bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning tunneling microscopy observations of single-crystal Fe∕MgO∕Fe magnetic tunnel junctions
Authors: Mizuguchi M. , Suzuki Y. , Nagahama T. , Yuasa S.
Published: June 2006

Scanning tunneling microscopy observations of a single-crystal Fe(001)∕MgO(001)∕Fe(001) magnetic tunnel junction which shows a large tunnel magnetoresistance effect were performed. Step-and-terrace structures of an epitaxial MgO barrier layer, which are very similar to surfaces of a bottom Fe underlayer, were observed. This indicates that the MgO terraces were grown flatly on each terrace of the Fe electrode. It is supposed that these atomically flat terraces enable a coherent tunneling of electrons through magnetic tunnel junctions.
Discrete track media for 600Gbits∕in2 recording
Authors: Greaves S. J. , Muraoka H. , Kanai Y.
Published: June 2006

Discrete track perpendicular recording media were simulated to determine the optimum conditions for achieving an areal density of 600Gbits∕in2. For a 90nm track pitch the best performance was obtained from a medium with 60nm land and 80nm wide write pole. Comparisons with continuous media showed higher on- and off-track signal-to-noise ratio in some discrete track media, mainly due to the absence of erase band noise. Reducing the average grain size narrowed the differences between the two types of media, resulting in almost identical performance for an average grain size of 6nm.
Postgrowth annealing effects on heteroepitaxial MnAs thin films grown on GaAs(001) and Si(001)
Authors: Song J. H. , Cui Y. , Lee J. J. , Kim M. Y. , Ketterson J. B.
Published: June 2006

We have carried out postgrowth annealing studies on heteroepitaxial MnAs thin films deposited on GaAs(001) and Si(001) by molecular-beam epitaxy. Before annealing, a paramagnetic behavior is exhibited for MnAs∕Si(001), whereas a ferromagnetic behavior is observed for MnAs∕GaAs(001). The paramagnetic β-MnAs phase domains of the as-grown MnAs∕GaAs(001) sample disappear completely after postgrowth annealing. Surprisingly, after postgrowth annealing, the crystal orientation of the MnAs∕Si(001) film changes, and is accompanied by a shift from paramagnetic to ferromagnetic behavior. We attribute these observations to relaxation of the biaxial strain associated with the substrates.
Magnetocaloric effect in MnFe(P,Si,Ge) compounds
Authors: Cam Thanh D. T. , Brück E. , Tegus O. , Klaasse J. C. P. , Gortenmulder T. J. , Buschow K. H. J.
Published: June 2006

We have studied the magnetocaloric effect in MnFe(P,Si,Ge) compounds. The structural properties of the compounds were determined by x-ray diffraction. The homogeneity and the stoichiometry of the compounds were checked by electron probe microanalysis. The Curie temperature is found to be near room temperature. Specific-heat measurements made on these compounds show a first-order ferromagnetic—paramagnetic phase transition. The magnetocaloric effect derived from magnetization data shows that this effect in the MnFe(P,Si,Ge) compounds is as large as that in Gd-based compounds and MnFeP1−xAsx compounds. This means that we have succeeded in totally replacing As by (Ge,Si) in the latter compounds without losing the favorable magnetic properties. The upshot is that we have found relatively low cost and nontoxic materials for room-temperature cooling applications.
Compositional change of MgO barrier and interface in CoFeB∕MgO∕CoFeB tunnel junction after annealing
Authors: Bae J. Y. , Lim W. C. , Kim H. J. , Lee T. D. , Kim K. W. , Kim T. W.
Published: June 2006

Recent experiments have demonstrated high tunneling magnetoresistance (TMR) ratios in magnetic tunnel junctions (MTJs) with the MgO barrier. The CoFeB∕MgO∕CoFeB junctions showed better properties than the CoFe∕MgO∕CoFe junctions because the MgO layer had a good crystalline structure with (001) texture and smooth and sharp interface between CoFeB∕MgO. In this work, the compositional changes in the MgO barrier and at the interface of CoFeB∕MgO∕CoFeB after the CoFeB crystallization were studied in annealed MTJs. X-ray photoelectron spectroscopy depth profiles were utilized for the as-deposited and 340°C annealed specimens. Transmission electron microscope analyses showed that the MgO barrier had (100) texture on CoFeB in the junctions and CoFeB was crystallized in the annealed junctions. B in the bottom CoFeB layer diffused into the MgO barrier and B–oxide was formed at the interface of CoFeB∕MgO∕CoFeB after the CoFeB crystallization. The B behavior will be discussed.
Magnetic nanoparticles produced by surfactant-assisted ball milling
Authors: Chakka V. M. , Altuncevahir B. , Jin Z. Q. , Li Y. , Liu J. P.
Published: June 2006

Nanoparticles of Fe, Co, FeCo, SmCo, and NdFeB systems with sizes smaller than 30nm and narrow size distribution have been successfully prepared by ball milling in the presence of surfactants and organic carrier liquid. It has been observed that the nanoparticles prepared by milling Fe and FeCo powders were close to spherical in their shapes, whereas those of Co, SmCo, and Nd–Fe–B showed elongated rod shapes. The nanoparticles showed superparamagnetic behavior at room temperature, except for the SmCo nanoparticles that were ferromagnetic. Nanoparticles of all types showed ferromagnetic behavior at low temperatures. The compositions of nanoparticles prepared by milling the SmCo, NdFeB, and FeCo powders were found to be deviated from the starting powders.
Structural and magnetic properties of epitaxially grown full-Heusler alloy Co2MnGe thin films deposited using magnetron sputtering
Authors: Ishikawa Takayuki , Marukame Takao , Matsuda Ken-ichi , Uemura Tetsuya , Arita Masashi , Yamamoto Masafumi
Published: June 2006

Full-Heusler alloy Co2MnGe thin films were epitaxially grown on MgO (001) substrates using magnetron sputtering. The films were deposited at room temperature and subsequently annealed in situ at temperatures ranging from 400to600°C. X-ray pole figure measurements for the annealed films showed (111) peaks with fourfold symmetry, which gives direct evidence that these films are epitaxial and crystallized in the L21 structure. Furthermore, cross-sectional transmission electron microscope images of a fabricated film indicated that it is single crystalline. The annealed films had sufficiently flat surface morphologies with roughnesses of about 0.26nm rms at film thicknesses of 45nm. The saturation magnetization of the annealed films was 4.49μB∕f.u. at 10K, corresponding to about 90% of the Slater–Pauling value for Co2MnGe.
Effect of Fe2O3 on the transport and magnetic properties of half metallic Fe3O4
Authors: Tripathy D. , Adeyeye A. O. , Boothroyd C. B.
Published: June 2006

We present a systematic study of the transport and magnetic properties of half metallic Fe3O4 films grown on Si (100) substrates with a Fe2O3 buffer layer using electron beam deposition technique. Transmission electron microscope images show the presence of small grains that are well separated by grain boundaries in our polycrystalline films. We observed that the Verwey transition does not appear for our Fe3O4 films and tunneling of spin polarized electrons across grain boundaries dominates the transport properties of the films. Magnetic measurements show a reduced magnetization in our films which does not saturate even at high fields. Coercivity of the films increases with decreasing temperature, suggesting the existence of additional anisotropy at low temperatures. Magnetoresistance curves show linear behavior at high fields which may be attributed to second order tunneling through intermediate states in the grain boundaries. At lower fields, the magnetoresistance behavior is governed by direct tunneling.
Nanostructure and giant Hall effect in TMx(SiO2)1−x (TM=Co,Fe,Ni) granular system
Authors: Socolovsky L. M. , Oliveira C. L. P. , Denardin J. C. , Knobel M. , Torriani I. L.
Published: June 2006

Granular TMx(SiO2)1−x (TM=Co,Fe,Ni) thin films were thermally treated at different temperatures and their magnetotransport and structural properties were studied. Hall resistivity decreases with thermal annealing. Structure was analyzed based on small angle x-ray scattering results. A model of polydisperse system of hard spheres was used for obtaining structural parameters. Analysis reveals that a volume fraction of transition-metal atoms (less than 29%) are forming nanospheres. Changes in giant Hall effect upon annealing can depend on a particular combination of nanoparticle diameter, interparticle distance, and size distribution.
Mössbauer studies of Fe-doped HoMnO3
Authors: Kim Sung Baek , Kim Sam Jin , Park J.-G. , Cheong S-W. , Kim Chul Sung
Published: June 2006

The crystallographic and magnetic properties of HoMn0.99Fe0.0157O3 powder have been studied by x-ray diffraction, superconducting quantum interference device measurements, and Mössbauer spectroscopy. It has a hexagonal space group P63cm with the lattice constants a0=6.139 and c0=11.402Å at room temperature. The magnetic susceptibility follows a Curie–Weiss law behavior, where the Curie–Weiss temperature was determined to be θCW=−18K. The Mössbauer spectra below TN=72K exhibit the six-line patterns, which coalesce into two lines above TN. The electric quadrupole splitting value at TN was ΔEQ=1.79±0.01mm∕s. An important point can be accessed that the direct observation of a coupling for the electric and magnetic order parameters was possible by Mössbauer spectroscopy.
Influence on the rectifiers of rotor losses in high-speed permanent magnet synchronous alternator
Authors: Jang Seok-Myeong , Cho Han-Wook , Jeong Yeon-Ho
Published: June 2006

This article deals with the rotor losses in the high-speed permanent magnet (PM) synchronous alternator for distributed power generation system. Specifically, the influence of rectifiers on the rotor losses is investigated. On the basis of analytical field analysis and two-dimensional finite element analysis, this article predicts the flux harmonics and rotor losses in the PM alternator considering the rectifier load. The prototype machine with the rectifier load has been fabricated and tested. Moreover, the difference of rotor losses between the high-speed alternator with and without the rectifier is made quantitatively clear in this work.
Investigation of superparamagnetic Fe3O4 nanoparticles by fluxgate magnetorelaxometry for use in magnetic relaxation immunoassays
Authors: Ludwig F. , Heim E. , Menzel D. , Schilling M.
Published: June 2006

We have investigated the magnetorelaxation (MRX) of various magnetite (Fe3O4) nanoparticle samples with organic shells with regard to their suitability for the realization of a magnetic relaxation immunoassay. The MRX of magnetic nanoparticles (MNP), immobilized by freeze-drying, was measured for magnetization fields between 0.2 and 2.0mT and for magnetization times between 0.2 and 20s using a differential fluxgate setup. The experimental data were analyzed on the basis of the magnetic-moment superposition model, providing information on magnetic properties, such as anisotropy constant and saturation magnetization, on the dynamics of the magnetization and relaxation process, as well as on the size distribution of MNP cores.
Effect of design variables on starting torque of single phase flux-reversal machine
Authors: Won Sung Hong , Kim Tae Heoung , Jang Ki-Bong , Choi Seung-Kil , Oh Won Seok , Lee Ju
Published: June 2006

This article introduces a single phase flux-reversal machine (FRM) and presents the design method to improve its starting torque. The effects of the design parameters on the characteristic and starting torque are analyzed by the finite element method. The design variables considered are tapered airgap, stepped airgap, slotted teeth, and asymmetric PM width. As a result, we can find the best model in producing starting torque of a single phase 2∕3 FRM.
Imaging of ferromagnetic-resonance excitations in Permalloy nanostructures on Si using scanning near-field thermal microscopy
Authors: Meckenstock R. , Barsukov I. , Bircan C. , Remhoff A. , Dietzel D. , Spoddig D.
Published: June 2006

The investigated structures were Permalloy (Py) stripes of 3×0.3μm2 and a thickness of 24nm. Two samples with lattices of stripes of 2μm distance between the stripes and a lattice constant of 5μm are reported in this paper. One of the samples had crossed perpendicular lattices. The samples were prepared using standard lithography lift-off processes and comprised large arrays of at least 1000 stripes, such that enough material was available to perform conventional ferromagnetic-resonance (FMR) measurements. The overall anisotropy and resonance line behavior of the samples were determined by conventional FMR measurements. The origin of the FMR modes was then deduced locally resolved in single stripes using a scanning thermal microscope (SThM), which features a lateral resolution of 100nm and a temperature resolution of the order of a few millikelvins, mounted on a conventional FMR setup. The technique is based on the detection of the dissipated heat due to microwave absorption while in FMR. This setup provides an exact correlation of the SThM-FMR image and the simultaneously taken topography. In the crossed lattice sample the two resonance lines in the conventional spectra were identified as the parallel and perpendicular FMR excitations in each sublattice, respectively. A homogenous heating of a single stripe is observed while in FMR. In the single Py stripe lattice with external field parallel to the long axis of the stripe an additional resonance was found with slightly higher resonance field than the uniform mode. SThM-FMR measurements prove that this additional excitation is located at the polar edges of one stripe and is due to the round edges of each stripe and stray field effects.
Magnetocaloric effect in Gd5−xDyxSi4 compounds
Authors: Shimotomai S. , Ido H.
Published: June 2006

The compound Gd5Si4 is known as a candidate for magnetic refrigerant in the vicinity of room temperature. Since Dy ion has a smaller de Gennes factor and larger angular momentum than those of Gd ion, it is expected that the Curie temperature of 335K and magnetocaloric effect for Gd5Si4 will be decreased and increased, respectively, by Dy substitution for Gd of Gd5Si4. In this study, Gd5−xDyxSi4 with x=0, 0.5, 1, and 2 have been prepared, and the magnetocaloric effects together with the magnetic properties have been measured in a magnetic field up to about 2T. Maximum temperature rise of 3.1K is obtained for Gd5Si4 at the Curie temperature of 335K and in a magnetic field of 1.92T. The Dy-substituted samples, which have a lower Curie temperature than that of Gd5Si4, have shown almost the same magnetocaloric effect as that of Gd5Si4. The data are discussed on the basis of calculation of magnetic entropy for Gd5Si4.
Detection of anisotropy by transverse susceptibility in (110)-oriented cubic systems
Authors: Presa B. , Matarranz R. , Calleja J. F. , Contreras M. C.
Published: June 2006

The transverse susceptibility has been calculated for a single-domain particle with cubic anisotropy and for an assembly of randomly oriented particles with cubic anisotropy. The special case with the [110] axis perpendicular to the plane determined by the bias field and the alternating field is considered. The particles are in the shape of oblate spheroids and the problem is solved in two dimensions. The role of interparticle interaction and anisotropy dispersion is studied. The model successfully explains the experimental results in magnetically isotropic island nanostructured Fe(110).
A method to obtain uniform magnetic-field energy density gradient distribution using discrete pole pieces for a microelectromechanical-system-based magnetic cell separator
Authors: Nath Pulak , Moore Lee R. , Zborowski Maciej , Roy Shuvo , Fleischman Aaron
Published: June 2006

A spatially uniform magnetic energy density gradient (∇B2) distribution offers a controlled environment to separate magnetically tagged cells or biomolecules based on their magnetophoretic mobility [L. R. Moore et al., J. Biochem. Biophys. Methods 37, 11 (1998)]. A design to obtain a uniform ∇B2 distribution for a microelectromechanical-systems-based magnetic cell separator was developed. The design consists of an external magnetic circuit and a microfabricated channel (biochip) with embedded discrete pole pieces on the channel walls. The two-dimensional and three-dimensional magnetostatic simulation softwares utilizing boundary element methods were used to optimize the positions and the dimensions of the discrete pole pieces, as well as the external magnetic circuit—the combination of which would generate a uniform ∇B2 profile over the channel cross section. It was found that the discrete pole pieces required specific magnetic properties (saturation magnetization constant >1.55T) to affect the overall ∇B2 distribution. Investigating different positions of the discrete pole pieces inside the external magnetic field indicated that the proposed design could generate uniform ∇B2 distribution with ±100μm displacements along the height/width and ±1° inclination from the optimum position.
Dynamic characteristics analysis of linear dc motor for the electric screen door
Authors: Won Sung-Hong , Ahn Joon-Seon , Lee Ju
Published: June 2006

In order to simulate the dynamic characteristics, we have developed a method of calculating the force of the linear dc motor screen door system which is using three-dimensional data of flux density in air gap from finite element analysis. We use the coil mesh data to calculate Lorentz forces of each coil. Then they are used for the dynamic characteristic analysis. The simulated dynamic characteristic is compared with experimental value.
Reduction of grain size and intergrain interaction in FePt∕Pt∕Cr trilayer thin films for perpendicular magnetic recording
Authors: Sun An-Cheng , Hsu Jen-Hwa , Huang H. L. , Kuo P. C.
Published: June 2006

A FePt single layer, a FePt∕Cr bilayer, and a FePt∕Pt∕Cr trilayer were fabricated. Transmission electron microscope images revealed that the grain size of a FePt single layer was around 50nm, and decreased to 20nm with a Cr underlayer. When a Pt layer was inserted between the FePt magnetic layer and the Cr underlayer, L10 FePt(001) thin films with perpendicular magnetic properties can be obtained with a grain size of around 20nm determined primarily by the Cr underlayer. The intergranular interactions determined from the Kelly-Henkel plot were the exchange coupling between magnetic grains in the FePt single layer. In contrast, negative values of the δM curve were obtained for the FePt∕Cr bilayer and the FePt∕Pt∕Cr trilayer, implying the presence of dipole interactions in both films. Smaller grains and the negative δM of FePt∕Cr were derived from the diffusion of Cr into the FePt layer.
In-plane anisotropy of coercive field in permalloy square ring arrays
Authors: Goncharov A. V. , Zhukov A. A. , Metlushko V. V. , Bordignon G. , Fangohr H. , Karapetrov G. , Ilic B. , de Groot P. A. J.
Published: June 2006

Magnetic ring arrays are promising candidates for application in magnetic random access memory devices. The magnetic reversal processes and anisotropy of the coercivity in arrays of square-shaped nanorings with different spacings were investigated by vector magneto-optical Kerr effect magnetometry, magnetic force microscopy, and micromagnetic simulations. Two-step magnetization reversal demonstrates fourfold symmetry in the film plane resulting from the shape anisotropy in rings. Our numerical simulations show good agreement with the experiment.
A design for improved performance of interior permanent magnet synchronous motor for hybrid electric vehicle
Authors: Lim Seong Yeop , Lee Ju
Published: June 2006

This paper investigates the layout of a magnet shape on the performance of an interior permanent magnet (IPM) synchronous motor. The motor is used in a hybrid electric vehicle. The IPM motor is a pancake shaped motor that has permanent magnets inside the rotor. The motor acts as a rotational electrodynamic machine between the engine and transmission. The main purpose of redesigning the shape of the magnet is to improve the motor performance, especially the back-emf wave form, the efficiency, and the rated torque, within a restricted volume. The electromagnetic performance of the conventional model and the proposed design is analyzed using the finite element method. The theoretical results have been confirmed by comparing them with experimental results for the back-emf wave form, the torque versus current characteristics, and the motor efficiency.
The magnetic properties of plasma-sprayed thick-film manganese zinc ferrite (MZF) and nickel iron alloy (Permalloy) composites
Authors: Liang S. , Gambino R. J. , Sampath S. , Raja M. M.
Published: June 2006

MnZn ferrite/Permalloy composites have potential in high frequency magnetic applications and can be made into thick-film devices by air plasma spray. The as-sprayed composites have lower saturation magnetization than the starting powder. After annealing below 600°C, the magnetic properties and electrical resistivity improve significantly. The changes in magnetic and electrical properties were correlated to structural changes and studied by x-ray-diffraction analysis, vibrating-sample magnetometer measurements, and microstructural analysis.
Magnetic and thermodynamic properties of Nd2Ni2Pb
Authors: Goruganti V. , Li Yang , Ross Joseph H. , Rathnayaka K. D. D. , Öner Y.
Published: June 2006

We report magnetic and thermodynamic measurements for Nd2Ni2Pb, one of the recently discovered R2Ni2Pb family of layered intermetallics. A specific heat jump at 19 K corresponds to an antiferromagnetic transition involving crystal-field-split Nd levels. Magnetization measurements show this phase to have a canted structure, with a metamagnetic transition to an aligned phase occurring in H=3T at low temperatures. The single antiferromagnetic phase stands in contrast to the more complex magnetic structures and multiple transitions in the heavy-rare-earth members of this family.
1
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noise in linearized low resistance MgO magnetic tunnel junctions
Authors: Almeida J. M. , Ferreira R. , Freitas P. P. , Langer J. , Ocker B. , Maass W.
Published: June 2006

Low RA MgO magnetic tunnel junctions prepared at Singulus (Ta3∕CuN30∕Ta5∕PtMn20∕CoFe2.5∕Ru0.7∕CoFeB3∕MgO1.2∕CoFeB3∕Ta5 (thickness in nanometers) were microfabricated at INESC-MN. The junctions were patterned into micron-sized sensors (5–20μm2) with controlled shape anisotropy (aspect ratio ranging from 2 to 20). A small external longitudinal bias field (15–30 Oe) was further used to improve sensor linearity. The MgO junctions have a resistance-area product of 150Ωμm2 and a maximum tunnel magnetoresistance of 130%. Noise measurements were done in linearized sensors, from dc to 500 kHz. The magnetic and nonmagnetic contributions to the 1∕f noise were determined. From the data fitting, Hooge parameters of ∼2.20×10−9μm2 were obtained for the nonmagnetic 1∕f noise. Analysis of direct experimental data revealed the possibility to detect variations of magnetic fields in the order of 10−10T∕Hz0.5 with these MgO junctions, demonstrating their potential for ultralow-field detection.
Investigation of end effect in permanent magnet brushless machines having magnets on the stator
Authors: Zhu Z. Q. , Pang Y. , Hua W. , Cheng M. , Howe D.
Published: June 2006

This paper investigates the influence of the end effect on the back-emf wave forms of flux-switching and doubly salient permanent magnet brushless machines, in which the magnets are located on the stator. Their electromagnetic performance is predicted from two-dimensional and three-dimensional finite element analyses and validated experimentally.
Interlayer exchange coupling dependence of thermal stability parameters in synthetic antiferromagnetic free layers
Authors: Saito Y. , Sugiyama H. , Inokuchi T. , Inomata K.
Published: June 2006

We conducted a detailed study of the interlayer exchange coupling (JEX) dependence of thermal stability properties of magnetic tunnel junctions (MTJs) with synthetic antiferromagnetic (Syn-AF) free layers. The thermal stability properties were investigated using the junction magnetoresistance of current-perpendicular MTJ devices with a word line as probes. The observed sweep-rate-dependent coercivities were analyzed using the Sharrock formula. The results confirmed the existence of strong JEX dependence on thermal stability parameters (KuV∕kT) in Syn-AF free layers. The values of KuV∕kT for MTJs with Syn-AF free layers decreased with a decrease in the strength of JEX, and the increase in the effective volume of the Syn-AF free layer disappeared at JEX⩽0.52erg∕cm2. The Syn-AF free layer with JEX>0.52erg∕cm2 is relevant for high-density spin electronic nanodevices with a low aspect ratio.
Parameter measurement of synchronous reluctance motor using LC resonance
Authors: Ahn JoonSeon , Kim Ki-Chan , Lee Ju
Published: June 2006

The motor characterizing parameters are most important factors to drive precisely, effectively, and robustly. Especially, the exact knowledge of synchronous inductance is necessary to control the torque precisely in synchronous reluctance motor (SynRM). Therefore many works have been done for the exact measurement of motor parameters. In this paper, we propose the simple method of measuring the motor parameters, especially measuring the synchronous inductance of SynRM, which can overcome the demerits of conventional methods and measure the exact values. The proposed method uses the resonance phenomenon between the phase inductance and capacitors externally connected.
Low power orthogonal fluxgate sensor with electroplated Ni80Fe20∕Cu wire
Authors: Fan J. , Li X. P. , Ripka P.
Published: June 2006

A single-core orthogonal fluxgate sensor based on electroplated Ni80Fe20∕Cu microwire was presented. Compared to the conventional amorphous wires, the core-shell structure of the sensing element has significant advantages in the sensor applications. No magnetic material in the central part results in smaller perming error and less power consumption. The composite wire has a helical anisotropy, which has favorable orthogonal fluxgate effects. The sensor was excited by an alternating current at 500 kHz and worked at the second-harmonic mode. The sensitivity of 20mV∕μT and power consumption within 100 mW were obtained by the sensor.
Magnetoresistance of Co-doped ZnO thin films
Authors: Stamenov P. , Venkatesan M. , Dorneles L. S. , Maude D. , Coey J. M. D.
Published: June 2006

Longitudinal, transverse, and perpendicular magnetoresistances were investigated at temperatures 1.2<T<300K in fields of up to 20 T for four ZnO films: one undoped, two with 4% Co (one paramagnetic, the other exhibiting anhysteretic ferromagnetism at room temperature), and one with 25% Co which exhibits hysteretic ferromagnetism, butterfly magnetoresistance, and presence of Co clusters. The magnetoresistance becomes negligibly small above 50–100 K, and magnetic terms are only evident below 20 K, where the mobility is sufficiently high. Quantum oscillations observed below 2 K in the paramagnetic sample with 4% Co give two different extremal Fermi surface cross sections. The data for dilute ferromagnetic samples are consistent with coherent spin transport in a ferromagnetic matrix; data for the x=25% films suggest that spin-polarized electrons can tunnel coherently between well-separated cobalt clusters.
Fe–Co and Fe–Ni magnetic fine particles encapsulated by graphite carbon
Authors: Tokoro Hisato , Fujii Shigeo , Muto Shunsuke , Nasu Saburo
Published: June 2006

Magnetic fine particles of Fe–Co and Fe–Ni alloys encapsulated by graphitic carbon (C) were synthesized by annealing Fe2O3,Co3O4, and NiO with carbon powders at 1273 K in nitrogen atmosphere. Saturation magnetizations of the Fe–Co and Fe–Ni particles were 122–150 and 7.8–105Am2∕kg, respectively. X-ray diffraction measurement showed that the Fe–Co was composed of two phases with face-centered-cubic (fcc) and body-centered-cubic phases, while the Fe–Ni was only a fcc phase. Lattice constants of both particles depended on their composition, which suggested that they were alloys. This was confirmed by Mössbauer spectroscopy. Electron microscope images and electron energy loss spectroscope spectra revealed that these particles with diameters of 100–200 nm were encapsulated by C layers with a thickness of several tens of nanometers.
Characterization of room temperature ferromagnetic Mn–Si compound synthesized on SiC substrate
Authors: Takano Fumiyoshi , Akinaga Hiro , Ofuchi Hironori , Kuroda Shinji , Takita Kôki
Published: June 2006

Manganese silicide (Mn–Si) related compound with a Curie temperature (TC) of 300K was synthesized on a 4H-SiC homoepitaxial wafer. Thin Mn layer was deposited on the SiC wafer, and then annealing was performed to diffuse the Mn atoms into the SiC epitaxial layer. Transmission magnetic circular dichroism spectra reflected that of the SiC wafer, although the structural investigations suggested that the dominant phase of the synthesized layer was paramagnetic Mn5Si2. At this stage, two possible explanations are considered the origin of the observed ferromagnetism. One is that a small amount of carbon (C) incorporated into the Mn5Si2 host induced the ferromagnetic order in Mn5Si2. On the other hand, the partial formation of a ferromagnetic SiC-related component at the vicinity of the lower side of the interface between SiC and Mn5Si2 layers is considered the other possible explanation.
Brownian magnetic relaxation of water-based cobalt nanoparticle ferrofluids
Authors: Bao Y. , Pakhomov A. B. , Krishnan Kannan M.
Published: June 2006

Following the synthesis of monodispersed 20nm cobalt nanoparticles via a thermal decomposition method we have successfully transferred these hydrophobic nanoparticles into the water phase using tetramethylamonium hydroxide pentahydrate as phase transfer agent and 12-aminododecanoic acid as a stabilizing agent. Frequency dependent ac susceptibility of water-based cobalt nanoparticle ferrofluids was measured at room temperature in the frequency range of 0.01–1000Hz. In addition to the “high” frequency magnetic relaxation peak at 200Hz, which is determined by the solvent viscosity and hydrodynamic volume of the nanoparticles, a lower frequency relaxation peak attributed to the interaction of surface coatings is observed. The position of the latter varies with the solution pH in the range of 0.02–0.05Hz. This variation is explained as due to the change of chemical and charge state of the surfactant molecules. The peak at low frequency may be potentially used to study protein configuration changes in solution or other dynamic properties of biomolecules.
Large (H,D) isotope effect on the metamagnetic transition in Y0.9R0.1Fe2(H,D)4.3 compounds
Authors: Leblond T. , Paul-Boncour V. , Guillot M.
Published: June 2006

The influence of the (H,D) isotope substitution on the metamagnetic transition in (Y1−xRx)Fe2(H1−yDy)4.2 (R=Tb, Er, x=0, 0.1, and y=0, 1) compounds has been studied by x-ray diffraction and magnetic measurements. All these compounds crystallize in the same monoclinic structure with larger cell volume for the hydrides compared to the deuterides. The metamagnetic transition temperature TM is not only field dependent but also strongly related to the volume change. The increase of TM is more strongly related to the (H,D) isotope substitution than by the rare earth substitution on the Y site.
A design of orthogonal fluxgate sensor
Authors: Li X. P. , Fan J. , Ding J. , Chiriac H. , Qian X. B. , Yi J. B.
Published: June 2006

A design of orthogonal fluxgate sensor is presented, in which the sensing element consists of multiple number of cores of soft ferromagnetic thin wires closely packed together. An orthogonal fluxgate sensor with the sensing element formed by a glass-coated amorphous wire of 16μm in diameter and another orthogonal fluxgate sensor with the sensing element formed by 16 closely packed glass-coated amorphous wires of 16μm in diameter were constructed and tested. In the tests, the excitation currents passing through the sensing elements for both sensors were set in such a way that each of the amorphous wires in the sensing elements was driven by a current of equal magnitude. The current excitation frequency for each sensing element was determined such that the sensor gave the maximum sensing output. The results showed that under the excitation current of optimum frequencies the sensitivity of the 16-core sensor was 65 times higher than that of the single-core sensor, in a trend of increasing exponentially against the increase of the number of cores in the sensing element.
Study of the effect of disorder on the local magnetism in Heusler alloys
Authors: Carbonari A. W. , Saxena R. N. , Mestnik-Filho J. , Cabrera-Pasca G. A. , Rao M. N. , Oliveira J. R. B. , Rizzuto M. A.
Published: June 2006

A local study of the influence of annealing temperature that can provoke structural defects and chemical disorder on the magnetism of Heusler alloys has been carried out by measuring hyperfine interactions in Pd2MnZ (Z=Ge, In, Sn, and Sb). Perturbed angular correlation method has been used to measure the hyperfine fields at Cd111 probe nuclei substituting the Mn and Z sites as a function of temperature. The fraction of In111-nuclei-occupying Mn sites was found to increase with the annealing of sample at higher temperatures followed by quenching that can leave the alloy in a disordered state. As a consequence, it was possible to observe the effect of temperature in the ordering of the alloys. Moreover, electric quadrupole interaction measurements clearly indicated chemical disorder after quenching in Pd2MnSn and an improvement in the ordering of the Pd2MnGe structure at high temperatures.
Spin-transfer-induced magnetization switching in magnetic tunnel junctions
Authors: Zhang Yisong , Zhang Zongzhi , Liu Yaowen , Ma Bin , Jin Q. Y.
Published: June 2006

Micromagnetic simulations for spin-transfer-induced magnetization dynamics in nanoscale low-resistance magnetic tunnel junctions (MTJs) are performed by using the modified Landau-Lifshitz equation in which a spin-transfer model for MTJs is included. Calculations show that critical switching current density (Jc) is about (4–8)×106A∕cm2, consistent with the experimental data, lower than the values found in metallic spin-valve nanopillars (typically in the order of ∼107A∕cm2). A slight asymmetry of the critical current is observed in the magnetization switching loop, due to the asymmetry of the spin-torque factor. The switching time is related to the applied current, and our calculation results show that a longer switching time, 10–15ns, is needed when the applied current density J is close to Jc, and it decreases down to 1ns for J>2×107A∕cm2.
Current induced bistability in giant magnetoresistive multilayer thin films
Authors: Prabhakar A.
Published: June 2006

The low frequency noise observed in giant magnetoresistive (GMR) sensors exhibited a bistability at certain critical values of bias current. As the sensor oscillated between the two states of a bistable system, the power spectral density (PSD) of the noise showed two peaks; a narrow low frequency peak corresponding to twice the average residence time in a bistable system and a broad high frequency peak corresponding to intrawell vibration. The peaks were visible in the PSD even when the bistability was not pronounced in a time trace. The PSD showed deviations from a Lorentzian behavior indicating that the energy minima and the barrier between them depended on the bias current. A simple analytic model was developed to describe the change in the energy of the system with bias current. The model was based on the physical structure of the sensor and the estimated path of current flow. At particular current induced bias field values, the system was described by multiple energy minima permitting thermal noise excitation of the free layer magnetization.
Study of head takeoff phenomenon influenced by stick-slip vibration of slider on head-disk interface
Authors: Tani H. , Goshi K. , Hamaguchi T. , Suzuki K.
Published: June 2006

Takeoff performance of the magnetic head slider on head-disk interface is influenced by a stick-slip vibration of slider enhanced by the friction of head-disk contact. We studied this phenomenon using altitude test and a simulation of slider vibration based on stick-slip analysis. Obvious degradation in the takeoff performance was observed for the disks with small roughness. This phenomenon can be explained using a simple stick-slip model of slider vibration enhanced by friction force, and investigated through the evaluation of the pressure hysteresis defined by the difference of takeoff pressure and touchdown pressure. Hysteresis simulation based on the stick-slip model revealed that large stick-slip vibration induces hysteresis for the disk with low roughness. We confirmed by the experiment and simulation that this stick-slip vibration of slider continues in the case of large friction coefficient after one slider-disk contact. We also confirmed that, slider-disk contact in low fly height occurs due to the trigger which the slider contacts on lubricant pooling. Reduction of friction force was found to be effective to improve the pressure hysteresis and takeoff performance.
Magnetic and structural properties of a DNA-maghemite nanocomposite
Authors: Dutta P. , Manivannan A. , Seehra M. S. , Shah N. , Huffman G. P.
Published: June 2006

Starting with 7 nm γFe2O3 nanoparticles, synthesis of DNA-γFe2O3 nanocomposite and its structural/magnetic properties vis-a-vis the parent γFe2O3 are reported. Analysis of the x-ray diffraction shows an increase in the particle strain and average particle size (to 9.7 nm) in DNA-γFe2O3 nanocomposite. Transmission electron microscopy also shows an increase in size and a considerably wider size distribution. Temperature (5–300 K) variation of the magnetization (M) shows a wider distribution of the blocking temperatures (TB), as expected from the wider size distribution. Above TB, the data of MvsH fit the modified Langevin function with magnetic moment/particle μp≈11000μB, somewhat larger than μp≈8000μB for the parent γFe2O3. However, M∕g(γFe2O3) is not significantly affected. In electron magnetic-resonance spectroscopy at 9.28 GHz, only a single line is observed in DNA-γFe2O3 nanocomposite compared to two lines in γFe2O3. These effects are discussed in terms of the above structural differences.
Magnetic characterization of samples using first- and second-order reversal curve diagrams
Authors: Stancu Alexandru , Andrei Petru , Stoleriu Laurentiu
Published: June 2006

The paper deals with the problem of magnetic characterization of samples with the first-order reversal curve (FORC) diagrams. Second-order reversal curves (SORCs) are introduced in a similar manner as in the generalized deltaM experimental procedure. SORC diagrams are calculated and compared with the well-known FORC diagrams. The difference between the FORC and SORC diagrams is explained. This difference represents an estimation of the errors made when the FORC distribution is considered as the distribution of coercive and interaction fields. Both Preisach and micromagnetic simulations of the FORC/SORC diagrams are presented and discussed.
Electronic and magnetic properties of Mn∕Ge digital ferromagnetic heterostructures: An ab initio investigation
Authors: Wang Huai-Yu , Qian M. C.
Published: June 2006

A digital ferromagnetic heterostructure composed of a δ-doped layer of Mn in a Ge substrate (Mn∕Ge-DFH) has been studied by using the density-functional theory within the generalized gradient approximation. We found that the ferromagnetic order in the Mn layer of the DFH is more favored than the antiferromagnetic order. However, the DFH exhibits metallic behaviors due to the small gap of the host semiconductor. In the majority spin channel, the hole carriers are originated from the hybridized states between the dt2g states of the Mn atom and the p state of its nearest neighbor Ge atoms. These hole states form three bands and are responsible for the ferromagnetic order. In the minority spin channel, the Fermi level is located below the valence band maximum of the host semiconductor, which gives rise to a number of hole carriers with the opposite spin direction in the host. We present the total and partial density of states and the band structures of the two spin channels. By fitting the exchange parameters, we predict the Curie temperature of this DFH.
Ferromagnetic resonance in the stripe domain state: A study in Co2MnGa (001)
Authors: Yu Chengtao , Pechan Michael J. , Carr David , Palmstrøm Chris J.
Published: June 2006

Heusler alloy films Co2MnGa grown on ScErAs∕GaAs(001) substrates form stripe domains in the remnant state due to its large strain-induced out-of-plane anisotropy. The dynamics of the stripe domains has been investigated using a microstrip ferromagnetic resonance device in a broad frequency range (∼3–25GHz). In both in-plane and out-of-plane measurement geometries, three modes were observed in fields less than the saturation field. The resulting frequency/field dispersion curve reveals that one mode has characteristics of an acoustic mode, the other of an optic mode, and with the third being nearly field independent. The acoustic mode continues into the saturated state, while the optic mode does not appear above saturation. The experimental data are analyzed using Wigen’s stripe domain theory.
Synthesis of Fe–Pt–B nanocomposite magnets with high coercivity by rapid solidification
Authors: Zhang Wei , Yubuta Kunio , Sharma Parmanand , Inoue Akihisa
Published: June 2006

The L10FePt∕Fe2B-type nanocomposite magnets with high coercivity have been obtained in the Febal.Pt30–32B18–20 alloys directly by the melt spinning technique. The as-spun ribbons showed good hard magnetic properties. The remanence, coercivity, and energy product for the Fe52Pt30B18 alloy melt spun at a wheel circumferential speed (Vs) of 35m∕s were 0.70 T, 783kA∕m, and 88.0kJ∕m3, respectively. The spring-back minor M-H loops were also observed for the alloy. The melt-spun alloy has a nanocomposite structure, consisting of L10 FePt and Fe2B phases with the average grain sizes of ∼40nm. The good hard magnetic properties are interpreted in terms of exchange magnetic coupling among the nanoscale hard L10 FePt and soft Fe2B magnetic phases. The present easy and single step process of forming the nanocomposite magnet having high coercivity is encouraging for the future development of Fe–Pt-based hard magnetic alloys.
Analysis of the fluctuation field in thermal magnetic aftereffect
Authors: Chen P. J. , Rao S. , Della Torre E. , Bennett L. H.
Published: June 2006

In order to determine the accuracy of an identification method of the fluctuation field, artificial data were generated. A major hysteresis loop, and its corresponding anhysteretic magnetization curve, was simulated and used to create thermal aftereffect curves as a function of a fluctuation field. Since the curves were idealized with known parameters, they could be used to test the method. In the Preisach-Arrhenius model, it was shown that the fluctuation field could be computed as the slope of the translation, in log time, of the aftereffect curves as a function of the holding fields. Gaussian noise was introduced into the curves to test the robustness of the method in the presence of experimental error. The limitations of the identification method are also discussed.
Electronic structures and magnetic properties of LaCo4B and LaNi4B
Authors: Ito Tadaei , Ido Hideaki
Published: June 2006

Electronic structures of LaCo4B and LaNi4B are calculated in a self-consistent linear muffin-tin orbital method and the atomic sphere approximation. Local spin moments of Co atoms at 2c and 6i sites in LaCo4B compound have been calculated to be 1.49 and 0.61μB, respectively, which are similar to the experimental and calculated values of local Co moments in YCo4B. Calculated total magnetic moment of 3.1μB∕f.u. of LaCo4B is in good agreement with 3.2μB obtained from the saturation magnetization. The Pauli paramagnetic nature of LaNi4B is also supported by the present energy band calculation. Electronic structures obtained by the present calculations for LaCo4B and LaNi4B are also discussed in comparison with those for LaCo5 and LaNi5.
Micromagnetic simulation of the magnetic exchange spring system DyFe2∕YFe2
Authors: Zimmermann Jürgen P. , Bordignon Giuliano , Boardman Richard P. , Fischbacher Thomas , Fangohr Hans , Martin Kevin N. , Bowden Graham J. , Zhukov Alexander A. , de Groot Peter A. J.
Published: June 2006

Magnetic measurements of [110] [50ÅDyFe2∕200ÅYFe2] reveal a rich switching behavior: the formation of exchange springs in this system of alternating hard and soft layers can be observed for low temperatures (LTs). For high temperatures (HTs), the appearance of the hysteresis loop changes significantly, implying a more complicated reversal process. In this article, we reproduce hysteresis loops for net and compound-specific magnetizations by means of micromagnetic simulations and assess the quality by a direct comparison to recent x-ray magnetic circular dichroism measurements. The HT switching characteristics, showing a magnetization reversal of the hard magnetic layer before the soft magnetic layer, are investigated and understood on the basis of detailed magnetic configuration plots. The crossover of LT to HT switching patterns is explained by energy considerations, and the dependence on different parameters is outlined.
Vapor deposition of perfluoropolyether lubricant on fluorinated diamondlike carbon surface
Authors: Kawaguchi Masahiro , Choi Junho , Kato Takahisa
Published: June 2006

According to the demand of extremely increased area density for magnetic data storage, contact recording systems have been proposed where stronger and thinner hard coatings and lubricant films for head-disk interface (HDI) are desired. In this study, two kinds of technique were accomplished and combined in order to satisfy the demands from the HDI development. One is the incorporation of fluorine into the standard diamondlike carbon film (F-DLC). The other is the vapor deposition of perfluoropolyether (VD-PFPE) lubricant on the DLC surface. Two developed techniques are sequentially combined without exposing samples to an atmosphere. The lateral force microscopy test showed that the developed system demonstrated better friction performance than the conventional system. From the results of ball-on-disk tests, it was also found that the improved surfaces of the F-DLC/VD-PFPE system showed good wear durability compared to those of the traditional system. The reason of this improvement will be discussed in this report.
The effect of Ti and C on the phase evolution and magnetic properties of Pr9FebalTixB11−yCy (x=0–4, y=0–11) nanocomposites
Authors: Chiu C. H. , Chang H. W. , Chang C. W. , Chang W. C.
Published: June 2006

Phase evolution, microstructure, and magnetic properties of melt-spun Pr9FebalTixB11−yCy (x=0, 2.5, and 4, y=0–11) ribbons have been investigated. For Pr9FebalTixB11−yCy series ribbons, addition of Ti suppresses the formation of metastable Pr2Fe23B3 phase and ensures the existence of a large amount of magnetically hard Pr2Fe14B phase in the ribbons. However, the increase of C substitution in the Pr9FebalTi2.5B11−yCy (y=0–5.5) ribbons diminishes the Br, Hci, and (BH)max monotonically, which comes from the increase of volume fraction of Pr2Fe17Cz and α-Fe phases and the rapid decrease of the 2:14:1 phase. Only in the higher Ti content Pr9FebalTi4B11−yCy ribbons, a slight C addition cannot only form the Pr2Fe14(B,C) phase but also refine the grain size, giving rise to the improvement of magnetic properties. The optimal properties of Br=9.4kG, Hci=11.1kOe, (BH)max=18.0MGOe, α=−0.207%∕°C, and β=−0.612%∕°C are achieved in Pr9FebalTi4B10.5C0.5 nanocomposites.