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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Magnetic modification at sub-surface of FeRh bulk by energetic ion beam irradiation

Ferromagnetic layered structure has been made at sub-surface of the antiferromagnetic FeRh bulk samples by high energy He ion beam irradiation. In accordance with the Transport of Ions in Matter simulation, such ion beam can effectively deposit the elastic collision energy in several μm regions in the depth from the surface. Measurement with a superconducting quantum interference device reveals the irradiated samples to be ferromagnetic. Assuming that only the part the energy deposited can be modified to be ferromagnetic, the corresponding irradiation induced magnetization is consistent with the data that we previously reported. On the other hand, the X-ray magnetic circular dichroism (XMCD) spectra for the irradiated samples are totally unchanged as those for the unirradiated samples. Since XMCD signal in total emission yield method is considered to be surface sensitive with a typical probing depth of several nm, the surface magnetic state is maintained to be antiferromagnetic. By utilizing these phenomena, three-dimensional magnetic patterning of FeRh can be realized, which may potentially be used for future magnetic exchange device application such as nano-scale sensors and memories.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Intrinsic synchronization of an array of spin-torque oscillators driven by the spin-Hall effect

This paper micromagnetically studies the magnetization dynamics driven by the spin-Hall effect in a Platinum/Permalloy bi-layer. For a certain field and current range, the excitation of a uniform mode, characterized by a power with a spatial distribution in the whole ferromagnetic cross section, is observed. We suggest to use the ferromagnet of the bi-layer as basis for the realization of an array of spin-torque oscillators (STOs): the Permalloy ferromagnet will act as shared free layer, whereas the spacers and the polarizers are built on top of it. Following this strategy, the frequency of the uniform mode will be the same for the whole device, creating an intrinsic synchronization. The synchronization of an array of parallely connected STOs will allow to increase the output power, as necessary for technological applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

First principles study of structural, electronic and mechanical properties of alkali nitride-KN

The structural, electronic and elastic properties of alkali- metal nitride (KN) is investigated by the first principles calculations based on density functional theory as implemented in Vienna ab-initio simulation package. At ambient pressure KN is stable in the ferromagnetic state with NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that the KN is half metallic ferromagnet at normal pressure. A pressure-induced structural phase transition from NaCl to ZB phase is observed in KN. Half metallicity and ferromagnetism is maintained at all pressures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Exchange bias in zinc ferrite-FeNiMoB based metallic glass composite thin films

The Exchange bias phenomenon and methods to manipulate the bias field in a controlled manner are thrust areas in magnetism due to its sophisticated theoretical concepts as well as advanced technological utility in the field of spintronics. The Exchange bias effect is observed as a result of ferromagnetic-antiferromagnetic (FM-AFM) exchange interaction, usually observed as a loop shift on field cooling below the Neel temperature of AFM. In the present study, we have chosen zinc ferrite which is a well known antiferromagnet, and FeNiMoB based metallic glass as the ferromagnet. The films were prepared by RF sputtering technique. The thickness and composition was obtained by RBS. The magnetic studies using SQUID VSM indicate exchange bias effect in the system. The effect of thermal annealing on exchange bias effect was studied. The observed exchange bias in the zinc ferrite-FeNiMoB system is not due to FM-AFM coupling but due to spin glass-ferromagnetic interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Unusual coercivity and zero-field stabilization of fully saturated magnetization in single crystals of LaCrGe 3

LaCrGe 3 is an itinerant, metallic ferromagnet with a Curie temperature (T C ) of ~86 K. Whereas LaCrGe 3 has been studied extensively as a function of pressure as an example of avoided ferromagnetic quantum criticality, questions about its ambient pressure-ordered state remain: specifically, whether there is a change in the nature of the ferromagnetically ordered state below T C ~86 K. We present anisotropic M(H) isotherms, coupled with anisotropic AC susceptibility data, and demonstrate that LaCrGe 3 has a remarkable, low temperature coercivity associated with exceptionally sharp, complete magnetization reversals to and from fully polarized states. This coercivity is temperature dependent; it drops to zero in the 40–55 K region and reappears in the 70–85 K regions. Furthermore, at low temperatures LaCrGe 3 has magnetization loops and behavior that has been previously associated with micromagnetic/nanocrystalline materials, not bulk macroscopic samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Graded orbital occupation near interfaces in a La[subscript 2]NiO[subscript 4]-La[subscript 2]CuO[subscript 4] superlattice

X-ray absorption spectroscopy and resonant soft x-ray reflectivity show a nonuniform distribution of oxygen holes in a La{sub 2}NiO{sub 4}-La{sub 2}CuO{sub 4} (LNO-LCO) superlattice, with excess holes concentrated in the LNO layers. Weak ferromagnetism with T{sub c} = 160 K suggests a coordinated tilting of NiO{sub 6} octahedra, similar to that of bulk LNO. Ni d{sub 3z{sup 2}-r{sup 2}} orbitals within the LNO layers have a spatially variable occupation. This variation of the Ni valence near LNO-LCO interfaces is observed with resonant soft x-ray reflectivity at the Ni and Cu L edges, at a reflection suppressed by the symmetry of the structure, and is possible through graded doping with holes, due to oxygen interstitials taken up preferentially by inner LNO layers. Since the density of oxygen atoms in the structure can be smoothly varied with standard procedures, this orbital occupation, robust up to at least 280 K, is tunable.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Griffiths phase and the magnetic and transport properties of doped manganites

A phenomenological model is proposed to describe the magnetic and magnetoresistance properties of ferromagnetic manganites. This model is based on the methods used to describe hysteretic systems, takes into account phase separation effects, and assumes the transition of ferromagnetic manganites into the Griffiths phase at above the Curie temperature. This formalism makes it possible to describe the conducting properties of the systems in the temperature range from low temperatures to the Griffiths temperature (T{sub G}). This approach is used to qualitatively explain the experimental laws of the behavior of ferromagnetic manganites using the temperature and field dependences of the electrical resistivity and magnetization, the hysteretic properties, and the magnetoresistive effect (MRE) and to classify manganites in the magnitude of the MRE. The parameter that is responsible for the response of a system to thermal effects is the ratio of the maximum energy barrier separating various states of a system at zero temperature W{sub A}(0) to thermal fluctuation energy W{sub Cfl} at T{sub G}. The W{sub A}(0)/W{sub Cfl} ratio is found to determine the temperature range of the Griffiths phase. The relation between the magnitudes of the MRE and parameter W{sub A}(0)/W{sub Cfl} for a certain system is revealed. The behavior of the magnetization and electrical resistivity of manganites in the Griffiths phase is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Smeared spin-flop transition in random antiferromagnetic Ising chain

At T = 0 and in a sufficiently large field, the nearest-neighbor antiferromagnetic Ising chain undergoes a first-order spin-flop transition into the ferromagnetic phase. We consider its smearing under the random-bond disorder such that all independent random bonds are antiferromagnetic (AF). It is shown that the ground-state thermodynamics of this random AF chain can be described exactly for an arbitrary distribution P(J) of AF bonds. Moreover, the site magnetizations of finite chains can be found analytically in this model. We consider a continuous P(J) that is zero above some -J{sub 1} and behaves near it as (-J{sub 1}-J){sup {lambda}}, {lambda} > -1. In this case, the ferromagnetic phase emerges continuously in a field H > H{sub c} = 2J{sub 1}. At 0 > {lambda} > -1, it has the usual second-order anomalies near H{sub c} with the critical indices obeying the scaling relation and depending on {lambda}. At {lambda} > 0, higher-order transitions occur (third, fourth, etc.), marked by a divergence of the corresponding nonlinear susceptibilities. In the chains with an even number of spins, the intermediate 'bow-tie' phase with linearly modulated AF order exists between the AF and ferromagnetic phases at J{sub 1} < H < H{sub c}. Its origin can be traced to the infinite correlation length of the degenerate AF phase from which it emerges. This implies the existence of similar inhomogeneous phases with size- and form-dependent order in a number of other systems with infinite correlation length. The possibility to observe the signs of the 'bow-tie' phase in low-T neutron diffraction experiments is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Effect of the dopant concentration on the luminescence properties of InGaAs/GaAs spin light-emitting diodes with a mn δ layer

The luminescence properties of light-emitting diodes based on GaAs/InGaAs heterostructures containing Mn-doped layers are studied. The dependences of the degree of electroluminescence circular polarization on the growth parameters, specifically, the Mn content and the hole concentration are obtained. A steady increase in the degree of electroluminescence circular polarization and in the Curie temperature of the ferromagnetic structure with increasing hole concentration is observed, and a change in sign of the degree of circular polarization under variations in the Mn content is revealed. The data are interpreted on the basis of well-known models of ferromagnetism in structures based on ferromagnetic semiconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Intra-molecular coupling within double-segmented molecules impacting magnetic tunnel junction-based molecular spintronics devices

The intra-molecular coupling within multiple units of paramagnetic molecules can produce various effects on molecular spintronics devices (MSD). Here, this paper focuses on double-segmented molecules as the device element to advance understanding of the Impact of internal molecular structure on magnetic tunnel junction-based MSD (MTJMSD). We performed Monte Carlo simulations (MCS) to fill the knowledge gap about the intramolecular coupling role in the magnetic properties of the MTJMSD. This study explored a double-segmented molecule containing two atomic sections, each with a net spin state interacting via Heisenberg exchange coupling within molecules and with ferromagnetic electrodes at different thermal energies, magnetic fields, and coupling strengths. This study also investigated the effect of magnetic field on the double-segmented molecule-based cross-junction-shaped MTJMSD. We also compared the effect of the magnetic field on the mono and double-segmented molecules when connected to two ferromagnetic electrodes. In the strong coupling regime, the intramolecular coupling and molecule coupling with the two ferromagnetic electrodes dominated the MTJMSD response near the molecular junction area. This study provides insight for evaluating the impact of molecular nanostructure internal connectedness on the integrated MSD.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Temperature Dependent Spin Dynamics in La 0.67 Sr 0.33 MnO 3 /Pt Bilayers

Complex ferromagnetic oxides such as La 0.67 Sr 0.33 MnO 3 (LSMO) offer pathways for creating energy‐efficient spintronic devices with new functionalities. LSMO exhibits high‐temperature ferromagnetism, half metallicity, sharp resonance linewidth, low damping, and a large anisotropic magnetoresistance response. Combined with Pt, a proven material with high spin‐charge conversion efficiency, LSMO can be used to create robust nano‐oscillators for neuromorphic computing. Ferromagnetic resonance (FMR) and device‐level spin‐pumping FMR measurements are performed to investigate the magnetization dynamics and spin transport in NdGaO 3 (110)/LSMO(15 nm)/Pt(0 and 5 nm) thin films ranging from 300 K to 90 K and compare the device performance with Py(7 nm)/Pt(5 nm) sample. The spin current pumped into Pt is quantified to determine the temperature‐dependent influence of interfacial interactions. The generated spin current in the micro‐device is maximum at 170 K for the optimally grown LSMO/Pt films. Additionally, this bilayer system exhibits low magnetic Gilbert damping (0.002), small linewidth (12 Oe), and a large spin Hall angle (≈3.2%) at 170 K. Ex situ deposited LSMO/Pt bilayers demonstrate excellent dynamic response, exhibiting fourfold enhancement in signal output, eightfold reduction in damping, and a threefold reduction in linewidth as compared to the Pt/Py system. Such robust device‐level performance can pave way for energy‐efficient spintronic‐based devices.

complex perovskite thin films↗
DOE OSTI2017

Study of Electronic, Mechanical, Magnetic, and Optical Properties of Mg{sub 0.75}TM{sub 0.25}S/Se (TM = Fe, Co, Ni): A First Principle Approach

A systematic study of the magnetism, mechanical, and optical behaviors of Mg{sub 0.75}TM{sub 0.25}S/Se (TM = Fe, Co, Ni) ordered alloys was conducted using the full-potential linearized augmented plane wave plus local orbital method. The ferromagnetic (FM) and antiferromagnetic (AFM) ground state energy differences and enthalpy of formation scrutinized their dynamical stability in the FM state. The elastic parameters decided their mechanical stability, ductile behavior, and partial ionic and covalent characters. Moreover, the calculated band structures and density of states revealed the type and origin of magnetism in terms of exchange splitting energies and exchange constants. The Fe- and Ni-doped MgS/Se alloys exhibited half metallic ferromagnetic (HMF) characteristics, while the Co-doped MgS/Se alloy depicted ferromagnetic semiconducting characters. A reduction in the magnetic moments of the transition metals was observed compared with their free space value, which is due to strong p-d hybridization. Furthermore, the optical spectrum showed the maximum light absorbed in the visible and in the UV region of the electromagnetic spectrum, which makes them potential candidates for optoelectronic and spintronic device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

A DFT Study on Structural, Electronic Mechanical and Thermodynamic Properties of 5f-Electron System BaAmO{sub 3}

The structural, electronic, mechanical and thermodynamic properties of the perovskite oxide BaAmO{sub 3} have been predicted using the full-potential linearized augmented plane wave (FP-LAPW) method. The equilibrium lattice constant, bulk modulus and pressure derivative were computed using different exchange correlations. The optimization of structure was carried out in ferromagnetic, anti-ferromagnetic and non-magnetic states, and the compound was found to be stable in the ferromagnetic state. A systematic study on the band structure and density of states was accomplished using generalized gradient approximation (GGA), Hubbard approximation (GGA + U) and modified Becke–Johnson exchange potential (mBJ),and the compound was found to have a half-metallic nature in all the approximations. The calculated total spin magnetic moment was found to be 5 μ{sub B} in all the approximations used. The second-order elastic constants, Young modulus, shear modulus, Poisson ratio and anisotropic factor have also been calculated. In order to have a complete understanding of BaAmO{sub 3}, the thermodynamic properties were studied in the pressure range of 0 to 40 GPa and the temperature range extending from 0 to 600 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Synthesis and Magnetic Properties of Nanocrystalline FeTiO{sub 3} Materials

Ilmenite (FeTiO{sub 3}) nanoparticles with different size distributions were prepared through a sol-gel auto-ignition method. As-prepared powder is annealed at moderate temperatures to get nanocrystalline FeTiO{sub 3}, and structural, micro-structural, and magnetization characterizations are carried out. Magnetization vs temperature shows antiferromagnetic ordering around 52 K and below 15 K a weak ferromagnetic order develops. The Curie-Weiss law is well obeyed above the Néel temperature (T{sub N}) for all samples. Hysteresis curves show finite coercivity below the peak temperature and none at room temperature. M-H curves for all the samples cooled with a bias magnetic field show exchange bias below T{sub N} which is interpreted due to the finite size and surface effects. The exchange bias is attributed to weak ferromagnetism due to surface spin disorder (Dzyaloshinskii-Moriya interaction) and ferromagnetic interaction (double exchange) due to mixed valence states of Fe ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Origin of the Magnetism in Undoped and Mn-Doped In{sub 2}O{sub 3}: A First-Principles Study

The magnetism of undoped and Mn-doped In{sub 2}O{sub 3} has been investigated by employing density functional calculations. For undoped In{sub 2}O{sub 3}, a neutral In vacancy in In{sub 2}O{sub 3} leads to the formation of a net moment of 3 μ{sub B}, which originates from the strong spin polarization of 2p orbitals of O atoms. While, Mn-doped In{sub 2}O{sub 3} system shows robust ferromagnetism which can be attributed to the p-d hybridization between Mn and their neighboring O atoms. In addition, because two O atoms between the two Mn atoms are removed, the ground state of the system have a transformation from the ferromagnetic to the antiferromagnetic state, which further demonstrates that the ferromagnetism is mediated through the p-d interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ab Initio Study of Electronic, Magnetic, and Thermoelectric Response of ZTi{sub 2}O{sub 4} (Z = Mg, Zn, and Cd) Through mBJ Potential

The electronic, magnetic, and thermoelectric properties of ZTi{sub 2}O{sub 4} (Z = Mg, Zn, and Cd) spinel oxides are analyzed by applying DFT approach. The band structure (BS) and density of states (DOS) illustrate a ferromagnetic state due to the evident exchange splitting leading to the energy shift in the spin-polarized sub-bands. Furthermore, ferromagnetic state stability is also justified through the computed crystal field, Jahn-Teller, and exchange energies. The exchange energy exceeding the crystal field energy reveals that ferromagnetism is mediated due to electrons, which is also consistent with the computed negative indirect exchange energy. Using BoltzTraP code, thermoelectric investigation illustrate that Mg, Zn, and Cd cations can tune the optimum power factor to intermediate and higher temperatures, which suggests potential energy harvesting applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of the Milling Conditions on the Properties of ZnO Doped with Fe

(Zn{sub 0.9}Fe{sub 0.1})O powders were produced with different ball to powder weight ratios (BPR) by ball milling of ZnO and Fe elemental powders. The BPR used were 15:1, 20:1, 25:1, and 30:1. The prepared samples were studied by x-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectroscopy (MS). The XRD patterns showed a zinc oxide (ZnO) single phase with wurtzite structure, except for the 15:1 ratio, which exhibits an additionally bcc structure associated to α-Fe. The mean crystallite sizes were found to be around 100 Å. The Mössbauer spectra were fitted using two doublets, associated to the incorporation of Fe ions into the ZnO lattice, which correspond to the Fe{sup 3+} and Fe{sup 2+} oxidation states except for the 15:1 ratio, for which an additional sextet was necessary to obtain a good fit, this sextet was associated to segregated Fe into the sample. The increase of the BPR allowed that all Fe penetrated into the ZnO matrix. The magnetization measurement using VSM reveals that the system exhibits ferromagnetic behavior at room temperature. For sample with BPR 15:1, the ferromagnetism is due to the segregated Fe, and for higher BPRs, from 20:1 up to 30:1, we propose that their ferromagnetism is due to the percolation of polarons. These polarons appear due to the oxygen vacancies (detected by XRD) which are occupied by electrons, which appear in the charge balance. Exchange interaction between the electron spins located in the vacancies or holes and those of the magnetic impurities (Fe atoms) leads to the formation of bound magnetic polarons, which percolate, producing in this way magnetic behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Benchmark Analysis on Magnetic and Photoluminescence Properties of Selective Metal Ions Doped ZnS Nanoparticles

The creation of diluted magnetic semiconductors (DMSs) at lower dimensions that exhibit room temperature ferromagnetism (RTFM) has been given immense significance for the fabrication of a new class of spintronic devices through utilizing spin degrees of freedom besides charge nature of electrons. In this view, nanocrystals of ZnS doped with 4% concentration of Fe, Co, Ni, Cr, Mn, Sr, Cu, and Ce have been synthesized at room temperature (RT) by chemical co-precipitation method. The samples were examined by various characterization techniques like energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and photoluminescence (PL). EDS spectra revealed the existence of parent elements in the prepared samples. XRD characterization disclosed hexagonal structures of nanocrystals, and no secondary phases were observed in all the samples except for Cu and Ni doped ZnS. FTIR data confirmed the proper substitution of dopants in the host lattice as all the graphs have almost same stretchings. The magnetic nature of each sample was evaluated from M-H graphs of VSM, and it corroborated the transition of magnetic properties due to doping. Pristine ZnS showed diamagnetic nature, while Fe and Sr doped ZnS evinced strong ferromagnetic and anti-ferromagnetic properties, respectively. Photoluminescence studies on Ce, Sr and Mn doped ZnS samples revealed strong emission peaks with enhanced luminescence properties compared to bare ZnS. Cu, Cr and Mn doped ZnS exhibited a red shift in emission wavelengths, whereas Co doped ZnS showed emission peak shifted towards the blue region as compared to the host lattice.

77 NANOSCIENCE AND NANOTECHNOLOGY↗