High-resolution Magnetic Measurements Research Articles

Comparison of annealing effects on Zn-doped GaMnAs and undoped GaMnAs epilayers

To compare the annealing effects on GaMnAs-doped with Zn (GaMnAs:Zn) and undoped GaMnAs (u-GaMnAs) epilayers, we grew GaMnAs thin films at 200 °C by molecular beam epitaxy (MBE) on GaAs substrates, and they were annealed at temperatures ranging from 220 °C to 380 °C for 100 min in air. These epilayers were characterized by high-resolution X-ray diffraction (XRD), electrical, and magnetic measurements. A maximum resistivity at temperatures T m close to the Curie temperatures T c was observed from the measurement of the temperature-dependent resistivity ρ( T) for both the GaMnAs:Zn and the u-GaMnAs samples. We found, however, that the maximum temperature T m observed for GaMnAs:Zn epilayers increased with increasing annealing temperature, which was different from the result with the u-GaMnAs epilayers. The formation of GaAs:Zn and MnAs or Mn–Zn–As complexes with increasing annealing temperature is most likely responsible for the differences in appearance.

Crystal chemistry, structure and magnetic properties of the Cu(Mo x W1− x )O4 solid solution series

For a solid solution series the common description of a crystal as a homogeneous solid formed by a repeating, three-dimensional pattern of a unit cell is in principle no longer applicable, taking the statistical chemical distribution of the substituting ions into account. The Cu(Mo x W1−x )O4 solid solution series represents an appropriate system to investigate how this chemical distribution affects the details of the crystal structure: Due to different coordination preferences of the isovalent diamagnetic ions W and Mo, a decisive magnetic exchange path couples ferromagnetically in CuWO4, but antiferromagnetically in the isostructural compound CuMoO4-III. From the investigations of the magnetic properties of the solid solution series it can be inferred for a certain range of stoichiometries that the Mo/W cation disorder of the solid solution series does not result in a corresponding disordered distribution of magnetic coupling constants but in the formation of a super structure of them. The magnetic superexchange here acts as a very sensitive probe for local bonding geometries. Consequently, in the solid solution cooperative structural processes dominate over individual coordination preferences. In the present work Cu(Mo x W1−x )O4 powder samples are characterized with high-resolution synchrotron diffraction, magnetization measurements and neutron diffraction. Cu(Mo x W1−x )O4 single crystals are characterized by electron probe micro-analysis, transmission electron microscopy, X-ray structure refinement and profile analyses, magnetization measurements and diffraction with ‘white’ and monochromatic neutrons.

Synthesis and Characterization of Bimetallic Pd-Co Nano Magnetic Materials in Mesoporous Silica

ABSTRACTAn one-pot procedure was developed for the synthesis of mesoporous silica containing bimetallic PdCo using Pd(NO3)2 and CoCl2, and cetyl trimethyl ammonium bromide (CTAB) as the templating agent, and tetramethoxy silane (TMOS) as the precursor. The materials were characterized using high resolution scanning transmission electron microscopy (HRSTEM), elemental analysis, X-ray diffraction (XRD), and magnetic measurements. The data indicate that the bimetallic Pd-Co nanoparticles are uniformly distributed on the inner pore walls of silica. The magnetic measurements of reduced Pd-Co nanoparticles (4-5 nm) in mesoporous silica reveal a typical ferromagnetic behavior up to 20 K and exhibit superparamagnetic properties above 30 K.

Detrital and early diagenetic processes in Late Pleistocene and Holocene sediments from the SW Galicia Bank inferred from high-resolution enviromagnetic and geochemical records

U-channel-based high-resolution magnetic and geochemical measurements supported by scanning electron microscopy, X-ray diffraction and fluorescence, and grain-size analyses of discrete samples were carried out on six sediment cores recovered from the SW flank of the Galicia Bank, at the Prestige' s wreck area. Five magnetochemical facies, reflecting the different sedimentary environments (i.e. hemipelagic, contouritic, turbiditic), sediment provenances and early diagenetic redoxomorphic processes (i.e. Mn peaks) are defined on the basis of a cluster analysis. The records showed climatically forced detrital signatures of regional importance, associated with continental slope sedimentary processes. The chronostratigraphy and correlation of the cores is based on 20 14C AMS-dating, recognition of Heinrich like Events H1 to H3 and well-documented Holocene climatic features. From a geochemical and enviromagnetic perspective, the Late Pleistocene to Holocene evolution of the area shows two different sedimentation contexts. MIS 2 is dominated by down-slope depositional processes. The highest sedimentation rates (9.1 cm/ky) were achieved during this interval. The major turbidite activity is recorded between ≈ 31 000 yr BP and ≈ 13 500 yr BP. Successive arrivals of IRD (H1 to H3) are also identified during this period. In contrast, Holocene sedimentation was dominated by a mixture of pelagic, hemipelagic and along-slope depositional processes and presented considerable lower sedimentation rates (3 cm/ky). Bottom-currents intensification at 7000 yr BP and 4500 yr BP coinciding with Late Holocene warm events are also recognised during this stage.

Glass forming ability, microstructure and magnetic property of NdAlNiCuFe alloys

The glass forming ability (GFA), microstructure and magnetic property in (Nd 60Al 10Ni 10)Cu 20- x Fe x (0 ≤ x ≤ 20) alloys were investigated by using X-ray diffraction (XRD), differential scanning calorimetry (DSC), high resolution transmission electron microscopy (HRTEM) and magnetic property measurement. It is shown that the GFA of the alloys decreases with Fe content. The samples for bulk cylinders with x ≤ 10 show a distinct endothermic peak in the DSC traces due to a glass transition in the range of 421–438 K. With further increasing Fe, the glass transition is masked by the crystallization. The microstructure of the Nd-based alloy can change progressively from full glassy state into composite state with nanocrystalline particles in the glassy matrix indicating the glass forming ability degrades with increasing Fe. The average size of nanocrystals increases with Fe and the distribution changes from homogenous to heterogeneous. The magnetic property varies from paramagnetic to hard magnetic when the Fe content increases up to about 4at% indicating that the magnetic property is related to the metastable phases.

Comparison of High Temperature Superconducting Gradiometers Using Flip Chip YBCO and TBCCO Antennas

To optimize our high-temperature superconducting (HTSC)-dc-SQUID gradiometric sensors with galvanically-coupled antennas, we investigated the performance of antennas on a separate substrate. These antennas are inductively coupled to a dc-SQUID-gradiometer in a flip-chip configuration. Different combinations of thin-film and substrate materials, including Tl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> _ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (TBCCO) on Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> or LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> (YBCO) on SrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , were used to produce antennas with variable layouts. These were then characterized concerning their critical current densities, critical temperature, and noise properties to demonstrate their suitability for high-resolution magnetic measurements in a flip-chip configuration. Field gradient resolution and noise properties of multiple dc-SQUID gradiometer antenna combinations were determined and compared.

New stabilized phases in the Sr/Ca–Mn–Co–O system: structural–magnetic properties relationship

Polycrystalline Sr3CaMn2CoO9 and (Sr0.5Ca0.5)15Mn7Co4O33 have been synthesized and characterised by X-ray and electron diffraction, high resolution electron microscopy and magnetic measurements. These oxides constitute the α = 3, β = 1 and α = 4, β = 1 terms of the homologous series (A3B2O6)α(A3B3O9)β, respectively. Isolated rows of polyhedra sharing faces along the c-axis are made up of units of two and one face-sharing octahedra (occupied by Mn) linked by one trigonal prism (occupied by Co) in an ordered way. The chains are separated by columns of Sr/Ca atoms. Magnetic measurements suggest antiferromagnetic correlations in the two new commensurate monodimensional oxides. The influence of the size of alkaline-earth atoms on the long-range magnetic interactions is discussed.

Chapter 11 magnetic nanoparticles in oxide glasses

Unique properties of the potassium-aluminum-boron glasses doped with low concentrations of MnO and Fe2O3 to make them magnetically ordered and optically transparent in the IR and visible ranges are due to the formation of nanoparticles of a cubic ferrite. Assembling and properties of nanosized ferrite particles in the glasses have been investigated by X-ray diffraction, differential dissolution analysis, high-resolution transmission electron microscopy, Mossbauer spectroscopy, magnetic measurements, and magnetooptical Faraday effect. It was shown that the ferrite particles vary highly in size, shape, stoichiometry, structural perfection, and space distribution depending on the preparation conditions. A correlation between the characteristics of nanostructured ferrite particles and magnetic properties of glasses has been established.

Magnetic records of Core MD77-181 in the Bay of Bengal and their paleoenvironmental implications

High-resolution environmental magnetic measurements were carried out on Core MD77-181 in the Bay of Bengal, including magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization of all samples, and temperature-dependence of magnetic susceptibilities and magnetic hysteresis parameters of representative samples. The results suggest that (1) the magnetic mineral assemblage of the upper 9.82 m sediments (corresponding to the last 160 ka) is dominated by pseudo-single domain magnetite, with more abundant coarse grains in glacial periods than in interglacial periods; (2) the uppermost 6.50 m of sediments (corresponding to the last 70 ka) shows significant temporal variations in grain sizes of magnetic minerals, possibly reflecting the teleconnection between variations of the Indian summer monsoon and rapid cold events of the North Atlantic (Heinrich events); (3) the sediments below 9.82 m are dominated by paramagnetic minerals (probably including pyrites), suggesting reductive diagenesis. The magnetic records of Core MD77-181 are comparable to those of Core MD77-180 in the Bay of Bengal, and ODP Hole 722B in the Arabian Sea. This study suggests that the paleoceanographic event at ∼160 ka significantly changed the redox state of the northern Indian Ocean, from a reductive environment before the event to an oxic or suboxic environment after the event.

Synthesis and Characterization of CoFe2O4 Nanoparticles Dispersed in a Silica Matrix by a Sol−Gel Autocombustion Method

A very fast self-combustion reaction was applied for the first time to the synthesis of a series of magnetic CoFe2O4−SiO2 nanocomposites in a wide range of compositions (from 5 to 50 wt % CoFe2O4). Combining a gelation method that adopts metal nitrates, citric acid and tetraethoxysilane as precursors with controlled thermal treatments, a wide variety of samples with properties finely modulated were obtained. Particle formation and evolution of the structural and magnetic properties with the temperature were investigated by thermal analysis, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, nitrogen physisorption, IR, and magnetic susceptibility measurements. It was shown that the formation of metal ammonium carboxylate complexes takes place in all the gel precursors, contributing to the control of nucleation and growth of the nanoparticles. Spherical particles with narrow particle size distribution, uniformly dispersed in the matrix, are obtained in the...

Coercivity of nanocrystalline Nd–Fe–Co–Al–B alloys with low rare-earth content

The controlled nanocrystallization of Nd–Fe–Co–Al–B bulk amorphous tunes the coercivity, which is enhanced to 23 kOe, with a Curie temperature of 692 K. Ferromagnetic Nd 2(Fe,Co,Al) 14B nanocrystallites isolated by amorphous clusters coexist with antiferromagnetic Nd 6(Fe,Co,Al) 14. These magnetic properties are examined by the combination of X-ray diffraction, high-resolution transmission electron microscopy, magnetization measurements, and Mossbauer spectrometry. The grain size for optimal magnetic properties is around 40 nm.

A coordination polymer precursor approach to the synthesis of NiFe bimetallic nanoparticles within hybrid mesoporous silica

An approach to the synthesis and the organization of magnetic bimetallic NiFe nanoparticles of controlled size and composition was developed using thermolysis of the cyano-bridged Ni2+/[Fe(CN)6]3− coordination polymer nanoparticles anchored within a hybrid mesostructured silica either under argon or under hydrogen atmospheres. The obtained NiFe nanoparticles were studied by high resolution transmission electronic microscopy (HRTEM), nitrogen sorption (BET), X-ray diffraction (XRD) and magnetic measurements, which reveal the presence of uniform bimetallic NiFe nanoparticles inside the silica pores. The size of these nanoparticles is controlled by the pore size of the silica used and by the size of the cyano-bridged coordination polymer nanoparticles. The magnetic measurements show a superparamagnetic behaviour of the nanoparticles with a decrease of the blocking temperature as the size of the nanoparticles decreases.

Investigating impact demagnetization through laser impacts and SQUID microscopy

Research Article| May 01, 2006 Investigating impact demagnetization through laser impacts and SQUID microscopy Jérôme Gattacceca; Jérôme Gattacceca 1CEREGE, CNRS/Université Aix-Marseille 3, France Search for other works by this author on: GSW Google Scholar Michel Boustie; Michel Boustie 2Laboratoire de Combustion et Détonique, CNRS/ENSMA, Poitiers, France Search for other works by this author on: GSW Google Scholar Benjamin P. Weiss; Benjamin P. Weiss 3Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts02139, USA Search for other works by this author on: GSW Google Scholar Pierre Rochette; Pierre Rochette 4CEREGE, CNRS/Université Aix-Marseille 3, France Search for other works by this author on: GSW Google Scholar Eduardo A. Lima; Eduardo A. Lima 5Vanderbilt University, 2201 West End Avenue, Nashville, Tennessee 37235, USA Search for other works by this author on: GSW Google Scholar Luis E. Fong; Luis E. Fong 5Vanderbilt University, 2201 West End Avenue, Nashville, Tennessee 37235, USA Search for other works by this author on: GSW Google Scholar Franz J. Baudenbacher Franz J. Baudenbacher 5Vanderbilt University, 2201 West End Avenue, Nashville, Tennessee 37235, USA Search for other works by this author on: GSW Google Scholar Geology (2006) 34 (5): 333–336. https://doi.org/10.1130/G21898.1 Article history received: 31 May 2005 rev-recd: 27 Oct 2005 accepted: 28 Nov 2005 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jérôme Gattacceca, Michel Boustie, Benjamin P. Weiss, Pierre Rochette, Eduardo A. Lima, Luis E. Fong, Franz J. Baudenbacher; Investigating impact demagnetization through laser impacts and SQUID microscopy. Geology 2006;; 34 (5): 333–336. doi: https://doi.org/10.1130/G21898.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Understanding demagnetization by hypervelocity impacts is crucial for the interpretation of planetary magnetic anomalies and remanent magnetization in meteorites. We describe an innovative approach for investigating the effects of impacts on the remanent magnetization of geologic materials. It consists of the combination of pulsed laser impacts and Superconducting Quantum Interference Device (SQUID) microscopy. Laser impacts are nondestructive, create shocks with peak pressures as high as several hundred GPa, and allow well-calibrated modeling of shock wave propagation within the impacted samples. High-resolution SQUID microscopy quantitatively maps the magnetic field of room-temperature samples with an unprecedented spatial resolution of ∼100 μm. We present shock modeling and magnetic field data obtained for two laser impacts on a magnetite-bearing basalt sample. Magnetic measurements show a demagnetized area at the impact locations. We also show that high-resolution magnetic measurements combined with impact modeling provide a continuous relation between the demagnetization intensity and the peak pressure undergone by the sample. This promising technique will allow for the investigation of the demagnetization behavior of a variety of geological materials upon impacts, with implications for our understanding of the magnetization of extraterrestrial materials and of terrestrial impact structures. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Contact-less high-resolution magnetic measurement of electron transport

Electronic transport studies are important tool to get information on the electronic system and quality of a material. Recent progress in experimental techniques leads to higher resolution data, providing insight in physical processes on much finer scale. Many intriguing, particularly quantum phenomena of electron transport in solids emerge when conduction electrons are 'cold', with field induced kinetic energy e < < κBT. We focus on phase transitions accompanied by abrupt changes of electrical conductivity in a narrow temperature range. Examples are superconducting-normal, metal-insulator, martensitic or the Verwey-transition in Fe3O4. In many cases a shape and details in the transition are blurred with increasing current density. But the 'cold' conduction electrons may reveal details and offer high-resolution data for detailed analysis of elastic and inelastic electron scattering.

Ultrafine, perfectly spherical Ni–Zn ferrite nanoparticles, with ultranarrow distribution, isolated in a silica matrix, prepared by a novel synthesis method in the liquid phase

Nanocomposites of the type (Ni–Zn)Fe2O4/SiO2 have been synthesized using a novel chemical route involving the liquid phase. Metallic nitrates (MN)–ethylene glycol (EG)–silica gels were prepared as a result of the polycondensation reaction, using as precursors MN of Fe, Ni, Zn and tetraethylorthosilicate, to which EG was added. After gelling and drying, the sols were first subjected to a thermal treatment at a temperature of ∼140°C, where heteropolynuclear complex combinations with carboxylic ligands are formed as a result of the redox reaction between EG and the nitrate ions. These have been investigated using Fourier transform infrared spectrometry and thermal analysis. The influence of EG on the gels was also studied. While observing the formation of Ni–Zn ferrite using this method, following the thermal treatment of the gels at higher temperatures (500–1000°C), nanocomposites were obtained made up of ultrafine Ni0.65Zn0.35Fe2O4 nanoparticles (4–6nm) that are perfectly spherical, with an ultranarrow distribution (∼1nm) of diameters around the mean value and homogeneously dispersed in a solid SiO2 matrix. The synthesized nanocomposites were characterized by means of X-ray diffraction, high-resolution transmission electron microscopy and magnetic measurements.

Growth and Properties of c-Axis Epitaxial Thin Films for La2-2xSr1+2xMn2O7 Bilayer Manganates by Sputtering

c-Axis epitaxial thin films of a layered manganate La2-2xSr1+2xMn2O7 have been grown on SrTiO3(100) substrates by on-axis rf-magnetron sputtering. The films have been characterized using energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), magnetoresistivity, and magnetization measurements. It is shown that the film chemical composition is sensitive to the deposition parameters, and that a small deviation of composition or deposition condition causes nucleation of the (La,Sr)MnO3 structure. It is found that the deposition rate is crucial for the c-axis film growth; stoichiometric c-axis La2-2xSr1+2xMn2O7 films have been grown under limited conditions of a low rate of 0.8 nm/min, an (Ar, O2 50%) atmospheric pressure of 120 mTorr, and a substrate temperature of 760°C. From X-ray diffraction simulation, it is inferred that the c-axis La2-2xSr1+2xMn2O7 films thus grown contain intergrowths comprised of (La,Sr)MnO3 and presumably (La,Sr)2MnO4 structures, and the total intergrowth fraction amounts to about 40%.

Synthesis, Structural and Magnetic Characterization of a New Scheelite Related Compound: Eu2Mo3O12.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis, Structural and Magnetic Characterization of a New Scheelite Related Compound: Eu2Mo3O12

AbstractPolycrystalline Eu2Mo3O12 has been synthesized and characterized by X‐ray and electron diffraction, high resolution electron microscopy and magnetic measurements. This oxide shows a complex scheelite superstructure whose essential feature is the existence of isolated Mo tetrahedra. Each Mo atom has four oxygen neighbors at distances ranging from 1.75 to 1.91 Å, whereas each Eu atom has eight oxygen neighbors at 2.43 Å. The temperature dependence of the inverse magnetic susceptibility shows that Eu2Mo3O12 behaves as a Curie–Weiss paramagnet at high temperature (160–300 K), whereas in the range 100–20 K it shows Van Vleck paramagnetism. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2005)

The microwave-assisted polyol synthesis of nanosized hard magnetic material, FePt

In this paper, we report on the first microwave synthesis of FePt nanoparticles. The advantages of the described process are its simplicity, the short reaction time, and their easy preparation. The structure and composition of FePt nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), magnetic measurements, and X-ray photoelectron spectroscopy (XPS). The particle size of the product was 23 nm, as determined from the XRD measurements, and 2.1 as measured from the HRTEM. The measured coercivity at room temperature was 4600 Oe.

Effect of La, B doping on the electrical resistivity and magnetic susceptibility of nanocrystalline vanadium nitride

High resolution electrical resistivity and magnetic susceptibility measurements on nanocrystalline VN samples doped with 0.2 at. % B and La, and 0.5 at. % B and La (crystallite size ∼6–11 nm) were done to study their normal state and superconducting properties. We analyze the resistivity data in the light of the existing theoretical framework. The resistivity of the former sample follows a Tn behavior at low temperature with n≈4 suggesting that electron-phonon scattering play a significant role in determining the low temperature normal state resistivity. While the latter follows a more complicated behavior with a negative temperature coefficient of resistivity indicating that electron-electron scattering in addition to disorder enhanced electron interaction determine the normal state resistivity. We observe that the system is driven towards a disordered state with increasing doping levels of B and La. The superconducting transition is found in the electrical resistivity and magnetic susceptibility studies. The susceptibility follows a Curie-like behavior above the superconducting transition temperature (Tc).