bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of pollutant outflow and CO sources during TRACE‐P using model‐calculated, aircraft‐based, and Measurements of Pollution in the Troposphere (MOPITT)‐derived CO concentrations
Authors: Allen Dale , Pickering Kenneth , Fox‐Rabinovitz Michael
Published: May 2004

Outflow of CO from Asia during March 2001 is evaluated using data from the Transport and Chemical Evolution over the Pacific (TRACE‐P) mission and the Measurements of Pollution in the Troposphere (MOPITT) instrument in conjunction with model‐calculated CO from the University of Maryland chemistry and transport model (UMD CTM). Comparison of model‐calculated CO with aircraft measurements indicates that temporal and spatial variations in CO are well captured by the model (mean correlation coefficient of 0.78); however, model‐calculated mixing ratios are lower than observed especially for pressures >850 hPa where negative biases of ∼60 ppbv were seen. Regression analysis is used to optimize the magnitudes of the bottom‐up TRACE‐P Asian fossil fuel (FF), biofuel (BF), and biomass burning (BB) CO emission inventories. Resulting Asian scaling factors are 1.59 ± 0.34 for FF + BF emissions and 0.47 ± 0.46 for BB emissions. Resulting FF + BF emissions are 27.7 ± 6.1 Tg for March 2001 (301 ± 67 Tg for an entire year). Resulting BB emissions for March 2001 are 8.5 ± 8.3 Tg. These results are consistent with recent inverse modeling studies. Scaling factors are lowest (highest) for experiments that assume a high (low) CO yield for the oxidation of anthropogenic and natural hydrocarbons and for experiments that use (do not use) an aerosol‐modified OH distribution. Comparison of model‐calculated CO with MOPITT measurements supports the results from our regression analysis. Without exception, mean March 2001 model‐calculated CO profiles in the TRACE‐P region from a simulation with adjusted CO sources are within a standard deviation of mean March 2001 MOPITT‐sampled profiles.
Oceanic germanium/silicon ratios: Evaluation of the potential overprint of temperature on weathering signals
Authors: Hammond Douglas E. , McManus James , Berelson William M.
Published: May 2004

Diatom remains indicate the oceanic Ge/Si ratio (μmol/mol) has varied temporally, ranging from Miocene values of 0.9 to Last Glacial Maximum (LGM) values of 0.55, with the present value of 0.69. These ratios lie between those for the primary sources for these elements: continental weathering (Ge/Si = 0.5) and hydrothermal fluids (Ge/Si = 11). Previous explanations for temporal variation have focused on variations in the relative strength of the primary inputs. Alternatively, the cause may be temporal variation in the relative strength of the two sinks for Ge, opal, and a nonopal sink found in margin sediments. The importance of the latter depends on the rate of opal rain to the seafloor in margin environments. As temperature decreases, opal dissolution rates in the water column decrease, permitting a larger fraction of the opal rain to reach the seafloor before dissolving. This increases the rate of Ge uptake into nonopal phases. A model calculation predicts that a decrease of 3.5°C in LGM ocean temperature should increase opal rain to the margin seafloor by a factor of 1.5; an increase of 3.5°C in Miocene temperature should decrease rain by a factor of 0.6. The predicted changes for Ge uptake in the nonopal sink can account for essentially all of the temporal Ge/Si variation recorded in diatoms. The absence of larger changes constrains silicate weathering rates relative to the present as 106 ± 16% during the LGM and 88 ± 12% during the mid‐Miocene (15–20 Ma). However, additional uncertainty exists because some factors of potential importance remain unconstrained.
Radiation analysis in the space domain of laterally shielded planar transmission lines: 1. Theory
Authors: Tornero J. L. Gómez , Melcón A. Álvarez
Published: May 2004

In this contribution, the propagation and radiation nature of laterally shielded top‐open planar waveguides (LShPW) is studied by using a discrete spectrum of parallel‐plate waveguide (PPW) TEz and TMz modes. This formulation allows for a simple but precise analysis of the propagation and radiation characteristics associated with the leaky‐wave modes which exist in such planar transmission lines. An approximate novel interpretation of the radiation mechanism is also given by describing each PPW mode as an inhomogeneous plane wave. Comparisons with previous works grant the accuracy of the proposed method. Besides, the analytical and rigorous nature of this approach makes it very suitable for the practical analysis and design of leaky‐wave antennas, as will be discussed in the second part of this work.
Testing the importance of precipitation loss mechanisms in the inner radiation belt
Authors: Rodger Craig J. , McCormick Robert J. , Clilverd Mark A.
Published: May 2004

Manmade control of the radiation belts for the protection of space‐based infrastructure has been suggested on the basis of theoretical calculations. In this paper we put forward an experimental test of the relative importance of either whistler‐induced electron precipitation (WEP) or manmade VLF transmitters as the most significant inner radiation belt loss mechanisms for 2 < L < 2.4. The experimental identification of seasonality in inner radiation belt electrons lifetimes would provide strong evidence for the relative significance of WEP‐ or manmade transmitter‐driven losses depending on the relative phasing found.
Toroidal mantle flow around the Calabrian slab (Italy) from SKS splitting
Authors: Civello Sara , Margheriti Lucia
Published: May 2004

SKS‐wave birefringence is likely caused by ongoing and/or fossil mantle flow. Splitting parameters in the southern Tyrrhenian subduction zone define a quite complex pattern of fast directions with large delay times up to 2.7 s. Fast directions are prevalently trench parallel below the slab and rotate to trench normal at the western edge of the slab depicting a ring around it. We interpret these anisotropic patterns, also observed in laboratory experiment, as toroidal mantle flow induced by rollback subduction.
Reflection of intraseasonal equatorial Rossby waves at the western boundary of the Pacific Ocean
Authors: Cravatte Sophie , Boulanger Jean‐Philippe , Picaut Joël
Published: May 2004

The present study focuses on the existence of equatorial Rossby waves at periods shorter than 180 days and on their potential reflection into equatorial Kelvin waves. Toward that objective, TOPEX/Poseidon sea level data are used from 1992 to 2002. No Rossby waves are evidenced at periods shorter than 100 days. At 120‐day period, Rossby waves of first meridional mode dominate in the western part of the basin. Their reflection efficiency at the western boundary in energy is found to be around 40–45% of theoretical estimates for low‐frequency waves reflecting at a perfect wall. It is suggested that the 120‐day reflected Rossby waves contribute to a large extent to the generation of 120‐day Kelvin waves and that they superimpose on the directly wind‐forced Kelvin waves, hence reinforcing this signal.
Carrier phase delay altimetry with GPS‐reflection/occultation interferometry from low Earth orbiters
Authors: Cardellach E. , Ao C. O. , de la Torre Juárez M. , Hajj G. A.
Published: May 2004

GPS signals reflected off the surface of the Earth can be detected by receivers aboard occulting Low Earth Orbiters (LEOs). In this work, carrier phase interferometry between the reflected and direct occultation signals is performed to infer its relative delay at centimetric error. Our analysis shows that submeter sensitivity on the surface heights can formally be reached with this technique. The potential applications to polar ice altimetry are discussed.
Nanoscale magnetic hysteresis of Ni80Fe20/Au/Co trilayers using ballistic electron magnetic microscopy
Authors: Haq E. , Gokcan H. , Banerjee T. , Postma F. M. , Siekman M. H. , Jansen R. , Lodder J. C.
Published: May 2004

Ballistic electron magnetic microscopy is used to study spin-dependent hot-electron transport and local magnetic switching of ferromagnetic thin films grown on a Au/Si(100) collector. For Ni80Fe20 films, the collector current is a factor of 2 larger than for Co, consistent with the shorter hot-electron attenuation length of Co. For Ni80Fe20/Au/Co spin valves, the collector current is reduced by a factor of 5 when the relative magnetization of the ferromagnetic layers changes from parallel to antiparallel. By sweeping the applied magnetic field, we obtain nanoscale hysteresis loops, where the hot electrons are collected from an area of about 10 nm.
Coercivity enhancement near blocking temperature in exchange biased Fe/FexMn1−x films on Cu(001)
Authors: Pan Wei , Jih Nai-Yeou , Kuo Chien-Cheng , Lin Minn-Tsong
Published: May 2004

Exchange bias is found in the Fe/FexMn1−x/Cu(001) bilayer films. The coercivity Hc is enhanced at blocking temperature Tb for the films with composition x between 0.25 and 0.35, but not for those between 0.1 and 0.25. A simple model based on the discrepancy of the Néel temperature TN and Tb is proposed, which may reveal the physical origins of these two temperature points.
Magnetic anisotropy of epitaxial Cu/Ni/Cu nanolines
Authors: Lyons E. S. , O’Handley R. C. , Ross C. A.
Published: May 2004

Continuous nickel films grown pseudoepitaxially between copper layers have been shown to have strong perpendicular magnetic anisotropy due to large magnetoelastic and interface magnetocrystalline anisotropy energies. These Cu/Ni/Cu films with tNi=6.9 nm have been patterned into lines approximately 200 nm wide using interferometric lithography and ion milling. Torque magnetometer measurements show the anisotropy of the nanolines to be significantly different from that of the continuous films. The magnetoelastic anisotropy (favoring perpendicular magnetization) decreases in the patterned films due to strain relaxation at the line edges. Although the anisotropy change for this line width is most likely due to shape anisotropy, we anticipate observation of magnetoelastic anisotropy due to strain relief at the edges of the lines at narrower line widths in future work.
Properties of incommensurate spin density waves in iron aluminides (invited)
Authors: Noakes D. R. , Arrott A. S. , Belk M. G. , Deevi S. C. , Lynn J. W. , Shull R. D. , Wu D.
Published: May 2004

Neutron diffraction in Fe(Al) reveals incommensurate spin density waves (SDWs) in alloys known to be spin glasses. The wave vectors for crystals of Fe(34Al), Fe(40Al) and Fe(43Al) show n varying from 11 to 6 for q=2π(h±1/n,k±1/n,l±1/n)/ao, where (h,k,l) and ao characterize the parent bcc lattice of the CsCl structure. The magnetic reflections are present far above the spin-glass freezing temperatures. These SDWs keep the spins on nearest-neighbor Fe atoms close to parallel, in contrast with SDWs in Cr, which keep nearest-neighbor spins close to antiparallel. The competition between near-neighbor Fe–Fe ferromagnetism and 180° superexchange through the Al site has been used to explain the spin-glass behavior, but the appearance of the SDWs calls for a more fundamental source of the periodicity. The phase shift mechanism for SDW interactions with magnetic moments is invoked to explain the breadth of the peaks, which resemble the results for Cu(Mn), Pd(Mn), and Pd(Cr). The data are interpreted using cubic symmetry, but it has yet to be established whether the wave vectors all occur in a single domain or whether there are multiple domains. There are 48 wave vectors of magnitude almost equal to the {110} wave vectors of the bcc lattice, which could stabilize the SDWs by spanning the Fermi surface. These unanticipated results should have pervasive ramifications for the theory of metallic magnetism.
Evolution of interface properties of electrodeposited Ni/GaAs(001) contacts upon annealing
Authors: Scheck C. , Liu Y.-K. , Evans P. , Schad R. , Zangari G.
Published: May 2004

We demonstrate how epitaxial FM (Ni) films can be grown by ECD directly onto GaAs(001) without outdiffusion or surface segregation of As or Ga. The thickness dependence of electrical and magnetic properties (saturation magnetic moment) verify the good quality of the layers and indicate that electrochemical deposition is a suitable candidate for the growth of epitaxial Ni films with sharp interfaces on GaAs(001). X-ray photoelectron spectroscopy (XPS) analysis on electroplated (epitaxial) Ni films showed no interdiffusion for annealing up to 250 °C. Annealing at higher temperatures, up to 350 °C, significantly increases both the As outdiffusion and the Schottky barrier heights, which indicates the correlation between intermixing and the diode quality.
Room-temperature growth of epitaxial Fe3O4 films by ion beam deposition
Authors: Lai Chih-Huang , Huang Po-Hsiang , Wang Yu-Jen , Huang R. T.
Published: May 2004

Epitaxial and polycrystalline Fe3O4 films were grown on MgO (100) and Si (100) substrates, respectively, at room temperature by using reactive ion beam deposition. The MS value of epitaxial Fe3O4 films was around 310 emu/cm3, and was almost independent of thickness from 45 to 195 nm. The MS value of polycrystalline films showed significant thickness dependence, which might be attributed to the formation of the initial layer. The Verwey transition at 110 K was observed on 195 nm epitaxial films, and decreased significantly with decreasing thickness. The reduction of the Verwey temperature may be related to the residual strain in the film.
Critical behavior dependence on Sr concentration in La1−xSrxMnO3
Authors: Oleaga A. , Salazar A. , Prabhakaran D. , Boothroyd A. T.
Published: May 2004

The thermal diffusivity in the vicinity of the magnetic transition of a set of La1−xSrxMnO3 (0⩽x⩽0.3) single crystals has been measured using the photopyroelectric technique. Taking into account that the inverse of the thermal diffusivity behaves as the specific heat, the critical exponent α has been obtained. In the pure and lightly doped samples (x=0,0.05) where the transition is antiferromagnetic-paramagnetic, the critical exponent is consistent with the Heisenberg model (α=−0.115). For Sr concentration higher than 0.20, where the low temperature phase is ferromagnetic, a drastic change in the critical exponent has been observed, approaching Ising behavior (α=+0.11) at the highest concentration.
Band filling versus bond bending in substituted LxSr2−xFeMoO6 (L=Ca, La, Nd) compounds
Authors: Rubi D. , Frontera C. , Herranz G. , Muñoz J. L. Garcı́a , Fontcuberta J. , Ritter C.
Published: May 2004

With the aim of determining and discriminating the influence of both steric and band-filling effects on the strength of the magnetic interactions of double perovskites, we have studied the structural and magnetic properties of substituted LxSr2−xFeMoO6 (L=Ca, La, and Nd) compounds. Our results show that the raising of Curie temperature in electron-doped samples (La and Nd substitutions) is mainly due to band-filling effects, being the influence of structural distortions (steric effects) is of less relevance. This fact contrasts with the well-known properties of manganites, where a strong correlation between structural properties and magnetic interactions is present. We argue that this disagreement relies on the different symmetries of the electronic orbitals involved in the magnetic interactions in both cases.
Crystalline electric field excitations in the heavy fermion superconductor CeCoIn5
Authors: Bauer E. D. , Christianson A. D. , Lawrence J. M. , Goremychkin E. A. , Moreno N. O. , Curro N. J. , Trouw F. R. , Sarrao J. L. , Thompson J. D. , McQueeney R. J. , Bao W. , Osborn R.
Published: May 2004

The crystalline electric field (CEF) energy level scheme of the heavy fermion superconductor CeCoIn5 has been determined by means of inelastic neutron scattering (INS). Peaks observed in the INS spectra at ∼8 and ∼27 meV with incident neutron energies between Ei=30 and 60 meV and at a temperature T=10 K correspond to transitions from the ground state to the two excited states, respectively. The wave vector and temperature dependence of these peaks are consistent with CEF excitations. Fits of the data to a CEF model yield the CEF parameters B20=−0.80 meV, B40=0.059 meV, and |B44|=0.137 meV corresponding to an energy level scheme: Γ7(1)(0)[=0.487|±5/2〉−0.873|∓3/2〉], Γ7(2)(8.6 meV,100 K), and Γ6(24.4 meV,283 K).
Thermal phenomena in IrMn exchange biased systems
Authors: Fernández-Outón L. E. , O’Grady K. , Carey M. J.
Published: May 2004

In this paper, we report on a detailed study of reversal in the antiferromagnetic layer in IrMn-based exchange-biased systems. By a process of careful field cycling and heating with the antiferromagnet aligned in the opposite direction to the original set direction, we are able to study thermal activation over the energy barriers in the antiferromagnetic material. We find that the peak in the coercivity is observed, but in no way correlates to the blocking temperature. We conclude that the origin of the coercivity enhancement in exchange-biased systems lies in effects at the interface.
Peak magnetocaloric effects in Al-Gd-Fe alloys
Authors: Provenzano V. , Shapiro A. J. , Shull R. D. , King T. , Canavan E. , Shirron P. , DiPirro M.
Published: May 2004

The magnetocaloric properties of several AlxGdyFez (with x+y+z=100) ternary alloys have been determined between 2 and 300 K. Three distinct peaks in the magnetic entropy change ΔSm versus T were found: a low-temperature peak (near 10 K), an intermediate temperature peak (80–160 K), and a higher temperature peak (210 to 280 K). The low-temperature peak coincides with a field-induced antiferromagnetic-to-ferromagnetic transition; the intermediate and high temperature peaks are associated with other magnetic transitions. Above 60 K, these alloys exhibited superparamagnetic behavior and possessed enhanced ΔSm values, as predicted earlier for magnetic nanocomposites.
The effect of boron purity on electric and magnetic properties of CaB6
Authors: Rhyee Jong-Soo , Cho B. K.
Published: May 2004

We present the consistent electronic and magnetic properties in high-quality defect-controlled single crystals of CaB6, based on temperature-dependent transport and isothermal magnetization. Pure CaB6 single crystals, synthesized with 99.9999%-pure boron, exhibited fully semiconducting characteristics, such as monotonic resistance for 2–300 K. Boron-related defects formed in CaB6 single crystals, synthesized with 99.9%-pure boron, induced extra free charge carriers. Remarkably, no ferromagnetic signals were detected from single crystals made with 99.9999%-pure boron, regardless of stoichiometry, whereas those made with 99.9%-boron exhibited ferromagnetism within a finite range of carrier density. This indicates that the boron-related defects generate both the local magnetic moments associated with the exotic ferromagnetism and extra free charge carriers.
Magnetic and magneto-transport properties of electrodeposited magnetic nano-network on laser modified Au surface
Authors: Zhu F. Q. , Fan D. L. , Cammarata R. C. , Chien C. L.
Published: May 2004

Magnetic nano-network structure has been fabricated by electrochemical deposition Ni onto laser modified Au film. Scanning electron microscopy images show that the network has a three-dimensional interconnecting branch structure with branch diameter of about 100 nm, constructed from grains with diameter of about 25 nm. Because of this structure, the Ni network has enhanced coercivity, in-plane isotropy, and a combination of longitudinal and transverse anisotropic magnetoresistance.
Magnetism of R2Ti3Ge4 (R=Sc, Gd, Tb, Dy, Ho, and Er) compounds
Authors: Nirmala R. , Sankaranarayanan V. , Sethupathi K. , Rangarajan G. , Morozkin A. V. , Kundaliya Darshan C. , Malik S. K.
Published: May 2004

Results of magnetization measurements down to 1.8 K on polycrystalline R2Ti3Ge4 (R=Sc, Gd, Tb, Dy, Ho, and Er) compounds of orthorhombic Sm5Ge4-type (space group Pnma) are presented and discussed. Gd2Ti3Ge4 is found to be a ferromagnet below 32 K while other R2Ti3Ge4 compounds, with magnetic rare earths (R=Tb, Dy, Ho, and Er), undergo a low temperature antiferromagnetic transition. The effective magnetic moment (μeff) values obtained from the Curie–Weiss paramagnetic susceptibility correspond to that of R3+ ions. Saturation of magnetization is not observed upto applied fields of 5.5 T at 1.8 K for all R2Ti3Ge4 compounds except Gd2Ti3Ge4, indicating the possible presence of crystal field effects. Electrical resistivity of these compounds is dominated by electron-phonon scattering above 20 K and signature of phonon and magnon drag effects are seen in the low temperature thermopower data.
Nonlinear magneto-optical Kerr effect in garnet magnetophotonic crystals
Authors: Dolgova T. V. , Fedyanin A. A. , Aktsipetrov O. A. , Nishimura K. , Uchida H. , Inoue M.
Published: May 2004

Magnetization-induced second-harmonic (SH) generation is studied in magnetophotonic crystals formed from a magnetic garnet spacer located between two dielectric Bragg reflectors, at the resonance of the fundamental radiation with the cavity mode. Longitudinal nonlinear magneto-optical Kerr effect manifests itself in the rotation of the polarization plane of a reflected SH wave which reaches a value up to 250°/μm. A magnetization-induced variation of the SH intensity is observed in transversal configuration with magnetic contrast up to 0.3.
Local structure and magnetic properties of mechanical alloyed Co–C compositions
Authors: Jiang Bingzhi , Yang Dong-Seok , Ulyanov A. N. , Yu Seong-Cho
Published: May 2004

Formation of nanocrystalline Co particles embedded in an amorphous C matrix produced by the mechanical alloying process was studied. The formation of the Co5C95 alloy was examined by the x-ray diffraction (XRD) and extended x-ray absorption fine structure methods. XRD analysis displayed the decrease in the Co grains size, the transformation from the face-center-cubic (fcc)+hexagonal close-packed (hcp) phases to the hcp phase and an amorphization of carbon matrix with milling time. At the early stage of milling, the coercivity, HC, increased because of the higher hcp phase HC than that of the fcc phase. Partial HC increase could be also caused by the decrease of Co particles size. The subsequent powder milling led to the decrease in the HC due to thermal process and/or due to the transformation of hcp-Co to a random close-packed phase under a long-term milling. Magnetization of the compositions decreased gradually with milling. The size of single domain particles after the 60 h of milling was about 10 nm. The Co–C and Co–Co bond distances, deduced by pair distribution function analysis, were equal to 1.92±0.02 Å and 2.48±0.02 Å, respectively.
High-frequency permalloy permeability extracted from scattering parameters
Authors: Wang Pingshan , Ni Weiping , Tien Norman C. , Kan Edwin C.
Published: May 2004

We report a ferromagnetic thin film characterization method and the measured microwave permeability of patterned permalloy films. The method incorporates ferromagnetic materials with transmission lines and extracts RLCG equivalent circuit elements from scattering parameters. The frequency-dependent effective permeability is then obtained from the incremental R and L caused by the ferromagnetic material. The measured high-frequency losses of thin permalloy (Ni80Fe20) films between 1 and 20 GHz show that geometry design restrains ferromagnetic resonance and eddy-current effects effectively. Above ∼22 GHz, mode conversion occurs in the test structures. Other broadband structures are necessary for further extractions.
Control of quantum well states in Ag/Fe(100) and Au/Fe(100)
Authors: Ogawa S. , Terada Y. , Heike S. , Hashizume T. , Ito K.
Published: May 2004

The quantum well (QW) energy dependence on the vacuum boundary condition is studied in Ag/Fe(100) and Au/Fe(100). With decreasing of the vacuum level by evaporating Cs atoms, the energy shift and broadening of the QW states are observed by one-photon photoemission spectra, which is well explained by a phase accumulation model. In Au/Fe(100), sharp QW states are still observed even after the reduction of the vacuum level by 1.4 eV, which changes the QW energy as large as 0.11 eV.
Magnetic domain imaging of ferromagnetic GaMnAs films
Authors: Pross Alexander , Bending Simon , Edmonds Kevin , Campion R. P. , Foxon C. T. , Gallagher Bryan
Published: May 2004

Scanning Hall probe microscopy has been used to study the magnetic domain structure of GaMnAs thin films after various low temperature anneals to increase the Curie temperature (TC). Samples with in-plane magnetization, which received short low temperature anneals in vacuum directly after growth, exhibit very small (∼2–5 μm) rather random domains. In stark contrast similar samples, which additionally received very long low temperature anneals in air, display large (10–100 μm) domains, which still contain clearly resolvable magnetic disorder. Preliminary scans of air-annealed samples with out-of-plane magnetization also reveal a very irregular, rather fine (1–3 μm) domain structure. In all samples micron-sized regions at domain walls frequently remain ferromagnetic well above the average TC, indicating either the presence of ferromagnetic precipitates (e.g., MnAs) or material there with higher than average Mn concentration.
Magnetic properties and microcolumnar structure of a TbFeCo memory layer for high-density magneto-optical recording
Authors: Murakami Motoyoshi , Birukawa Masahiro
Published: May 2004

The MsHc value of the TbFeCo magneto-optical medium was reported as a key factor in high-density recording. Microstructure control of the magnetic underlayer was identified as an effective method for increasing the value of MsHc. This article describes the relationship between the magnetic properties and microcolumnar structure, which depends on the growth process and sputtering conditions of the TbFeCo recording film and the layer structure. It has been found that the columnar structure of the film self grows under the low migration energy process without any magnetic underlayer. The process uses a target in-face type dc magnetron sputtering system with a low temperature substrate. The amount of sputtering gas was observed to play a dominant role in the self growth of the film. The coercivity Hc value increases by creating a microcolumnar structure, but the squareness ratio of the Kerr hysteresis loop of the film is reduced. And the perpendicular anisotropy constant Ku is decreased to less than 1×106 erg/cm3 when Hc is more than 8×103 A/cm. As a result, it is difficult to record a tiny mark because the magnetic transition width of the magnetic domain wall would be extended. This is considered that the self-grown columnar structure is intrinsically different from the film grown over a magnetic underlayer because the TbFeCo film grown over a magnetic underlayer with seeding effect has large coercivity Hc and a high squareness ratio of Kerr hysteresis. These results indicate that it is suitable for tiny mark recording of the recording film with the seeding effect.
Structural and magnetic properties of perpendicular FePt thin films with inserted Ag layer
Authors: Zhou Y. Z. , Chen J. S. , Chow G. M. , Wang J. P.
Published: May 2004

Improved coercivity was achieved in perpendicular 10-nm-thick FePt film through an inserted Ag layer. The out-of-plane coercivity increased with increasing Ag thickness, from 2.0 kOe, for the sample without Ag, to 4.4 kOe, for the sample with 3 nm Ag. Silver insertion also reduced the magnetic grain size and affected the magnetic reversal mode in these films.
Ar ion milling process for fabricating CoCrPt patterned media using a self-assembled PS-PMMA diblock copolymer mask
Authors: Kamata Y. , Kikitsu A. , Hieda H. , Sakurai M. , Naito K.
Published: May 2004

Etching the damage of a patterned media fabricated with an artificially assisted self-assembled mask is estimated. CoCrPt thin films were etched by ion milling into aligned dots with a diameter of 40 nm. The milling condition was optimized for reducing the etching damage. As a result, the damage to the crystal lattice and crystal orientation was estimated to be slight by transmission electron microscope (TEM) and scanning electron microscope (SEM) analyses. Though strong perpendicular anisotropy was induced by the patterning process, magnetic measurements and Landau-Lifshitz-Gilbert simulation revealed that the magnetic anisotropy energy was almost unchanged throughout this etching process.
Temperature dependence of the resonant tunneling fields in high-spin molecules
Authors: Tsai Hui-Lien , Chang Ching-Ray , Cheng Tai-Chung , Jwo Tyn-Yih , Wang Bor-Kai
Published: May 2004

Herein we have made two Mn-based high spin molecule samples, S=10 and S=9. Both samples show step hysteresis below 3 K, and their resonant fields are regularly spaced. Changes in temperature shift the resonant fields. The temperature dependence of the observed resonant fields can be fitted well with only a single-state tunneling if the mean-field interaction is taken into account. We also find that both the upward shift of the small step-index resonant fields and the downward shift of the large step-index resonant fields are due to mutual interactions.
Exchange biasing field of NiFe/[IrMn–Mn]/CoFe multilayers depending on Mn content
Authors: Lee Sang-Suk , Kim Bo-Kyung , Lee Jin-Yong , Hwang Do-Guwn , Kim Sun-Wook , Kim Mee-Yang , Hwang Jae-Youn , Rhee Jang-Roh
Published: May 2004

Exchange bias by inserting a submonolayer of Mn between two neighboring IrMn layers in NiFe/[IrMn–Mn]/CoFe multilayers was investigated. As-deposited CoFe pinned layers with an [IrMn–Mn] layer resulted in larger exchange biasing field (Hex) and blocking temperature (Tb) than when pure Ir22Mn78 was used. Hex and Tb improved with content of 76.8–78.1 vol % Mn, but Hex and Tb of NiFe/IrMn/CoFe dropped considerably with addition of more than 0.6 vol % Mn. The Hex obtained for as-grown two multilayer samples with 77.5 and 78.7 vol % Mn, were 259 and 150 Oe, respectively. In the case of IrMn with 77.5 vol % Mn, Hex increased to 475 Oe at 350 °C but decreased to 200 Oe at 450 °C. The magnetic properties and thermal stabilities of the NiFe/[IrMn–Mn]/CoFe multilayer were enhanced by suitable additions of Mn. In applications where higher Hex and Tb were required, the proper contents of Mn could be used.
Effects of postdeposition annealing on structural and magnetic properties of CoCrPt/Ti thin films
Authors: Sun C. J. , Wang J. P. , Soo E. W. , Chow G. M.
Published: May 2004

The effects of postdeposition annealing on the structural properties of CoCrPt/Ti magnetic thin films were investigated. The improvement of out-of-plane coercivity and squareness resulted from enhancement of both the crystallinity and texture of the CoCrPt (002) peak. The initial growth region of the CoCrPt layer and the Ti underlayer greatly improved in structural and magnetic properties through annealing.
Internal friction and modulus changes associated with martensitic and reverse transformations in a single crystal Ni48.5Mn31.4Ga20.1 alloy
Authors: Peng Zhiming , Jin Xuejun , Fan Yongzhong , Hsu T. Y. , Allen Samuel M. , O’Handley Robert C.
Published: May 2004

Internal friction and the elastic modulus of Ni–Mn–Ga single crystals have been simultaneously measured as a function of the temperature during cooling and heating at 3 °C/min between 140 and 20 or 0 °C. The measurements were done in single cantilever mode. Two distinct internal friction peaks indicate martensitic and reverse transformation, respectively. The martensitic transformation temperature TM and reverse transformation temperature TA agree with that determined by differential scanning calorimetry. Softening of the modulus is observed near both the martensitic transformation and the reverse transformation.
High-field magnetization in the quantum spin magnet NiCl24SC(NH2)2
Authors: Paduan-Filho Armando , Gratens Xavier , Oliveira Nei F.
Published: May 2004

The field-induced antiferromagnetic phase transitions in NiCl24SC(NH2)2 have been determined in fields up to 18 T and temperatures down to 0.016 K. This is an S=1 system with a singlet ground state separated from an excited doublet by D/kB. In zero field this spin-gap system remains nonmagnetic down to T=0, because the small antiferromagnetic exchange interaction (J) is “subcritical” (2zJ<D). However, a magnetic field applied along the uniaxial direction lowers one of the excited energy levels, thus creating a condition for the establishment of long-range order. At T=0 this happens between B1=2.11±0.01 T and B2=12.11±0.03 T. The onset of this long-range order has been treated as Bose–Einstein condensation of magnons. The phase-boundaries B1(T) and B2(T) determined follow power-law dependence, Bi(T)−Bi(0)∝Tφ, with φ=2.6±0.2 for both.
Effect of Si substitution on the magnetic and magnetocaloric properties of ErCo2
Authors: Singh Niraj K. , Tripathy S. K. , Banerjee D. , Tomy C. V. , Suresh K. G. , Nigam A. K.
Published: May 2004

The magnetic and magnetocaloric properties of Er(Co1−xSix)2 compounds with 0⩽x⩽0.075 have been studied to determine their suitability as magnetic refrigerant materials. The strength of itinerant electron metamagnetism was found to decrease with Si concentration, which is responsible for the reduction of the magnetocaloric effect. Magnetization curves at low temperatures show the existence of a critical field for magnetization to increase, which is a consequence of domain wall pinning. The critical field and the coercive field were found to increase with Si concentration.
Magnetic moments of ferromagnetic, superparamagnetic, and submonolayer Fe on a GaAs (100) surface
Authors: Claydon J. S. , Xu Y. B. , Tselepi M. , Bland J. A. C. , van der Laan G.
Published: May 2004

We have used x-ray magnetic circular dichroism (XMCD) to determine the spin and orbital magnetic moments of Fe atoms at the ferromagnetic/superparamagnetic boundary, superparamagnetic thickness, and submonolayer thickness at the interface. The samples, grown by molecular beam epitaxy at room temperature, were 5, 4, and 0.5 ML (monolayer) Fe on GaAs (100)-4×6 capped with 7 ML Cr, preceded in the case of the 0.5 ML Fe by 9 ML Co. The XMCD results show orbital moments enhanced by almost 300% with respect to the bulk and bulklike spin moments for all three thicknesses demonstrating unambiguously that the Fe/GaAs interface is magnetic.
Microstructural characterization of Ni-Mn-Ga ferromagnetic shape memory alloy powders
Authors: Solomon Virgil C. , Smith David J. , Tang YunJun , Berkowitz Ami E.
Published: May 2004

Powders of Ni-Mn-Ga ferromagnetic shape memory alloy (FSMA) were produced by spark erosion. Powders quenched in liquid nitrogen are primarily hollow spherical particles, whereas those quenched in liquid argon are mostly solid spheres. Electron microscopy observations of powders as-sparked in nitrogen show highly disordered nanocrystalline grains with an average size of less than 100 nm whereas those sparked in liquid argon display extensive crystallinity. Magnetic measurements indicate that the powders do not become fully ferromagnetic until after annealing at 973 K for 5 h. Investigations of annealed powders using differential scanning calorimetry reveal thermoelastic martensitic transition behavior. The annealed powders have a microtwinned martensite with many large grains showing a five-layer period modulation. These Ni-Mn-Ga powders should be suitable for the development of magnetic-field-driven FSMA powder/polymer microcomposites.
Magnetization steps in the phase-separated Cr-doped Nd0.5Ca0.5MnO3 compounds
Authors: Fonseca F. C. , Carneiro A. S. , Jardim R. F. , O’Brien J. R. , Kimura T.
Published: May 2004

The manganite Nd0.5Ca0.5MnO3 has a CE-type antiferromagnetic-insulating (AFI) ground state at low temperatures. This compound undergoes a charge-ordering (CO) transition at TCO∼250 K followed by a paramagnetic to AFI (orbital-ordered) OO phase transition at TN∼170 K. The ferromagnetic (FM) double-exchange interaction between Mn ions is quenched by such a CO effect. Upon Cr doping, as in single crystals of Nd0.5Ca0.5Mn0.96Cr0.04O3, suppression of the quenched CO-OO state occurs at TC∼140 K and is accompanied by a FM-metal-insulator transition. These Cr-doped materials have a low temperature ground state comprised of a mixture of 20–30 nm domains of the FM phase embedded in the CO-OO matrix, as inferred from Lorentz microscopy. Our results show that these Cr-doped materials undergo a field-dependent magnetic transition in a large range of temperature T<50 K, signed by a pronounced magnetization step in M(H) virgin curves. Moreover, from several isothermal hysteresis M(H) curves, we have observed that the FM state remains at H→0 and does not collapse back to the AFI state in M(H) cycles performed up to 18 T and T<50 K. These results are different from those found in La0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3 compounds, where the induced FM state by H collapses back to AFI at low H. At 1.4 K, the M(H) virgin curves exhibit a sharp ΔH∼0.1 T magnetization step at Hj∼4.3 T, which is followed by saturation of M(H)∼110 emu/g in magnetic fields up to H=18 T. The temperature dependence of Hj was found to obey an exponential decay up to T∼50 K. Such a temperature dependence of Hj indicates that the magnetization steps may not be related to a classical metamagnetic transition, as has been proposed for these manganite compounds.
Magnetic properties of NiMnSb(001) films grown on InGaAs/InP(001)
Authors: Heinrich B. , Woltersdorf G. , Urban R. , Mosendz O. , Schmidt G. , Bach P. , Molenkamp L. , Rozenberg E.
Published: May 2004

NiMnSb half Heusler alloy films were prepared by molecular beam epitaxy (MBE) on InP(001). The dc and rf magnetic properties were investigated by ferromagnetic resonance (FMR). The effective uniaxial anisotropy fields increased with increasing film thickness and reached nonzero asymptotic values. FMR linewidths rapidly increased with the film thickness due to the presence of two magnon scattering. Bulklike uniaxial anisotropies and two magnon scattering were caused by a self-assembled network of lattice defects. Gilbert damping parameter and spectroscopic g factor were found to be 3.1×107 and 2.03, respectively, indicating a weak role of spin orbit interaction.
Spin-polarized scanning tunneling spectroscopy study of Fe nanomagnets on W(001)
Authors: Yamasaki A. , Wulfhekel W. , Hertel R. , Suga S. , Kirschner J.
Published: May 2004

We have studied the magnetic states of self-organized Fe islands on W(001) by means of spin-polarized scanning tunneling spectroscopy (Sp-STS). Single-domain and vortex states in the nanoscale islands have been observed. The high-resolution magnetic images enable to experimentally determine the boundary between the single-domain and vortex states. The single-domain state was always found below a thickness of 6 nm and a diameter of 120 nm in Fe islands. The boundary directly observed with Sp-STS is consistent with theoretical predictions.
Annealing effect on the Fe/Pt multilayers grown on Al2O3 (0001) substrates
Authors: Chou S. C. , Yu C. C. , Liou Y. , Yao Y. D. , Wei D. H. , Chin T. S. , Tai M. F.
Published: May 2004

We studied the structure and magnetic properties of molecular-beam epitaxy grown 300 Å thick Fe/Pt multilayers with different bilayer thickness and annealing temperature. The Fe/Pt multilayers were deposited on 100 Å thick Pt buffer layers at 100 °C on Al2O3 (0001) substrates. The structure of as-deposited Fe/Pt films was fcc(111). While the postannealing temperature ⩾400 °C, an additional FePt(100) orientation was observed. A large coercivity range, namely, 200–16 000 Oe can be tuned by varying the bilayer thickness and annealing temperature.
Ab initio calculations of zinc-blende CrAs/GaAs superlattices
Authors: Nagao Kazutaka , Shirai Masafumi , Miura Yoshio
Published: May 2004

We investigate the properties of interfaces between highly spin-polarized zinc-blende (ZB) CrAs and GaAs using first-principles density functional calculations. It is found that the local spin polarization at the Fermi level is very high even at ZB-CrAs/GaAs interface and then exhibits gradual decay from the interface to the inside of GaAs, reflecting their ideal structural matching. We further study the properties of ZB-CrAs/GaAs multilayer where two-monolayer ZB-CrAs and two-monolayer GaAs stack alternately. The multilayer shows high spin polarization throughout its entire region. Since the spin polarization is found insensitive to Cr-Ga substitutional disorder, both ZB-CrAs and ZB-CrAs/GaAs multilayer may work as efficient filter for spin-polarized current injection into GaAs.
Room temperature operation of magnetic tunnel transistors with half-metallic Fe3O4 emitter source
Authors: Yoon Kap Soo , Yang Jung Yup , Kim Ki Woong , Koo Ja Hyun , Kim Chae Ok , Hong Jin Pyo
Published: May 2004

Magnetic tunnel transistors (MTTs) based on a half-metallic Fe3O4 emitter source were investigated to obtain a high efficiency of spin-dependent hot electron transport. The MTTs include magnetic tunnel junctions with an AlOx insulating barrier. The insulating barrier formed by a remote rf plasma oxidation method was used to enhance electrical and structural properties of MTTs. The highest magnetocurrent ratio of the MTTs was experimentally observed to be about 51% at room temperature. Especially, the transfer ratio of about 10−2 was obtained by systematically varying the heights of emitter and collector barrier.
Superparamagnetic transitions in ultrathin film NiFe nanolines
Authors: Uhlig W. Casey , Shi Jing
Published: May 2004

We found that the coercivity of electron-beam patterned nanoscale NiFe and Co lines (width ranging from 55 nm to 1 μm) has a distinct inverse-width dependence when the film thickness is greater than 3.5 nm. This inverse-width dependence is consistent with a nucleation picture in which the magnetization reversal is controlled by a small nucleus, which spreads across the width of the nanoline but is independent of the length. However, the inverse-width dependence breaks down for the narrowest NiFe lines at room temperature in films below 3.5 nm in thickness. In this thickness regime the coercivity drops rapidly as a function of decreasing width as the controlling nucleus size approaches the superparamagnetic limit. The Arrhenius–Néel equation for this equivalent volume very effectively models the data. As the temperature is decreased, the coercivity of the narrowest lines rapidly increases and the inverse-width trend is recovered.
Imaging spiral magnetic domains in Ho metal using circularly polarized Bragg diffraction
Authors: Lang J. C. , Lee D. R. , Haskel D. , Srajer G.
Published: May 2004

We have used circularly polarized x rays to image the spiral magnetic domain structure in a single crystal of Ho metal. In these structures, the magnetization direction rotates between successive atomic layers forming a helix. At magnetic Bragg diffraction peaks, circularly polarized x rays are sensitive to the handedness of such a helix (i.e., either right or left handed). By reversing the helicity of the incident beam with phase-retarding optics and measuring the difference in the Bragg scattering, contrast between domains of opposing handedness can be obtained.
Fingerprinting hysteresis
Authors: Zimányi G. T. , Friedman Gary , Liu K.
Published: May 2004

We test the predictive power of first-order reversal curve (FORC) diagrams using simulations of random magnets. In particular, we compute a histogram of the switching fields of the underlying microscopic switching units along the major hysteresis loop, and compare to the corresponding FORC diagram. We find qualitative agreement between the switching-field histogram and the FORC diagram, yet differences are noticeable. We discuss possible sources for these differences and present results for frustrated systems where the discrepancies are more pronounced.
Structural and magnetic properties of MSr2Y1.5Ce0.5Cu2Oz (M-1222) compounds with M=Fe and Co
Authors: Awana V. P. S. , Gupta Anurag , Kishan H. , Malik S. K. , Yelon W. B. , Lindén J. , Karppinen M. , Yamauchi H. , Kundaliya Darshan C.
Published: May 2004

The MSr2Y1.5Ce0.5Cu2Oz (M-1222) compounds, with M=Fe and Co, have been synthesized through a solid-state reaction route. Both compounds crystallize in a tetragonal structure (space group 14/mmm). A Rietveld structural refinement of the room-temperature neutron diffraction data for Fe-1222 reveals that nearly half the Fe remains at the M site, while the other half goes to the Cu site in the CuO2 planes. Existence of Fe at two different lattice sites is also confirmed by 57Fe Mössbauer spectroscopy from which it is inferred that ∼50% of the total Fe occupies the Cu site in the CuO2 planes as Fe3+, whereas the other ∼50% is located at the M site with ∼40% as Fe4+ and ∼10% as Fe3+. For the M=Co compound, nearly 84% of Co remains at its designated M site, while the rest occupies the Cu site in the CuO2 planes.
qEffect of gas pressure on properties of FePt film sputtered on polymer substrate
Authors: Nguyen L. T. , Lisfi A. , Lodder J. C.
Published: May 2004

FePt thin films (70 nm thick) have been prepared by dc sputtering under a variable Ar pressure (4×10−3–4×10−2 mb) and have been annealed at temperatures ranging from 300 to 400 °C. With increasing Ar pressure, the ordering process requires a lower annealing temperature. However, further increase of Ar pressure deteriorates the crystallinity of the film which hinders the transformation from fcc to fct structure. The structural analyses show a strong correlation between the ordering process and the microstructure.
Magnetic tuning of hysteresis loop properties in antiferromagnetically coupled bilayers
Authors: Berger A. , Margulies D. T. , Do H.
Published: May 2004

We have utilized antiferromagnetically coupled bilayer structures to magnetically tune hysteresis loop properties. A key element of this approach is the nonoverlapping switching field distribution of the two magnetic layers, which allows for the measurement of magnetic reversal of the soft Co film at low fields while keeping the magnetization state of the hardmagnetic CoPtCrB film unperturbed. The effective disorder level in the Co film can be tuned easily by applying an appropriate field sequence to set the desired magnetization state of the CoPtCrB layer prior to hysteresis loop measurements of the Co film. This tuning procedure is fully reversible, temperature independent, and highly effective.
Geometrical effect on spin current in magnetic nanostructures
Authors: Ichimura M. , Takahashi S. , Ito K. , Maekawa S.
Published: May 2004

The spatial distribution of the spin current is studied in the nonlocal geometry of a contact between ferromagnetic and nonmagnetic metals taking into account the finite size effect of the contact area by applying finite element method in two dimensions. The sign and the order of magnitude of the obtained spin accumulation signal are consistent with the experiment. It is shown that, with a tunneling-like contact, the two-dimensional inhomogeneous distribution in spin current is slightly observed, and the one-dimensional analysis is appropriate to evaluate the experimental results.
Magnetism and magnetoresistance of polycrystalline composite of (ZnFe)3O4 and α-Fe2O3
Authors: Zhang Jian H. , Chen Liying , Tung Le. D. , Spinu Leonard , Thang P. D.
Published: May 2004

We have investigated the magnetic and electric transport properties of polycrystalline composite systems ZnxFe3−xO4/α-Fe2O3 (x=0.50–0.57), prepared by the sol–gel method. Power x-ray diffraction analysis and electron microprobe analysis show the presence of both spinel (ZnFe)3O4 phase and α-Fe2O3. The magnetic study indicates the ferromagnetic phases ZnxFe3−xO4 (x=0.50,0.55, and 0.57) in the composites have quite high Curie temperatures (685–795 K). It seems that the collinear ferrimagnetic structure is retained after zinc substitution. The composites exhibit large negative magnetoresistance (MR) ratio at low temperatures. The MR ratios reach 52%–72% at 20 K and 8.5 T.