bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhancement of magneto-optical transverse electric–transverse magnetic mode conversion efficiency of (Cd,Mn)Te waveguide by graded-index clad layers
Authors: Debnath M. C. , Zayets V. , Ando K.
Published: May 2004

Graded-index clad layers with different thickness were used in (Cd,Mn)Te waveguide, and magneto-optical mode conversion was investigated as a function of the thickness of the graded-index layers. Magneto-optical mode conversion efficiency increased with the graded-index layer thickness, and high efficiency of 98%±2% was obtained for the waveguide with 4000- to 5000-Å-thick graded layers. The waveguide also showed low optical loss of 0.5 dB/cm and high magneto-optical figure-of-merit above 500 deg/dB/kG.
Domain-specific magnetization reversals on a Permalloy square ring array
Authors: Lee D. R. , Freeland J. W. , Srajer G. , Metlushko V. , You Chun-Yeol
Published: May 2004

We present domain-specific magnetization reversals extracted from soft x-ray resonant magnetic scattering measurements on a Permalloy square ring array. The extracted domain-specific hysteresis loops reveal that the magnetization of the domain parallel to the field is strongly pinned, while those of other domains rotate continuously. In comparison with the micromagnetic simulation, the hysteresis loop on the pinned domain indicates a possibility of the coexistence of the square rings with the vortex and onion states.
Mechanochemical synthesis of Co, Ni, Fe nanoparticles in polymer matrices
Authors: Rakhimov R. R. , Jackson E. M. , Hwang J. S. , Prokof’ev A. I. , Alexandrov I. A. , Karmilov A. Y. , Aleksandrov A. I.
Published: May 2004

We report on synthesis of Co, Ni, and Fe nanoparticles by the action of elastic wave pulses on solid phase sandwich type samples containing metal salt, reducing agent, polyethylene, and polyacrylamide. The formation of metal nanoparticles is evidenced by ferromagnetic resonance and scanning electron microscopy. The product yield for the nanoparticles formation has a threshold character with the pressure in the elastic wave pulse. The maximum amount of Co, Ni, and Fe nanoparticles is observed around 20 kbar of pressure in elastic wave pulses. The presence of polyacrylamide in reaction composites increases the stability of metal nanoparticles to oxidation by two orders of magnitude.
Substrate effects on the room-temperature ferromagnetism in Co-doped TiO2 thin films grown by pulsed laser deposition
Authors: Nguyen Hoa Hong , Prellier W. , Sakai Joe , Ruyter Antoine
Published: May 2004

Co:TiO 2 films were fabricated by laser ablation on Si, LaAlO3 (LAO), and SrTiO3 (STO) substrates from a ceramic target. Films on all types of substrates have Curie temperature (TC) above 400 K. All films are highly crystallized with different structures. While films on Si substrates are rutile, films on LAO and STO substrates are single phased anatase. Due to the different lattice mismatch, films grown under the same growth conditions on Si, LAO, and STO substrates have different saturation magnetization and coercivity. While Co atoms are mostly localized near the surface of the films, magnetic measurements suggested that the ferromagnetism unlikely originates from Co clusters.
Magnetization switching and thermal stability of CoCrPtB/CoDy composite perpendicular layer
Authors: Ren H. B. , Chong T. C. , Wang J. P.
Published: May 2004

In this article, the magnetization reversal process and thermal stability of perpendicular coupled film glass/Ti 40 nm/CoCrPtB 35 nm/CoDy 20 nm/Ti 4 nm were presented. The exchange coupling constant with Dy content near the compensated point is as high as 1.3 erg/cm2. The dependence of exchange coupling strength on the Dy content and the thickness of CoDy layer was investigated. The thermal stability of the coupled films showed an increase over 100%.
Influence of the FM/AFM interface morphology on the exchange coupling in epitaxial Co(001)/fct-Mn(001)
Authors: Kohlhepp J. T. , de Jonge W. J. M.
Published: May 2004

The Co thickness dependence of the exchange interaction between ferromagnetic (FM) fct-Co(001) and antiferromagnetic (AFM) fct-Mn(001) thin layers, epitaxially grown on Cu(001) single crystals, is studied. In the pseudomorphic Co growth regime, oscillations of the coercivity (HC) and the exchange bias (HE) with a Co atomic monolayer period are observed. These oscillations are explained by a biquadratic exchange interaction component at the FM/AFM interface which, in this thickness range, is modulated by the layer-by-layer growth mode of Co on Cu(001).
First-principles study on half-metallicity of disordered Co2(Cr1−xFex)Al
Authors: Miura Yoshio , Shirai Masafumi , Nagao Kazutaka
Published: May 2004

We have investigated theoretically the effects of atomic disorder on the electronic and magnetic structures of the full-Heusler alloy Co2(Cr1−xFex)Al using the first-principles density functional calculation with the Korringa–Kohn–Rostoker coherent-potential approximation. It was found that Co2(Cr0.6Fe0.4)Al preserves the high spin polarization even in the disordered B2 structure, where (Cr,Fe) and Al randomly occupy octahedral sites of the alloy. On the other hand, the disorder between Co and (Cr,Fe) considerably reduces the spin polarization. Furthermore, the total magnetic moment of Co2(Cr0.6Fe0.4)Al decreases with increasing disorder between Co and (Cr,Fe) due to the antiferromagnetic coupling of the antisite Cr with the ordinary site Cr. These results indicate that control of the disorder between Co and (Cr,Fe) is crucial in order to obtain highly spin polarized full-Heusler alloys Co2(Cr1−xFex)Al.
Orientational dependence of exchange anisotropy of Mn-Ir/Co-Fe epitaxial bilayers
Authors: Sato Takashi , Tsunoda Masakiyo , Takahashi Migaku
Published: May 2004

The exchange anisotropy of pseudo-single crystalline Mn-Ir/Co-Fe bilayers with different crystallographic orientations, such as (110), (001), and (111), was investigated. As a result, we found that the unidirectional anisotropy constant JK strongly depends on the crystallographic orientation, while the critical thickness of the antiferromagnetic layer dAFcr is similarly ∼3 nm. As a notable result, the JK of the (110)-epitaxial bilayer with dAF=4 nm shows extra large value of 0.73 erg/cm2. The magnetic anisotropy of the Mn-Ir layer determined from the saturation torque amplitude was 8.5×105 erg/cm3 for the (110) bilayer, 5.0×104 erg/cm3 for the (001) bilayer, and 103–104 erg/cm3 for (111) bilayer, respectively. From the correlation between the exchange anisotropy and the magnetic anisotropy of the Mn-Ir layer, we conclude that the domain wall model is inadequate to explain these experimental results and the single spin model can do it qualitatively, assuming that the interfacial exchange coupling energy differs in the respective crystallographic orientation.
Fabrication of nanoscale antidot arrays and magnetic observations using x-ray photoemission electron microscopy
Authors: Heyderman L. J. , Solak H. H. , Nolting F. , Quitmann C.
Published: May 2004

Antidot arrays in thin cobalt films have been fabricated with periods ranging from 2 μm down to 100 nm and with different size to separation ratios. The resulting magnetic domains were observed with a photoemission electron microscope using x-rays. For periods larger than 1 μm, we observe magnetic domain configurations which substantiate micromagnetic calculations found in the literature. At smaller periods the domain configuration changes dramatically resulting in chains of magnetic domains running parallel to the intrinsic hard axis.
Spin polarization of excitons in nonmagnetic quantum dots induced by a neighboring magnetic semiconductor quantum well
Authors: Lee S. , Park K. , Dobrowolska M. , Furdyna J. K.
Published: May 2004

Magneto-photoluminescence (PL) experiments were carried out on double layer structures consisting of self-assembled nonmagnetic CdSe quantum dots (QDs) and a ZnCdMnSe diluted magnetic semiconductors quantum well (QW), separated by a thin ZnSe barrier layer. We observe two clearly defined PL peaks in all samples, corresponding to CdSe QD and ZnCdMnSe QW layers, respectively. The PL signal was detected using circular polarization. The degree of PL polarization from CdSe QDs in the double layer structures was much larger than that observed in single layers of nonmagnetic CdSe QD system. The effect was systematically studied by examining intensities, energy shifts, and polarizations of the PL peaks. We discuss the observed behavior in terms of antiparallel spin interaction between excitons localized in the nonmagnetic QDs and in the magnetic QWs.
Magnetic domain investigation in Co/Cu/FeMn trilayers
Authors: Wang J. , Kuch W. , Offi F. , Chelaru L. I. , Kotsugi M. , Kirschner J.
Published: May 2004

The magnetic domain patterns of epitaxial single-crystalline Co/FeMn bilayers and Co/Cu/FeMn trilayers were investigated by magnetic circular dichroism domain imaging using photoelectron emission microscopy. The as-grown domain size increases continuously with increasing Cu layer thickness, which is attributed to the decrease of the interlayer exchange coupling between ferromagnetic Co and antiferromagnetic FeMn layers. Domain images of the Co layer acquired after applying different external magnetic fields show a decrease in coercivity with increasing Cu layer thickness, confirming the reduction of magnetic coupling energy with increasing Cu thickness.
Local magnetoresistance and ferromagnetic resonance measurements with a sliding probe contact
Authors: Meckenstock R. , Rastei M. V. , Bucher J. P.
Published: May 2004

Local magnetoresistance (MR) and ferromagnetic resonance (FMR) measurements on submicrometer Ni wires were performed by using an electrically conducting atomic force microscope tip as a sliding contact. It is found that large positive jumps in the MR curves across the full wires are due to the presence of domain walls related to different diameters of the wire. Directly at the same position of the sliding contact for the MR the magnetic characterization was performed by scanning, thermally modulated FMR. The anisotropy fields, in particular the ratio of the radial anisotropy and the shape anisotropy, change for the constricted portion of the Ni wire.
Electronic and magnetic properties of Fe1−xCuxPt
Authors: Willoughby S. D.
Published: May 2004

Electronic structure calculations have been performed for the disordered alloy series Fe1−xCuxPt using the layer Korringa–Kohn–Rostoker method. Total energies as a function of x have been calculated in order to yield the Gibbs free energy of mixing. From these data a pseudobinary phase diagram has been constructed predicting temperature dependent phase separation occuring below 450 K and alloying above this temperature. Ordering and alloying processes are discussed. The magnetocrystalline anisotropy has been calculated as a function of x to elucidate the effect of Cu additives on the magnetic properties of L10 FePt. These calculations show that the anisotropy falls smoothly with increasing Cu content. Results of these calculations are compared to available experimental data.
Neutron reflectivity on CoFe2O4 exchange springs for spin valve applications
Authors: O’Donovan K. V. , Borchers J. A. , Maat S. , Carey M. J. , Gurney B. A.
Published: May 2004

Insulating CoFe2O4 is a candidate for biasing ferromagnetic layers in spin valves because it does not shunt current. Ferrimagnetic CoFe2O4 pins the neighboring ferromagnetic layer via an exchange-spring mechanism. We have examined the field-dependent layer switching in a CoFe2O4/CoFe10 bilayer using back/front polarized neutron reflectometry. A magnetic twist is evident in intermediate fields and gradually collapses as the field is increased. However, the twist is confined mostly to the interface or to the magnetically hard CoFe2O4 layer. This result contrasts with the expectation that the magnetic twist should reside in the soft layer in the field region of magnetic reversibility.
Modeling of the magnetic behavior of γ-Fe2O3 nanoparticles mineralized in ferritin
Authors: Resnick Damon , Gilmore Keith , Idzerda Y. U. , Klem Michael , Smith Eric , Douglas Trevor
Published: May 2004

The temperature dependent initial magnetization of γ-Fe2O3 (maghemite) mineralized inside ferritin protein cages has been investigated with a vibrating sample magnetometer up to 8 T. The data are fit to different magnetic models to extract values of the magnetic moment of each cluster. It is found that the application of a simple Langevin model with a first and second order term in the susceptibility greatly enhances the quality of the fit to the data suggesting that the inclusion of crystalline anisotropy is important in extracting the magnetic moment of each core.
Magnetic tunnel junctions with L1-ordered FePt alloy electrodes
Authors: Moriyama T. , Mitani S. , Seki T. , Shima T. , Takanashi K. , Sakuma A.
Published: May 2004

Magnetic tunnel junctions (MTJs) with L10-ordered FePt alloy electrodes were prepared on MgO(110) substrates, and structure and magnetotransport properties of the MTJs have been investigated. Tunnel magnetoresistance (TMR) of 34% is observed at 77 K for a junction with the FePt alloy electrode in which the degree of chemical order S is estimated to be ∼0.7. From S dependence of TMR in the MTJs, it is suggested that the spin polarization of FePt alloy electrodes increases with chemical ordering, which is consistent with first principles band structure calculations.
Structural and magnetic studies of nanocomposite FePt-MgO films for perpendicular magnetic recording applications
Authors: Kang K. , Suzuki T. , Zhang Z. G. , Papusoi C.
Published: May 2004

Composite FePt–MgO films composed of L10 FePt nanograins were fabricated on glass substrates by annealing multilayer films of [FePt/MgO]3. Films with 2 nm FePt layer thickness that have Mr/Ms∼1.0 show a significantly improved (001) texture of L10 FePt with a narrow c axis texture dispersion resulting from insertion of 2 nm MgO layers between the FePt layers. Annealing the [FePt 2 nm/MgO 2 nm]3 film creates grains as small as 8.0 nm that confer a relatively high magnetic anisotropy constant Ku=5×106 erg/cc and thus fosters a high coercivity of approximately 10.0 kOe.
Spin-polarized photoemission spectroscopy of the MgO/Fe interface on GaAs(100)
Authors: Matthes F. , Tong L.-N. , Schneider C. M.
Published: May 2004

We studied the electronic band states at the Fe/MgO interface with spin-polarized photoemission using excitation energies between 35 and 60 eV. Epitaxial Fe films on GaAs(100) were covered with 0.5, 1, and 1.5 ML thick MgO films. The photoemission spectra revealed a spin-dependent attenuation for photoelectrons related to direct transitions from initial bulk Fe bands having minority or majority spin character.
Spin dynamics in ultrathin film structures with a network of misfit dislocations
Authors: Woltersdorf G. , Heinrich B. , Woltersdorf J. , Scholz R.
Published: May 2004

Using ferromagnetic resonance (FMR) and transmission electron microscopy we studied the structural and magnetic properties of lattice mismatched magnetic ultrathin multilayers of the system Au/Fe/Au/Pd/Fe(001) prepared on GaAs(001). We observed a correlation between the periodic lattice irregularities due to the misfit accommodation processes and the resulting magnetic properties of the multilayer system: In samples with a network of misfit dislocations the FMR measurements have shown that a significant part of the damping is extrinsic and caused by two magnon scattering. The angular dependence of the FMR linewidth reflects the in-plane symmetry of the dislocation arrangement.
Studies of two- and three-dimensional ZnO:Co structures through different synthetic routes
Authors: Pakhomov A. B. , Roberts B. K. , Tuan A. , Shutthanandan V. , McCready D. , Thevuthasan S. , Chambers S. A. , Krishnan Kannan M.
Published: May 2004

Multilayers of Co and ZnO, with nominal layer thicknesses on the atomic scale with up to 25 bilayers, were deposited by ion beam sputtering on silicon and glass substrates at ambient temperature. Thick epitaxial CoxZn1−xO films on Al2O3(012) substrates were grown by metalorganic chemical vapor deposition using a liquid precursor delivery system. All were co-doped with Al. Comparative analysis of magnetization, resistivity, and magnetoresistance measurements, performed in the temperature range 2.5–300 K, is presented. At small thickness of Co layers in the multilayer samples, these structures are diluted magnetic semiconductor (DMS) superlattices, with properties close to the epitaxial films. A crossover from DMS to discontinuous magnetic metal/semiconductor multilayers is observed with increasing metal content in the multilayers. This leads to changes in conduction mechanisms, with increasing contribution of quasithree-dimensional or quasitwo-dimensional intergranular hopping, and superparamagnetism.
Magnetic properties of ultrathin Fe3O4 on GaAs(100)
Authors: Lu Y. X. , Claydon J. S. , Xu Y. B. , Schofield D. M. , Thompson S. M.
Published: May 2004

The evolution of magnetic phase and anisotropy of epitaxial half-metallic Fe3O4 ultrathin films on GaAs(100) has been studied using magneto-optical Kerr effect (MOKE) measurements. While no magnetic signal was detected below 1 nm, the film shows a superparamagnetic response at a thickness of around 1.6 nm. Ferromagnetic MOKE loops with strong in-plane anisotropies were observed above 2.0 nm. The films show a magnetic uniaxial anisotropy in a thickness range of about 2.0–6.0 nm with the easy axis along the [01̄1] direction.
Epitaxial diodes of a half-metallic ferromagnet on an oxide semiconductor
Authors: Postma F. M. , Ramaneti R. , Banerjee T. , Gokcan H. , Haq E. , Blank D. H. A. , Jansen R. , Lodder J. C.
Published: May 2004

We report on the fabrication and electrical characterization of epitaxial Schottky diodes of a half-metallic ferromagnet on an oxide semiconductor. La0.67Sr0.33MnO3 thin films are grown by pulsed laser deposition on niobium-doped SrTiO3 semiconductor substrates with two doping concentrations and a TiO2 surface termination. The current across the diodes is dominated by thermionic emission and shows high rectification and low reverse bias leakage. At room temperature, the Schottky barrier height is 0.95 eV (0.65 eV) and the ideality factor is 1.08 (1.18) for the diodes with a low (high) doped semiconductor. With decreasing temperature the Schottky barrier height decreases and the ideality factor increases.
Dynamic Jahn–Teller effect in the near-infrared spectra of Fe2+ ions in ZnS
Authors: Zhou Yi-Yang
Published: May 2004

The fine-structure splittings, the magnetic specific heat and susceptibility, and the Jahn–Teller couplings are performed for Fe2+ ions in ZnS by taking into account the cubic crystal–field interaction, the spin–orbit coupling associated with not only the central-metal ions but also the ligands, and the Jahn–Teller coupling of the orbital manifolds of Fe2+ ions with overtones of E and T2 symmetry phonons of ligands. The results are in good agreement with the experimental observations. Some theoretical Jahn–Teller splittings presented are in need of further theoretical and experimental studies. A significant charge transfer in ZnS:Fe2+ is found.
Effects of atomic ordering on the Curie temperature of FePd L1 type alloys
Authors: Wang Lisha , Fan Zhaohui , Roy Anup G. , Laughlin David E.
Published: May 2004

In this work, we systematically studied the effects of atomic ordering on the Curie temperature of FePd alloys in the composition region of L10 phase. The Curie temperatures of the bulk Fe–50 at. % Pd, Fe–55 at. % Pd, Fe–60 at. % Pd alloys for both ordered and disordered structures have been measured. Unlike the Curie temperatures reported in the literature, atomic ordering decreases the Curie temperature by about 30 K for each of the compositions. Using a molecular field model, we calculated the Curie temperatures of Fe–Pd alloys. The simulation results show that the difference of the Curie temperature of the disordered and ordered states arises from the change of the nearest-neighbor occupation probabilities and the change of atomic interactions.
Black soliton formation from phase-adjusted spin wave packets
Authors: Serga A. A. , Andre A. , Demokritov S. O. , Hillebrands B. , Slavin A. N.
Published: May 2004

Formation of dark and black spin wave envelope solitons was achieved in a magnetic film waveguide by using as an input signal a sequence of two microwave wave packets with a controlled time delay and phase shift between them. A nonlinear phase shift acquired in the process of dark soliton excitation was detected and measured. Generation of a single black soliton with a 180° phase jump was realized when the excitation-related nonlinear phase shift was compensated for by the adjustment of the relative phase in the sequence of the input wave packets.
Synthesis and phase transition of self-assembled FePd and FePdPt nanoparticles
Authors: Kang Shishou , Jia Zhiyong , Nikles David E. , Harrell J. W.
Published: May 2004

Fe 54 Pd 46 nanoparticles were prepared by the simultaneous chemical reduction of palladium acetylacetonate and iron chloride. The particle size can be tunable from 2 to 10 nm by controlling the amount of surfactants. Similarly, Fe50PdxPt50−x (x=8, 15, 25) nanoparticles were prepared by the simultaneous reduction of palladium acetylacetonate, platinum acetylacetonate, and iron chloride. The average diameter for the Fe50PdxPt50−x particles was always 3.5 nm and independent of the amount of surfactants. Films of the particles were cast onto silicon wafers from hydrocarbon dispersion. The coercivity of Fe54Pd46 nanoparticles increases with annealing temperature up to 550 °C, indicating fcc to fct phase transition. After further increasing the annealing temperature, the coercivity of the Fe54Pd46 nanoparticles decreased, suggesting the formation of a soft magnetic phase. This new phase (Fe3Pd) was confirmed from x-ray diffraction measurements. For Fe50PdxPt50−x nanoparticles, the coercivity increases to more than 10 kOe with annealing temperature up to 650 °C (x=8). With increasing Pd content, the coercivity of the Fe50PdxPt50−x nanoparticles decreased, as expected since the anisotropy energy of bulk FePd material is only one third of that of bulk FePt.
Using circularly polarized soft x rays to probe antiferromagnetically correlated Co/Cu multilayers
Authors: Stadler S. , Idzerda Y. U. , Dvorak J. , Borchers J. A.
Published: May 2004

X-ray resonant magnetic scattering was used to study the antiferromagnetic correlation between weakly coupled Co layers in a [Co(6 nm)|Cu(6 nm)]20 multilayer. Half-order peaks were observed for standard specular θ–2θ scans with the energy of the incident x rays tuned to the Co L3 absorption edge. Three characteristic lengths were extracted from fits to the multicomponent 3/2-order diffuse spectrum: average correlated domain size, average correlated domain wall thickness, and average in-plane structural correlation length.
Influence of the Mn interstitial on the magnetic and transport properties of (Ga,Mn)As
Authors: Wang K. Y. , Edmonds K. W. , Campion R. P. , Gallagher B. L. , Farley N. R. S. , Foxon C. T. , Sawicki M. , Boguslawski P. , Dietl T.
Published: May 2004

We report on measurements of the hole density, ferromagnetic transition temperature TC, and magnetization in a series of as-grown and annealed (Ga,Mn)As samples. Estimating the fraction of incorporated Mn occupying interstitial and substitutional sites allows a direct comparison of the predictions of mean field theory with experiment, and a determination of the magnetic moment per substitutional Mn. The saturation of TC at high Mn concentration is consistent with the mean field prediction. The estimated magnetic moment per Mn is close to the expected 5μB for all samples studied if an antiferromagnetic coupling between interstitial and substitutional Mn is assumed.
Systematic control of high-speed damping in doped/undoped Ni81Fe19 (50 nm) bilayer thin films
Authors: Song Hajung , Cheng Lili , Bailey William E.
Published: May 2004

We show that the relaxation of GHz precessional motion in soft ferromagnetic thin films can be controlled through the inhomogeneous placement of dopants. Bilayers of doped and undoped permalloy (Ni81Fe19), Ni81Fe19/Ni81Fe19:Tb (Tb 5%), varied in net relaxation rate λ according to the thickness fraction of the doped layer. The behavior is roughly independent of total bilayer thickness and deposition order in the range studied (50–100 nm). The technique provides a means to control the high-speed response of magnetoelectronic devices with limited effect on signal, as magnetically active dopants can be separated from the interfaces relevant for spin transport.
Photoemission electron microscopy and atomic force microscopy of epitaxial iron oxide films on α-Al2O3(0001)
Authors: Schedin F. , Leung L. , Muryn C. A. , Hill E. W. , Scholl A. , Thornton G.
Published: May 2004

The morphology and stoichiometry of a model iron oxide magnetic tunneling junction heterostructure has been investigated using x-ray photoemission electron microscopy (X-PEEM) and atomic force microscopy (AFM). AFM data evidence islands of width a few μ m and height 10 nm. X-PEEM data show that two types of iron oxide are present, the islands being Fe3O4(111) and the terraces α-Fe2O3(0001). The Fe3O4(111) islands appear as dark areas in X-PEEM, which is attributed to difference in work function and/or mean free path of the two iron oxide phases.
Frequency domain studies of CoZr continuous thin films and FeNi wires using coplanar transmission lines
Authors: Kerekes M. , Viegas A. D. C. , Stanescu D. , Ebels U. , Xavier P. , Suran G.
Published: May 2004

A ferromagnetic resonance measurement technique based on coplanar waveguides is presented. This technique is adapted to measure the high frequency response of metallic magnetic materials in the frequency domain up to 20 GHz and is complementary to the inductive time-domain method. Upon scanning the frequency at constant field, for varying field angle, the frequency-field dispersion as well as the frequency linewidth can be obtained. The absorption spectra for a Co90Zr10 continuous film and for Fe20Ni80 wires of different thickness are presented. For the latter an increase in the linewidth and damping parameter is observed with increasing wire thickness.
Magnetic and recording properties of Co/Pd islands on prepatterned substrates
Authors: Hu G. , Thomson T. , Albrecht M. , Best M. E. , Terris B. D. , Rettner C. T. , Raoux S. , McClelland G. M. , Hart M. W.
Published: May 2004

Magnetically isolated single domain islands with perpendicular anisotropy have been prepared by depositing Co/Pd multilayer films on prepatterned sub-50 nm SiO2/Si islands. The island arrays were fabricated by both direct write electron beam lithography and nanoimprinting. Nanoimprinting allows the creation of large area, 4 mm×4 mm, samples appropriate for characterization by conventional measurement techniques. Magnetic force microscopy and vibrating sample magnetometry showed that the reversal behavior of the patterned islands is quite different from that of the continuous films with a large increase in both switching field and switching field distribution. Recording on island arrays with a periodicity of 100 nm, produced from prepatterned substrates, was demonstrated using a quasistatic tester.
Magnetic and structural studies of the Verwey transition in Fe3−δO4 nanoparticles
Authors: Yang J. B. , Zhou X. D. , Yelon W. B. , James W. J. , Cai Q. , Gopalakrishnan K. V. , Malik S. K. , Sun X. C. , Nikles D. E.
Published: May 2004

Stoichiometric and cation-deficient magnetite Fe3−δO4 and γ-Fe2O3 particles have been prepared by the chemical method followed by heat treatments. The magnetic and structural properties were studied using neutron diffraction, magnetic measurements, and Mössbauer spectroscopy. Charge ordering of Fe3+ and Fe2+ and lattice distortion are not observed below the Verwey transition temperature in the stoichiometric and cation-deficient magnetite. It is found that the lattice parameter and the Verwey transition temperature decrease as the cation vacancy increases. The Verwey transition almost disappears in the Fe3−δO4 sample with δ=0.066. Mössbauer spectra show that the ratio of Fe3+/Fe2.5+ in stoichiometric magnetite can be modified by heat treatment. The Fe vacancies on the B sites change the nature of the Verwey transition. No cation vacancy ordering is observed for γ-Fe2O3, due to the small amount of cation vacancies in the compound.
Growth effects (rotation rate) on the characteristics of bismuth substituted lutetium iron garnets
Authors: Rojas R. , Krafft C. , Nistor I. , Zhang D. , Mayergoyz I. D.
Published: May 2004

The effect of substrate rotation rate on the characteristics of liquid phase epitaxy grown Bi:LuGaFe garnets is described. This parameter can be used not only to change the growth rate and lattice mismatch, but also to change other characteristics such as Faraday rotation rate and index of refraction of the resulting film. The results show that increasing the substrate rotation rate can also increase: the growth rate by a factor of 2, Faraday effect by up to 50%, and index of refraction by 1.6×10−2, and can decrease lattice mismatch by an order of magnitude.
Electron holography of Fe-based nanocrystalline magnetic materials (invited)
Authors: Shindo Daisuke , Park Young-Gil , Gao Youhui , Park Hyun Soon
Published: May 2004

Magnetic domain structures of nanocrystalline magnetic materials were extensively investigated by electron holography with a change in temperature or magnetic field applied. In both soft and hard magnetic materials, the distribution of lines of magnetic flux clarified in situ by electron holography was found to correspond well to their magnetic properties. An attempt to produce a strong magnetic field using a sharp needle made of a permanent magnet, whose movement is controlled by piezo drives has been presented. This article demonstrates that the attempt is promising to investigate the magnetization process of hard magnetic materials by electron holography.
Magnetic coupling in La–Ca–Mn–O/La–Sr–Co–O/La–Ca–Mn–O sandwiches
Authors: Zhao Kun , Zhang Li , Li Ho , Wong H. K.
Published: May 2004

La 0.67 Ca 0.33 MnO 3 / La 0.67 Sr 0.33 CoO 3 / La 0.67 Ca 0.33 MnO 3 (LCMO/LSCO/LCMO) trilayers are fabricated on single-crystal substrates NdGaO3 (110) and the interlayer coupling are investigated. The magnetoresistance (MR) is dependent on spacer thickness and the peak value of MR dramatically decreases when the LSCO layer is thick enough because of shorting by the LSCO layer. Compared with the LCMO single layer, trilayer films showed the enhanced metal–semiconductor transition temperature of LCMO layers. The magnetic coercivity HC shows a nonmonotonic behavior with changing the spacer layer thickness and the waist-like hysteresis indicates that there is an indirect exchange coupling between the top and bottom LCMO layers across the spacer layer.
Nuclear quadrupole resonance and nuclear magnetic resonance studies of heavy fermion Ce1−xRxRhIn5 (R=Y,La)
Authors: Iwamoto Y. , Ueda K. , Kohara T. , Kohori Y. , Zapf V. S. , Sayles T. A. , Maple M. B. , Pagliuso P. G. , Moreno N. O. , Sarrao J. L.
Published: May 2004

The results of In115 nuclear quadrupole resonance (NQR) measurements on Ce1−xYxRhIn5 and Ce1−xLaxRhIn5 are reported. The observed NQR frequency at an In(1) site varies linearly with lattice parameter and dopant concentration for Y- and La-substituted systems. For the samples of LaMIn5 (M=Co,Rh,Ir) and YRhIn5, T1−1’s are proportional to the temperature, which means the system is in the Fermi liquid state in a wide temperature range. On the other hand, in Ce0.1La0.9RhIn5 and Ce0.5Y0.5RhIn5, T1−1’s have power-law temperature dependences (close to T1/4), which are expected to be from non-Fermi-liquid behavior near a quantum critical point. For Ce0.5La0.5RhIn5 and Ce0.25La0.75RhIn5, T1−1’s stay temperature independent below 4.2 K and the observed linewidths of In115 become broader with decreasing temperature. This behavior may be associated with a short-range magnetic order of Ce expected from the macroscopic measurements.
Fast latching type optical switch
Authors: Didosyan Yuri S. , Hauser Hans , Reider Georg A. , Toriser Walter
Published: May 2004

A magneto-optical latching switch with a yttrium orthoferrite optical rotator is described. The crystal remains in a given magnetic state for unlimited duration without energy supply. The response time is about 20 ns and the aperture of the optical rotator is 350 μm.
Averaging technique for the analysis of magnetization relaxations
Authors: Bertotti G. , Mayergoyz I. , Serpico C.
Published: May 2004

The averaging technique is developed for the analysis of magnetization relaxations to equilibrium. This technique leads to the first-order separable differential equation for the free energy that can be used instead of the Landau–Lifshitz equation to study magnetization relaxations. This free energy differential equation is applied to the analysis of “ringing” in the case of precessional switching and the accuracy of the averaging technique is validated through the comparison with numerical solutions of the Landau–Lifshitz equation.
Anisotropy field distribution of partially ordered FePt nanoparticles
Authors: Sakuma H. , Taniyama T. , Kitamoto Y. , Yamazaki Y. , Nishio H. , Yamamoto H.
Published: May 2004

The anisotropy field distribution of various Fe–Pt nanoparticle samples with a partially ordered structure is investigated up to 90 kOe using the Flanders and Shtrikman’s method. The distribution of the Fe–Pt samples with a low order parameter of 0.66 or a nonequiatomic composition of Fe58Pt42 or Fe41Pt59 is broader than that of the Fe–Pt sample with an almost full order parameter of 0.96 at 5 K. The broad distribution is attributed to an inhomogeneous atomic arrangement with L10, L12, and disordered structures. The distribution measured at 300 K, on the other hand, is quite different from that at 5 K, indicating a significant thermal effect on the magnetization reversal.
Plausibility of antiferromagnetism in and around the vortex cores of Bi2212 and Tl2223
Authors: Lee J. , Prudchenko K. , Ruiz E. J. , Boekema C.
Published: May 2004

Muon-spin-resonance (μSR) vortex data of underdoped Bi2Sr2CaCu2Ox (Bi2212) and Tl2Ba2Ca2Cu3Oy (Tl2223) have been analyzed to search for antiferromagnetism in and around their vortex cores. The temperature-dependent magnetic field distributions in the vortex states are obtained by maximum-entropy μSR analysis. The grain-boundary signal is well fitted by a narrow Gaussian. For the vortex μSR signals, deviations from a Gaussian are observed well below Tc, especially at the high-field side associated with the vortex core. For both Bi2212 and Tl2223, Lorentzians fit the μSR vortex signals better below 0.4 Tc, indicating that extra magnetic fields occur near and in the vortex cores. An estimated Neél temperature is 0.4 Tc. Our vortex-μSR results are compared with those of RBa2Cu3O7−δ (R=Eu,Ho,Y). The relevance to a potential magnetic origin of cuprate superconductivity is discussed.
Hysteretic properties of epitaxial Fe/GaAs(100) ultrathin films under external uniaxial strain
Authors: Ahmad E. , Will I. G. , Lu Y. X. , Xu Y. B. , Morley N. A. , Gibbs M. R. J.
Published: May 2004

We report an experimental and theoretical study of the influence of uniaxial strain on the magnetic properties of Fe/GaAs(100) ultrathin film systems. In-plane tensile strains have been applied along different directions relative to the intrinsic uniaxial magnetic anisotropy axes of the Fe/GaAs(100) films, and the M-H loops were measured. In an attempt to interpret the observed behavior, a phenomenological energy model is considered, which incorporates both intrinsic and strain-induced uniaxial anisotropy terms. Theoretical magnetization reversal loops were obtained from the model, assuming that the magnetoelastic coefficients of the thin films are same as the bulk bcc Fe. The model qualitatively predicted the magnetization loops for all the experimental data, assuming a positive uniaxial anisotropy constant.
Effect of f-band dispersion on the magnetic properties of periodic Anderson lattice model
Authors: Shik H. Y. , Wang Y. Q. , Gubernatis J. E. , Lin H. Q.
Published: May 2004

Using the exact diagonalization and constrained path Monte Carlo methods, we investigate the effects of impurity f-band dispersion on the magnetic properties of Periodic Anderson lattice model in one and two dimensions (square lattice). The model is defined by the Hamiltonian: H=td ∑ i,j,σ(diσ†djσ+H.c.)+tf ∑ i,j,σ(fiσ†fjσ+H.c.)+V ∑ i,σ(diσ†fiσ+H.c.)+U ∑ ini↑fni↓f+μf ∑ i,σniσf.We fix td=−1 be the energy scale. When tf=0, previous studies [Phy. Rev. B 63, 184 428 (2001)] showed that the system could be in partially saturated ferromagnet phase for low concentrations of conduction electrons. In the noninteracting limit, a nonzero tf changes the f-band from being flat to dispersive. By calculating the ground state energy as a function of total spin S we demonstrate that the inclusion of f-band dispersion (tf≠0) could destabilize the ferromagnetic phase depending on values of tf and μf. Both tf and μf have profound effects on the shape of the fermi surface and hence on the magnetic properties of the system, exemplified by the calculation of the fourier transform of the spin–spin correlation functions. Antiferromagnetic correlation is induced by the f-band dispersion.
Possible indication of interlayer exchange coupling in GaMnAs/GaAs ferromagnetic semiconductor superlattices
Authors: Chung S. J. , Lee S. , Park I. W. , Liu X. , Furdyna J. K.
Published: May 2004

We studied the effect of free carriers in the nonmagnetic spacer layer on the magnetic properties of GaMnAs/GaAs superlattice (SL) systems. One of the SLs contained GaAs layers doped with Be (which acts as a p-type dopant), while the GaAs layers of the other SL were undoped. While the Be-doped SL exhibited relatively robust temperature dependence of remanent magnetization and large coercivity, the undoped SL showed a fast decrease of remanent magnetization with the temperature and rather small coercivity. We propose that the observed hardness of magnetization in the SL with Be-doped GaAs layers is related to interlayer coupling introduced by doping of the nonmagnetic layers.
SnO
2
doped with Mn, Fe or Co: Room temperature dilute magnetic semiconductors
Authors: Fitzgerald C. B. , Venkatesan M. , Douvalis A. P. , Huber S. , Coey J. M. D. , Bakas T.
Published: May 2004

Room temperature ferromagnetism is found in (Sn1−xMx)O2 (M=Mn, Fe, Co, x=0.05) ceramics where x-ray diffraction confirms the formation of a rutile-structure phase. Room temperature saturation magnetization of 0.2 and 1.8 Am2 kg−1 for (Sn0.95Mn0.05)O2 and (Sn0.95Fe0.05)O2, respectively, corresponds to a moment of 0.11 or 0.95 μB per Mn or Fe atom. The Curie temperatures are 340 and 360 K, respectively. The magnetization cannot be attributed to any identified impurity phase. Fe57 Mössbauer spectra of the Fe-doped SnO2 samples, recorded at room temperature and 16 K, show that about 85% of the iron is in a magnetically ordered high spin Fe3+ state, the remainder being paramagnetic.
Time and layer resolved magnetic domain imagig of FeNi/Cu/Co trilayers using x-ray photoelectron emission microscopy (invited)
Authors: Vogel J. , Kuch W. , Camarero J. , Fukumoto K. , Pennec Y. , Bonfim M. , Pizzini S. , Petroff F. , Fontaine A. , Kirschner J.
Published: May 2004

We have performed magnetic domain imaging with spatial, temporal, and layer resolution using x-ray photoelectron emission microscopy. The element selectivity of x-ray magnetic circular dichroism allows the magnetization dynamics of the different magnetic layers in spin-valve-like FeNi/Cu/Co trilayers to be studied separately, using the time structure of synchrotron radiation. The unique possibilities of this technique have been used to study the influence of the intrinsic magnetic properties of the different layers on the magnetization dynamics and the interlayer magnetic coupling.
Characterization of spinel iron-oxide nanocrystals grown on Fe whiskers
Authors: Yi W. , MoberlyChan W. , Narayanamurti V. , Hu Y. F. , Li Q. , Kaya I. , Burns M. , Chen D. M.
Published: May 2004

Passive iron-oxide nanocrystals are grown on Fe(100) and Fe(110) facets of single-crystal Fe whiskers. Transmission electron microscopy and electron diffraction characterize the oxide spinel structure and their epitaxial growth on Fe whiskers. Iron-oxide nanocrystals grown on Fe(100) facets have sizes close to that of the single magnetic domain Fe3O4 particles, which is supported by our preliminary magnetic force microscopy measurement at room temperature.
Magnetic behaviors of antiferromagnetic films under external field
Authors: Wang Huai-Yu , Huang Chen , Qian Meichun , Wang En-Ge
Published: May 2004

In this paper, we deal with antiferromagnetic (AFM) films using the many-body Green’s function theory under random phase approximation (RPA). This is the first time to be able to calculate all three components of the magnetization of AFM systems simultaneously under RPA. The magnetization of AFM films is not so easily affected by external fields as FM films and the magnetic behavior is rather different from FM films. When an external field Bz is applied along the z direction, the parallel susceptibility χ∥ is zero at 0 K, and then increases with temperature until Néel point TN. If a field along the x-direction Bx is applied, the perpendicular susceptibility can be approximately expressed as χ⊥=1/2γ|J|, which is a temperature-independent constant, where γ is the nearest neighbor and J is the exchange interaction. In this case the z-component magnetization is nonzero above TN. This is because the x-component magnetizations of both sublattices are not zero and the AFM exchange should play a role, which results in the antiparallel z-component magnetizations of the two sublattices.
Characterization and magnetic properties of core/shell structured Fe/Au nanoparticles
Authors: Cho Sung-Jin , Kauzlarich Susan M. , Olamit Justin , Liu Kai , Grandjean Fernande , Rebbouh Leila , Long Gary J.
Published: May 2004

Au-coated Fe nanoparticles have been prepared by using a reverse micelle method through reduction of an aqueous solution. Characterizations have been carried out over time to probe the oxidation of Fe. Immediately after synthesis, the samples exhibit metallic conduction and a negative magnetoresistance, consistent with the presence of α-Fe. The temperature dependence of magnetization displays a maximum at a blocking temperature of around 150 K. After a period of 1 month, the samples exhibit insulating behavior, indicating the oxidation of the Fe core. Mössbauer spectroscopy indicates the presence of an α-Fe component and a broad distribution of local environments.
Effect of the kinds of ferromagnetic layers on exchange coupling strength in IrMn/FM films
Authors: Jung H. S. , Traistaru O. , Fujiwara H.
Published: May 2004

Antiferromagnet (AFM)/ferromagnet (FM) exchange coupling in polycrystalline IrMn/FM films with the saturation magnetization Ms=200–1910 emu/cm3 has been investigated through observation of both exchange-bias field and coercivity increase. It was found that there is some critical Ms below which the exchange coupling effect becomes almost zero. A critical FM thickness has also been found for the exchange coupling effect to appear, below which FM layers exhibit M-H curves characteristic of superparamagnetism, which increases exponentially with decreasing Ms. It suggests that frustrated FM spins caused by the exchange coupling with the AFM layer are responsible for these phenomena.
Three-dimensional magnetophotonic crystals based on artificial opals
Authors: Baryshev A. V. , Kodama T. , Nishimura K. , Uchida H. , Inoue M.
Published: May 2004

We fabricated and experimentally investigated three-dimensional magnetophotonic crystals (3D MPCs) based on artificial opals. Opal samples with three-dimensional dielectric lattices were impregnated with different types of magnetic material. Magnetic and structural properties of 3D MPCs were studied by field emission scanning electron microscopy, x-ray diffraction analysis, and vibrating sample magnetometer. We have shown that magnetic materials synthesized in voids of opal lattices and the composites obtained have typical magnetic properties.
High coercivity of melt-spun (Fe0.55Pt0.45)78Zr2–4B18–20 nanocrystalline alloys with L10 structure
Authors: Makino A. , Bitoh T.
Published: May 2004

The structure and the coercivity (Hc) of rapidly quenched (Fe0.55Pt0.45)bal.Zr0–8B0–24 alloys prepared by the melt-spinning technique have been investigated. Ordered L10 Fe–Pt phase of 20–100 nm was obtained by rapidly quenching the melt for (Fe0.55Pt0.45)78Zr2B20 and (Fe0.55Pt0.45)78Zr4B18 alloys with high Hc of 341 and 649 kA/m in an as-quenched state, respectively. On the other hand, the (Fe0.55Pt0.45)78Zr4B18 alloy produced by Cu mold casting at a lower cooling rate than melt spinning is found to be composed of a mixed structure of Fe–Pt L10, ZrB12, PtZr and Fe3B phases and the alloy has much lower Hc of 74 kA/m than that of the melt-spun (Fe0.55Pt0.45)78Zr4B18 alloy. The lattice parameters (a and c) of the L10 phase in the melt-spun alloys suggest that Zr and B elements are contained in the L10 phase for the melt-spun alloys, which is possibly related to direct formation of the L10 structure by rapidly quenching the melt.
Paramagnetic anisotropic magnetoresistance in thin films of SrRuO3
Authors: Genish Isaschar , Kats Yevgeny , Klein Lior , Reiner James W. , Beasley M. R.
Published: May 2004

SrRuO 3 is an itinerant ferromagnet and in its thin film form when grown on miscut SrTiO3 has Tc of ∼150 K and strong uniaxial anisotropy. We measured both the Hall effect and the magnetoresistance (MR) of the films as a function of the angle between the field applied and the normal to the films above Tc. We extracted the extraordinary Hall effect that is proportional to the perpendicular component of the magnetization and thus the MR for each angle of field applied could be correlated with the magnitude and orientation of the magnetization induced. We fit the MR data with a second order magnetization expansion, and it indicated large anisotropic MR in the paramagnetic state. The extremum values of resistivity were not obtained for currents parallel or perpendicular to the magnetization, probably due to crystal symmetry.
Interactions and switching behavior of anisotropic magnetic dots
Authors: Sorge K. D. , Kashyap A. , Skomski R. , Yue L. , Gao L. , Kirby R. D. , Liou S. H. , Sellmyer D. J.
Published: May 2004

The magnetic properties of collections of three soft magnetic nanodots with various aspect ratios are investigated. Permalloy films are first produced by dc magnetron sputtering. Focused ion beam milling is then used to mill dots, each with different shape anisotropy. We find that each of the three dots in the system has a unique switching field, and that there is significant magnetostatic coupling. Micromagnetic simulations suggest that for dot separations of less than 50 nm there exists strong interdot interaction, leading to the possibility of controlled switching of neighboring dots. This switching behavior is of interest in magnetic information processing.
Magnetic anisotropy of FeGa alloys
Authors: Rafique Sadia , Cullen James R. , Wuttig Manfred , Cui Jun
Published: May 2004

Cubic magnetocrystalline anisotropy constants, K1 and K2, for Fe1−xGax alloys were measured using magnetization curves with x=0.05, 0.125, 0.14, 0.18, and 0.20. Thin circular (110) disks all with 〈100〉, 〈110〉, and 〈111〉 in the plane of the disk were used to measure K1 and K2. K1 was also measured with (100) circular disks. K1 for 5 at. % Ga content was found to be larger than that of pure Fe. (All compositions mentioned hereafter are atomic percents.) K1 and K2 both drop gradually up to 18 at. % Ga substitution. Then there is a sharp drop in the magnitude of both constants. K2 was found to be equal to −9K1/4 and the 〈110〉 and 〈111〉 directions were equally hard magnetically for all compositions considered in this study. Calculation of the anisotropy energy density verifies this result. K1 measured from both (110) and (100) disks was reasonably consistent.