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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Microstructure and magnetic properties of ultrathin FePt granular films

FePt granular films with grain size smaller than 10 nm are promising candidates for storage media used in the next generation heat-assisted magnetic recording technology. However, FePt films show degraded magnetic properties when the grain size is reduced to this scale, which cannot be explained solely by the finite size theory. In this study, we explored the structural cause of property degradation by employing advanced electron microscopy and atomistic modeling. Structural features unique to the nanostructured FePt granular films at significantly reduced grain sizes of 2~8 nm were studied by high-resolution scanning transmission electron microscopy with geometric aberrations corrected up to the third order. Two critical structural parameters, the threshold grain size corresponding to the upper size limit of the FePt grains with zero chemical ordering and the sub-nanometer thin interfacial impurity at grain boundaries, were identified. A new atomistic model was developed to correlate these structural characteristics with key magnetic properties such as Curie temperature, saturation magnetization, magnetocrystalline anisotropy, and their grain-to-grain variation. The model shows good agreement with the experimental magnetic data and explains the gap in magnetic properties between the bulk and nanostructured FePt.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Tuning the Magnetic Properties of ZnFe{sub 2}O{sub 4} Nanoparticles Through Partial Doping and Annealing

The aim of this study was to investigate the effect of annealing temperature and cobalt cation (Co{sup 2+}) doping on the magnetic properties of zinc ferrite (ZFO) nanoparticles. The nanoparticles were prepared through sol-gel combustion process with citric acid as the fuel. The obtained nanoparticles were annealed at several temperatures from 300 to 1000 °C for 2 h. Spinel formation was proved by X-ray diffraction (XRD) patterns, and the average crystallite size in all samples was estimated between 22 and 32 nm. It is worthwhile to mention that Fe{sub 2}O{sub 3} and ZnO are detected as the medium phases. Meanwhile, Fe{sub 2}O{sub 3} phase transformation to the other allotropes has happened around 400 °C and was characterized via the simultaneous thermal analysis (STA) and XRD. For higher annealing temperatures, diffusion has gradually been completed and, finally, the single phase of spinel structure was prepared at 1000 °C. In addition, field-emission scanning electron microscopy (FESEM) images revealed that the nanoparticle size after annealing was between 30 and 200 nm for the whole samples. The formation of the spinel phase was considered the most important factor on the magnetic properties of ZFO. Cobalt doping, annealing temperature, and also Fe{sub 2}O{sub 3} phase were the main factors on changing magnetic properties. Paramagnetic nanoparticles with higher coercivity for doped samples rather than un-doped samples have been obtained.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Tunable structural and magnetic properties of NiAs-type Mn x Sb (1.00≤x≤1.30) compounds

Mn-based alloys can exhibit a variety of magnetic properties related to their tunable exchange interactions. Here, structural and magnetic properties of hexagonal NiAs-type Mn x Sb (1.00≤x≤1.30) compounds are studied with a combination of X-ray diffraction, neutron diffraction, and magnetic measurements. It is found that the magnetization, Curie temperature, and magnetocrystalline anisotropy of Mn x Sb compounds can be tuned by controlling Mn concentration and doping at interstitial (2d) sites. With increasing Mn concentration, magnetic moments of Mn atoms decrease and deviate gradually from the ab-plane to the c-axis for 1.20≤x≤1.22 at room temperature, which leads to a decrease of the Curie temperature T c and the spin reorientation temperature T SR . By doping with nonmagnetic elements, a substantial room-temperature magnetocaloric effect without magnetic hysteresis was achieved for Mn 1.12 Zr 0.1 Sb compound, which is highly beneficial to the practical magnetic refrigeration application.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effects of magnetic field annealing on the hard magnetic properties of milled Nd-Fe-B powders

In this study, we report the effect of magnetic field annealing (MA) in relieving the stress induced during the milling of Nd-Fe-B sintered magnets. The effect of MA processing parameters and particle size on the magnetic properties were investigated. Based on the results, magnetic field annealing is more effective in improving the magnetic properties of larger size particles, compared to finer particles. Our computational study on the role of particle surface defects in bi-modal particle distribution agrees with results obtained experimentally. In conclusion, magnetic field annealed powder has been successfully used to develop 4.6 g.cm -3 density bonded magnets with 75 vol% of magnetic powder and polyamide 12 (nylon 12) polymer binder resulting in 11.3 MGOe energy product.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Magnetic Properties of Eu{sub 0.9}Yb{sub 0.1}B{sub 6}

The magnetic properties of substitutional solid solutions Eu{sub 0.9}Yb{sub 0.1}B{sub 6} have been investigated in the temperature range of 2–300 K in fields up to 5 T. The data obtained confirm that the state with the electronic and magnetic phase separation (typical of europium hexaboride) is implemented in Eu{sub 0.9}Yb{sub 0.1}B{sub 6} when the system metallization (T{sub M} ≈ 15 K) precedes the ferromagnetic ordering (T{sub C} ≈ 11.4 K). An analysis of the curves M(H) in the Belov–Arrott coordinates makes it possible to evaluate spontaneous magnetization M{sub sp} and zero field susceptibility χ{sub 0} and determine the character of their critical behavior near the Curie point. The calculated critical indices (γ ≈ 1.28 and β ≈ 0.34) are in agreement with the predictions of the three-dimensional Heisenberg model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ab Initio Investigation of Structural Stability and Electronic and Magnetic Properties of the Half-Heusler Alloys: MTiSb (M = Fe, Co, and Ni)

The structural, electronic, and magnetic properties of the half-Heusler MTiSb (M = Fe, Co, Ni) compounds have been examined using the first-principles calculations with the full-potential linear augmented plane wave (FP-LAPW) method within the density functional theory. The electronic structures and magnetic properties of MTiSb (M = Fe, Co, Ni) are studied. It is found that the calculated lattice parameter is in good agreement with the theoretical values. Using the general gradient approximation (GGA), we observe that for the three compounds, the α phase is more stable than β and γ phases. CoTiSb is a semiconductor, NiTiSb is a metal, while the FeTiSb compound is a half-metallic, and the total magnetic moments are 0.00085, − 0.26074, and 0.99353 μ B, respectively, which is in agreement with the Slater–Pauling rule, Furthermore, the origin for the appearance of the half-metallic band gap in the FeTiSb compound was also discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effects of Interface Induced Natural Strains on Magnetic Properties of FeRh

FeRh is a unique alloy which shows temperature dependent phase transition magnetic properties. The lattice parameter (a) of this CsCl-type (B2) structure is 4.1712 Å. It undergoes a first order transition from antiferromagnetic (AFM) to ferromagnetic (FM) order at around 370K and hysteretic behavior while cooling and heating. This meta-magnetic transition of FeRh is accompanied by an isotropic expansion in the unit cell volume, which indicates strong coupling between magnetic and structural properties of FeRh. Consequently, the magnetic and transport properties, such as magnetoresistance (MR), are changed during the transition. Due to its unique thermo-magnetic behaviors, FeRh is very important for future spintronic devices. The structure could be applicable for MR devices such as memory, sensors, and many other applications. It is critical to understand how to systematically influence phase transition of FeRh from naturally applied strains. Here, we investigate magnetic properties of FeRh in different strain environments induced by the substrates with different lattice parameters. The study was performed using synchrotron radiation, temperature dependent magnetometry, and magnetic scanning probe microscopy in addition to Landau theory calculations. We found that the naturally induced strains could modulate the magnetic phase locally and globally. The presence of the segments from the nucleation of the ferromagnetic domains, with a very thin layer in the antiferromagnetic matrix and the domain growth, were observed gradually. Using the systematic phenomena, it could be used for immediate applications in the future generation of phase change random access memory (PC-RAM) devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Ti on structure and soft magnetic properties of Si-rich Finemet-type nanocrystalline Fe73.5Cu1Nb3-xSi17.5B5Tix alloys

Highlights: • Substitution of Nb by Ti can reduce the T{sub x1} and enlarge the ΔT{sub x}. • Fe{sub 73.5}Cu{sub 1}Nb{sub 2}Si{sub 17.5}B{sub 5}Ti{sub 1} alloy exhibits high μ{sub i} of 18,000 and low H{sub c} of 0.54 Oe. • Magnetic properties were analysed in terms of the relationship between H{sub c} and μ{sub i}. • Soft magnetic properties will deteriorate when Nb is completely replaced by Ti. • The reasons of variation of permeability at high temperature were analyzed. - Abstract: Fe{sub 73.5}Cu{sub 1}Nb{sub 3-x}Si{sub 17.5}B{sub 5}Ti{sub x} (x = 0, 1, 2, 3) amorphous alloys were prepared by the single roller melt spinning method. The effects of Ti substitution for Nb on the crystallization behavior, microstructure and soft magnetic properties were investigated. Compared to the previously reported Finemet alloy, the onset primary crystallization temperature T{sub x1} becomes lower which has dropped from 803K to 758K. The crystallization temperature interval ΔT{sub x} increases from 468K to 488K as the x increases from 0 to 3. However, the Curie temperature of amorphous phase shows a downward tendency with the increase of Ti content. Compared to the previously reported Finemet alloy, the μ{sub i} increases obviously to more than 18,000 at x = 1, the H{sub c} decreases from 0.59 Oe to 0.54 Oe. When Ti replaces Nb completely, the optimum annealing temperature range for precipitating single soft magnetic phase is enlarged, but the permeability at room- and high-temperature is deteriorated, the reason of which was also analysed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Investigation of Microstructural and Magnetic Properties of BaV{sub x}Fe{sub 12−x}O{sub 19} Nanohexaferrites

Nanohexaferrites of BaV{sub x}Fe{sub 12−x}O{sub 19} (0.0 ≤ x ≤ 0.1) were prepared using sol–gel auto-combustion. The structure and morphology of BaV{sub x}Fe{sub 12−x}O{sub 19} (0.0 ≤ x ≤ 0.1) nano-sized hexaferrites were explored by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with EDXS. XRD analysis indicated particle size in the 55–60-nm interval. SEM and EDXS investigations confirmed the formation of the desired composition of V-substituted Ba-hexaferrites. The magnetic properties of products were studied. The magnetic M(H) hysteresis loops revealed that all produced nanohexaferrites display ferromagnetic-like comportment. The deduced saturation magnetization (M{sub s}), retentivity (M{sub r}), magneto-crystalline anisotropy fields (H{sub a}), and coercive field (H{sub c}) were enhanced for low V{sup 3+} contents and were maximum for BaV{sub 0.04}Fe{sub 11.96}O{sub 19} (x = 0.04) nanohexaferrites, showing the strengthening of magnetic properties.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Complex magnetic properties associated with competing local and itinerant magnetism in \({\text {Pr}}_2 {\text {Co}}_{0.86} {\text {Si}}_{2.88}\)

Ternary intermetallic compound \({\text {Pr}}_2 {\text {Co}}_{0.86} {\text {Si}}_{2.88}\) has been synthesized in single phase and characterized by x-ray diffraction, scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX) analysis, magnetization, heat capacity, neutron diffraction and muon spin rotation/relaxation ( \(\mu\) SR) measurements. The polycrystalline compound was synthesized in single phase by introducing necessary vacancies in Co/Si sites. Magnetic, heat capacity, and zero-field neutron diffraction studies reveal that the system undergoes magnetic transition below \(\sim\) 4 K. Neutron diffraction measurement further reveals that the magnetic ordering is antiferromagnetic in nature with an weak ordered moment. The high temperature magnetic phase has been attributed to glassy in nature consisting of ferromagnetic clusters of itinerant (3 d ) Co moments as evident by the development of internal field in zero-field \(\mu\) SR below 50 K. The density-functional theory (DFT) calculations suggest that the low temperature magnetic transition is associated with antiferromagnetic coupling between Pr 4 f and Co 3 d spins. Pr moments show spin fluctuation along with unconventional orbital moment quenching due to crystal field. The evolution of the symmetry and the crystalline electric field environment of Pr-ions are also studied and compared theoretically between the elemental Pr and when it is coupled with other elements such as Co. The localized moment of Pr 4 f and itinerant moment of Co 3 d compete with each other below \(\sim\) 20 K resulting in an unusual temperature dependence of magnetic coercivity in the system.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Bi{sup 3+} Substitution on Structural, Morphological, and Magnetic Properties of Cobalt Ferrite Nanoparticles

In this research, the structural, morphological, and magnetic properties of Bi-doped cobalt ferrite (CoFe{sub 2-x}Bi{sub x}O{sub 4}) nanoparticles with x = 0.0, 0.05, 1, 0.15, and 0.2, prepared by the sol-gel method, were studied. In order to characterize the samples, several equipment and analyses including thermo-gravimetric and differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Fourier transform infrared spectrometer (FT-IR), and vibrating sample magnetometer (VSM) were used. The average crystallite sizes of the prepared CoFe{sub 2-x}Bi{sub x}O{sub 4} were calculated using the Scherer, UDM, SSP, and Halder-Wagner methods. The average crystallite sizes for the samples were found in the range of 26 to 44 nm, which can be attributed to the grain growth of the particles. FT-IR spectrum showed bands in the range of 430 to 590 cm{sup −1} due to the stretching vibration of an oxygen atom and metal ions (Fe-O), confirming the formation of spinel ferrite. Surface morphology of the samples was studied using FESEM. The VSM results showed that the saturation and remanence magnetizations increased by raising the doping values up to x = 0.1. The Curie temperature of the cobalt nanoferrites was determined using Faraday’s technique. The highest Curie temperature was found to be 580 °C for the undoped sample.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Effects of Sintering Temperature on Structural, Morphological and Magnetic Properties of Strontium Ferrite Nanoparticles

In the present investigation, structural, morphological and magnetic properties of SrFe{sub 2}O{sub 4} ferrite nanoparticles prepared by a sol–gel method were studied. The techniques used in this investigation were thermogravimetric analysis/differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectrometry (FT-IR), vibrating sample magnetometry (VSM) and Curie temperature analysis. The average crystallite sizes of the SrFe{sub 2}O{sub 4} were calculated using the Scherrer formula and found in the range of 11–22 nm, and this can be attributed to the grain growth of the particles. The lattice parameter of SrFe{sub 2}O{sub 4} nanoparticles decreased from 6.64 to 6.51 nm as the sintering temperature was raised from 600 to 900 °C. FT-IR analysis confirmed that bands in the range 430–590 cm{sup − 1} are due to the stretching vibration of oxygen atom and metal ions (M–O) that is Fe–O confirming the formation of spinel ferrite. Surface morphology of the samples has been studied using FESEM. The elemental composition along with their relative ratios was given by EDX and was found to be in agreement with their initial calculated values. The saturation magnetization, magnetic coercivity and remanence increase with an increasing sintering temperature from 600 to 900 °C. The present study reports the Curie temperature with an amount of 551 °C of the synthesized strontium nanoferrites using the Faraday technique.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Designing Magnetic Properties in CrSBr through Hydrostatic Pressure and Ligand Substitution

Abstract Magnetic van der Waals (vdW) materials are a promising platform for producing atomically thin spintronic and optoelectronic devices. The A‐type antiferromagnet CrSBr has emerged as a particularly exciting material due to its high magnetic ordering temperature, semiconducting electrical properties, and enhanced chemical stability compared to other vdW magnets. Exploring mechanisms to tune its magnetic properties will facilitate the development of nanoscale devices based on vdW materials with designer magnetic properties. Here it is investigated how the magnetic properties of CrSBr change under pressure and ligand substitution. Pressure compresses the unit cell, increasing the interlayer exchange energy while lowering the Néel temperature. Ligand substitution, realized synthetically through Cl alloying, anisotropically compresses the unit cell and suppresses the Cr‐halogen covalency, reducing the magnetocrystalline anisotropy energy and decreasing the Néel temperature. A detailed structural analysis combined with first‐principles calculations reveals that alterations in the magnetic properties are intricately related to changes in direct Cr–Cr exchange interactions and the Cr–anion superexchange pathways. Further, it is demonstrated that Cl alloying enables chemical tuning of the interlayer coupling from antiferromagnetic to ferromagnetic, which is unique among known two‐dimensional magnets.

Telford, Evan J.↗
DOE OSTI2020

Influence of non-magnetic Cu on enhancing the low temperature magnetic properties and Curie temperature of FeCoNiCrCu(x) high entropy alloys

The microstructure and magnetic properties of three face-centered cubic (FCC) FeCoNiCrCu(x) high entropy alloys (HEAs) (x=0, 0.5, 1) are investigated. Interestingly, addition of the nonmagnetic element Cu to FeCoNiCr HEA is found to enhance exchange interactions and low temperature saturation magnetization. The paramagnetic to ferromagnetic Curie transition temperature increases from 85 K for FeCoNiCr to 118 K for FeCoNiCrCu. This is counterintuitive since Cu is nonmagnetic; however, atom probe tomography revealed Cu rich clusters containing 5 at% Ni and 1 at% each of Fe, Co, Cr, within FCC matrix, these clusters altered the matrix composition and consequently its magnetic properties.

Chaudhary, Varun↗
DOE OSTI2019

The Magnetic Properties of the Spin-1 Ising Fullerene Cage with a Core-Shell Structure

Magnetic properties of Ising-type endohedral fullerene (IEF), which are formed by an atom encapsulated inside a diluted magnetic spherical cage, have been investigated theoretically as a function of its system parameters, and magnetism calculations by using effective field theory (EFT) were performed. Theoretical studies have been carried out to understand the effect on magnetic behaviors by the diluted magnetic surface, crystal field, and exchange couplings. The results display the first second-order phase transitions and tricritical point. The reentrant phenomena have been observed within a certain parameter range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic Properties of Vacancies and Doped Chromium in a ZnO Crystal

The electronic and magnetic properties of ZnO containing Cr doped atoms and Zn and O vacancies in its crystal structure are theoretically investigated. Calculations are performed using Atomistix Tool Kit and Vienna Ab-initio Simulation Package software implementing the electron density functional theory method with the Hubbard correction. It is shown that the magnetic moment of a defect supercell strongly depends on the impurity concentration and presence of vacancies. The doping of an oxygen atom increases the probability of zinc-vacancy formation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation of Fe/Mo Ordering and Magnetic Properties of Ca{sub 2}Fe{sub x}Mo{sub 2−x}O{sub 6} (x = 0.9, 1.0, 1.1 and 1.2) Double Perovskites Prepared by Sonochemical Method

Characterization, Fe/Mo ordering and magnetic properties of Ca{sub 2}Fe{sub x}Mo{sub 2−x}O{sub 6} (x = 0.9, 1.0, 1.1 and 1.2) (CFMO) double perovskite have been studied. Sonochemical methodology is adopted to synthesize Ca{sub 2}Fe{sub x}Mo{sub 2−x}O{sub 6} double perovskite at low temperature (950 {sup ∘} C) under Ar/H{sub 2} atmosphere. Single-phase monoclinic structure by space group P2{sub 1}/n, lattice parameters (a, b and c) and unit cell volume (V ) have been confirmed from X-ray diffraction (XRD) patterns. Average grain sizes of 145 nm with a variation of porosity were observed from scanning electron microscopy (SEM) pictures. Elemental analysis using energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of elements Ca, Fe, Mo and O with no trace of foreign elements, and the compound is found to be pure. Fourier transform infrared spectroscopy (FTIR) data confirmed perovskite formation by identifying three characteristic absorption bands in the wave number range 400–1000 cm{sup − 1} for Mo-O and Fe-O vibrations. Magnetic properties like M{sub s}, M{sub r} and H{sub c} were studied for CFMO series using vibrating sample magnetometer (VSM). Saturation magnetization is found to vary with Fe composition (x).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Structure, Morphology, Cation Distribution and Magnetic Properties of Cr{sup 3+}-Substituted CoFe{sub 2}O{sub 4} Nanoparticles

The present investigations deal with the effect of trivalent chromium ions (Cr{sup 3+}) on structural and magnetic properties of nanocrystalline cobalt ferrite (CoFe{sub 2}O{sub 4}) nanoparticles. The samples of CoCr{sub x}Fe{sub 2−x}O{sub 4} (where x = 0.0 to 1.0 in step of 0.2) were successfully synthesized by citric acid-assisted sol-gel auto combustion method. Further, the prepared samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR) and pulsed field hysteresis loop technique for structural, morphological and magnetic properties analysis, respectively. XRD patterns showed the formation of single-phase cubic spinel structure with broad Bragg’s peak for all the samples. The value of lattice parameter was found to be decreased with chromium substitution x. Cation distribution studies revealed that Co{sup 2+} and Fe{sup 3+} occupied both A and B sites, whereas Cr{sup 3+} ions occupied only B site. SEM analysis of the prepared samples confirmed the nanocrystalline nature of the material. The two absorption bands belonging to spinel structure were observed in IR spectra. Saturation magnetization (M{sub S}), remanence magnetization (M{sub r}) and coercivity (H{sub C}) was found to be decreased with increase in chromium substitution x.

77 NANOSCIENCE AND NANOTECHNOLOGY↗