bluuebunny/crossref_metadata_2025 huggingface dataset:
AM404, an inhibitor of anandamide uptake, prevents pain behaviour and modulates cytokine and apoptotic pathways in a rat model of neuropathic pain
Authors: Costa Barbara , Siniscalco Dario , Trovato Anna Elisa , Comelli Francesca , Sotgiu Maria Luisa , Colleoni Mariapia , Maione Sabatino , Rossi Francesco , Giagnoni Gabriella
Published: June 2006

An attractive alternative to the use of direct agonists at the cannabinoid receptor type 1 (CB1) in the control of neuropathic pain may be to potentiate the actions of endogenous cannabinoids. Thus, the effects of AM404, an inhibitor of anandamide uptake, were assessed in an experimental model of neuropathic pain in rats.

Daily treatment with AM404 prevented, time‐ and dose‐dependently, the development of thermal hyperalgesia and mechanical allodynia in neuropathic rats. Antagonists at cannabinoid CB1 or CB2 receptors, or at the transient receptor potential vanilloid type 1 receptor, each partially reversed effects induced by AM404. A complete reversal was obtained when the three antagonists were given together, suggesting that all three receptors are involved.

AM404 treatment affected two pathways involved in the generation and maintenance of neuropathic pain, one mediated by nitric oxide (NO) and the other by cytokines. AM404 completely prevented the overproduction of NO and the overexpression of nNOS, inhibited the increase in tumour necrosis factorα(TNFα) and enhanced the production of interleukin‐10. Both NO and TNFαare known to contribute to the apoptotic process, which plays an important role in the establishment of chronic pain states. AM404 treatment prevented the increase in the ratio between pro‐ and anti‐apoptotic genebax/bcl‐2expression observed in the spinal cord of neuropathic rats.

Taken together, these findings suggest that inhibition of endocannabinoid uptake, by blocking the putative anandamide carrier, results in the relief of neuropathic pain and may represent a novel strategy for treating chronic pain.

British Journal of Pharmacology(2006)148, 1022–1032. doi:10.1038/sj.bjp.0706798
Kallidin‐like peptide mediates the cardioprotective effect of the ACE inhibitor captopril against ischaemic reperfusion injury of rat heart
Authors: Liu Xiuxin , Lukasova Martina , Zubakova Radka , Lewicka Sabina , Hilgenfeldt Ulrich
Published: June 2006

The potential cardioprotective effect of ACE inhibitors has been attributed to the inhibition of bradykinin degradation. Recent data in rats documented a kallidin‐like peptide, which mimics the cardioprotective effect of ischaemic preconditioning. This study investigates in isolated Langendorff rat heart the effect of the ACE inhibitor captopril, the role of bradykinin, kallidin‐like peptide, and nitric oxide (NO).

The bradykinin level in the effluent of the control group was 14.6 pg ml−1and was not affected by captopril in the presence or absence of kinin B2‐receptor antagonist, HOE140.

The kallidin‐like peptide levels were approximately six‐fold higher (89.8 pg ml−1) and increased significantly by treatment with captopril (144 pg ml−1), and simultaneous treatment with captopril and HOE140 (197 pg ml−1).

Following 30 min ischaemia in the control group, the creatine kinase activity increased from 0.4 to 53.4 U l−1. In the captopril group and in the captopril+L‐NAME group, the creatine kinase activity was significantly lower (18.5 and 22.8 U l−1). This beneficial effect of captopril was completely abolished by the kinin B2‐receptor antagonist, HOE140, as well as by the kallidin antiserum.

Perfusion of the hearts with kallidin before the 30 min ischaemia, but not with bradykinin, yielded an approximately 50% reduction in creatine kinase activity after reperfusion.

Pretreatment withL‐NAME alone and simultaneously with captopril, and with kallidin, respectively, suggests a kinin‐independent action of NO before the 30 min ischaemia on coronary flow and a kinin‐dependent action after ischaemia.

These data show that captopril increases kallidin‐like peptide in the effluent. Kallidin‐like peptideviakinin B2receptor seems to be the physiological mediator of cardioprotective actions of captopril against ischaemic reperfusion injury. HOE140 as well as the kallidin antiserum abolished the cardioprotective effects of captopril.

British Journal of Pharmacology(2006)148, 825–832. doi:10.1038/sj.bjp.0706799
Rectification of current for tunneling through metallic nano-particles
Authors: Iovan A. , Korenivski V. , Haviland D. B.
Published: June 2006

Double tunnel barrier structures were obtained by using a scanning tunneling microscope and samples composed of metallic nanoparticles deposited onto an oxidized bottom electrode. The nanoparticles were formed by evaporating subpercolation thin metallic layers. Due to the small size of the particles their energy spectrum is discrete, which is evidenced by the measured quantized current-voltage characteristics. Current rectification ratios of 100–1000 for tunneling through such quantum dots are demonstrated at room temperature.
Electronic phase separation in epitaxial La2∕3Ca1∕3MnO3 films on (001) and (110) SrTiO3 substrates
Authors: Fontcuberta J. , Infante I. C. , Laukhin V. , Sánchez F. , Wojcik M. , Jedryka E.
Published: June 2006

We report here on the structural and magnetic characterization of La2∕3Ca1∕3MnO3 epitaxial films on (001) and (110) SrTiO3 substrates. The (001) films display depressed magnetic properties (lower Curie temperature and magnetization) with respect to the bulk counterpart values. In contrast, the (110) films invariably display optimal magnetic properties. Mn55 nuclear magnetic resonance experiments show that, in contrast to (001) films, the (110) films do not show traces of electronic phase separation and thus provide evidence that no weakening of double exchange coupling at interfaces takes place in (110) films.
Structural and magnetic properties of Co∕α-Al2O3∕Fe magnetic tunneling junction system: Ab initio investigations
Authors: Kim Chiho , Chung Yong-Chae
Published: June 2006

Using the density functional theory calculations, the structural effects on the spin polarizations and change of tunneling magnetoresistance for Co∕α-Al2O3∕Fe magnetic tunneling junction were predicted. Hybridization of 3d orbitals of ferromagnetic atoms and O 2p orbital resulted in the covalent bond formations of Co–O and Fe–O at the interface and, subsequently, layer fluctuations of interfacial slabs occurred to the extent of 34.5% and 37.2% of the interlayer distances, 1.94Å for Co and 1.91Å for Fe. The magnetic moment of Co-interface atoms was enhanced to 2.03μB, while that for the Fe-interface atoms was reduced to 1.59μB from the corresponding bulk magnetization. Large asymmetric distributions of layer decomposed density of states for majority and minority spin electrons led the spin polarizations of 35.2% and 65.9% for top and bottom ferromagnetic electrodes, respectively. The change of magnetoresistance was calculated to be 37.7%.
Normal mode splitting in interacting arrays of cylindrical permalloy dots
Authors: Gubbiotti G. , Madami M. , Tacchi S. , Carlotti G. , Okuno T.
Published: June 2006

Brillouin light scattering has been exploited to study the dependence of the spin-wave spectrum on the interdot distance in squared arrays of circular permalloy dots with radius R=100nm, thickness L=50nm, and interdot spacing (s) variable in the range between 50 and 800nm. The experimental data have been satisfactorily reproduced using a micromagnetic approach which solves the discretized Landau-Lifshitz-Gilbert equation over a 3×3 matrix of differently spaced circular dots and performing a local Fourier transform. This approach enabled us to clarify that, on reducing the s∕R ratio, some of the normal modes existing within each isolated dot increase their frequency retaining their own character. The fundamental mode, instead, splits into three modes characterized by different profiles of the dynamic magnetization. For all these modes, hybriditazion effects have also been observed.
Anisotropic magnetoresistance in epitaxial (110) manganite films
Authors: Infante I. C. , Laukhin V. , Sánchez F. , Fontcuberta J. , Melnikov O. , Gorbenko O. Yu , Kaul A. R.
Published: June 2006

We report on measurements of anisotropic magnetoresistance (AMR) (∼ρ‖−ρ⊥) along two orthogonal directions ([001] and [1−10]) of a manganite (La0.95Ag0.05MnO3) epitaxial thin film grown on a (011) SrTiO3 substrate. We show that AMR along [001] is negative whereas along the [1−10] direction is positive at low temperature, changing to negative when approaching the Curie temperature. We argue that temperature dependent anisotropic spin-orbit coupling and spin-dependent scattering effects could be at the basis of these experimental results.
Two-dimensional finite element method simulation of a four-quadrant transducer prototype machine considering skewed slots
Authors: Zheng Ping , Thelin Peter , Nordlund Erik , Sadarangani Chandur
Published: June 2006

A four-quadrant transducer (4QT) electric machine is an integrated electric machine used for hybrid electric vehicles. In this article a 4QT prototype machine that is radially integrated by two permanent-magnet synchronous machines is analyzed. Skewed slots are adopted for the two machines, and the multislice two-dimensional time-stepping finite element method is used to calculate the performance. The dividing method of the 4QT, the choice of calculated cutplanes and the determination of the number of slices are discussed. The no-load and load performance of the 4QT are calculated. The 4QT prototype machine was tested. The tested no-load line-to-line back electromotive force curves are in good agreement with the calculated ones, which verifies the feasibility of the proposed method.
Electronic structure of LaSrMnO4: X-ray photoelectron spectroscopy and x-ray emission spectroscopy studies
Authors: Kuepper K. , Klingeler R. , Reutler P. , Büchner B. , Neumann M.
Published: June 2006

We present a comprehensive investigation of the valence band of the single-layered manganite LaSrMnO4. X-ray photoelectron spectroscopy and x-ray emission spectroscopy were used to reveal a detailed picture of the total and partial densities of states in this compound. The results are discussed in the light of available theory.
Spin-polarized current-induced torque in magnetic tunnel junctions
Authors: Kalitsov A. , Theodonis I. , Kioussis N. , Chshiev M. , Butler W. H. , Vedyayev A.
Published: June 2006

We present tight-binding calculations of the spin torque in noncollinear magnetic tunnel junctions based on the nonequilibrium Green functions approach. We have calculated the spin torque via the effective local magnetic moment approach and the divergence of the spin current. We show that both methods are equivalent, i.e., the absorption of the spin current at the interface is equivalent to the exchange interaction between the electron spins and the local magnetization. The transverse components of the spin torque parallel and perpendicular to the interface oscillate with different phase and decay in the ferromagnetic layer (FM) as a function of the distance from the interface. The period of oscillations is inversely proportional to the difference between the Fermi momentum of the majority and minority electrons. The phase difference between the two transverse components of the spin torque is due to the precession of the electron spins around the exchange field in the FM layer. In the absence of applied bias and for a relatively thin barrier, the component of the spin torque perpendicular to the interface is nonzero due to the exchange coupling between the FM layers across the barrier.
Micromagnetic simulations of the magnetization precession induced by a spin-polarized current in a point-contact geometry (Invited)
Authors: Berkov D. V. , Gorn N. L.
Published: June 2006

This paper is devoted to numerical simulations of the magnetization dynamics driven by a spin-polarized current in extended ferromagnetic multilayers when a point-contact setup is used. We present (i) detailed analysis of methodological problems arising by such simulations and (ii) physical results obtained on a system similar to that studied in Rippard et al. [Phys. Rev. Lett. 92, 027201 (2004)]. We demonstrate that the usage of a standard Slonczewski formalism for the phenomenological treatment of a spin-induced torque leads to a qualitative disagreement between simulation results and experimental observations, and discuss possible reasons for this discrepancy.
Angular dependence of positive exchange biasing in GdFe∕FeMn bilayers
Authors: Du J. , Yang D. Z. , Bai X. J. , Wu X. S. , Hu A. , Zhou S. M. , Sun L.
Published: June 2006

For Gd45Fe55∕Fe50Mn50 bilayers, both negative and positive exchange biasing have been observed for low and high magnetic cooling field HCF, respectively. These results can be attributed to a competition between antiferromagnetic coupling at GdFe∕FeMn interface and the Zeeman energy of FeMn spins under HCF. In order to reveal the magnetization reversal mechanism, the angular dependence of HE and HC has been investigated. It is found that the negative exchange biasing and the positive one have similar angular dependence that can be described by a magnetization coherent rotation model.
Spin-dependent tunneling in FM∣semiconductor∣FM structures
Authors: Vutukuri S. , Chshiev M. , Butler W. H.
Published: June 2006

Here we show that ordinary band-structure codes can be used to understand the mechanisms of coherent spin-injection at interfaces between ferromagnets and semiconductors. This approach allows the screening of different material combinations for properties useful for obtaining high tunneling magnetoresistance (TMR). We used the Vienna Ab-initio Simulation Code (VASP) to calculate the wave-function character of each band in periodic epitaxial Fe(100)∣GaAs(100) and Fe(100)∣ZnSe(100) structures. It is shown that Fe wave functions of different symmetry near Fermi energy decay differently in the GaAs and ZnSe.
Bragg-Williams model of Fe-Co order-disorder phase transformations in a strong magnetic field
Authors: Hanlumyuang Y. , Ohodnicki P. R. , Laughlin D. E. , McHenry M. E.
Published: June 2006

A modified Bragg-Williams statistical model with nearest-neighbor magnetic exchange and chemical interactions and an additional Zeeman energy term has been used to predict an increase in the critical ordering temperature (Torder) of Fe-Co alloys in the presence of a large magnetic field (ΔTorder∼20K near equiatomic composition for H=100T). The magnitude of the predicted ΔTorder increases with increasing field and is only predicted to be significant (ΔTorder≳2−3K near equiatomic) for H≳10T. The predicted shift in the ordering temperature is due to the higher average exchange interaction per atom in the ordered phase resulting in a larger theoretical Curie temperature as compared to the disordered phase. The dependence of the average magnetic moment of Fe on the degree of order was neglected in this work, however it is expected to contribute to an additional shift in Torder. Theoretical magnetization versus temperature curves are also presented for equiatomic FeCo subject to uniform applied magnetic fields.
Manipulation of superparamagnetic beads using on-chip current lines placed on a ferrite magnet
Authors: Wang Z. H. , Lew W. S. , Bland J. A. C.
Published: June 2006

Manipulation of superparamagnetic beads in a static solution is demonstrated using on-chip current striplines placed on a ferrite magnet. The ferrite magnet fits the requirement to enhance the bead’s magnetic moment while still keeping beads randomly dispersed in the liquid, so allowing easy and selective manipulation of single beads. By applying currents up to hundreds of milliampere, the tapered stripline first attracts the beads to its edge, then the magnetic force along the edge drives the trapped beads moving continuously towards the chip center. On arriving into the chip central area (a square zone which acts as a site to collect the arriving beads), fine manipulation of selected single beads is further performed by switching on/off and/or tuning the current passing through the nearby quadruple striplines. We suggest that the present system may provide a simple but effective platform for handling magnetic tags for biological and biomedical applications.
Synthesis of gold/magnetic iron oxide composite nanoparticles for biomedical applications with good dispersibility
Authors: Seino Satoshi , Kusunose Takafumi , Sekino Tohru , Kinoshita Takuya , Nakagawa Takashi , Kakimi Yuki , Kawabe Yoshinobu , Iida Junichi , Yamamoto Takao A. , Mizukoshi Yoshiteru
Published: June 2006

Composite nanoparticles consisting of gold and magnetic iron oxide were synthesized in an aqueous solution system by sonochemical and radiochemical processes. Small Au nanoparticles were immobilized on the surface of the iron oxide nanoparticles. Removal of the excess polymers in the solution leads to the good dispersibility of the composite nanoparticles. The composite nanoparticles are expected as a type of nanocarrier for biomedical applications.
Local-magnetic-field generation with a scanning tunneling microscope
Authors: Michlmayr T. , Saratz N. , Vaterlaus A. , Pescia D. , Ramsperger U.
Published: June 2006

We report on the manipulation of magnetic ultrathin structures of small lateral size by applying a local magnetic field generated with a ferromagnetic scanning tunneling microscope (STM) tip. The range and strength of the stray field of a ferromagnetic tip depends largely on the curvature at the tip’s apex and on the cone angle. The ability to vary these parameters renders it possible to produce tailored ferromagnetic STM tips for the experiment. The technique is applied to the ferromagnetic system of Fe epitaxially grown on Cu(001). At room temperature, 1.8 monolayers (ML) to 2.9 ML Fe films show a perpendicular magnetic anisotropy. The local magnetic field was applied to particles of Fe∕Cu(001) with lateral size in the order of a few micrometers, after which magnetic switching was observed. Theoretical studies based on experimental data of ferromagnetic STM tips reveal that the magnitude of the stray field is in the order of the bulk magnetization M of the used ferromagnetic tip material. Furthermore, the spatial range of the stray field is in the order of the tip’s apex radius.
Study of high-precision (10−4) transverse Kerr effect measurement method applied for laser gyroscope
Authors: Cai Huanfu , Zhang Hong , Zheng Chun , Li Zuoyi , Chen Yinli
Published: June 2006

Magneto-optic transverse Kerr effects were measured and studied in this paper. The measurement precision can be improved by two orders of magnitude (10−4) when using small vibrating method and magneto-optical rotation angle amplified as compared to a conventional instrument. Our proposed model was verified through an experimental study. A useful result for designing and reference has been obtained.
The effect of a trailing shield for perpendicular write heads
Authors: van der Heijden P. , Bonhôte C. , Carey K. , Le Q. , Li J. , MacDonald S. , Nguyen H. , Nix L. , Robertson N. , Smith N. , Tsang C. , Williams M.
Published: June 2006

The effect of a magnetic trailing shield located in close proximity of the pole tip for a perpendicular write head has been studied in a perpendicular recording system. For a 150nm wide write pole, the write field gradient is improved yielding a 40% decrease in jitter and 2.2dB increase in the signal-to-noise ratio (SNR). As the pole width is narrowed further, modeling and experiments show that the trailing shield leads to a tradeoff between maintaining a high write field (writeability) and achieving an optimal write field gradient (jitter). For a 70nm writer, the addition of a trailing shield results only in a small 0.5dB SNR gain despite a 25% decrease in jitter as a result of the concomitant loss in writeability. The latter results in an increased dc noise and becomes more significant with trailing shield throat thickness.
Vortex magnetodynamics: Ferromagnetic resonance in permalloy dot arrays
Authors: Pechan Michael J. , Yu Chengtao , Owen Dane , Katine Jordan , Folks Liesl , Carey Matthew
Published: June 2006

Permalloy dot arrays (square lattices of 100, 200, 500, and 1000 nm dots, 40 nm thick) have been fabricated using e-beam lithography. Hysteresis loops show vortex states at remanence in all samples. Variable frequency ferromagnetic resonance was used to probe the dynamics of both vortex and single domain states. The uniform resonance mode is present at fields above the vortex annihilation when field sweeping up and vortex nucleation field when field sweeping down. In the vortex state multiple resonances are observed in the 500 and 1000 nm samples, but interestingly, not in the 100 and 200 nm. In the frequency/field dispersion curve, these vortex resonances exhibit optical mode characteristics, whereas the uniform mode exhibits the expected acoustic mode behavior. Resonance modes corresponding to the annihilation and creation field (transition from vortex to single domain or verse versa) are also observed and discussed.
(Pr,Nd)–Fe–B nanocrystalline magnetic materials with TiC additions
Authors: Murakami Regina K. , Rechenberg Hercílio R. , Villas-Boas Valquíria , McCallum R. William
Published: June 2006

The effect of titanium carbide (TiC) addition and Pr substitution in nanocrystalline Nd-Fe-B based magnetic materials has been investigated. Rapidly solidified (Pr,Nd)-Fe-B alloys were prepared by melt spinning. The compositions studied were (PrxNd1−x)9.5Fe84.5B6 (x=0, 0.1, 0.25, 0.5, 0.75, and 1) with the addition of 3at.% TiC. Varying the wheel speed from 15to30m∕s, the best magnetic properties were found for samples prepared at 20m∕s. All samples were nanocrystalline in the as-cast state. The average coercive field ranged from 10.0to12.6kOe and energy product from 7.8to9.0MGOe. The improvement in the coercive field compared to similar Nd based alloys was about 30%. Rietveld analysis of x-ray data for the Pr9.5Fe84.5B6 sample revealed that this material consists of approximately 70wt.% of 2:14:1 phase and 30wt.% of α-Fe. This result was confirmed by Mössbauer data analysis and is in agreement with compositions expected from the ternary phase diagram.
Magnetic and transport properties of MnBi∕Bi nanocomposites
Authors: Kang Kyongha , Lewis L. H. , Hu Y. F. , Li Qiang , Moodenbaugh A. R. , Choi Young-Suk
Published: June 2006

The magnetic and transport properties of a nanostructured Mn-Bi eutectic composition (∼Mn5Bi95) produced by melt spinning and low-temperature/short time vacuum annealing were studied. A hysteretic magnetostructural transformation from low-temperature phase to high-temperature phase MnBi is confirmed at 520K. The fact that the transition temperature is lower than that reported for bulk MnBi (633K), is tentatively attributed to interfacial strain between MnBi and the Bi matrix. A positive temperature coefficient of coercivity is confirmed in the nanocomposites, with a maximum coercivity value of 36kOe at 500K. Magnetic field annealing the as-spun composites (525K at 10kOe) produces nanoparticle alignment. Annealed MnBi∕Bi composites have a very large ordinary magnetoresistance (MR) ratio normal to the ribbon at 5T, 275% at room temperature and 10 000% at 5K.
FePt clusters synthesized by thermal pyrolysis of Fe and Pt compounds in an organic solvent
Authors: Sui Y. C. , Zhao Y. , Daniil M. , Li X. Z. , Sellmyer D. J.
Published: June 2006

A simple synthetic procedure involving the pyrolysis of Fe and Pt acetylacetonates mixed in trioctylamine results in the formation of alloy clusters with an average cluster around 4.2nm and narrow size distribution. When the clusters are dispersed onto silicon wafers and heated under the protection of forming gas or nitrogen, the fcc structured clusters transform into hard magnetic FePt clusters with L10 chemical order. Coercivity values as high as 23kOe are reached after rapid thermal annealing at 750°C for 5min.
A high-temperature superconducting magnet system for sensitive measurement instrumentation
Authors: Dilley N. R. , Cherry J. J. , Diederichs J. , Spagna S.
Published: June 2006

A high-temperature superconducting magnet system for investigations of physical properties of bulk, powder, and thin-film samples is presented. This system provides a capability for a commercial vibrating-sample magnetometer, as well as thermal and electric characterization techniques to be employed in an environment with reduced refrigeration demands. These measurements can be performed over a wide range of temperatures down to 77K and in applied magnetic fields to 1T. In this report, we outline important elements of the cryogenic design, as well as measurements of the magnetic properties of a high-quality CoMn ferromagnetic thin film.
A high-performance axial-field magnetic gear
Authors: Mezani S. , Atallah K. , Howe D.
Published: June 2006

The paper describes an axial-field topology of magnetic gear, which is particularly suitable for applications which require a hermetic isolation between the input and output shafts, such as pumps for use in the chemical/pharmaceutical, food, and aerospace industries. It is shown that a torque density in excess of 70kNm∕m3 can be achieved, and that the axial forces, which are exerted on the high-speed and low-speed rotors, are relatively low.
First-principles study on half-metallicity at surface and interface of zinc-blende CrS∕GaAs(001)
Authors: Byun Y. , Lee J. I. , Jang Y.-R.
Published: June 2006

We have investigated the half-metallicity and magnetism at the surface and interface of CrS(001) on GaAs using the full-potential linearized augmented plane-wave method within the generalized gradient approximation. Two different terminations, Cr-terminated and S-terminated surfaces, have been considered. We found, from the calculated local density of states, that both of the Cr-terminated and the S-terminated surfaces retain the half-metallicity, but the band gap for the S surface is much reduced compared to that of bulk. The magnetic moment of the Cr-terminated surface (4.08μB) is enhanced much compared to the value of bulk (3.61μB) while that of the interface Cr (3.29μB) is smaller than the bulk value.
Erbium-doped gold sensor films for magnetic microcalorimeter x-ray detectors
Authors: Zink B. L. , Irwin K. D. , Hilton G. C. , Ullom J. N. , Pappas D. P.
Published: June 2006

We briefly review the principles of a magnetic microcalorimeter x-ray detector and the requirements for fabricating an array of such sensors, which include a paramagnetic sensor fabricated with thin-film techniques. We discuss two methods for depositing an Er-doped Au sensor film and present magnetization measurements from 4to300K in 5T and near the detector’s operating temperature and field. The properties of the deposited films that we have studied to date deviate from the expected behavior of bulk materials.
Influence of He-ion irradiation on thin NiMn∕FeNi exchange bias films
Authors: Cantelli V. , von Borany J. , Grenzer J. , Fassbender J. , Kaltofen R. , Schumann J.
Published: June 2006

Using synchrotron x-ray diffraction and reflectivity, we studied the transition from the paramagnetic NiMn phase to the chemically ordered, antiferromagnetic L10 phase of NiMn∕Fe19Ni81 thin films deposited on a Si∕SiO2 substrate as a function of the annealing temperature. The transformation to a dominating L10-ordered NiMn film takes place between 300 and 400°C irrespective of the irradiation. This is also consistent with magnetization reversal measurements of the corresponding permalloy layers. The benefit of the ion irradiation is a reduction of the mosaicity for both the NiMn and the permalloy film, and a smoothening of internal interfaces.
Magneto-optic linear-displacement sensor with high spatial resolution and low noise
Authors: Lee S. J. , Melikhov Y. , Jiles D. C. , Park C. M. , Hauser H.
Published: June 2006

A magneto-optic linear-displacement (MOLD) sensor is reported for measuring linear displacements of the surfaces of materials remotely. It is based on observation of temporal changes in the intensity of the reflected polarized light beam, which passes through a magneto-optic thin garnet film with controlled periodical displacement of one domain wall. The MOLD sensor allows observation of linear displacement of a material located remotely from the laser and detector with a spatial resolution of 4μm.
Microstructure and magnetic properties of isotropic bulk NdxFe94−xB6 (x=6,8,10) nanocomposite magnets prepared by spark plasma sintering
Authors: Yue Ming , Zhang Jiuxing , Tian Meng , Liu X. B.
Published: June 2006

Nd 2 Fe 14 B ∕ α - Fe isotropic bulk nanocomposite magnets were prepared by spark plasma sintering (SPS) technique using melt-spun powders with a nominated composition of NdxFe94−xB6, with x=6, 8, and 10. It was found that higher sintering temperature improved the densification of the magnets, while it deteriorated their magnetic properties simultaneously due to the excess crystal grain growth. An increased compressive pressure led to better magnetic properties and higher density for the SPS magnets. An increase in the Nd amount resulted in a gradual increase in intrinsic coercivity and an obvious reduction of the remanence of the magnets simultaneously. A magnet with the composition of Nd8Fe86B6 possessed a Br of 0.99T, a Hci of 386kA∕m, and a (BH)max of 101kJ∕m3 under the optimal sintering condition. In addition, microstructure observation using transmission electron microscopy showed that compared with the starting powders the full-density magnets nearly maintain the morphology, indicating that there was no sign of pronounced crystal grain growth during the densification process.
Indirect exchange in dilute magnetic semiconductors
Authors: Skomski R. , Zhou J. , Zhang J. , Sellmyer D. J.
Published: June 2006

A generalized Ruderman-Kittel-Kasuya-Yosida (RKKY) approach is used to calculate indirect exchange interactions between localized spins in doped magnetic semiconductors. The exchange is mediated by electron or hole states centered around shallow impurities. The states hybridize and may or may not form a narrow band, but in both cases, the exchange is obtained from the hybridized states by second-order perturbation theory. As in the free-electron RKKY model, both positive and negative exchange interactions occur, but the strength Jij of the exchange is no longer a unique function of the distance between the localized spins. A closed expression with simple geometric interpretation is obtained in the dilute limit of exchange mediated by two overlapping orbitals.
Spin-torque driven excitations and hysteresis in magnetic point contacts
Authors: Konovalenko A. , Korenivski V. , Yanson I. K. , Naidyuk Yu. G.
Published: June 2006

Magnetic multilayers are known to exhibit magnetization excitations, which are due to exchange fields produced by densely distributed spin-polarized electron currents. We report an observation of such excitations as well as hysteretic spin states produced by unpolarized currents in point contacts to single ferromagnetic layers. By measuring diffusive and ballistic contacts for various material combinations, we investigate the microscopic mechanism of the single interface spin-torque effect and discuss the possible origin of the observed hysteresis.
A method of preparing anisotropic Nd–Fe–B film magnets by pulsed laser deposition
Authors: Nakano M. , Sato S. , Fukunaga H. , Yamashita F.
Published: June 2006

The interceptive deposition method (IDM) was applied to the high-speed pulsed laser deposition (PLD) method with a substrate heating system, and it was clarified that anisotropic Nd-Fe-B thick-film magnets can be obtained under a high deposition rate larger than 20–50μm∕h. The obtained coercivity, remanence, and (BH)max values of a film were 577kA∕m, 0.90T, and 118kJ∕m3, respectively. In addition, we succeeded in increasing the thickness up to 90μm for an anisotropic Nd-Fe-B film magnet by using IDM.
Torque magnetometry studies of metamagnetic transitions in single-crystal HoNi2B2C and ErNi2B2C at T≈1.9K
Authors: Naugle D. G. , Rathnayaka K. D. D. , Adegbenro S. A. , Belevtsev B. I. , Canfield P. C. , Lee S.-I.
Published: June 2006

The metamagnetic transitions in single-crystal rare-earth nickel borocarbide HoNi2B2C and ErNi2B2C have been studied at 1.9K with a Quantum Design torque magnetometer. The critical fields of the transitions depend crucially on the angle between applied field and the easy axis [110] for HoNi2B2C and [100] for ErNi2B2C. Torque measurements have been made while changing angular direction of the magnetic field (parallel to basal tetragonal ab planes) in a wide angular range (more than two quadrants). The results are used not only to check and refine the angular diagram for metamagnetic transitions in these compounds, but also to find new features of the metamagnetic states. Among new results for the Ho borocarbide are the influence of a multidomain antiferromagnetic state, and “frustrated” behavior of the magnetic system for field directions close to the hard axis [100]. Torque measurements of the Er borocarbide clearly show that the sequence of metamagnetic transitions with increasing field (and the corresponding number of metamagnetic states) depends on the angular direction of the magnetic field relative to the easy axis.
Effect of surfactants on the size and shape of cobalt nanoparticles synthesized by thermal decomposition
Authors: Shao Huiping , Huang Yuqiang , Lee HyoSook , Suh Yong Jae , Kim ChongOh
Published: June 2006

Cobalt nanoparticles with various morphologies were synthesized by thermal decomposition of cobalt acetate in the presence of various surfactants at 260°C. A combination of surfactants consisting of sufficient amount of oleic acid together with polyvinylpyrrolidone and oleylamine resulted in well-dispersed cubic cobalt nanoparticles of ∼25nm in average size. When 1,2-dodecanediol was added as a reducing agent to the surfactant mixture, triangular-prism-shaped nanoparticles of ∼50nm in average size were synthesized. Furthermore, an injection of trioctylphosphine into the reactor as an additional surfactant decreased the particle size to ∼10nm. The XRD pattern of the prism-like particles corresponded to hexagonal close-packed crystalline phase of cobalt.
Magnetization switching in a mesoscopic NiFe ring with nanoconstrictions of wire
Authors: Lu Zhengqi , Zhou Yun , Du Yuqing , Wilton D. , Pan G. , Chen Yifang , Cui Zheng
Published: June 2006

Magnetoresistance in a mesoscopic NiFe ring with nanoconstrictions of wire has been measured. For the applied field tilted from the perpendicular direction, it is shown that the applied current has an effect on the switching fields and finally the transition process due to the spin torque effect. The decrease or increase in the switching field from the vortex state to the onion state depends on the electron flow with respect to the direction of domain propagation. The magnetization in the ring exhibits only a double switching process at a low applied current. However, when the applied current is higher than the critical current density, the magnetization shows a combination of single and double switching processes. For the applied field direction perpendicular to the wire, an enhancement in magnetoresistance is obtained around zero fields at a low applied current, which is due to the domain wall trapped at nanoconstrictions. Furthermore, it is found that the magnetization in the ring goes via a single onion to onion switching process at whatever value of the applied current.
Spontaneous generation of voltage in single-crystal Gd5Si2Ge2 during magnetostructural phase transformations
Authors: Zou M. , Tang H. , Schlagel D. L. , Lograsso T. A. , Gschneidner K. A. , Pecharsky V. K.
Published: June 2006

The spontaneous generation of voltage (SGV) in single-crystal and polycrystalline Gd5Si2Ge2 during the coupled magnetostructural transformation has been examined. Our experiments show reversible, measurable, and repeatable SGV responses of the materials to the temperature and magnetic field. The parameters of the response and the magnitude of the signal are anisotropic and rate dependent. The magnitude of the SGV signal and the critical temperatures and critical magnetic fields at which the SGV occurs vary with the rate of temperature and magnetic-field changes.
Glassy ferromagnetism and frustration in La0.7Ba0.3Mn0.7Ti0.3O3
Authors: Bau Le Viet , Phuc Nguyen Xuan , Phan The-Long , Yu Seong-Cho , Nordblad Per
Published: June 2006

Glassy ferromagnetism and the magnetic frustration effect in La0.7Ba0.3Mn0.7Ti0.3O3 were investigated by means of dc magnetization, ac susceptibility, and electron-spin-resonance (ESR) measurements. As a result, the spin-glass (SG) phase-transition temperature, Tg, was observed at 27.6 K. The in-phase component of the ac susceptibility χ′(T) indicated that the SG freezing temperature, Tf, shifted to low temperatures with lowering frequency. Dynamic processes on the frequency dependence of Tf have been analyzed by the slowing-down scaling law, τ∕τ0∝(Tf∕Tg−1)−zv, where the characteristic time τ0 and an exponent zv obtained were about 3.7×10−16s and 9.66, respectively. The microscopic picture characterizing phase separation and competing interactions in the compound were observed by ESR.
Manipulation of the magnetic state of a small ferromagnetic particle by means of nonlocal spin-injection techniques (invited)
Authors: Otani Y. , Kimura T.
Published: June 2006

Nonlocal spin-valve configuration is used for spin current injection into a nanoscale ferromagnetic particle to reverse its magnetization. The nonlocal spin injection aligns the magnetization of the nanoscale particle along the spin injector, whereas the reverse switching is hardly observed up to the available maximum exciting current of about 15 mA. This asymmetric behavior implies the presence of asymmetric barrier formed in the vicinity of the interface. The magnitude of the essential spin current for the reversal is determined to be about 160μA, on the reasonable order of magnitude compared with the experimental values for conventional pillar structures.
Giant magnetocaloric effect in clathrates
Authors: Srinath S. , Gass J. , Rebar D. J. , Woods G. T. , Srikanth H. , Nolas G. S.
Published: June 2006

We report an observation of large magnetocaloric effect in clathrate compounds. Systematic dc magnetization in polycrystalline Eu8Ga16Ge30 clathrates was studied in the temperature range of 5–60 K and over an applied field range of 0–3 T. Change in entropy (ΔSmag) was calculated using the Maxwell relation from the family of M-H curves at different temperatures in the vicinity of the ferromagnetic Curie temperatures. Large entropy changes of 6 and 9.3J∕kgK were observed for the type-I and type-VIII phases, respectively. The larger effect in type-VIII samples can be associated with the sharper ferromagnetic transition. Overall, these results indicate that the clathrates known to have potential for excellent thermoelectric properties are also promising candidates as magnetic refrigerant materials.
Dynamic spin-spin interactions in magnetically concentrated II1−xMnxVI semiconductors: A study by high-field electron paramagnetic resonance
Authors: McCarty A. D. , Hassan A. K. , Brunel L.-C. , Dziatkowski K. , Furdyna J. K.
Published: June 2006

High-field electron paramagnetic resonance (EPR) is used to investigate two magnetically concentrated II1−xMnxVI alloys, Cd1−xMnxSe and Cd1−xMnxSe, for x>0.15. Earlier EPR studies carried out between 9.0 and 35 GHz had shown that the EPR linewidths in II1−xMnxVI alloys are determined by anisotropic Dzyaloshinskii-Moriya superexchange. However, broadening of the resonance prevented those early EPR studies to be performed at high Mn concentration x and low temperature T, i.e., precisely when II1−xMnxVI systems become magnetically most interesting. We circumvent this problem by performing EPR measurements at high magnetic fields, using frequencies between 95 and 380 GHz. In addition to information on resonance broadening, the ability to measure EPR at very high x and low T (i.e., when the magnetic moments are very strongly coupled) revealed significant shifts of the resonance from the EPR position of Mn++ ions. We tentatively ascribe these shifts to internal fields produced by the spin sublattice within the II1−xMnxVI alloy.
Hybrid perovskite-spinel magnetic tunnel junctions based on conductive ferrimagnetic NiFe2O4
Authors: Lüders U. , Herranz G. , Bibes M. , Bouzehouane K. , Jacquet E. , Contour J.-P. , Fusil S. , Bobo J.-F. , Fontcuberta J. , Barthélémy A. , Fert A.
Published: June 2006

Ultrathin epitaxial films of NiFe2O4, when grown under specific conditions, show a large enhancement of their magnetic moment and electrical conductivity. This allowed us to use such layers as electrodes in magnetic tunnel junctions. In this paper, we report on the observation of a large tunnel magnetoresistance at low temperature in La2∕3Sr1∕3MnO3∕SrTiO3∕NiFe2O4 junctions. From these results we infer a spin polarization of up to 45% for NiFe2O4, which stays constant up to ∼300K. NiFe2O4 can therefore be considered as an alternative to Fe3O4 as a high-temperature spin-polarized Fe oxide. Furthermore, our findings provide a way to design materials for spintronics based on the stabilization of nonthermodynamically stable magnetic phases of spinel oxides.
Intergrain interactions in nanocomposite Fe–Pt powders
Authors: Lyubina Julia , Khlopkov Kirill , Gutfleisch Oliver , Müller Karl-Hartmut , Schultz Ludwig
Published: June 2006

The structure and magnetic properties of nanocomposite Fe100−xPtx (x=40, 50, and 60) powders prepared by mechanical alloying followed by annealing are investigated. Various combinations of phases, away from thermodynamic equilibrium, were obtained using this technique. Remanence curves and magnetic force microscopy data were used to provide insight into the nature of intergrain interactions in such powders. The analysis points to strong intergrain coupling in the Fe100−xPtx powders. An additional small magnetostatic contribution can be observed for the Pt-rich powders.
Detection of magnetically labeled DNA using pseudomorphic AlGaAs∕InGaAs∕GaAs heterostructure micro-Hall biosensors
Authors: Togawa Kiyoshi , Sanbonsugi Hideaki , Sandhu Adarsh , Abe Masanori , Narimatsu Hiroki , Nishio Kousuke , Handa Hiroshi
Published: June 2006

Hall-effect biosensors with a magnetic-field sensitivity of 23nT∕(Hz)1∕2 (30×30μm2, at a drive current of 400μA) were fabricated using pseudomorphic AlGaAs∕InGaAs∕GaAs heterostructures for detection of DNA labeled with magnetic beads. Magnetic beads with diameters of 120 nm were selectively immobilized onto the surfaces of the Hall biosensors using highly specific hybridization of complementary oligonucleotides and were subsequently detected by measurement of the ac magnetic susceptibility of the beads.
Optimized giant magnetoimpedance effect in amorphous and nanocrystalline materials
Authors: Phan Manh-Huong , Peng Hua-Xin , Yu Seong-Cho , Vázquez Manuel
Published: June 2006

This letter reports the giant magnetoimpedance (GMI) effect and its magnetic response in optimized Co70Fe5Si15Nb2.2Cu0.8B7 amorphous and Fe71Al2Si14B8.5Cu1Nb3.5 nanocrystalline ribbons. At a given frequency of 5 MHz, the largest GMI ratios of 513% and 640% were observed for the Co-based amorphous and Fe-based nanocrystalline samples, respectively. More interestingly, the magnetic response reached the largest value of 144%/Oe at the frequency of 4 MHz for the Co-based amorphous sample and of 40%/Oe at the frequency of 5 MHz for the Fe-based nanocrystalline sample. This is ideal for high-frequency and high-performance GMI-based sensor applications. The skin effect model was used to interpret the obtained results of GMI in connection with the magnetic-field and frequency dependences of the longitudinal permeability.
Microstructure and magnetoelectric properties in Pb(ZrxTi1−x)O3–Ni composite ferroic films
Authors: Bi Xiaofang , Chu Shaoyan , Zhu Jian-Gang , Laughlin David E.
Published: June 2006

Ferroic composite thin films consisting of Pb(ZrxTi1−x)O3 and Ni were prepared using rf magnetron sputtering at room temperature in an argon atmosphere. The film structure depends strongly on the Ni content. After annealing the ferroic composite films grown on SiO2∕Si substrates at 650 °C, a perovskite structure was obtained when the Ni content was in the range of 17–27.5 at. %. It has been found that the role of Ni in obtaining the perovskite is attributed to the formation of NiO, which acts as a nucleation site for the crystallization of the perovskite structure. The coercivity was evaluated at 10 and 293 K by superconducting quantum interference device magnetometry to estimate magnetoelectric effect for the films with and without the perovskite structure.
Barrier-height and bias-voltage-controlled spin-filter effect and tunneling magnetoresistance in full ferromagnetic junctions
Authors: Jin Dafei , Ren Yuan , Li Zheng-zhong , Xiao Ming-wen , Jin Guojun , Hu An
Published: June 2006

Within the framework of the single electron spintronic model, we systematically studied the barrier-height and bias-voltage-controlled spin-filter effect and tunneling magnetoresistance (TMR) in ferromagnetic metal/ferromagnetic insulator/ferromagnetic metal (FM/FI/FM) tunnel junctions. We find that it is the extended quantum-coherence factor of Slonczewski, κL↑2−kL↑kL↓, that physically controls the sign of the zero-bias TMR. This factor is a linear function of the mean barrier height. The zero-bias TMR is positive when the mean barrier is high, and negative when the mean barrier gets low, which agrees well with the experimental results observed in GdOx-barrier junctions. As a cooperative result of the mean barrier and spin-filter effect, a positively or negatively large TMR can be maintained in a rather wide range near the zero bias if the mean barrier of the FI spacer is much higher or much lower. This property is believed to be of practical use in designing spintronic devices. Besides, the TMR can oscillate positively, or negatively, or alternately with the applied voltage within the high bias region, which is different from conventional FM/I/FM tunnel junctions.
Magnetic entropy change in melt-spun MnFePGe (invited)
Authors: Yan A. , Müller K.-H. , Schultz L. , Gutfleisch O.
Published: June 2006

Giant magnetocaloric effect was observed in Mn1.1Fe0.9P1−xGex (x=0.2, 0.24) melt-spun ribbons. The maximum magnetic entropy change ∣ΔSM∣ of Mn1.1Fe0.9P0.76Ge0.24 reaches 35.4J∕kgK in a field change from 0 to 5 T at around 317 K. This value is superior to that reported for Mn1.1Fe0.9P0.76Ge0.24 synthesized by mechanical alloying (∼30J∕kgK at 306 K). The large magnetocaloric effect results from a more homogenous element distribution related to the very high cooling rate during melt spinning. The excellent magnetocaloric effect properties, the low material cost, and the accelerated aging regime make the melt-spun-type MnFePGe materials an excellent candidate for magnetic refrigerant applications.