bluuebunny/crossref_metadata_2025 huggingface dataset:
Antiferromagnetic coupling by spin polarized tunneling
Authors: Faure-Vincent J. , Tiusan C. , Bellouard C. , Popova E. , Hehn M. , Montaigne F. , Schuhl A. , Snoeck E.
Published: May 2003

By performing magnetic studies on Fe/MgO/Fe magnetic tunnel junctions, we provide experimental evidence of room-temperature antiferromagnetic coupling between two ferromagnetic layers across a very thin insulating barrier. Epitaxial growth of the MgO barrier on a very flat Fe layer leads to an extremely low “orange peel” magnetic coupling. Then, antiferromagnetic coupling is observed for MgO thickness, tMgO, below 0.8 nm. The strength of this coupling increases abruptly when reducing tMgO down to 0.5 nm. The shape of the variation of experimental coupling strength J with tMgO, the quantitative value of |J|, and finally, the thickness range of tMgO for which the antiferromagnetic coupling is observed are in good agreement with the equilibrium interlayer exchange theory by the spin polarized quantum tunneling of electrons between the ferromagnetic layers.
Phase coexistence in Cr-doped Nd0.5Ca0.5MnO3 compounds
Authors: Carneiro A. S. , Fonseca F. C. , Jardim R. F. , Kimura T.
Published: May 2003

We have performed measurements of dc electrical resistivity ρ(T), magnetic susceptibility χ(T), and impedance spectroscopy Z(T, ω) in both single crystals and polycrystalline samples of Nd0.5Ca0.5Mn1−xCrxO3 (0.00⩽x⩽0.07). The pristine compound exhibits a transition to a charge ordered (CO) state at TCO∼250 K. However, no evidence of either metal-insulator (MI) or ferromagnetic (FM) transitions are observed at lower temperatures. The substitution of Mn by Cr partially suppresses the CO transition and induces a FM/MI ordering at lower temperatures TC=TMI∼140 K, which is essentially Cr independent. Both ρ(T) and χ(T) measurements indicate the development of a ferromagnetic (FM) component at low temperatures T<TMI that gradually increases with increasing Cr content. The ρ(T) and χ(T) data also revealed irreversibility at temperatures T<TCO suggesting a coexistence of different phases. In addition, the Z(T,ω) curves close to TMI exhibit a clear relaxation process. The specific capacitances calculated from the Z(T,ω) curves have a percolation-like behavior, characteristic of a metal-insulator transition in samples comprised of two phases.
Anomalous Hall effect of calcium-doped lanthanum cobaltite films
Authors: Baily S. A. , Salamon M. B.
Published: May 2003

The Hall resistivity, magnetoresistance, and magnetization of La1−xCaxCoO3 epitaxial films with 0.25⩾x⩾0.4 grown on lanthanum aluminate were measured in fields up to 7 T. The x=1/3 film shows a reentrant metal insulator transition. Below 100 K, the x=1/3 and 0.4 films have significant coercivity which increases with decreasing temperature. At low temperature the Hall resistivity remains large and essentially field independent in these films, except for a sign change at the coercive field that is more abrupt than the switching of the magnetization. A unique magnetoresistance behavior accompanies this effect. These results are discussed in terms of a percolation picture and the mixed spin state model for this system. We propose that the low-temperature Hall effect is caused by spin-polarized carriers scattering off of orbital disorder in the spin-ordered clusters.
Electronic structure of Li3FeN2, a nearly half-ferromagnetic metal?
Authors: Ching W. Y. , Xu Yong-Nian , Rulis Paul
Published: May 2003

The electronic structure and magnetic properties of crystalline Li3FeN2 were studied by a first-principles method. It is shown that Li3FeN2 is nearly a half metal with a large degree of spin polarization at the Fermi level. The calculated Fe moment of 1.49μB is in good agreement with the measured value. It is also shown that the ferromagnetic interaction is along the one-dimensional chain of Fe atoms, modified by the large degree of polarization of the Li ions. Based on the analysis of the spin-polarized band structure and the density of states, it is argued that a genuine half metal in the ternary Fe nitride compounds may be possible.
Effect of Mo content on the structure stability of R3(Fe,Co,Mo)29
Authors: Li W. X. , Cao L. Z. , Shen J. , Chen N. X. , Liu B. D. , Wang J. L. , Wu G. H. , Yang F. M. , Li Y. X.
Published: May 2003

Formation of Ce3Fe29−x−yCoxMoy(x=0,3,6,10) compounds has been investigated by means of x-ray diffraction and magnetic measurements. It is found that the required Mo content to stabilize the 3:29 compounds decreases monotonically as Co content increases, totally different from the discovery in the Gd3(Fe1−xCox)29−yCry compounds. Meanwhile, we adopted a lattice inversion method in acquiring the interatomic potentials to rare-earth-transition metal intermetallic compounds, and investigated the substitution behaviors of Mo, Cr, V, and Mn in Fe-based and Co-based 3:29 compounds, respectively, by combining these potentials with computer simulation. The calculated results show that the required Mo content in R3Co29−xMox compounds is lower than that in R3Fe29−xMox compounds, whereas the Cr content in R3Co29−xCrx compounds higher than that in R3Fe29−xCrx compounds, coinciding well with the previous discovery and the experimental results in this work.
Structural and magnetic properties of Nd60Fe30−xCoxAl10 melt-spun ribbons
Authors: Sun Z. G. , Löser W. , Eckert J. , Müller K.-H. , Schultz L. , Zhu T. , Cheng Z. H.
Published: May 2003

The effects of Co addition on the structure and magnetic properties of melt-spun Nd60Fe30−xCoxAl10 (x=0, 2, 5, 10, 20, and 30) ribbons have been investigated. Except an amorphous matrix, nanocrystalline Nd was found in the Fe-containing alloys. Its relative amount decreases with increasing Co addition, and a fully amorphous structure was observed for x=30, indicating that glass-forming ability increases with Co addition. The room-temperature coercivity and magnetization are found to decrease sharply with increasing Co content. Thermomagnetic measurements show two magnetic transitions occurring at about 50 K and 480 K, respectively. Combining the isothermal differential scanning calorimetry measurement, it demonstrated that the amorphous phase in the Fe-contained alloys further separates into Nd-rich regions and Fe-rich regions. The relative amount of each phase is estimated by the magnetization of each phase.
Structure and magnetic properties of Sm(Co1−xZrx)y alloys (x=0.03–0.05,y=12–15) and melt-spun Sm(Co,Fe,Zr,Cu,Ga,B)12 material
Authors: Huang M. Q. , Turqut Z. , Chu S. Y. , Horwath J. C. , Fingers R. T. , Smith B. R. , Chen Z. M. , Ma B. M.
Published: May 2003

Alloys with nominal compositions of Sm(Co1−xZrx)y (x=0.03–0.05, y=12–15) were synthesized by arc melting and characterized in the temperature range of 10–1473 K and with a magnetic field up to 5 T. Near-single-phase materials with Th2Ni17 structure were formed in the as-cast alloys with x=0.05. Similar to Ti, Zr also stabilizes the Th2Ni17 structure. Hard magnetic properties with Tc∼1142–1179 K, Ms∼110–123 emu/g, and Ha∼63–86 kOe at 300 K have been observed. An alloy with a nominal composition of Sm(Co0.75Fe0.1Zr0.05Cu0.08Ga0.01B0.01)12 was also prepared by melt spinning. The melt spun materials were nanostructured in nature and magnetically hard in the as-spun states. Hci∼10 kOe, Bs∼9.5 kG, and Hci∼27 kOe, Bs∼9.8 kG were obtained at 300 and 10 K, respectively. The effects of the heat treatment conditions on magnetic properties of both alloys and ribbon will be also discussed.
Magnetic anisotropy and domain structure in epitaxial CoFe2O4 thin films
Authors: Lisfi A. , Williams C. M.
Published: May 2003

Magnetic properties of CoFe2O4 thin films epitaxially grown on (100) MgO by pulsed layer deposition are controlled by substrate temperature and film thickness. At 300 °C a strong dependence of magnetic anisotropy on thickness is observed indicating that stress is dominant. However at 800 °C magnetic properties are less sensitive to film thickness suggesting that magnetocrystalline is the only prevailing form of anisotropy. We also show that magnetic domains exhibit a cluster-like structure rather than stripe.
Microstructures and resistivity of cuprate/manganite bilayer deposited on SrTiO3 substrate
Authors: Tan W. S. , Wu X. S. , Du J. , Liu J. S. , Hu A. , Jiang S. S. , Wang J. , Wu Z. H. , Zheng W. L. , Jia Q. J. , Gao J.
Published: May 2003

Thin YBa2Cu3O7-δ/La0.67Ca0.33MnO3 (YBCO/LCMO) films were grown on SrTiO3(STO) substrates by magnetron sputtering technique. The microstructures of the bilayers were characterized and a standard four-probe technique was applied to measure the resistivity of the samples. The interdiffusions at the YBCO/LCMO and LCMO/STO interfaces formed two transient layers with the thickness of about 3 and 2 nm, respectively. All the bilayers were well textured along the c axis. At low temperature, the superconductivity can only be observed when the thickness of YBCO is more than 25 nm. When the thickness of YBCO is less than 8 nm, the bilayers show only ferromagnetism. The superconductivity and ferromagnetism perhaps coexist in the bilayer with the YBCO thickness of 12.5 nm. These interesting properties are related to the interaction between spin polarized electrons in the manganites and the cooper pairs in the cuprates.
Metal–insulator transition, Cu K-edge x-ray absorption near-edge structures and pairing symmetry for electron-doped Pr1.85Ce0.15CuO4+δ superconductors
Authors: Hsu Y. Y. , Lin B. N. , Ku H. C.
Published: May 2003

A metal–insulator transition near oxygen content parameter δ∼0.018(5) was observed for the Ce-optimal-doped (x=0.15) Pr1.85Ce0.15CuO4+δ (−0.003⩽δ⩽0.03) electron superconductors. Cu K-edge x-ray absorption near-edge structure reflects the 3dn character where low-energy peak A1 reflects the 3d10 configuration of Cu(I) oxidation state and A2 peak reflects the 3d10L (L for oxygen ligand hole) for Cu(II) state. The abrupt increase of A1 peak intensity and energy separation ΔE(A2−A1) near δ=0.018 coincide with the metal–insulator transition due to the formation of a broader 3d conduction band. The basal-plane penetration depth λab(T) for c-axis aligned powders show a d-wave power-law behavior with a linear-T temperature dependence for the 17.5 K underdoped superconductor [δ=0.011(5)], while a quadratic-T2 temperature dependence was observed for the 21 K optimal-doped superconductor (δ=−0.002–0.003). The superfluid density ns∼λab−2 increases from the underdoped to the optimal-doped region.
Evaluation of high data rate disk drive recording subsystem
Authors: Kaiser David , Dakroub Housan , van der Schans Al , Haftek Elzbieta , Li Shaoping , Zhu Wenzhong , Pro John , Vorasarn Ko , Stankiewick Andrzej , Cox Richard , Liu Yan , Zhang Huaan , Radish Karstan W. , Klarquest  , Sharma Sarit , Champion Eric
Published: May 2003

An effort has been made to evaluate disk drive components at high data rates. Fully functional write-head/media components to 2.6 Gbit/s have been demonstrated in spin-stand testing and magnetic force microscopy characterizations. In addition, the drive front-end electronics examined possess complete functionality up to 4.0 Gbit/s without significant performance degradation, which is consistent with electric modeling results. Furthermore, our experimental data clearly indicate that the pre-amp’s performance at high frequency is becoming a limiting factor to achieving an ultrahigh data rate in present write-head/media designs. The magnetic moment on write gap edges for certain recording heads shows signs of becoming insensitive to following the write current switching speed at ultrahigh frequency.
Neighborhood induced reader bias shift in perpendicular recording
Authors: Dhagat P. , Palmer D. , Xu B.
Published: May 2003

A spin-stand technique to determine the influence of the neighborhood on readback in perpendicular recording is presented. A square wave was recorded on an ac erased medium. Stray fields from neighboring tracks resulted in reader bias shift and thereby second-harmonic distortion in the spectrum of the square wave. An external perpendicular field applied to compensate the distortion provided a measure of the neighborhood effect on readback. A dc magnetized track written approximately a track width away was found to change the required compensating field by 5 Oe. Additional dc tracks further enhanced or diminished the compensating field depending on their relative magnetization direction. The immediate neighborhood was proven to have a dominating influence on the reader bias.
Stray fields of iron electrodes for spin-polarized transport
Authors: Barthelmess M. , Thieme A. , Eiselt R. , Meier G.
Published: May 2003

In semiconductor spintronic devices that incorporate ferromagnetic materials the stray-field configuration in the plane of the two-dimensional electron system is of crucial importance. We investigate the stray fields of iron electrodes suitable as injector and detector for spin-polarized transport in hybrid semiconductor/ferromagnet devices. Magnetic-force microscopy images of an electrode pair are derived from simulated magnetization patterns. The calculated averaged stray field is compared to the experimental signal of a ballistic Hall micromagnetometer comprising a two-dimensional electron system in a GaAs/AlGaAs-heterostructure 90 nm below the electrodes. Good agreement between simulation and experiment is obtained.
Coverage and properties of a-SiNx hard disk overcoat
Authors: Yen Bing K. , White Richard L. , Waltman Robert J. , Mate C. Mathew , Sonobe Yoshiaki , Marchon Bruno
Published: May 2003

Amorphous silicon nitride (a-SiNx) overcoats are deposited on magnetic disks by rf-reactive sputtering to study their coverage and properties. According to the x-ray photoelectron spectroscopy analysis, a-SiNx has a low coverage-limit of ∼10 Å compared with that of the reference a-CNx (∼20 Å). The lower coverage-limit of a-SiNx may be attributed to its high density of 3.2 g/cm3, which corresponds to 93% bulk density. By contrast, the density of diamond-like carbon is only 54% that of diamond. This is in agreement with the results of coverage simulation, which reveal that the film coverage thickness decreases by ∼3 Å per 10% increase in the relative density. Compared with 45 Å a-CNx coated disks, 15 Å a-SiNx coated disks have fewer pinhole defects and are more durable in the accelerated flyability test. The superior performance of a-SiNx disk overcoat may be attributed to its dense structure and high hardness (25 GPa).
Raman and infrared modes of the single molecule magnet Fe8Br8 and analogs
Authors: North J. M. , Dalal N. S.
Published: May 2003

We present Raman and infrared data for the S=10 single-molecule magnet (SMM) Fe8Br8, O17-labeled Fe8Br8 and their analogs, Fe8Br6.4(ClO4))1.6 and Fe8Br4(ClO4))4, over a range of 100–1600 cm−1. The Raman modes were assigned through group theoretical analysis of smaller model compounds. These results could help understand the structural basis of the SMM behavior of these compounds. Additionally, Raman scattering appears to have high potential as an analytical technique for the identification of SMM analogs.
Magnetic properties of FePt and FePt–Al2O3 granular films by post annealing
Authors: Matsumoto M. , Morisako A. , Katayama N.
Published: May 2003

FePt and FePt–Al2O3 alloy thin films were prepared by rf magnetron sputtering system, then post annealed in vacuum. The as-deposited films were in disordered state and the ordered L10 structure was obtained by post annealing. The temperature for L10 structure of FePt and FePt–Al2O3 films was about 400 and 550 °C, respectively. The effect of film thickness on magnetic properties was studied. The coercivity decreased rapidly from 8 to 1.5 kOe at the thickness below 10 nm for the FePt L10 films. The decrease of coercivity is due the diffusion and compositional deviation. The surface roughness is as low as 0.3 nm for FePt–Al2O3 films with coercivity of about 3.3 kOe.
Synthesis, chemical ordering, and magnetic properties of self-assembled FePt–Ag nanoparticles
Authors: Kang S. S. , Nikles D. E. , Harrell J. W.
Published: May 2003

[ FePt ] 1−x Ag x nanoparticles were chemically synthesized. Self-assembled arrays were characterized by transmission electron microscopy and small angle x-ray diffraction (XRD). Particles were annealed at temperatures from 300 to 500 °C for 30 min and degree of chemical ordering was characterized by large angle XRD and by magnetometry. Compared with pure FePt nanoparticles, additive Ag reduced the A1 to L10 ordering temperature by more than 100 °C. A maximum coercivity of more than 10 kOe was measured for samples with ∼15% Ag annealed at 500 °C, compared with about 2 kOe for samples without Ag. This reduction in required annealing temperature significantly reduces particle coalescence and loss in positional order. XRD measurements suggest that the reduction of the ordering temperature is due to defects and lattice strain introduced by the Ag and the subsequent segregation of the Ag upon annealing, activating the nucleation of the ordered phase.
Enhanced magnetic anisotropy in granular cobalt–copper alloys
Authors: Pujada B. R. , Sinnecker E. H. C. P. , Rossi A. M. , Guimarães A. P.
Published: May 2003

We have used the X-band ferromagnetic resonance (FMR) spectra of granular Co5Cu95 ribbons, as cast, and heat treated as a function of temperature, in order to study their magnetic and structural properties. From a model derived for the temperature dependence of the FMR linewidth, the mean diameter and effective anisotropy constant (Keff) of the magnetic grains were obtained. Enhanced values of Keff in comparison to the bulk materials, and also a decrease with increasing mean diameter, have been found. Our results indicate a large influence of the surface magnetic anisotropy in the smaller grains and also on the behavior of the resonance field and linewidth.
Hexagonal lattice of 10-nm magnetic dots
Authors: Malkinski L. , Camley R. E. , Celinski Z. , Winningham T. A. , Whipple S. G. , Douglas K.
Published: May 2003

We have grown precisely ordered and precisely located arrays of ultra-small magnetic dots. The nanofabrication process is based on the use of a protein crystal etch mask which is used to create a hexagonal lattice of holes in Si substrates. An assembly of (Fe/Pd)4 dots with the average dot size of 10 nm in diameter, 6.5 nm height, and an average separation between dot centers of 22 nm was grown using molecular-beam epitaxy. The dot locations are determined by the biological mask that is used to create ordered arrays of ∼4 nm deep holes in Si. Fe/Pd multilayers (1 nm thick Fe and 0.4 nm thick Pd layers) were deposited to create dots within these holes. The dots extend ∼2.5 nm above the surface, with a thicker (1.5 nm) final layer of Pd for protection of these structures during measurements. Magneto-optical Kerr effect and magnetometry data showed that these objects are magnetic even at room temperature and are fairly soft with a coercive field of ∼40 Oe. Measurements of the hysteresis loop revealed that magnetization is in plane and that 4πMeff is on the order of 15 kG.
Magnetic properties of submicron permalloy elements: Effects of heat treatment
Authors: Kazakova O. , Hanson M. , Blixt A. M. , Hjörvarsson B.
Published: May 2003

We present the results of the effect of annealing in hydrogen atmosphere on the magnetic properties of continuous magnetic films and patterned structures. Rectangular and elliptical particles, with lateral dimensions in the range 150–900 nm, were made of 24 and 66 nm thick permalloy films. The domain structure and the magnetization reversal processes were investigated by magnetic force microscopy and alternating gradient magnetometry. While the performed annealing at 200 °C during 48 h did not noticeably change the properties of the continuous films, it influenced the patterned structures significantly. The difference between patterned elements and the continuous films can be explained by enhanced relaxation and vacancy diffusion in the particles.
Synthesis, chemical ordering, and magnetic properties of FePtCu nanoparticle films
Authors: Sun Xiangcheng , Kang Shishou , Harrell J. W. , Nikles David E. , Dai Z. R. , Li J. , Wang Z. L.
Published: May 2003

FePtCu nanoparticles with varying composition were prepared by the simultaneous polyol reduction of platinum acetylacetonate and copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate) and the thermal decomposition of iron pentacarbonyl. As prepared the particles had a fcc structure with an average diameter of 3.5 nm and were superparamagnetic. Heat treatment of the self-assembled films at temperatures above 550 °C transformed the particles from the fcc to the L10 phase, give in-plane coercivities as high as 9000 Oe. X-ray diffraction revealed that the Cu remained in the films and the presence of an extra peak, indicating a second phase was present. Consistent with two or more phases, the magnetic hysteresis curves could be decomposed into a hard component (Hc>5000 Oe) and a soft component (Hc<2000 Oe). Unlike our earlier results for Ag in FePt, adding Cu to FePt did not lower the temperature required for phase transformation from the fcc to the L10 phase.
X-ray studies of magnetic nanoparticle assemblies
Authors: Anders S. , Toney M. F. , Thomson T. , Thiele J.-U. , Terris B. D. , Sun Shouheng , Murray C. B.
Published: May 2003

Monodisperse FePt nanoparticles were prepared using high-temperature solution phase synthesis. Polymer-mediated layer-by-layer growth leads to precise control of the particle self assembly. The narrow particle size distribution (σ⩽5%) offers the potential for increased data storage density by utilizing a smaller mean particle size and ultimately storage of one bit per individual nanoparticle. We have studied self-assembled multilayers of magnetic FePt nanoparticles. The L10 phase of FePt has a very high magnetic anisotropy that allows the magnetization of particles of about 4 nm diameter to be thermally stable at room temperature. Magnetic measurements using a vibrating sample magnetometer were combined with x-ray diffraction (XRD) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy to study the annealed FePt nanoparticle assemblies and to optimize annealing conditions. NEXAFS spectra showed that a fraction of the iron in the as-deposited particles was oxidized, and this fraction was reduced by annealing in inert or reducing atmospheres. A very thin layer (<0.4 nm) of oxide surrounding the particle is sufficient to explain the observed spectra. Structural analysis using XRD showed that a minimum temperature of 450 °C was required to start the formation of the ordered ferromagnetic phase. Annealing for longer times and at higher temperatures led to higher coercivity and a larger fraction of ordered phase but also to the onset of some agglomeration of the nanoparticles.
Magnetic tunnel junction pattern technique
Authors: Chen Eugene , Schwarz Benjamin , Choi Chang Ju , Kula Witold , Wolfman Jerome , Ounadjela Kamel , Geha Sam
Published: May 2003

We have developed a magnetic tunnel junction (MTJ) pattern technique that involves transforming the magnetic layer above the tunnel barrier in unwanted areas into an insulator, thus providing insulation between different MTJ devices without suffering common tunnel barrier shorting problems. With this technique, 90%–100% yielding MTJ devices have been observed. MTJ results using this process are superior to an etching based process. Switching distribution of patterned magnetic bits is also narrower using this novel technique. Process control and the ability to stop on the tunnel barrier have been demonstrated.
Hard x-ray magnetic circular dichroism study of a surface-driven twisted state in Gd/Fe multilayers
Authors: Haskel D. , Choi Y. , Lee D. R. , Lang J. C. , Srajer G. , Jiang J. S. , Bader S. D.
Published: May 2003

By tuning the incidence angle of hard, circularly polarized x-rays with respect to the sample surface, we are able to independently probe surface and bulk magnetic states in a Fe(35 Å)[Gd(50 Å)/Fe(35 Å)]15 ferrimagnetic multilayer by magnetic circular dichroism (MCD). We show that a twisted magnetic state nucleates at the surface of the multilayer at T≈0.7 Tcomp, where Tcomp is the ferrimagnetic compensation temperature. At nucleation, the twist penetrates ≈170 Å or two bilayers. Despite its theoretical prediction by LePage and Camley more than 15 years ago [J. G. LePage and R. E. Camley, Phys. Rev. Lett. 65, 1152 (1990); R. E. Camley, Phys. Rev. B 35, 3608 (1987)], this surface-twisted state has eluded direct experimental detection up to now. Its clear observation here demonstrates the power of grazing incidence, hard x-ray, MCD measurements for studies of magnetic phase transitions in layered structures.
Body centered cubic buffer layers for enhanced lateral grain growth of Co/Cu multilayers
Authors: Tsunoda Masakiyo , Takahashi Daisuke , Takahashi Migaku
Published: May 2003

The effect of buffer layers (BLs) on metallurgical microstructure and giant magnetoresistance of Co/Cu multilayers fabricated on them is discussed. The lateral grain size and the magnetoresistance (MR) ratio of multilayers are generally enlarged with changing the chemical composition of BLs toward a limiting concentration, within the range where the solid solution of body-centered-cubic (bcc) structure is formed. A guiding principle for material research for the BLs, which realize flat interfaces with large lateral grain size in the multilayers, is deduced from the correlation between the MR ratio of the multilayers and the surface energy of bcc BLs: the difference between the surface energy of BL (γS) and the interfacial energy (γSL) in Young–Dupré’s equation (cos θ=(γS−γSL)/γL) should agree with the surface energy of Co layer (γL), which is deposited first on the BL.
Quasi-stable microwave envelope pulse propagation in wide ferrite films
Authors: Zaspel C. E.
Published: May 2003

Magnetic microwave envelope pulses propagating in ferrite films can be modeled by a nonlinear Schrödinger equation. In a wide film, this process is modeled by a two-dimensional nonlinear Schrödinger equation, which exhibits instability and eventual collapse of an envelope pulse. However, it is also known that dissipation can stop the collapse, resulting in the formation of a quasi-stable spin-wave “bullet,” which eventually broadens and dissipates as it propagates down the film. In experiments, it has been shown that the bullet has an elliptical cross-section and it propagates for about 100 ns as a quasi-stable structure. Here, it is shown that the standard two-dimensional nonlinear Schrödinger model with dissipation will model these data.
Abrupt jumps in the metamagnetic transitions of orbitally ordered manganites
Authors: Maignan A. , Hardy V. , Martin C. , Hébert S. , Raveau B.
Published: May 2003

An experimental study of the magnetic properties of the Pr0.5Ca0.5Mn0.97Ga0.03O3 perovskite manganite is presented. The ac magnetic susceptibility measurements show that the low T orbitally and charge ordered state has been destabilized by the nonmagnetic impurity substituted for Mn. In this compound, at 2.5 K, well-defined, sharp steps on the field-dependent magnetization curves are observed. This unusual metamagnetic transition is found to be sensitive to thermal cycling. The latter induces a training effect for the transition, which strongly supports the proposed martensitic-like physics of some phase-separated manganites.
Crystal and magnetic structure of NdBaCo2O5+δ: Spin states in a perovskite-derived, mixed-valent cobaltite
Authors: Mitchell J. F. , Burley Jonathan , Short Simine
Published: May 2003

We report results of neutron powder diffraction studies on the crystallographic and magnetic structures of the compounds NdBaCo2O5+δ (δ=0.0, 0.5). Long-range antiferromagnetic order is found for the δ=0.0 compound, but no evidence of long-range charge-ordering is observed. The δ=0.5 compound shows poor long-range magnetic order, and the absence of such magnetic order is speculated to result from the particular ordered defect crystal structure of this material.
Anomalous Hall effect and magnetoresistance in Nd1−xSrxMnO3 single crystals
Authors: Kuwahara H. , Kawasaki R. , Hirobe Y. , Kodama S. , Kakishima A.
Published: May 2003

We have investigated Hall-effect and magnetotransport properties of Nd-based manganite crystals with controlled band filling. We have determined normal (RH) and anomalous (RS) Hall coefficients as a function of temperature in the ferromagnetic metallic crystal. The obtained effective carrier number (1/eRH) is about 1.0 hole/Mn site, which does not depend on temperature and nominal hole concentration. We have also found magnetoresistance (MR) in the over-doped samples showing various electronic, magnetic, and orbital structures. In C-type antiferromagnetic insulator (0.63⩽x), the ρ−T curve below 45 K is well explained by the variable-range hopping (VRH) mechanism. A large negative MR, which is increased with decreasing temperature, was observed in VRH region. The localization length from the characteristic temperature of VRH increases with magnetic field, which indicates that application of magnetic field induces a reduction of energy gap from EF to the mobility edge by the Zeeman shift.
Ordering phenomena and transport properties of Bi1/2Sr1/2MnO3 single crystals
Authors: Hejtmánek J. , Knı́žek K. , Jirák Z. , Hervieu M. , Martin C. , Nevřiva M. , Beran P.
Published: May 2003

Measurements of the electrical and thermal conductivities, thermopower, and paramagnetic susceptibility have been performed on single-crystal samples of Bi1/2Sr1/2MnO3, complemented with the x-ray powder diffraction data. A pronounced hysteretic behavior, observed below the cubic-to-orthorhombic transition at Tcrit=535 K, is related to the onset of long-range charge order (CO) at TCO=450 K and its further evolution down to about 330 K. The diffraction data suggest that the charge-ordered state is formed by Zener pairs, represented by Mn4+ dimers linked by one extra eg electron, and is possibly stabilized by cooperative Bi,Sr displacements. An extremely low thermal conductivity is observed down to the lowest temperatures, without any recovery at the antiferromagnetic ordering temperature TN=150 K. Such behavior points to a presence of strong scatterers of phonons. Their possible origin can be linked to “optical-like” oscillations that are associated with fluctuating charges within the Zener pairs.
Magnetic ordering in ultrathin cobalt film covered by an overlayer of noble metals
Authors: Kisielewski M. , Maziewski A. , Kurant Z. , Tekielak M. , Wawro A. , Baczewski L. T.
Published: May 2003

The spatial distribution of magnetic properties studied by polar Kerr-effect-based magnetometry are carried out on an ultrathin cobalt wedge covered with a silver wedge whose slopes are perpendicular to each other and subsequently capped with a gold layer. The coercivity field was studied as a function of both cobalt thickness d and silver thickness h. A few monolayers of Ag were found to have a substantial influence on the coercivity field. A similar strong influence of silver coverage on the magnetic anisotropy field was observed. Domain structure evolution during magnetization reversal is investigated using an optical microscope. With an increase of the magnetic field, a magnetization reversal process occurs: first by domain nucleation and next by a domain wall movement towards the higher coercivity region of the sample. Changes of the fractal dimension of the domain wall as well as nucleation center density are investigated. A rapid increase of these parameters is observed while d increases towards the value of spin reorientation transition, which goes from easy-axis to easy-plane magnetization. Similar strong changes were observed while decreasing d to the lowest thickness available for observation. The problem discussed here, of tuning magnetic properties by silver–gold structure, is important from both a general physics and an application point of view, especially because of the possibilities for magnetic film patterning.
Structure and magnetic properties of electrodeposited, ferromagnetic, group 3-d element films grown onto GaAs (011) substrate
Authors: Scheck C. , Evans P. , Schad R. , Zangari G.
Published: May 2003

Ni, Co, and iron-rich FeNi films were grown onto n-GaAs (011) substrates using electrodeposition from metal sulfate solutions, at room temperature, with a current density of 3.5 mA/cm2 at a pH of 2.5. The structure of Ni film is found to be fcc with a (111) preferred orientation, whereas Co films show a mixed fcc and hcp structure that is confirmed by x-ray diffraction and transmission electron microscopy data. The structure of iron-rich (>90%) FeNi films remains unclear at the moment. The films show a well-defined, in-plane, uniaxial anisotropy with the easy axis along the [011] GaAs direction for Ni, and [011̄] GaAs direction for Co and FeNi films (i.e., anisotropy rotated by 90° compared to Ni). Co films maintain their anisotropy even for large thicknesses (>250 nm) and so does Ni (up to 90 nm). Surprisingly, thin Ni films exhibit a larger HK value (950 Oe) than what would be expected from a purely crystalline anisotropy. This effect is ascribed to internal stresses in the as-deposited films.
Micromagnetic study of side-writing phenomena using thin-film heads and Co–CoO metal-evaporated tape
Authors: Ogawa Kazushi , Miyauchi Teiichi , Ozue Tadashi
Published: May 2003

The recording process and the relationship between the side-written band and the pole shape of thin-film recording heads, which have an upper pole with a narrow track width and a trimmed lower pole, using Co–CoO, obliquely evaporated magnetic tape, have been investigated. In nonazimuth recording, the lower pole of the thin-film head on the trailing side is better than that on the leading side for generating a sharp-edged, side-writing band. In azimuth recording, the relationship between side-writing phenomena and the pole shape of a thin-film head is complicated, because the position recorded by the leading gap-field shifts across the track width from that recorded by the trailing gap-field due to the azimuth angle. The thin-film recording head with trapezoidal upper and lower poles to minimize the effect of the side-fringing field can generate a sharp-edged, side-writing band, particularly in azimuth recording, but it is critical that the lower pole be on the trailing side. The thin-film recording head, which has a trapezoidal upper pole on the leading side and a trapezoidal lower pole on the trailing side, is most effective in generating a sharp-edged, side-writing band.
The digital-recording performance of obliquely oriented metal-evaporated tape in the reverse direction
Authors: Kawashima Takashi , Kanemaki Youichi , Sato Takanori , Okawa Wataru , Okazaki Yutaka
Published: May 2003

We have investigated the signal-to-noise ratio (SNR) and the nonlinear transition shift (NLTS) properties of recording in both the forward and the reverse directions by using obliquely oriented metal-evaporated (ME) tape. The pulse width at 50% threshold of the reverse direction is 28% wider than that of the forward direction, but the SNR after equalization is almost the same by reducing linear recording density by 14% from that of the forward direction. It is possible, therefore, to use the high-density read/write performance of obliquely oriented ME tape in a linear tape system, which would yield a less-than 7% loss of total recording capacity.
J
-mixing linear theory for 3d–4f intermetallic compounds
Authors: Magnani N. , Carretta S. , Liviotti E. , Amoretti G.
Published: May 2003

The linear theory for the magnetic anisotropy of 3d–4f intermetallic compounds is generalized in order to account for the J-mixing effects. This is particularly useful for samarium-based alloys, since Sm3+ has a small spin-orbit gap between the fundamental and the first excited multiplets. The analytical formulas obtained from this technique are used to analyze the basal-plane anisotropy of Sm2Co17, for which the J mixing plays a crucial role, and the results are compared with exact numerical calculations.
Effect of hydrogen absorption on the mixed-valent compound CeRhIn
Authors: Malik S. K. , Kundaliya Darshan , Sathyamoorthy A. , Shashikala K. , Raj P. , Krishnamurthy V. V.
Published: May 2003

The mixed valent Ce-based compound, CeRhIn, is found to absorb hydrogen and form two distinct hydride phases, CeRhInHx with x=0.55 and 1.58. The x=0.55 hydride retains the hexagonal structure of the parent compound. The x=1.58 hydride also has the hexagonal phase but contains an orthorhombic phase as well in nearly equal proportions. The higher hydride is found to be relatively unstable and transforms to the x=0.55 phase in a short time. Magnetization studies reveal that Ce ions continue to be in a mixed valent state in the x=0.55 hydride. The susceptibility of the x=1.58 sample exhibits Curie–Weiss behavior between 40 and 330 K with μeff=2.25 μB and θP=−92 K indicating the formation of nearly trivalent Ce ions in this hydride phase. It is suggested that hydrogenation results in increased d-band occupancy of Rh, due to partial transfer of electrons from hydrogen. This, in turn, results in decreased hybridization between Ce 4f electrons and those on the neighboring atoms, and a consequent shift of the valence of Ce towards 3+.
Conductivity tensor imaging of the brain using diffusion-weighted magnetic resonance imaging
Authors: Sekino Masaki , Yamaguchi Kikuo , Iriguchi Norio , Ueno Shoogo
Published: May 2003

Conductivity tensor images of the rat brain were obtained by a method based on diffusion-weighted magnetic resonance imaging (MRI). Diffusion-weighted images were acquired by a 4.7 T MRI system with motion probing gradients (MPGs) applied in three directions. Conductivities in each MPG direction were calculated from the fast component of the apparent diffusion coefficient and the fraction of the fast component, and two-dimensional conductivity tensor was estimated. Regions of interest (ROIs) were selected in the cortex and the corpus callosum. The mean conductivities in each ROI were 0.014 S/m and 0.018 S/m, respectively. The corpus callosum exhibited higher conductivity anisotropy resulting from anisotropic tissue structures such as axons and dendrites.
Giant magnetoresistance properties of the La1−2xRxAxMnO3 (R=Nd, A=Ca) perovskites
Authors: Kundaliya Darshan C. , Tulapurkar A. A. , Shinde S. R. , Pinto R. , Yelon W. B. , Kulkarni R. G. , Malik S. K.
Published: May 2003

The effect of simultaneous substitution of Nd and Ca in the antiferromagnetic insulator, LaMnO3, is studied by x-ray diffraction, magnetoresistance, and magnetization measurements. X-ray powder diffraction patterns of La1−2xNdxCaxMnO3 polycrystalline bulk samples for x=0.2, 0.33, and 0.4 confirm the single-phase formation of orthorhombic perovskite structure (space group Pbnm). The unit cell volume decreases with increasing Nd/Ca substitution. Changes in the temperature dependence of resistivity from semiconducting to metallic, and an increase of the ferromagnetic transition temperature, are observed in this series with increasing x. For x=0.2, 0.33, and 0.4, the metal-insulator transition temperature (Tp) is 72, 140, and 155 K, respectively, and the magnetoresistance (MR) observed in this system in 2 T applied magnetic field around Tp is 35%, 99% and 65%, respectively. The MR of 99% for the x=0.33 sample is promising for practical device applications where MR at low fields is of special interest. The magnetic moment values, obtained from the magnetization data in the magnetically ordered state, agree reasonably well with the free ion Mn moments for all the samples.
Magnetic tunnel junctions with high magnetoresistance and small bias voltage dependence using epitaxial NiFe(111) ferromagnetic bottom electrodes
Authors: Yu Ji Hyung , Lee Hyuck Mo , Hayashi Masamitsu , Oogane Mikihiko , Daibou Tadaomi , Nakamura Hiroaki , Kubota Hitoshi , Ando Yasuo , Miyazaki Terunobu
Published: May 2003

Magnetic tunnel junctions (MTJs) were fabricated using an Al–O insulating layer prepared on an epitaxially grown Ni80Fe20 bottom electrode and on a polycrystalline Ni80Fe20 bottom electrode. Crystallographic orientations and surface morphology of the films were examined using x-ray diffraction and atomic force microscopy, respectively. The MTJ with an epitaxial bottom electrode showed a tunnel magnetoresistance (TMR) ratio of 51% after annealing at 250 °C. This value was about two times larger than that of the MTJ with a polycrystalline bottom electrode (27%). The applied bias voltage dependences of the TMR ratios were also much different. The Vhalf values of epitaxial and polycrystalline samples were about 750 and 400 mV, respectively.
Surface alloy formation of Co on Al surface: Molecular dynamics simulation
Authors: Kim Sang-Pil , Chung Yong-Chae , Lee Seung-Cheol , Lee Kwang-Ryeol , Lee Kyu-Hwan
Published: May 2003

Control of the interface structure of atomic scale multilayers is a fundamental issue to improve the performance of spin electronic devices. Deposition behavior of Co on Al surface at 300 K was investigated by molecular dynamics simulation. The deposited Co resulted in the formation of CoAl surface alloy regardless of the Al surface orientation. Structure of the surface alloy was dependent on the substrate orientation. Crystalline B2 structure was formed on Al (001) surface. On the contrary, amorphous mixed layers were evolved on Al (011) and (111) surfaces. In the case of Al (001) surface, 4 ML of the surface alloy were observed, which is consistent with the previous experimental observation. The present work shows that the formation of CoAl surface alloy should be considered even at the low substrate temperature and the low incident energy of deposited atoms.
Spin wave modes in submicron cylindrical dots
Authors: Gubbiotti G. , Carlotti G. , Zivieri R. , Nizzoli F. , Okuno T. , Shinjo T.
Published: May 2003

The dynamic properties of a squared array of cylindrical Ni81Fe19 dots with thickness L=50 nm, radius R=100 nm, and separation 2R have been investigated by Brillouin light scattering. The sample was prepared by means of electron-beam lithography and evaporation in ultrahigh vacuum. The lateral confinement of spin waves within each dot causes a marked discretization of the spin wave spectrum. Several discrete peaks were measured in the saturated state as a function of both the incidence angle of light and the applied magnetic field. The detected modes are classified as surface dipolar and bulk magnetostatic modes at frequencies higher and lower than the Kittel uniform mode, respectively.
Unusual electronic transport properties in La0.96−xNdxK0.04MnO3
Authors: Guo Yongquan , Roy Sujoy , Ali Naushad , Zhang Xinhui , Wäppling Roger
Published: May 2003

Polycrystalline La0.96−xNdxK0.04MnO3 has been studied by means of x-ray powder diffraction, dc magnetization, and electrical resistance measurement. La0.96−xNdxK0.04MnO3 initially crystallizes in a rhombohedral distorted perovskite structure. However, an orthorhombic structure is obtained with increasing Nd content more than 20%. Both the rhombohedral and the orthorhombic phases show ferromagnetic order. However, the compound shows a magnetic inhomogeneity behavior with increasing Nd content. With increasing Nd doping, the ferromagnetic order is significantly weakened, and the second magnetic transition occurs at a low temperature and its peak intensity enhances. The resistivity of these compounds also exhibits an imhomogeneity behavior. The rhombohedral phase shows a metal–insulator (MI) transition but the MI transition peak intensity is obviously weakened and broadens with increasing Nd content and a low temperature insulator state is observed in the orthorhombic phase. It is interesting that the second magnetoresistance ratio peak appears at low temperature. It might be due to Nd induced low temperature phase separation between the ferromagnetic metallic and antiferromagnetic insulating state.
Needle-probe techniques for local magnetic flux measurements
Authors: De Wulf Marc , Dupré Luc , Makaveev Dimitre , Melkebeek Jan
Published: May 2003

Numerical two-dimensional field investigations in the cross section of laminated nonoriented electrical steel sheet are performed in order to verify the possibilities and limitations of the two needle-probe technique for the measurement of local magnetic flux near the cutting edge. If one of the needles approaches the lamination edge or when inhomogeneities are present in the flux distribution along the strip width due to magnetic properties altered by the cutting procedure, then the signal from the needle probes no longer represents the flux through a rectangular surface under the needles because of E-field components perpendicular to the lamination surface. The flux calculated from the needles is compared to the actual flux passing through the rectangular surface under the needles and corresponding correction factors as a function of the needle position away from the cutting edge are computed. Depending on the positioning method, the needle probes can give an under- or overestimation of the actual flux. Corrections from 15% to 80% are necessary if distances of about the lamination thickness are considered. This work suggests an iterative numerical procedure for the interpretation of experimental data obtained from local flux needle-probe measurements.
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quantization of the conduction in Cu nanowires
Authors: Gillingham D. M. , Linington I. , Müller C. , Bland J. A. C.
Published: May 2003

We have investigated the quantum transport behavior of Cu nanowires created by bringing two macroscopic Cu wires into and out of contact at room temperature. We have observed quantum conductance with steps of both e2/h and 2e2/h. We conclude that the spin degeneracy can be broken in nonmagnetic Cu nanowires.
Phase transformation and magnetic moment in FePt nanoparticles
Authors: Ding Y. , Yamamuro S. , Farrell D. , Majetich S. A.
Published: May 2003

The phase transformation from fcc to L10 in FePt nanoparticles was investigated in both thick film samples and self-assembled arrays as a function of the annealing temperature, using transmission electron microscopy, x-ray diffraction, differential scanning calorimetry, and magnetometry. A significant fraction of the surfactant decomposes into gaseous products below 500 °C, removing the steric barrier between particle cores. This causes the particles to coalesce at the same annealing temperatures where the transformation to the high anisotropy phase occurs.
Observation of a flux closure state in NiFe/IrMn exchange biased rings
Authors: Guo Z. B. , Zheng Y. K. , Li K. B. , Liu Z. Y. , Luo P. , Shen Y. T. , Wu Y. H.
Published: May 2003

We have investigated the magnetic behaviors of the array of NiFe/IrMn rings, where a remarkably asymmetrical, kinked hysteresis loop has been observed in the sample. The kinked hysteresis loop has been attributed to the magnetization reversal, which starts from a single domain state to an opposite single domain state on one side of the loop, and takes place via the transition from a single domain state to a flux closure state and then into the opposite single domain state on the other side of the loop. This phenomenon is dramatically different from that of NiFe single layer rings.
Synthesis and magnetic behavior of SmCo5(1−x)Fex nanocomposite magnets
Authors: Chu Shaoyan , Majetich Sara A. , Huang Meiqing , Fingers Richard T.
Published: May 2003

SmCo 5(1−x) Fe x  (x=0.2, 0.4, 0.6, and 0.7) nanocomposites were synthesized by ball milling a mixture of SmCo5 and nanosize iron powders. Composites were made using different kinds of soft ferromagnetic phase nanoparticles, either α-Fe crystallized from amorphous iron generated by sonochemical decomposition of Fe(CO)5, or acicular metallic iron particles with an average length of 200 nm and average diameter of 18 nm. After milling the powder mixtures were compacted by hot isostatic pressing at 3000 psi for ∼5 min at a temperature of 530–570 °C. The compacted solids were magnetically characterized between 5 and 300 K. Hysteresis loop measurements and recoil measurements for the (SmCo5)0.8/acicular-Fe0.2 composite show stronger magnetic coupling when compared with the properties of (SmCo5)0.8/amorphous-Fe0.2, am-Fe coated SmCo5, and pure SmCo5 powders alone.