration of 3d (V, Cr, and Mn) Impurities

The doping effect of aluminum arsenide (AlAs) with 3d (TM = V, Cr, and Mn) of transition metal impurities gives new materials called diluted magnetic semiconductors, which have interesting electronic and magnetic properties for spintronics applications. We have used the full-potential linearized augmented plane wave (FP-LAPW) method to calculate the electronic band structures and magnetic properties of Al{sub 1−x}TM{sub x}As at low concentration x = 0.0625 of transition metal (TM = V, Cr, and Mn) atoms. We have found that the majority-spin states of Al{sub 0.9375}TM{sub 0.0625}As compounds are metallic due to large p-d hybridization between 3d levels of TM and the 4p levels of As around Fermi level, whereas the minority-spin states have semiconductor character. These compounds exhibit a half-metallic behavior with spin polarization of 100%, where the ferromagnetism is originated from double-exchange mechanism. Therefore, Al{sub 0.9375}TM{sub 0.0625}As (TM = V, Cr, and Mn) materials seem to be good candidates for spin injection in the field of spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic, Optoelectronic, and Thermodynamic Properties of Sr{sub 2}CrXO{sub 6} (X = La and Y): Half-Metallic and Ferromagnetic Behavior

The effects of spin polarization on the structure, magnetic, and optoelectronic properties of Cr-based series of double perovskites Sr{sub 2}CrXO{sub 6} (X = La and Y) have been studied by using the full-potential linearized augmented plane-wave method (FP-LAPW), based on the density functional theory (DFT) as implemented in the Wien2k code, within the generalized gradient approximation (GGA), GGA + U, and GGA plus Trans-Blaha-modified Becke–Johnson (TB-mBJ) as the exchange correlation. Our results show a similar half-metallic ferromagnetic ground state for both materials. From the electronic properties, it is found that Sr{sub 2}CrYO{sub 6} has a direct band gap at (Γ-Γ) direction and Sr{sub 2}CrLaO{sub 6} has an indirect band gap at (Γ-W) direction. Furthermore, we have computed the optic and thermodynamic properties which are investigated for the first time. Consequently, the magnetic, optoelectronic, and thermodynamic properties show these compounds are promising for high technological applications, namely spintronic materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ferromagnetic Nanoparticles of Ising Spin-1 with a Rubik’s Cube Structure: Monte Carlo Simulations

Using Monte Carlo simulations, magnetic properties of the ferromagnetic nanoparticles of Ising spin-1 are investigated in the framework of the Ising model. The system is considered to have a Rubik’s cube structure composed of nanocubes having an equivalent exchange coupling, while, between adjacent nanocubes, the exchange coupling is assumed to vary. Both size effects and system parameters’ influence on phase diagrams of the nanosystem are studied. Thus, the magnetic properties of the system such as the critical temperature, the magnetization, and the coercive field are computed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Development of Room-Temperature Ferromagnetism in Nanocomposite CdO Codoped with Al and Gd: Treatment in Hydrogen Atmosphere

Cadmium oxide codoped with Al and Gd ion powders was synthesised by thermal codecomposition of a mixture of complexes of cadmium acetate dihydrate, gadolinium acetate hydrate, and aluminum nitrate nonahydrate. The mass ratio of Al/Cd was fixed while the mass ratio of Gd/Cd varied systematically. The purpose of the present study is to synthesise and study the transparent conducting oxide (TCO) CdO powder having room-temperature ferromagnetic (RT-FM) properties. To realize that purpose, the synthesised Al/Gd-codoped CdO powder was annealed under hydrogen gas with certain conditions. The X-ray diffraction (XRD) method confirmed the formation of a single nanocrystalline structure; thus, both Al/Gd ions were incorporated into CdO lattice forming solid solutions. Magnetic measurements revealed that some of the doped CdO powders gained paramagnetic (PM) properties where the susceptibility increases with increasing dopant Gd content; the measured effective magnetic moment of dopant Gd{sup 3+} was around 8 μ{sub B}. Furthermore, the magnetic energy of the created RT-FM of the codoped CdO samples by hydrogenation was found to be dependent on the Gd% doping level. For hydrogenated CdO powder doped with 3% Gd, the coercivity (H{sub c}) was 195.9 Oe, the remanence (M{sub r}) was 0.77 memu/g, the saturation magnetisation (M{sub s}) was 5.05 memu/g, and the energy product (U{sub m}) was 150.6 merg/g. Thus, the possibility of production of TCO CdO with RT-FM, where magnetic characteristics can be tailored by doping and post treatment under H{sub 2} gas, was proven. Thus, a new potential candidate to be used as a dilute magnetic semiconductor (DMS) was successfully synthesised.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Half Metallic Ferromagnetic Character in ZnXP{sub 2} (X = Ge, Si) Chalcopyrites Doped with Mn

The electronic and the magnetic properties of ZnXP{sub 2} (X = Ge, Si) were studied using the Korring-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA). The total and partial density of state (DOS) are computed for different Mn concentrations. The total magnetic moment, FM and DLM energies, and their variation as well as Curie temperature are also given. It is shown that the substitution of X cations (X = Ge, Si) by Mn atoms in ZnXP{sub 2} chalcopyrites leads to half metallic ferromagnetic character with double exchange mechanism. Thus, the critical temperature can be controlled by varying the concentration of manganese impurity.

36 MATERIALS SCIENCE↗
DOE OSTI2019

First-Principles Investigation of Half-Metallic Ferromagnetism of a New 1:1:1:1 Type Quaternary Heusler Compound YRhTiSi

First-principles theory was applied to study the electronic, magnetic, and half-metallic behaviors of a new Y-based equiatomic quaternary Heusler compound YRhTiSi. We will come to study the physical properties of this compound and find it has the half-metallic nature in the ferromagnetic (FM) state. The total magnetic moment of this compound YRhTiSi is 2 μ{sub B}, which follows the famous Slater-Pauling rule, Mt = Zt − 18, Mt is the total magnetic moment and Zt is the total number of valence electrons. Based on its equilibrium and strained lattice constants, the magnetic and half-metallic behaviors of this compound have been discussed in detail. And we find that the H–M gap and the band gap can be regulated through the effect of uniform strain and the tetragonal deformation. A large H–M gap of 0.48 eV has been found in our work, which is nearly larger than any previous study. Furthermore, the formation and cohesive energies have also been discussed in our work to examine the phase stability of YRhTiSi. This theoretical investigation provides further insight into the application of Y-based compounds as spintronic materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Evidence of Room Temperature Ferromagnetism in Zn{sub 1−x}Sn{sub x}S Thin Films

Tin (Sn)-doped zinc sulfide (Zn{sub 1−x}Sn{sub x}S) thin films at different tin (Sn) concentrations (= 0.00, 0.02, 0.05, and 0.08) were coated onto Corning 7059 glass substrates using the electron beam evaporation technique. The films were subjected to different characterization techniques to study the physical properties of the thin films. The structural properties of the films were studied using a powder X-ray diffractometer (XRD), and it was found that the films were cubic in structure without any impurity phases. The crystallite size increased with an increase of Sn concentration, and the mean crystallite size was 21 nm. The chemical composition and surface morphology of the films were studied using scanning electron microscopy (FE-SEM) with energy-dispersive analysis of X-rays (EDAX). Optical properties such as transmittance and absorbance were recorded using a diffuse reflectance spectroscope (UV–vis–NIR). All the films exhibited high optical transmittance of 85% in the visible region of the solar spectrum. The band gap of the films was calculated using Tauc’s relation, and it was found that it increased from 3.53 to 3.57 eV with an increase in the Sn doping concentration from x = 0.02 to x = 0.08. The room temperature photoluminescence studies of the films were recorded using a fluorescence spectrophotometer, and it was found that the films exhibited a prominent emission peak at 420 nm. The magnetic properties of the films and glass substrates at room temperature were studied using a vibrating sample magnetometer. From this, it was found that the films were weakly ferromagnetic at room temperature and the strength of magnetization increased with an increase of doping concentration from x = 0.02 to x = 0.05 and decreased at higher doping concentrations (x = 0.08). The films showed high magnetization at x = 0.05. The films at x = 0.05 exhibited the magnetization (M{sub s}), retentivity (M{sub r}), and coercive fields (H{sub c}) 18 × 10{sup − 6} emu/cm{sup 3}, 1.6 × 10{sup − 6} emu/cm{sup 3}, and 91.80 Oe, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Investigation to the Structural, Optical, and Magnetic Properties of Synthesized Ni-Doped Anatase Nanoparticles: Essential Role of Treatment in Hydrogen on Long-Range Ferromagnetic Order

Nanocomposite powders of anatase TiO{sub 2} doped with Ni ions (TiO{sub 2}:Ni) were synthesized by facile thermal co-decomposition of a mixture of metals complexes. The X-ray diffraction (XRD) analyses using the Rietveld method confirm the formation of almost single nanocrystalline anatase structure. Anatase TiO{sub 2} incorporated with Ni ions (TiO{sub 2}:Ni) illustrated the formation of a substitutional solid solutions (SSS). The diffuse reflection spectroscopy (DRS) method used to study the optical properties of the prepared samples revealed a redshift associated with Ni doping and hydrogenation, which is explained by the creation of point defects including O-vacancies. This study showed the essential importance of hydrogenation process in order to create or boost room-temperature ferromagnetism (RT-FM). The magnetic measurements indicated that anatase TiO{sub 2} doped with 4.8 mol% Ni produce a magnetic saturation of 0.84 emu/g, which is a remarkable result compared with that related to the similar studies on doped TiO{sub 2}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Hydrogen-Induced Room-Temperature Ferromagnetism in Carbon-Incorporated CdO

Carbon-incorporated CdO (CdO–C) nanocrystallites were synthesised by sol–gel technique including sucrose (C{sub 12}H{sub 22}O{sub 11}) as a source of carbon ions. This investigation aimed to disclose the necessary synthesis conditions to create room-temperature ferromagnetic (RT-FM) properties in host CdO–C system. Therefore, structural, optical and magnetic properties of CdO–C samples were systematically investigated. The X-ray diffraction (XRD) method was used to study the structural properties, and the diffuse reflection spectroscopy (DRS) method was used to study the optical properties. It was established that post-annealing of synthesised samples in H{sub 2} atmosphere could create RT-FM. The experimental results were discussed in the framework of previous studies of other transparent conducting oxides (TCOs). The magnetic properties of CdO–C system were studied here for the first time. It was found that CdO–C nanopowder of tailored FM properties could be used as a candidate for TCO applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Asymptotic Behaviour of Ground States for Mixtures of Ferromagnetic and Antiferromagnetic Interactions in a Dilute Regime

We consider randomly distributed mixtures of bonds of ferromagnetic and antiferromagnetic type in a two-dimensional square lattice with probability 1−p and p, respectively, according to an i.i.d. random variable. We study minimizers of the corresponding nearest-neighbour spin energy on large domains in ℤ{sup 2}. We prove that there exists p{sub 0} such that for p≤p{sub 0} such minimizers are characterized by a majority phase; i.e., they take identically the value 1 or − 1 except for small disconnected sets. A deterministic analogue is also proved.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗