bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic actuator intended for left ventricular assist system
Authors: Saotome H. , Okada T.
Published: June 2006

With the goal of developing an artificial heart, the authors fabricated a prototype pump employing a linear motion magnetic actuator, and carried out performance tests. The actuator is composed of two disk-shaped Nd–Fe–B magnets having a diameter of 80 mm and a thickness of 7 mm. The disks are magnetized in the direction normal to the circular surface, and are formed by semicircular pieces; one semicircle serves as a N pole and the other as a S pole. The magnets face each other in the actuator. One magnet is limited to spin around its axis while the second magnet is limited to move in linear motion along its axis. In this way, the circumferential rotation of one of the magnets produces reciprocating forces on the other magnet, causing it to move back and forth. This coupled action produces a pumping motion. Because the two magnets are magnetically coupled without any mechanical contact, the rotating magnet does not have to be implanted and should be placed outside the body. The rotating magnet is driven by a motor. The motor power is magnetically conveyed, via the rotating magnet, to the implanted linear motion magnet through the skin. The proposed system yields no problems with infection that would otherwise require careful treatment in a system employing a tube penetrating the skin for power transmission. Comparison of the proposed system with another system using a transcutaneous transformer shows that our system has good potential to occupy a smaller space in the body, because it obviates implantation of a secondary part of the transformer, a power supply, and armature windings. The dimensions of the trial pump are designed in accordance with the fluid mechanical specifications of a human left ventricle, by computing magnetic fields that provide the magnetic forces on the magnets. The output power of the trial pump, 1.0 W at 87beats∕min, is experimentally obtained under the pressure and flow conditions of water, 100 mm Hg and 4.5l∕min.
Growth of epitaxial bismuth and gallium substituted lutetium iron garnet films by pulsed laser deposition
Authors: Leitenmeier Stephan , Heinrich Andreas , Lindner Jörg K. N. , Stritzker Bernd
Published: June 2006

Epitaxial bismuth and gallium substituted lutetium iron garnet thin films have been grown on (100) oriented gadolinium gallium garnet Gd3Ga5O12 substrates by pulsed laser deposition. The films have been studied using x-ray diffraction, high resolution x-ray diffraction, Rutherford backscattering spectroscopy, transmission electron microscopy, and electron diffraction. We obtained smooth films with thicknesses between 0.3 and 1.0μm showing good crystalline quality and epitaxial growth.
Compositional stability of FePt nanoparticles on SiO2∕Si during annealing
Authors: Yao B. , Petrova R. V. , Vanfleet R. R. , Coffey K. R.
Published: June 2006

The loss of Fe due to oxidation or diffusion into the substrate can prevent the successful preparation of well-ordered, stoichiometric, FePt nanoparticles. In this work we report the composition changes during annealing observed for small (<10nm) FePt nanoparticles on thermally grown SiO2 layers on Si wafer substrates. Additionally, we describe the use of a controlled reducing gas mixture, Ar+H2+H2O, to reduce the loss of Fe.
Response of oscillation-controlled magnetic sensing
Authors: Saisho K. , Shiiki K.
Published: June 2006

In the oscillation-controlled magnetic sensing system, the dependence of the response on the gain of the feedback loop and the oscillation frequency is investigated. Two types of response were observed according to the gain of the feedback loop. In the first response type, referred to herein as type A, the oscillation starts when the oscillation condition is satisfied and stops when the oscillation condition is not satisfied. In the second response type, referred to herein as type B, when the magnetic field changes, the oscillation starts and then stops because the oscillation condition was at the limit of being fulfilled. For an oscillation frequency of 31MHz, the rise time tR and the fall time tF were 179ns and 1.27μs, respectively, for the type-B response. These times were approximately 1∕10 of those observed for the type-A response. The linearity of the oscillation frequency and the response time in both logarithms was observed for the type-B response, and the rise time tR and fall time tF were reduced as the oscillation frequency was increased.
The effect of stress-induced anisotropy in patterned FeCo thin-film structures
Authors: Yu Winnie , Bain James A. , Uhlig Willard C. , Unguris John
Published: June 2006

In this work, 1-μm-thick FeCo films with −320MPa compressive stress and FeCo∕NiFe films with 600MPa tensile stress were patterned into 5×20μm2 elements. The stress anisotropy resulting from patterning was measured using x-ray diffraction to be 220MPa for the tensile films and −170MPa for the compressive films and is in agreement with finite element modeling. Scanning electron microscopy with spin-polarization analysis imaging shows that the domain structure of the elements was influenced by this stress-induced anisotropy. Calculations of the effect of stress anisotropy were performed on domain configurations for the patterned structures. Results indicate that tensile stresses should reinforce closure domains, while compressive stresses of magnitude greater than 50MPa should result in an easy axis rotation, and are in agreement with the experimental results.
Progress toward a thousandfold reduction in 1∕f noise in magnetic sensors using an ac microelectromechanical system flux concentrator (invited)
Authors: Edelstein A. S. , Fischer G. A. , Pedersen M. , Nowak E. R. , Cheng Shu Fan , Nordman C. A.
Published: June 2006

The potential advantage of some magnetic sensors having a large response is greatly decreased because of the 1∕f noise. We are developing a device, the microelectromechanical system (MEMS) flux concentrator, that will mitigate the effect of this 1∕f noise. It does this by placing flux concentrators on MEMS structures that oscillate at kilohertz frequencies. By shifting the operating frequency, the 1∕f noise will be reduced by one to three orders of magnitude depending upon the sensor and the desired operating frequency. We have succeeded in fabricating the necessary MEMS structures and observing the desired kilohertz normal-mode resonant frequencies. Only microwatts are required to drive the motion. We have used spin valves for our magnetic sensors. The measured field enhancement provided by the flux concentrators agrees to within 4% with the value estimated from finite element calculations. No difference was detected in noise measurements on spin valves with and without the flux concentrators. This result provides strong evidence for the validity of our device concept. Solutions to the sole remaining fabrication problem will be discussed.
Atomic-scale studies of cobalt distribution in Co–TiO2 anatase thin films: Processing, microstructure, and the origin of ferromagnetism
Authors: Griffin K. A. , Varela M. , Pennycook S. J. , Pakhomov A. B. , Krishnan Kannan M.
Published: June 2006

Using high-resolution, aberration-corrected, scanning transmission electron microscopy and electron-energy-loss spectroscopy we show that in films of single-phase anatase Co:TiO2, the Co distribution and magnetic properties are strongly dependent both on the overall crystalline quality and postgrowth vacuum annealing process. The Co:TiO2 films are coherent, epitaxial anatase with no secondary phases or metallic Co. Films of lower crystalline quality reveal a relatively homogeneous Co concentration, while films of higher crystalline quality show a tendency for Co enrichment near the surface region, around grain boundaries, and the substrate interface. Both uniform and nonuniform samples show a notable enhancement in the saturation magnetization with annealing, while the coercive field is considerably higher in the samples with uniform Co distribution. These experiments confirm that films of single-phase anatase Co:TiO2 with both uniform and nonuniform Co distributions exhibit room-temperature ferromagnetism in the insulating ground state, while the compositional uniformity and film microstructure play a role in the bulk magnetic properties of the material and the mechanisms for ferromagnetic ordering.
Diode effect in all-oxide Sr2FeMoO6-based magnetic tunnel junctions
Authors: Fix T. , Stoeffler D. , Henry Y. , Colis S. , Dinia A. , Dimopoulos T. , Bär L. , Wecker J.
Published: June 2006

Sr 2 Fe Mo O 6 ( 70 nm ) ∕ Sr Ti O 3 ( 3 nm ) ∕ Co Fe 2 O 4 ( 30 nm ) magnetic tunnel junctions are grown by pulsed laser deposition and patterned using optical lithography. The square tunnel elements with lateral size of 50μm exhibit nonlinear zero-field current-voltage (I-V) variation. More interesting, when the temperature is decreased, the I-V curves become highly asymmetric and present a diodelike behavior. In order to explain this behavior, ab initio calculations are performed to obtain the electronic structure for each oxide layer. It is shown that our structure behaves like a usual metal∕insulator∕semiconductor diode due to the small gap into the majority-spin band of the CoFe2O4 layer. Finally, we point out that the I-V characteristic can be magnetically controlled.
Compositional dependencies of ferromagnetic Ge1−xMnxTe grown by solid-source molecular-beam epitaxy
Authors: Chen W. Q. , Teo K. L. , Jalil M. B. A. , Liew T.
Published: June 2006

The IV-VI diluted magnetic semiconductor Ge1−xMnxTe thin films on BaF2 (111) substrate have been prepared using solid-source molecular-beam epitaxy technique by varying the Mn concentrations from x=0.25 to 0.98. The chemical Mn concentration was determined by x-ray photoelectron spectroscopy measurement. The in situ reflection high-energy electron diffraction pattern indicates that the growth mechanism is in the island-growth mode. The x-ray diffraction shows that the Ge1−xMnxTe films crystallize in the NaCl phase with (111) orientation. A clear ferromagnetic ordering is observed in the detailed temperature-dependent magnetization measurement for 0.25<x<0.98. The dependence of Curie temperature TC on Mn concentration x tends to follow a quadratic behavior. This phenomenon can be attributed to the increase of antiferromagnetic interaction since MnTe is an antiferromagnet.
Bloch-line generation in cross-tie walls by fast magnetic-field pulses
Authors: Neudert Andreas , McCord Jeffrey , Schäfer Rudolf , Kaltofen Rainer , Mönch Ingolf , Vinzelberg Hartmut , Schultz Ludwig
Published: June 2006

The magnetization dynamics of a constrained cross-tie wall in a 50-nm-thick Ni81Fe19 element is investigated using static and time-resolved wide-field Kerr microscopy. By applying a series of short magnetic-field pulses to the sample the creation of additional vortex antivortex pairs within the cross-tie wall is observed. The cross-tie spacing decreases by a factor of 2–4 relative to the initial equilibrium state. By using sinusoidal and pulsed magnetic-field excitations, a discrimination between the influence of the repetition rate and the rise time of the applied fields is possible. We found a logarithmic increase of the Bloch-line number with decreasing rise time. A resonant excitation with increased repetition rate decreases the cross-tie spacing even further. From direct stroboscopic observation of the precessional remagnetization process, a mechanism for vortex multiplication is proposed.
Vector vibrating-sample magnetometer with permanent magnet flux source
Authors: Stamenov P. , Coey J. M. D.
Published: June 2006

A compact magnetometer, which uses two nested 1T Halbach cylinders to generate a variable magnetic field of up to 2T in any direction in the xy plane, has two sets of quadrupole pickup coils to detect the components mx and my of the magnetic moment of a sample vibrating along Oz. Sensitivity is 1.10−7Am2 with integration time of 100ms. The instrument is used to measure longitudinal and transverse hysteresis loops and torque curves, under automatic software control. Three examples illustrating its versatility and sensitivity are provided: CrO2 magnetic recording tape, a cobalt nanowire array in a porous membrane, and a FePt thin film.
Evaluating material degradation by the inspection of minor loop magnetic behavior using the moving Preisach formalism
Authors: Vandenbossche Lode , Dupré Luc , Melkebeek Jan
Published: June 2006

The application of two magnetic nondestructive evaluation techniques is investigated to monitor material degradation caused by metal fatigue. First, a set of experimentally obtained major and minor quasistatic magnetization loops is analyzed within the framework of the moving Preisach formalism: the mean-field parameter k is found to increase with the number of stress cycles n and, moreover, the ratio dk∕dn is higher during the last 10% of the fatigue lifetime. Second, during the fatigue test a constant magnetic field is applied to the sample and the magnetization variation during each stress cycle due to the magnetomechanical effect is monitored: the peak-to-peak magnetization first increases, then stabilizes, and finally starts to decrease at 95% of the fatigue lifetime.
Magnetism and metastability of melt-spun Pd40(Fe,Ni)40P20 metallic glass
Authors: Hsiao A. C. , Lewis L. H. , Kang K. , Moodenbaugh A. R.
Published: June 2006

The magnetic character of Pd40FexNi40−xP20, a metallic glass where x=17.5, is experimentally studied over a temperature range of 10–375K. Hysteresis and temperature-dependent magnetization measurements derived from superconducting quantum interference device magnetometry on the amorphous alloy provide insight into the role of applied magnetic field on magnetic phase formation during the nanocrystallization process. Specifically, the microstructure of the melt-spun form of Pd40(Fe,Ni)40P20 is discussed in correlation to the observed superparamagnetic and spin-glass behavior. Despite the extremely high quenching rate used to synthesize the alloy, this composition shows evidence of chemical segregation on the nanoscale in the as-solidified state.
Evidence of a barrier oxidation dependence on the interfacial magnetism in Co/alumina based magnetic tunnel junctions
Authors: Telling N. D. , van der Laan G. , Ladak S. , Hicken R. J. , Arenholz E.
Published: June 2006

Soft x-ray absorption spectroscopy and magnetic circular dichroism at the CoL2,3 edge have been applied to explore the near-interfacial magnetism of Co electrodes in Co/alumina based magnetic tunnel junctions. By taking into account the formation of CoO at the ferromagnetic (FM)/barrier interface, the change in the total magnetic moment on metallic Co atoms as a function of barrier oxidation has been determined. The results demonstrate a strong correlation between the Co moments and measured TMR values, and an enhancement in the Co moments for moderate oxidation times.
Magnetoresistance and performance of amorphous-CoNbZr∕Co∕Cu∕Co magnetic multilayers
Authors: Wen Qi-Ye , Zhang Huai-Wu , Jiang Xiang-Dong , Zhang Wan-Li , Xiao John Q.
Published: June 2006

A pseudo spin-valve (PSV) using amorphous CoNbZr alloy as a soft magnetic layer and buffer layer was proposed. The giant magnetoresistance (GMR), thermal annealing effect, and the performance were investigated. Antiparallel magnetization alignments were observed in the samples with 2–4nm CoNbZr layer and a maximum GMR of 6.5% was obtained. Furthermore, sandwich with relatively thick CoNbZr layer has a superior thermal stability to 400°C and a GMR enhancement to about 9%. After patterning to 6μm×1μm elliptic stripe, a single domain forms and the dynamic MR behavior indicates the stripe has a linear and stable GMR response. Therefore, it is believed that the PSVs with amorphous CoNbZr layers have good potentials for spin-electronic devices.
Transient thermal modeling of a nanoscale hot spot in multilayered film
Authors: Ghai Sartaj S. , Kim Woo Tae , Amon Cristina H. , Jhon Myung S.
Published: June 2006

A subcontinuum based lattice Boltzmann method is used to accurately model the transient thermal response of a nanoscale hot spot in solids. We developed the numerical scheme for the hot spot in a thin uniform material and extended the approach to study the multilayered materials. We observed that subcontinuum effects of high temperature rise become more prominent as the size of the film reduces to the scale of carrier mean free path. The thermal transport through a double layer is also considered, both for constant temperature difference across the double layer and hot-spot generation in one of the layers, using the diffusive mismatch scattering model at the interface. A finite temperature jump is observed at the interface whose magnitude depends upon the dimensions and properties of the material on the either side of the interface. The insight into the nanoscale thermal modeling, acquired in this work via a relatively simple model, will be critical for the design and operation of complex data storage and electronic systems, dealing with subcontinuum systems.
Spontaneous magnetization and ferromagnetism in PbSe quantum dots
Authors: Jian W. B. , Lu Weigang , Fang Jiye , Lan M. D. , Lin J. J.
Published: June 2006

A high-temperature organic solution approach was applied to prepare crystalline PbSe quantum dots. It is diamagnetic with an atomic susceptibility of ∼−1.0×10−4emu∕molOe for bulk PbSe. The core diamagnetism of bulk PbSe was subtracted from our raw data. While transforming into the nanophase, orbital susceptibility including finite-size corrections to the Landau susceptibility has been observed. A paramagnetic zero-field peak with a large diamagnetic susceptibility in high fields exhibit in the field dependent susceptibility as characteristics of the Landau orbital susceptibility. At low temperatures and fields the paramagnetism dominates the contribution of magnetization of quantum dots while the diamagnetism dominates at high temperatures and fields. All these measurements, showing paramagnetism at low fields, indicate the existence of spontaneous magnetization in the quantum dot. In addition, we have observed profound hysteresis loops implying ferromagnetism among the quantum dots even at room temperature, which is spontaneous magnetization in the quantum dot and of the ferromagnetic order among these quantum dots.
Magnetic motion capture system using LC resonant magnetic marker composed of Ni–Zn ferrite core
Authors: Hashi S. , Toyoda M. , Ohya M. , Okazaki Y. , Yabukami S. , Ishiyama K. , Arai K. I.
Published: June 2006

We have proposed a magnetic motion capture system using an LC resonant magnetic marker. The proposed system is composed of an exciting coil, an LC marker, and a 5×5-matrix search coil array (25 search coils). The LC marker is small and has a minimal circuit with no battery and can be driven wirelessly by the action of electromagnetic induction. It consists of a Ni–Zn ferrite core (3mmϕ×10mm) with a wound coil and a chip capacitor, forming an LC series circuit with a resonant frequency of 186kHz. The relative position accuracy of the system is less than 1mm within the area of 100mm3 up to 150mm from the search coil array. Compared with dc magnetic systems, the proposed system is applicable for precision motion capture in optically isolated spaces without magnetic shielding because the system is not greatly influenced by earth field noise.
Effects of MgO tunnel barrier thickness on magnetohysteresis in perpendicularly magnetized magnetic tunnel junctions of GdFeCo∕FeCo∕MgO∕FeCo∕TbFe∕Co
Authors: Li Simon C. , Chen T.-J. , Chang C.-H. , Liao K.-A. , Hou C.-K. , Wu Te-Ho
Published: June 2006

The effects of MgO tunnel barrier thickness on the magnetic-transport characteristics of perpendicularly magnetized magnetic tunnel junction device are explored. Saturation magnetization and initial switching field of the free layer decrease with MgO barrier thickness. Increased MgO thickness that extended interaction distance and diminished the influence from the magnetized pinned layer leads to a smaller initial switching applied field required for saturation. The oscillating dependences of the high coercivity of pinned layer and the low coercivity of free layer on MgO thickness are discovered. Moreover, an out-of-phase feature between both layers’ coercivity cyclic variation is exhibited. This unique cyclic varying of coercivity with MgO barrier thickness is revealed and analogous to the recent finding of the magnetoresistance’s periodic variation with MgO thickness.
Synthesis and magnetic behavior of silica-coated cobalt ferrite hollow spheres
Authors: Lin Chun-Rong , Wang Cheng-Chien , Chen I-Han
Published: June 2006

We have used functional polymer poly(methyl methacrylate-co-methacrylic acid) latex (500nm) as a core template to prepare magnetic hollow SiO2∕CoFe2O4 spheres. The mean crystallite sizes of coated CoFe2O4 nanoparticles, depending on the calcined temperature, are in the range from 2.2to10.1nm. The thickness of the CoFe2O4∕SiO2 composite shell is between 40 and 50nm and the content of CoFe2O4 in the composites is 73wt%. The magnetic properties of the hollow spherical particles can go from superparamagnetic to ferromagnetic behavior depending on the sizes of CoFe2O4 nanoparticles.
Molecular rheology of perfluoropolyether lubricant via nonequilibrium molecular dynamics simulation
Authors: Guo Qian , Chung Pil Seung , Chen Haigang , Jhon Myung S.
Published: June 2006

Molecular rheology of perfluoropolyether (PFPE) systems is particularly important in designing effective lubricants that control the friction and wear in tribological applications. Using the coarse-grained, bead-spring model, equilibrium molecular dynamics based on the Langevin equation in a quiescent flow was first employed to examine the nanostructure of PFPE. Further, by integrating the modified Langevin equation and imposing the Lees-Edwards boundary condition, nonequilibrium molecular dynamics of steady shear was investigated. We observe that the shear viscosity of PFPE system depends strongly on molecular architecture (e.g., molecular weight and endgroup functionality) and external conditions (e.g., temperature and shear rate). Our study of the flow activation energy/entropy and their correlations with nanostructure visualization showed that the PFPE structure was substantially modified.
Single-crystalline Fe∕Cr∕Fe∕MgO∕Fe magnetotunnel junctions grown on GaAs(001)
Authors: Grabowski J. , Przybylski M. , Nyvlt M. , Zukrowski J. , Wulfhekel W. , Kirschner J.
Published: June 2006

Fe ∕ Mg O ∕ Fe ∕ Cr ∕ Fe tunneling structures were epitaxially grown directly on GaAs(001) without buffer layer. Interdiffusion in the Fe∕GaAs interface was investigated using conversion electron Mössbauer spectroscopy. An independent magnetization switching in the Fe electrodes was achieved by pinning the magnetization of the Fe-top electrode by antiferromagnetic coupling across a Cr spacer to another Fe film. For transport measurements, optical lithography and ion etching were applied to reduce the junction area. A tunneling magnetoresistance of 10%–12% at room temperature was found.
Structure and magnetic properties of Cr∕Fe-doped SnO2 thin films
Authors: Wang Wendong , Wang Zhenjun , Hong Yuanjia , Tang Jinke , Yu Minghui
Published: June 2006

Cr- and Fe-doped SnO2 films were deposited on Al2O3 substrates by pulsed-laser deposition. X-ray-diffraction patterns show that the films have rutile structure and grow epitaxially along the (101) plane. The diffraction peaks of Cr-doped samples exhibit a systematic shift toward higher angles with increasing Cr concentration. This indicates that Cr dissolves in SnO2. On the other hand, there is no obvious shift of the diffraction peaks of the Fe-doped samples. The magnetization curves indicate that the Cr-doped SnO2 films are paramagnetic at 300 and 5K. The Fe-doped SnO2 samples exhibit ferromagnetic behavior at 300 and 5K. Zero-field-cooled and field-cooled curves indicate superparamagnetic behavior above the blocking temperature of 100K, suggesting that it is possible that there are ferromagnetic particles in the Fe-doped films. The anisotropic magnetoresistance was not observed in any of the samples.
Delta-sigma digital magnetometer utilizing bistable spin-dependent-tunneling magnetic sensors
Authors: Deak J. , Jander A. , Lange E. , Mundon S. , Brownell D. , Tran L.
Published: June 2006

A digital magnetometer, utilizing a micron-sized spin-dependent-tunneling (SDT) sensor as a field-dependent bistable difference node within an oversampling first-order delta-sigma (Δ−Σ) analog-to-digital converter, was designed and prototyped. The Δ−Σ magnetometer can be fabricated as a single-chip device. It is intended for integration directly with digital components, facilitating development of low-cost magnetic-field sensing systems for commercial and military navigation, security, and linear-magnetic-field sensing applications. The Δ−Σ magnetometer operates by pulsing the SDT element along its hard axis (HA) in order to set the magnetization of the free layer into an unstable equilibrium orientation along the HA. In the absence of an easy-axis (EA) magnetic field, thermal fluctuations result in an equal probability for the magnetization to relax into one of the two stable orientations along the EA. Application of an EA magnetic field increases the probability for the magnetization to relax into the EA orientation parallel to the applied field. Thus, repeatedly pulsing the SDT sensor along the HA and monitoring the magnetoresistance results in a digital bitstream, where the number of 1s within a fixed length of the bitstream provides a measure of the applied field. The SDT sensor bitstream is thus integrated in order to produce an EA feedback signal. The raw bitstream from the SDT sensor provides the digital output of the magnetometer. The length of the bitstream summing window is the oversampling ratio, which determines the minimum possible digital resolution. A prototype Δ−Σ magnetometer was constructed, and several different bit shapes were tested in order to optimize performance. The digital output of the device was found to provide a count that is linearly proportional to the applied field over a range determined by the EA feedback driver current limit and loop gain.
Molecular-orbital solution of magnetic exchange in spinel ferrites
Authors: Dionne Gerald F.
Published: June 2006

A one-electron molecular-orbital model of magnetic exchange was applied to the spinel ferrite family A[B2]O4. Hybridized metal-oxygen eigenfunctions were used to compute estimates of the transfer integrals between orbital states of ions at sites i and j from which the molecular-field coefficients (Nij) are derived. A set of coefficients was first determined from magnetization data for the standard Mn ferrite cation distribution Fe0.23+Mn0.82+[Mn0.22+Fe1.83+]O4, and then used for extrapolation to the fully inverted Fe3+[Mn2+Fe3+]O4. It is concluded that the large content of Mn2+ in the A sublattice combined with its smaller valence charge in the standard cation distribution is responsible for its low Curie temperature (575K). The model was then used to examine other inverted spinel ferrites, including Fe3+[Fe2+Fe3+]O4 (magnetite), where ferromagnetic exchange between t2g states influences the NBB coefficient. Computations reveal that the coefficients vary according to theory within the spinel family and that exchange among the 3d orbitals of divalent cations is significantly weaker than that of trivalent cations because the smaller ionization potentials and ionic lattice energies lead to smaller transfer integrals. The calculated results are consistent with traditional reasoning based on thermomagnetism properties.
rf-Mössbauer study of the magnetic properties of nanocrystalline FeNiZrB and FeNiCoZrB alloys
Authors: Kopcewicz M. , Kulik T.
Published: June 2006

Magnetic properties of amorphous and nanocrystalline Fe31Ni50Zr7B12 and Fe41Ni40−xCoxZr7B12 (x=10,20) alloys are studied by an unconventional “rf-Mössbauer” technique. The introduction of Co atoms into FeNiZrB amorphous and nanocrystalline alloys leads to a large increase of anisotropy field that limits the rf-collapse effect. The rf-Mössbauer measurements are very useful for the estimation of magnetic anisotropy field. The rf sidebands vanish when the nanocrystalline structure is formed. The rf-induced crystallization effect observed in Co-containing alloys is particularly strong in magnetostrictive amorphous alloys and in nanocrystalline alloys containing significant fraction of amorphous matrix. This effect does not occur in Co-free alloy.
Micropatterned high permeability films with narrow bandwidth resonance loss for the band stop filter
Authors: Ikeda Shinji , Nagae Tatsuya , Shimada Yutaka , Kim Ki Hyeon , Yamaguchi Masahiro
Published: June 2006

In this work the micropatterned CoNbZr films designed for the band stop filter are reported. It was already reported that a 400-μm-wide coplanar line equipped with a 4-mm-wide CoNbZr film exhibits band stop characteristics, but practically the width of the film must be about the same size as the signal line. This limited width of the micropattern gives rise to dispersion of the shape anisotropy, resulting in degradation of band stop characteristics. Here we fabricated 150-μm-wide patterned films with adjusted edge dimensions which widths have been enlarged from 20to40μm that were optimized on the permeability database. The resonance loss profile for the adjusted pattern is compared with that of a film without adjusted edges. The half width is appreciably decreased from 2.2to0.77GHz. In conclusion an improvement of the resonance profile of micropatterned films was achieved by optimizing the edge dimensions. This will enable us to utilize magnetic films for more downsized signal lines.
Variation of magnetostriction with temperature in Tb5Si2.2Ge1.8 single crystal
Authors: Ring A. P. , Ziegler H. L. , Lograsso T. , Schlagel D. , Snyder J. E. , Jiles D. C.
Published: June 2006

The Tb5(SixGe4−x) alloy system is similar to the better known Gd5(SixGe4−x), except it has a more complex magnetic and structural phase diagram. Gd5(SixGe1−x)4 has received much attention recently due to its giant magnetocaloric effect, colossal magnetostriction and giant magnetoresistance in the vicinity of a first order combined magnetic-structural phase transition. The magnetostriction changes that accompany the phase transitions of single crystal Tb5(Si2.2Ge1.8) have been investigated at temperatures between 20 and 150K by measurements of magnetostriction along the a axis. Over this temperature range the shape and slope of the magnetostriction curves change, indicative of changes in the magnetic state, crystal structure, and magnetic anisotropy. The results appear to indicate a phase transition that occurs near 106K (onset-completion range of 116–100K). The steepness of the strain transition, its unusual hysteresis, and its temperature dependence appear to indicate a first order phase transition which is activated by applied magnetic field in addition to temperature (see Fig. 1). Magnetostriction measurements at temperature below the transition region appear to indicate a magnetostriction of small overall magnitude (about 30×10−6) but high anisotropy, with anistropy showing considerable temperature dependence.
Preparation of anisotropic Nd(Fe,Mo)12Nx magnetic materials by the strip-casting technique
Authors: Han Jing-Zhi , Liu Shun-Quan , Wang Chang-Sheng , Du Hong-Lin , Yang Jin-Bo , Yang Ying-Chang
Published: June 2006

Strip-casting technique is used to prepare anisotropic Nd(Fe,Mo)12Nx compounds. It is found that, by this technique, the single-phase Nd(Fe,Mo)12 compounds can be directly obtained without postannealing at a rolling velocity of 3m∕s and with an Fe-to-Mo ratio of 7. Under the same nitrogenation conditions, it is easier to introduce the nitrogen atoms into the strip-cast Nd(Fe,Mo)12 powders than into the conventionally cast powders. The microstructure studies of the ingots show that not only the size of strip cast Nd(Fe,Mo)12 grains is small, but also the size distribution of the grains is narrow as compared with those of conventionally cast ingots. Thus, the strip-casting technique is used to synthesize the anisotropic powders of Nd(Fe,Mo)12Nx with a Br of 1.10T, an Hci of 448kA∕m, and a (BH)max of 160kJ∕m3.
Phase-separated alloys for bulk exchange-biased permanent magnets
Authors: Lewis L. H. , Harland C. L. , McCallum R. W. , Kramer M. J. , Dennis K. W.
Published: June 2006

Explorations in the metallurgical synthesis from the melt of bulk permanent magnets with coercivity conferred by the exchange bias mechanism were carried out in a two-phase materials system composed of ferromagnetic FeCo and antiferromagnetic, nominally equiatomic AuMn. Rapid solidification synthesis of composite alloys of nominal composition (Fe65Co35)100−x(AuMn)x (x=5, 10, and 15) was carried out. The ribbons possess AuMn and Au2Mn spherical phases in a bcc (Fe,Co) matrix with a bimodal size distribution of nanoscaled and micron sizes. Magnetization measurements of the composite confirm an exchange bias effect correlated with a coercivity increase over that of the (Fe,Co) melt-spun base alloy. While the exchange bias effect is small, the enhanced coercivity and shifted hysteresis loop observed in a single sample create a strong argument for coercivity enhancement conferred by the exchange bias interaction between antiferromagnetic and ferromagnetic phases in a bulk melt-spun nanocomposite material.
Evolution and propagation of magnetic vortices in chains of Permalloy nanospheres
Authors: Barpanda P. , Kasama T. , Dunin-Borkowski R. E. , Scheinfein M. R. , Arrott A. S.
Published: June 2006

Magnetization reversal in a chain of Permalloy Fe0.2Ni0.8 spheres, whose diameters of 40–60nm are large enough to support vortex structures, is investigated using micromagnetic modeling based on the Landau-Lifshitz-Gilbert equations. The emphasis is on a chain of two spheres with fields applied along and perpendicular to the axis of rotational symmetry. Magnetization processes and critical fields are given for (1) inversion symmetry, with opposite senses of vortex rotation in the two spheres, and (2) a more uniform curling mode, with the sense of rotation the same in both spheres. Symmetry breaking perturbations are shown to be important in the nucleation of changes from one magnetic configuration to the next. As the geometry is approximated by cubic grid cells, whose centers lie within the boundaries of the ideally smooth surfaces, the critical fields are influenced by the grid size. The results for two spheres are generalized in the description of a chain of n spheres, in which at least 2n symmetry states can be selected by the application of inhomogeneous fields.
Bulk anisotropic composite rare earth magnets
Authors: Lee D. , Bauser S. , Higgins A. , Chen C. , Liu S. , Huang M. Q. , Peng Y. G. , Laughlin D. E.
Published: June 2006

Bulk anisotropic composite Nd13.5Fe80Ga0.5B6∕α-Fe and Nd14Fe79.5Ga0.5B6∕Fe–Co magnets with (BH)max=45–50MGOe have been synthesized by blending a Nd–Fe–Ga–B powder with an α-Fe or Fe–Co powder followed by hot compaction at 600–700 °C and hot deformation (die upsetting) at 850–950 °C with a height reduction of 71%. The composite Nd13.5Fe80Ga0.5B6∕α-Fe and Nd14Fe79.5Ga0.5B6∕Fe–Co magnets show microstructures consisting of a very large soft phase up to ∼50μm, which is more than 1000 times larger than the upper size limit of the soft phase expected from the existing models of interface exchange coupling.
Heat deposition in iron oxide and iron nanoparticles for localized hyperthermia
Authors: Baker Ian , Zeng Qi , Li Weidong , Sullivan Charles R.
Published: June 2006

The structural and magnetic properties of four different iron oxide and iron nanoparticles were investigated with respect to the possible application for magnetic hyperthermia treatments. The specific power absorption rates were measured in alternating magnetic fields of 75–150 Oe at frequencies of 10–300 kHz. The heating behavior is discussed in relation to the magnetic behavior of the nanoparticles. It was found that the largest specific absorption rate of 2.8W∕g occurred for the 20–30-nm-diam Fe2O3 nanoparticles.
Tunneling spectroscopy of magnetic tunnel junctions: Comparison between CoFeB∕MgO∕CoFeB and CoFeB∕Al–O∕CoFeB
Authors: Mizuguchi M. , Hamada Y. , Matsumoto R. , Nishioka S. , Maehara H. , Tsunekawa K. , Djayaprawira D. D. , Watanabe N. , Nagahama T. , Fukushima A. , Kubota H. , Yuasa S. , Shiraishi M. , Suzuki Y.
Published: June 2006

Tunneling spectroscopy measurements of magnetic tunneling junctions including two different barrier layers were performed. Intense dips at bias voltages of ±0.3V were observed in second derivative conductance spectra only for a magnetic tunneling junction with a MgO barrier. It was concluded that the electronic structure of the MgO barrier has significant influence on the tunneling process of electrons through magnetic tunnel junctions.
Vacuum hot pressing of Fe–Si–B–Nb-based amorphous powder cores and their high-frequency magnetic properties
Authors: Kang E. Y. , Kim Yoon B. , Kim K. Y. , Chung Y. H. , Baik H. K.
Published: June 2006

FeSiBNb amorphous powder was prepared by gas atomization and subsequently consolidated into bulk amorphous cores by hot pressing after creating an oxide layer on the surface of the powder. FeSiBNb amorphous powders exhibiting a saturation magnetization of 127emu∕g and a coercivity of 0.34 Oe were successfully obtained by gas atomization. Hot pressing enabled consolidation of the FeSiBNb amorphous powder core within the supercooled liquid region. The core prepared from the FeSiBNb amorphous powder covered with an oxide layer of 1μm thickness showed excellent high-frequency characteristics with a stable permeability over 10 MHz and a core loss of 400mW∕cm3 at 50 kHz for Bm=0.1T. The oxide layer formed on the FeSiBNb amorphous powder was effective in improving the frequency dependence of magnetic properties and in reducing the core loss for the FeSiBNb amorphous powder cores.
Rotor position sensing in brushless ac motors with self-shielding magnets using linear Hall sensors
Authors: Zhu Z. Q. , Shi Y. F. , Howe D.
Published: June 2006

This paper investigates the use of low cost linear Hall sensors for rotor position sensing in brushless ac motors equipped with self-shielding magnets, addresses practical issues, such as the influence of magnetic and mechanical tolerances, temperature variations, and the armature reaction field, and describes the performance which is achieved.
Wave front reversal of nonreciprocal surface dipolar spin waves
Authors: Melkov G. A. , Vasyuchka V. I. , Chumak A. V. , Tiberkevich V. S. , Slavin A. N.
Published: June 2006

The process of wave front reversal for nonreciprocal magnetostatic surface waves (MSSWs), propagating in ferromagnetic yttrium iron garnet films, has been studied theoretically and experimentally. The efficiency of wave front reversal for nonreciprocal MSSWs turned out to be approximately ten times smaller than for reciprocal backward volume magnetostatic waves under similar conditions.
Spatially periodic magnetic structure produced by femtosecond laser-interference crystallization of amorphous Co2MnSi thin film
Authors: Kim Jung H. , Kim Jeon , Lim Sang U. , Kim Chang K. , Yoon Chong Seung , Lee Geon Joon , Lee Young Pak
Published: June 2006

Femtosecond laser-interference crystallization (FLIC) was used to form a spatially periodic magnetic structure by selectively crystallizing a paramagnetic amorphous Co2MnSi thin film. Regularly spaced alternating lines of polycrystalline and microcrystalline regions with a periodicity of 2μm were produced by FLIC. The crystalline region composed of ∼100-nm-sized grains contained a nonequilibrium ferromagnetic phase intermixed with β-Mn. The areas between the crystallized lines also received sufficient energy, crystallizing into a microcrystalline state with its grain size ranging from 1 to 5 nm. The magnetic force microscopy of the samples clearly revealed the one-dimensional periodic magnetic domains resulting from the modulated microstructure.
The influence of static-electric field on the transport properties in La0.7Ca0.3MnO3 epitaxial thin films
Authors: Hu F. X. , Gao J.
Published: June 2006

We investigated the effect of static-electric field on the transport properties in La0.7Ca0.3MnO3 (LCMO) epitaxial thin films using a field effect configuration (FEC). A single layer LCMO film with thickness about 100nm was grown on LaAlO3 (LAO) substrate by pulsed laser deposition technique. A simple FEC was then formed on it using lithography technique, in which the LCMO film was used as channel, and LAO substrate as gate. Such a simple configuration is much easier to fabricate compared to the previously reported multilayer FEC. The transport behaviors of the LCMO channel for electric field bias ranging from +80to−80V were studied. Field effect is found to be significant. The maximum of electroresistance (ER) reaches 32%. An important feature is that the ER changes sign with the field direction, but the temperature TP, at which the resistance peaks, keeps nearly unchanged upon any bias. The films could return to their pristine state completely after the bias was removed, and the ER effect can be fully reproducible. However, we found a critical bias exists for these films. When the applied bias reaches +170V, the system could not revert to its initial state, instead a high resistive peak appears at low temperature. The appeared resistive peak behaves sensitively to small currents. A weak current could remarkably depress the resistance. The observed phenomena are discussed in the framework of phase separation mechanism.
Correlations between magnetic and electrical orderings in multiferroic manganites (invited)
Authors: Fiebig M. , Lottermoser Th. , Kneip M. K. , Bayer M.
Published: June 2006

The multiferroic rare-earth compounds RMnO3 with R=Ho–Yb are shown to be the source of “gigantic” magnetoelectric effects. Application of static magnetic or electric field induces a phase transition with antiferromagnetic reordering of the Mn3+ sublattice and ferromagnetic ordering in the rare-earth sublattices. An imbalance of the Mn3+–R3+ superexchange induced by the ferroelectric distortion is revealed as the microscopic origin of the magnetoelectric effect.
Effect of skewing the rotor teeth on the performance of doubly salient permanent magnet motors
Authors: Sheth N. K. , Sekharbabu A. R. C. , Rajagopal K. R.
Published: June 2006

This paper presents the effects of skewing the rotor teeth on the performance characteristics such as flux linkage, back emf, phase inductance, and reluctance torque of an 8∕6 doubly salient permanent magnet motor using a simple method, which utilizes the results obtained from the two-dimensional finite element analysis. The optimum skewing angle is obtained as 12°–15° for the least ripple torque without much reduction in the back emf. Skewing the rotor teeth of an 8∕6 doubly salient permanent magnet motor by 12°–15° will reduce the total harmonic distortion of the back emf profile to 29.69% from the original value of 44.69%. The reduction in the amplitude of the back emf in this case will be 18.79% only.
The dependence of specularity behavior and thermal stability on capping layer thickness in spin valves
Authors: Kim Jong Soo , Lee Seong-Rae
Published: June 2006

We investigated the dependence of capping layer thickness and composition on Mn diffusion and specular reflection behavior in top spin valves. The capping layer materials used included an amorphous ZrAl alloy that was oxidized completely when its thickness was 2nm, improving both the thermal stability and magnetoresistance ratio of the spin valves (SVs). Mn diffusion into the active sensing layer was inhibited markedly when the 2-nm-thick capping layer was present, as this oxide layer provides an oxygen potential gradient along which Mn diffuses preferentially. The thermal stability of a ZrAl-based SV proved greater than that of a traditional Ta-based SV owing to its interdiffusion-resistive microstructure, which provides both a smoother surface and a fine and dense microstructure that lacks crystallinity.
Reconfigurable ferromagnetic resonance properties in nanostructured multilayers
Authors: Zhang M. , Nozaki Y. , Matsuyama K.
Published: June 2006

Ferromagnetic resonance properties in nanostructured multilayers are numerically investigated for the application of spintronics devices. The resonance frequency can be shifted by switching the magnetization state between a parallel and an antiparallel configuration. These remanent states are selectively initialized by choosing the saturation direction of magnetization. In this paper, the signal independency between the two resonant states, the amplitude of the magnetization rotation at the resonance frequency, and the response time to reach equilibrium resonance are systematically studied as a function of the geometrical and magnetic parameters.
A medium microstructure for high area density perpendicular recording
Authors: Zhu Jian-Gang , Tang Yuhui
Published: June 2006

A perpendicular medium microstructure consisting of fully exchange coupled grains with densely distributed nonmagnetic pinning sites, referred to as the percolated perpendicular medium, is proposed. In this medium, the ferromagnetic exchange coupling between the grains ensures sufficient thermal stability, while the densely distributed domain wall pinning sites ensure relatively smooth transition boundaries. The detailed magnetic hysteresis properties and recording characteristics of the percolated perpendicular media are investigated via micromagnetic modeling. The study found that the percolated medium could offer much improved recording properties in terms of enhanced transition sharpness and reduced transition noise while maintaining thermal stability in comparison to present granular perpendicular medium.
Effects of reader response on medium noise modes
Authors: Wang Xiaobin , Feng Xuebing , Jin Zhen , Fernandez-de-Castro Juan
Published: June 2006

Normal-mode analysis is an effective approach to characterize the magnetic noise in recording media. One important application of this technique is to infer the media transition parameter from experimentally measured read-back wave forms. In this paper, micromagnetic simulated media wave forms and read-back wave forms are used to study the effectiveness of extracting media noise characteristics from read-back wave forms. Our results indicate that there could be a fundamental problem in using a normal-mode expansion of read-back wave forms to infer the media-intrinsic transition parameter based on the transition noise model. This is due to the reader effects on media noise eigenmode orthogonality and an oversimplified approximation of the transition noise model. A procedure is described in the paper that could be used to recognize the problem and minimize its effect.
Large scale growth and magnetic properties of Fe and Fe3O4 nanowires
Authors: Yang J. B. , Xu H. , You S. X. , Zhou X. D. , Wang C. S. , Yelon W. B. , James W. J.
Published: June 2006

Fe and Fe3O4 nanowires have been synthesized by thermal decomposition of Fe(CO)5, followed by heat treatments. The Fe wires are formed through the aggregation of nanoparticles generated by decomposition of Fe(CO)5. A core-shell structure with an iron oxide shell and Fe core is observed for the as-prepared Fe wires. Annealing in air leads to the formation of Fe2O3∕Fe3O4 wires, which after heat treatment in a N2/alcohol atmosphere form Fe3O4 wires with a sharp Verwey [Nature (London) 144, 327 (1939)] transition at 125K. The Fe3O4 wires have coercivities of 261 and 735Oe along the wire axis at RT and 5K, respectively. The large increase of coercivity at 5K as compared to RT is due to the increase of anisotropy resulting from the Verwey transition.