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At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Structural and magnetic properties of chromium doped zinc ferrite

Zinc chromium ferrites with chemical formula ZnCr{sub x}Fe{sub 2−x}O{sub 4} (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared by Sol - Gel technique. The structural as well as magnetic properties of the synthesized samples have been studied and reported here. The structural characterizations of the samples were analyzed by using X – Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), and Transmission Electron Microscope (TEM). The single phase spinel cubic structure of all the prepared samples was tested by XRD and FTIR. The particle size was observed to decrease from 18.636 nm to 6.125 nm by chromium doping and induced a tensile strain in all the zinc chromium mixed ferrites. The magnetic properties of few samples (x = 0.0, 0.4, 1.0) were investigated using Vibrating Sample Magnetometer (VSM)

36 MATERIALS SCIENCE↗
DOE OSTI2014

Double dumbbell shaped AgNi alloy by pulsed electrodeposition

Silver-Nickel is the well-known thermally immiscible system that makes them quite complex for the formation of alloy. This kind of alloy can be attained from electrodeposition method. In the present work, AgNi alloy was synthesized by pulsed electrodeposition in a single bath two electrode system with the use of anodic alumina membrane. The prepared AgNi alloy and pure Ag were characterized with X-ray Diffraction (XRD) for structural confirmation, Scanning Electron Microscopy (SEM) for morphological, and magnetic properties by Vibrating Sample Magnetometer, respectively. The X-ray Diffraction study shows the formation of cubic structure for pure Ag. SEM analysis reveals the double dumbbell morphology for AgNi alloy and spherically agglomeration for pure silver. Hysteresis behaviour from VSM measurement indicates that the AgNi alloy have good ferro-magnetic properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Experimental investigation of magnetic anisotropy in spin vortex discs

We present experimental 2D vector vibrating sample magnetometer measurements to demonstrate the shape anisotropy effects occurring in micrometer-diameter supermalloy spin vortex discs. Measurements made for different disc sizes and orientations confirm the out-of-plane susceptibility is several orders of magnitude smaller than the in-plane susceptibility. These results validate with a high certitude that spin vortices with high diameter to thickness ratio retain in-plane-only magnetization, even when subjected to fields in the out-of-plane direction. These results contribute to further computational simulations of the dynamics of spin vortex structures in colloidal suspensions where external fields may be applied in any arbitrary direction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Synthesis of multiferroic Er-Fe-O thin films by atomic layer and chemical vapor deposition

R-Fe-O (R = rare earth) compounds have recently attracted high interest as potential new multiferroic materials. Here, we report a method based on the solid-state reaction between Er{sub 2}O{sub 3} and Fe layers, respectively grown by atomic layer deposition and chemical vapor deposition, to synthesize Er-Fe-O thin films. The reaction is induced by thermal annealing and evolution of the formed phases is followed by in situ grazing incidence X-ray diffraction. Dominant ErFeO{sub 3} and ErFe{sub 2}O{sub 4} phases develop following subsequent thermal annealing processes at 850 °C in air and N{sub 2}. Structural, chemical, and morphological characterization of the layers are conducted through X-ray diffraction and reflectivity, time-of-flight secondary ion-mass spectrometry, and atomic force microscopy. Magnetic properties are evaluated by magnetic force microscopy, conversion electron Mössbauer spectroscopy, and vibrating sample magnetometer, being consistent with the presence of the phases identified by X-ray diffraction. Our results constitute a first step toward the use of cost-effective chemical methods for the synthesis of this class of multiferroic thin films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Magnetic properties of Zn doped Co{sub 2}Y hexaferrite by using high-field Mössbauer spectroscopy

The polycrystalline samples of Ba{sub 2}Co{sub 2−x}Zn{sub x}Fe{sub 12}O{sub 22} (x = 0.5, 1.0, 1.5) were synthesized by using solid-state-reaction method. From the XRD patterns, analyzed by Rietveld refinement, the prepared samples are found to be single-phased with rhombohedral structure (R-3m). The magnetic properties of samples were investigated with vibrating sample magnetometer, and high-field Mössbauer spectrometer. From the zero-field-cooled curves under 100 Oe between 4.2 and 740 K, we observe that the samples show spin transition from helicalmagnetic to ferrimagnetic order. With increasing Zn ion concentration, the spin transition temperature (T{sub s}) and Curie temperature (T{sub C}) decrease linearly. We have obtained Zero-field Mössbauer spectra of all samples at various temperatures ranging from 4.2 to 650 K, and analyzed the spectra below T{sub C} as six-sextets for Fe sites. From the temperature dependence of hyperfine field (H{sub hf}), we have noticed an abrupt change in H{sub hf} at T{sub s}. In addition, Mössbauer spectra of all samples at 4.2 K were taken with applied field ranging from 0 to 50 kOe, indicating the canting angle between applied field and H{sub hf} decreased with increasing Zn concentration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A multi-functional testing instrument for heat assisted magnetic recording media

With recent developments in heat assisted magnetic recording (HAMR), characterization of HAMR media is becoming very important. We present a multi-functional instrument for testing HAMR media, which integrates HAMR writing, reading, and a micro-magneto-optic Kerr effect (μ-MOKE) testing function. A potential application of the present instrument is to make temperature dependent magnetic property measurement using a pump-probe configuration. In the measurement, the media is heated up by a heating (intense) beam while a testing (weak) beam is overlapped with the heating beam for MOKE measurement. By heating the media with different heating beam power, magnetic measurements by MOKE at different temperatures can be performed. Compared to traditional existing tools such as the vibrating sample magnetometer, the present instrument provides localized and efficient heating at the measurement spot. The integration of HAMR writing and μ-MOKE system can also facilitate a localized full investigation of the magnetic media by potential correlation of HAMR head independent write/read performance to localized magnetic properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Structure and magnetic properties of low-temperature phase Mn-Bi nanosheets with ultra-high coercivity and significant anisotropy

The microstructure, crystal structure, and magnetic properties of low-temperature phase (LTP) Mn-Bi nanosheets, prepared by surfactant assistant high-energy ball milling (SA-HEBM) with oleylamine and oleic acid as the surfactant, were examined with scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometer, respectively. Effect of ball-milling time on the coercivity of LTP Mn-Bi nanosheets was systematically investigated. Results show that the high energy ball milling time from tens of minutes to several hours results in the coercivity increase of Mn-Bi powders and peak values of 14.3 kOe around 10 h. LTP Mn-Bi nanosheets are characterized by an average thickness of tens of nanometers, an average diameter of ∼1.5 μm, and possess a relatively large aspect ratio, an ultra-high room temperature coercivity of 22.3 kOe, a significant geometrical and magnetic anisotropy, and a strong (00l) crystal texture. Magnetization and demagnetization behaviors reveal that wall pinning is the dominant coercivity mechanism in these LTP Mn-Bi nanosheets. The ultrafine grain refinement introduced by the SA-HEBM process contribute to the ultra-high coercivity of LTP Mn-Bi nanosheets and a large number of defects put a powerful pinning effect on the magnetic domain movement, simultaneously. Further magnetic measurement at 437 K shows that a high coercivity of 17.8 kOe and a strong positive temperature coefficient of coercivity existed in the bonded permanent magnet made by LTP Mn-Bi nanosheets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The crystal structure and magnetic properties of Ba{sub 2−x}Sr{sub x}Co{sub 2}Fe{sub 12}O{sub 22}

We have synthesized the Ba{sub 2−x}Sr{sub x}Co{sub 2}Fe{sub 12}O{sub 22} samples (x = 0.1, 0.2, 0.3, 0.4, 0.5) by the solid-state reaction method and investigated their crystalline and magnetic properties by X-ray diffractometer (XRD), Mössbauer spectrometer, vibrating sample magnetometer, and network analyzer. XRD patterns show that all samples are rhombohedral with space group R-3m. The lattice constants a{sub 0} and c{sub 0} decrease with Sr substitution due to smaller ion radius of Sr{sup 2+} (1.27 Å) than that of Ba{sup 2+} (1.43 Å). The Mössbauer spectroscopy measurements show that the relative area ratios of Fe ion were maintained constant regardless of the Sr concentration. However, average magnetic hyperfine field slightly increased with the Sr concentration. This observation agrees with the fact that the saturation magnetization (M{sub s}) linearly increases due to the increasing super-exchange interaction, originated from the difference in the ionic radius between Ba{sup 2+} and Sr{sup 2+}. To investigate its properties at high frequency range, all samples were sintered at 1100 °C, and complex permeability and permittivity were measured by network analyzer between 100 MHz and 4 GHz. For x below 0.3, the initial permeability at 100 MHz increases, at higher values of x, its value decreases. Our study shows that magnetic properties of Sr{sup 2+} substitution for Ba{sup 2+} in Y-type hexaferrite as well as low magnetic loss less than 0.1 in 1 GHz band, indicating the potential application of Ba{sub 2−x}Sr{sub x}Co{sub 2}Fe{sub 12}O{sub 22} samples for RF and antenna devices in ultra high frequency band.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Study of polyvinyl alcohol nanofibrous membrane by electrospinning as a magnetic nanoparticle delivery approach

Electrospinning technique was used to fabricate polyvinyl alcohol (PVA)-based magnetic biodegradable nanofibers. PVA solution was mixed with ferrofluid or magnetic nanoparticles (MNPs) powder and formed two individual nanofibrous membranes (PVA/ferrofluid and PVA/MNPs powder) by electrospinning. The surface morphology of the nanofibrous membrane was characterized by scanning electron microscopy and the magnetic properties were measured by vibrating sample magnetometer. Macrophages (RAW 264.7) were co-cultured with the nanofibrous membranes for 12, 24, and 48 h and exhibited good cell viability (>95%). Results showed that the PVA fibers would be degraded and the embedded Fe{sub 3}O{sub 4} nanoparticles would be released and delivered to cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Phase structure and magnetic properties of Mn{sub 3}Ga{sub 2} alloy

In this paper, Mn{sub 3}Ga{sub 2} alloys with high saturation magnetization and high Curie temperatures were prepared by levitation melting high pure Mn and Ga elements followed by annealing. The effect of annealing temperature on phase structure and magnetic properties was investigated by means of x-ray diffraction and a vibrating sample magnetometer. A single phase alloy Mn{sub 3}Ga{sub 2}, which has tetragonal P4/mmm structure, was obtained with an annealing temperature of 773 K and annealing time of 24 h. The hysteresis curve of its easy axis for this single phase alloy shows that the room temperature coercivity and saturation magnetization are 4.18 kOe and 50.81 emu/g, respectively. The thermomagnetic curves indicate that the Curie temperature is about 650 K and a phase transformation occurs above 823 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Note: A fast pneumatic sample-shuttle with attenuated shocks

We describe a home-built pneumatic shuttle suitable for the fast displacement of samples in the vicinity of a highly sensitive atomic magnetometer. The samples are magnetized at 1 T using a Halbach assembly of magnets. The device enables the remote detection of free-induction-decay in ultra-low-field and zero-field nuclear magnetic resonance (NMR) experiments, in relaxometric measurements and in other applications involving the displacement of magnetized samples within time intervals as short as a few tens of milliseconds. Other possible applications of fast sample shuttling exist in radiological studies, where samples have to be irradiated and then analyzed in a cold environment.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Post magnetic field annealing effect on magnetic and structural properties of Co{sub 80}Pt{sub 20} nanowires and nanotubes fabricated by electrochemical method

Highly ordered Co{sub 80}Pt{sub 20} nanowires (NWs) and nanotubes (NTs) have been synthesized by low cost DC electrochemical deposition method with constant stirring during the fabrication process in anodic aluminum oxide nano-templates with average pore diameter of about 200 nm. The structural and magnetic properties of nanostructures have been investigated before and after simple and magnetic field annealing. Magnetic field of 1 T has been applied during annealing process in the direction perpendicular to NWs and NTs axis. X-Ray Diffraction analysis shows face centered cubic (fcc) as the dominant phase for Co{sub 80}Pt{sub 20} NWs and post annealing led to better crystallinity with retained fcc phase. Furthermore, magnetic properties, including saturation magnetization (M{sub s}), squareness ratio (M{sub r}/M{sub s}), and coercivity (H{sub c}), have been investigated as a function of annealing temperature by Vibrating Sample Magnetometer.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Magnetic properties of Nd-Ga-Fe{sub bal}-Nb-B alloy

Here, we have synthesized Nd-Ga-Fe{sub bal}-Nb-B alloy by strip casting method. The crystalline and magnetic properties of sample were investigated with x-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectrometer. The XRD pattern was analyzed with the Rietveld refinement method, indicating a tetragonal structure and the space group of P4{sub 2}/mnm. The temperature dependence of zero-field cooled (ZFC) magnetization curve was measured under applied field at temperature ranging from 4.2 to 740 K. From the ZFC curve, Curie temperature and spin reorientation temperature are determined to be 615 K and 130 K, respectively. Also, Mössbauer spectra were measured at various temperatures ranging from 4.2 to 620 K. Each spectrum was fitted with 6-sextets for Fe site (8j{sub 1}, 8j{sub 2}, 16k{sub 1}, 16k{sub 2}, 4c, and 4e), and magnetic hyperfine field, Isomer shift, electric quadrupole shift, and area ratio values were obtained from the fit. We observed the change in slope of magnetic hyperfine field and electric quadrupole shift at 130 K while the Curie temperature was determined to be 615 K from the measurement of zero velocity counter, agreeing with the values obtained from VSM measurements.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Rapid phase synthesis of nanocrystalline cobalt ferrite

Synthesis of single phase nanocrystalline Cobalt Ferrite (CoFe{sub 2}O{sub 4}) was achieved by single step autocombustion technique with the use of citric acid as a chelating agent in mono proportion with metal. Specimens prepared with this method showed significantly higher initial permeability's than with the conventional process. Single phase nanocrystalline cobalt ferrites were formed at very low temperature. Surface morphology identification were carried out by transmission electron microscopy (TEM) analysis. The average grain size and density at low temperature increased gradually with increasing the temperature. The single phase formation is confirmed through powder X-ray diffraction analysis. Magnetization measurements were obtained at room temperature by using a vibrating sample magnetometer (VSM), which showed that the calcined samples exhibited typical magnetic behaviors. Temperature dependent magnetization results showed improved behavior for the nanocrystalline form of cobalt ferrite when compared to the bulk nature of materials synthesized by other methods.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Mass production of magnetic nickel nanoparticle in thermal plasma reactor

We report the mass production of Ni metal nanoparticles using dc transferred arc thermal plasma reactor by homogeneous gas phase condensation process. To increase the evaporation rate and purity of Ni nanoparticles small amount of hydrogen added along with argon in the plasma. Crystal structure analysis was done by using X-ray diffraction technique. The morphology of as synthesized nanoparticles was carried out using FESEM images. The magnetic properties were measured by using vibrating sample magnetometer at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microwave properties of RF- sputtered ZnFe{sub 2}O{sub 4} thin films

In this work, RF- magnetron sputtering technique has been employed to deposit nanocrystalline ZnFe{sub 2}O{sub 4} thin films at room temperature. The as grown films were ex-situ annealed in air for 2 h at temperatures from 150°C to 650°C. X-ray diffraction, vibrating sample magnetometer and ferromagnetic resonance were used to analyze the phase formation, magnetic properties and microwave properties respectively. From the hysteresis loops and ferromagnetic resonance spectra taken at room temperature, a systematic study on the effect of O{sub 2} plasma on microwave properties with respect to processing temperature has been carried out.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of Co{sub 2+} substitution in Mg{sub 0.5}Zn{sub 0.5−x}Co{sub x}Fe{sub 2}O{sub 4} ferrite nanoparticles: Study of structural, dielectric and magnetic properties

Polycrystalline samples of Mg{sub 0.5}Zn{sub 0.5−x}Co{sub x}Fe{sub 2}O{sub 4} (0 ≤ x ≤ 0.5) with x varying from 0.0-0.5 synthesized by sol-gel auto ignition method. The X-ray diffraction analysis with Retvield refinement reveals the formation of single phase cubic spinel structure. The frequency dependent of real part of dielectric constant has been measured at room temperature and at 100 °C by using an ac impedance analyzer. Except x = 0.5, an increase in the dielectric constant is observed with increase in Co{sup 2+} substitution. Magnetic response has been seen by vibrating sample magnetometer (VSM) at room temperature. The saturation magnetization (M{sub S}) and coercivity (H{sub C}) increase with increasing the Co{sub 2+} substitution. The cation distribution estimated by Mössbauer spectroscopy shows that Co{sub 2+} and Mg{sub 2+} ions have their preference towards octahedral B site, on the other hand Zn{sub 2+} ions preferentially occupy tetrahedral A site, whereas Fe{sub 3+} ions are randomly distributed over A- and B-site. The as obtained results indicated that the substitution of Co{sub 2+} has brought the significant changes in the structural, electrical and magnetic properties of as prepared Mg-Zn-Co multioxide nanocrystals.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Magnetic field role on the structure and optical response of photonic crystals based on ferrofluids containing Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} nanoparticles

Ferrofluids based on magnetic Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} ferrite nanoparticles were prepared by co-precipitation method from aqueous salt solutions of Co (II), ZnSO{sub 4}, and Fe (III) in an alkaline medium. Ferrofluids placed in an external magnetic field show properties that make them interesting as magneto-controllable soft photonic crystals. Morphological and structural characterizations of the samples were obtained from Scanning Electron Microscopy and Transmission Electron Microscopy studies. Magnetic properties were investigated with the aid of a vibrating sample magnetometer at room temperature. Herein, the Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} samples showed superparamagnetic behavior, according to hysteresis loop results. Taking in mind that the Co-Zn ferrite hysteresis loop is very small, our magnetic nanoparticles can be considered soft magnetic material with interesting technological applications. In addition, by using the plane-wave expansion method, we studied the photonic band structure of 2D photonic crystals made of ferrofluids with the same nanoparticles. Previous experimental results show that a magnetic field applied perpendicular to the ferrofluid plane agglomerates the magnetic nanoparticles in parallel rods to form a hexagonal 2D photonic crystal. We calculated the photonic band structure of photonic crystals by means of the effective refractive index of the magnetic fluid, basing the study on the Maxwell-Garnett theory, finding that the photonic band structure does not present any band gaps under the action of applied magnetic field strengths used in our experimental conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗