bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetoresistance effect of planar-type ferromagnetic tunnel junctions
Authors: Tomoda Yusuke , Shibata Yoshio , Shirakashi Jun-ichi , Takemura Yasushi
Published: June 2006

Planar-type Ni∕Ni oxide/Ni ferromagnetic tunnel junctions were fabricated by using nanolithography techniques. Ni oxide barriers were formed by scanning probe microscope local oxidation. For the observation of magnetoresistance (MR) difference across the junction, source and drain electrodes were patterned into different shapes by focused ion beam lithography, in order to induce magnetic shape anisotropy. The resistance of planar-type Ni∕Ni oxide/Ni ferromagnetic tunnel junction was changed by applying a magnetic field, and MR ratio exhibited above 100% at 16.3K. With increasing the bias voltage from 0.15to1.0mV at 16.3K, the MR ratio decreases from 103% to 5%. Furthermore, the MR ratio at 0.5mV decreases from 8.5% to 0.2% with increasing the temperature from 16.3to200K. This result implies that planar-type ferromagnetic tunnel junctions have potential use as nanoscale magnetoresistive elements.
Effect of external magnetic field on anisotropy of Co∕Cu multilayer nanowires
Authors: Cho Ji Ung , Min Ji Hyun , Ko Seung Pil , Soh Joon Young , Kim Young Keun , Wu Jun-Hua , Choi Sung H.
Published: June 2006

We have investigated the effect of external magnetic field exercised during the fabrication of the Co and Co∕Cu multilayer nanowires in anodic aluminum oxide (AAO) templates using pulse electrodeposition. It is found that the effect becomes significant when the pore size is small. Deterioration occurs in the magnetic properties for the Co nanowires studied, whereas a distinct enhancement in the magnetic properties for the Cu∕Co multilayer nanowires is achieved by applying an external magnetic field during nanowire growth using the AAO template comprising pores of 50nm diameter.
Suppression of insertion loss by slit patterning of a magnetic film in a CoFeB/polyimide hybrid thin-film coplanar line for a rf impedance matching device
Authors: Nakayama Hidetoshi , Yamamoto Tomohiro , Mizoguchi Yuko , Nakazawa Masahiro , Sato Toshiro , Yamasawa Kiyohito , Miura Yoshimasa , Miyake Yuko , Akie Masanori , Uehara Yuji , Munakata Makoto , Yagi Masaaki
Published: June 2006

A hybrid thin-film coplanar line with a slit-patterned CoFeB magnetic film for a rf impedance matching was fabricated, and an effect of the loss reduction by introducing a slit-patterned magnetic film was investigated. The fabricated hybrid thin-film coplanar-line device consisted of the top and bottom 5μm thick copper conductors and an inner (0.5μm thick polyimide)/(0.15μm thick CoFeB)/(0.5μm thick polyimide) trilayer. A signal linewidth was 6μm. The total width of the slit-patterned magnetic film was about 200μm. The devices with some kinds of the width of the magnetic film stripe were fabricated. As a result, insertion loss per unit line length decreased greatly above 1.5GHz with decreasing width of the magnetic film. The loss suppression was due to an effect of reducing the in-plane eddy current of the magnetic film. On the other hand, the propagation signal wavelength of the device increased with decreasing width of the magnetic film, which was due to a decrease of distributed inductance. When applying the device to a quarter-wavelength impedance matching device, the slit-patterned magnetic film was effective for decreasing the insertion loss at high frequencies beyond 1.8GHz.
Substrate effects on microstructure and magnetic properties of electrodeposited Co nanowire arrays
Authors: Min Ji Hyun , Cho Ji Ung , Kim Young Keun , Wu Jun-Hua , Ko Young-Dong , Chung Jin-Seok
Published: June 2006

The effect of substrates on the microstructure and magnetic properties of electrodeposited Co nanowire arrays in porous anodic aluminum oxide membrane was investigated. It is found that the nanowires possess dominant (002) and (110) textures on the Co-coated nanocrystalline Finemet™ and Au substrates, respectively. Magnetic measurements show that the easy axis of the nanowire arrays switches from perpendicular to the wire axis on Au to parallel to the wire axis on the Co-coated nanocrystalline Finemet™ substrate.
Precessionless spin transport wire confined in quasi-two-dimensional electron systems
Authors: Liu Ming-Hao , Chen Son-Hsien , Chang Ching-Ray
Published: June 2006

We demonstrate that in an inversion-asymmetric two-dimensional electron system (2DES) with both Rashba and Dresselhaus spin-orbit couplings taken into account, certain transport directions on which no spin precession occurs can be found when the injected spin is properly polarized. By analyzing the expectation value of spin with respect to the injected electron state on each space point in the 2DES, we further show that the adjacent regions with technically reachable widths along these directions exhibit nearly conserved spin. Hence a possible application in semiconductor spintronics, namely, precessionless spin transport wire, is proposed.
Pure paramagnetic behavior in Mn-doped ZnO semiconductors
Authors: Alaria J. , Bouloudenine M. , Schmerber G. , Colis S. , Dinia A. , Turek P. , Bernard M.
Published: June 2006

Polycrystaline Mn-doped zinc oxides (Zn1−xMnxO) were synthesized by coprecipitation method with x varying between 0.01 and 0.1. Raman spectroscopy indicates the appearance of an additional mode which is an indicator for the incorporation of Mn ions into the ZnO host matrix. The magnetic properties have been studied by electron paramagnetic resonance (EPR) spectroscopy. The Mn-related EPR spectra exhibit the expected pattern for isolated Mn ions. Temperature dependence of the reciprocal integrated EPR signal follows a Curie law indicating a typical paramagnetic behavior for x⩽0.05.
Ultrafast magnetization dynamics investigated in real space (invited)
Authors: Vomir M. , Andrade L. H. F. , Beaurepaire E. , Albrecht M. , Bigot J.-Y.
Published: June 2006

The ultrafast magnetization dynamics induced in ferromagnetic thin films by femtosecond optical pulses is investigated in real space. Our experimental method allows us to retrieve the three-dimensional trajectory of the magnetization vector over a large temporal range, from ∼100fsto∼1ns. This approach carries important information both on the initial spin dynamics and the magnetization precession. An ultrafast decrease of the magnetization modulus, occurring within ∼100fs, reveals the initial laser induced demagnetization. It is accompanied by a reorientation of the magnetization vector, taking place during the first picosecond, a process which strongly depends on the material anisotropy. Finally, the three-dimensional trajectory of the magnetization during its precession and damping undertakes a complex pathway as the magnetization modulus varies until the energy is dissipated to the environment in the nanosecond time scale.
The temperature dependence of magnetization in ferrofluids
Authors: Virden A. E. , O’Grady K.
Published: June 2006

Ferrofluid samples were prepared for magnetic characterization prior to use in a ESA experiment on convection currents in microgravity conditions on the International Space Station. The experiment requires a fluid with a highly temperature dependent magnetization at low field over the temperature range of 30–100°C. Ni–Zn ferrites of varying chemical composition were prepared in order to investigate the effect of a change in the Curie temperature on the temperature dependence of magnetization. Ni0.5Zn0.5 was found to be the composition with the largest ΔM of 0.4emu∕g. Magnetite samples were prepared to investigate the effect of high MS and varying particle size on ΔM. Magnetite fluids with particle sizes of 6 and 10nm have ΔM’s of 0.8 and 1.6emu∕g, respectively. Therefore, the dominant effect is high MS and particle size driven by the field dependence of the Langevin function.
10
GHz
bandstop microstrip filter using excitation of magnetostatic surface wave in a patterned Ni78Fe22 ferromagnetic film
Authors: Vroubel Marina , Zhuang Yan , Rejaei Behzad , Burghartz Joachim N.
Published: June 2006

Various microstrips with a ferromagnetic core were designed and fabricated on a silicon substrate. The core was formed by a 0.5-μm-thick Ni78Fe22 film, patterned into rectangular prisms. Measurement results for attenuation constant versus frequency show a peak value of ∼50dB∕cm around 10GHz. Electromagnetic simulations show that the attenuation observed is due to the energy exchange between the quasi-TEM mode of the microstrip and magnetostatic surface modes excited in the direction perpendicular to the signal line.
Micromagnetic simulation for detection of a single magnetic microbead or nanobead by spin-valve sensors
Authors: Liu Yaowen , Jin Wei , Yang Yaping , Wang Zhiguo
Published: June 2006

Micromagnetic simulation for detecting magnetic beads is performed by using a high-sensitivity spin-valve sensor as the detector. The magnetic beads polarized by a dc magnetic field contribute to a nonuniform dipole field, which can affect the magnetization state of spin-valve sensor, leading to a detectable resistance change. Simulations show that 2μm diam microbeads can be detected with ∼98μV voltage change per bead, which is consistent with the experimental results (∼118μV per bead), indicating that single molecule detection with a micron-sized bead marker is possible. Detection of a single 250nm nanobead shows a sensitivity of ∼34μV, which is close to the present experimental noise level. This suggests that the detection of a single nanosized marker requires enhanced electronic signal by either reducing sensor dimensions or using high-moment ferromagnetic particles as labels.
Study of stacking fault effect on magnetic anisotropy of CoPtCr–SiO2 perpendicular media by synchrotron radiation x-ray diffraction
Authors: Kubo T. , Kuboki Y. , Tanuma R. , Saito A. , Watanabe S. , Shimatsu T.
Published: June 2006

Thin films of CoPtCr and CoPtCr–SiO2, perpendicular magnetic media materials, were investigated by synchrotron radiation grazing-incidence x-ray diffraction. The analysis of diffraction peaks in a reciprocal space provided the variation of stacking faults as functions of Pt content in these materials. It was found that stacking faults start increasing at 15–20 and 25–30at.% Pt for CoPtCr–SiO2 and CoPtCr films, respectively. These results can well explain the phenomenon whereby the magnetic anisotropy of CoPtCr–SiO2 increases with an increasing Pt content and decreases above 20at.% Pt, whereas that of CoPtCr increases up to 30at.% Pt and then decreases.
Magneto-optical and optical spectroscopic ellipsometries of La2∕3Sr1∕3MnO3 thin films
Authors: Mistrik J. , Yamaguchi T. , Veis M. , Liskova E. , Visnovsky S. , Koubaa M. , Haghiri-Gosnet A. M. , Lecoeur Ph. , Renard J. P. , Prellier W. , Mercey B.
Published: June 2006

Magneto-optical (MO) spectroscopy combined with spectroscopic ellipsometry has been used to learn about the electronic transitions in La2∕3Sr1∕3MnO3 (LSMO) film pulse laser deposited onto SrTiO3 (100) substrates. The dispersion function of LSMO films was parametrized by the sum of three damped Lorentz oscillators and adjusted together with the film thickness numerically. With the knowledge of film optical properties the off-diagonal elements of the LSMO permittivity tensor (magneto-optical constants) were calculated from the complex polar Kerr effect measured on the thickest (60nm) LSMO film (considered as optically thick). The considered approximation as well as the reliability of the obtained optical and MO constants was verified by the consistence of the calculated and experimental MO spectra for the thinner LSMO films (where the propagation effect plays an important role). The resolved electronic transition centered at about 4eV features the spectral dependences of diagonal and off-diagonal elements of LSMO permittivity in the studied spectral range. In the molecular orbital picture this could be assigned to the charge transfer electronic transition from the O 2p states to the Mn 3d t2g states, split by the spin-orbit interaction.
Room temperature magnetism in semiconducting films of ZnO doped with ferric ions
Authors: Yoon S. D. , Chen Yajie , Heiman Don , Yang Aria , Sun Nian , Vittoria C. , Harris V. G.
Published: June 2006

Films consisting of Zn1−xFexO were prepared by alternating-target laser ablation deposition. The Fe doping levels ranged from x=0.016to0.125at.%. X-ray diffraction and energy dispersive x-ray spectroscopy measurements showed only (002n) reflections of the ZnO host and confirmation of the Fe concentration, respectively. For films grown on (001) Al2O3 at 300K, room temperature average saturation magnetization, ⟨4πMs⟩, measured from superconducting quantum interference device (SQUID) hysteresis loops for x=0.125±0.025 was 172G. Although SQUID measurements were sensitive to the average value of the saturation magnetization, ferrimagnetic resonance measurements appeared to be sensitive only to the saturation magnetization of the so-called magnetic layer containing ferric ions. We believe that we have produced a host semiconductor material doped with impurities of ferrimagnetic ordering.
Electromagnetic body force calculation based on virtual air gap
Authors: Choi Hong-soon , Park Il-han , Lee Se-Hee
Published: June 2006

Up to this date, the conventional electromagnetic force calculation methods such as Maxwell stress, virtual work, Kelvin’s formula, equivalent magnetic charge, and equivalent magnetizing current produce results where the surface component takes up a major portion of the total force, with the portion of the body force being very small or even none. As the formulation of the above mentioned methods starts from the concept of body or volume force, there has been controversy over the true concept of electromagnetic force identity. In this paper, it is shown that electromagnetic body force, which is also called volume force, can be calculated using virtual air-gap scheme that is derived from the generalized equivalent source methods. For the body force calculation, the application of virtual air gap is extended to calculate the force of each finite element as if an element is an independent body surrounded by virtual air gap. The force calculation methods adopted in this paper include Maxwell stress, magnetic charge, and magnetizing current. The examination of the calculated force distribution shows that the force can be expressed only as body force distribution. The total force calculated by the volume integration of the body force on the magnetized body agrees well with the total force calculated by conventional approaches.
Ion implantation of rare-earth dopants in ferromagnetic thin films
Authors: Dasgupta V. , Litombe N. , Bailey W. E. , Bakhru H.
Published: June 2006

We show that high-dose ion implantation can be used to introduce rare-earth dopants for the control of precessional dynamics in magnetic thin films. Tb and Gd ions have been implanted in Ni81Fe19 through Ta masks at dosages from 1×1014∕cm2 to 1×1015∕cm2. Effects on dynamics are found to be similar to those contributed by cosputtered Tb and Gd dopants in Ni81Fe19 (50nm). Broadband ferromagnetic resonance measurements from 0to18GHz show that adjustments in damping α from 0.008 to 0.040 are fully intrinsic (Gilbert type) and roughly proportional to dose. The technique enables the creation of films with spatially modulated precessional characteristics.
Thermal fluctuations in a titanomagnetite mineral: A two-level subsystem approach
Authors: Viddal C. A. , Roshko R. M.
Published: June 2006

We present measurements of the field and temperature dependences of the relaxation of the magnetic moment of a magnetic mineral consisting of nanodimensional particles of titanomagnetite Fe3−xTixO4, with x≅0.1, embedded in a volcanic glass, over an observation time window of 10s⩽t⩽104s, following recoil from a positive saturating field to negative holding fields in the vicinity of the coercive field. The relaxation data are analyzed within the framework of a model which decomposes the free energy landscape into an ensemble of double well potentials, and the thermal fluctuation field Hf for this system is shown to exhibit a maximum as a function of temperature. Numerical simulations of viscosity isotherms based on the double well formalism are presented, which show that this maximum is a natural feature of the formalism, related to the distribution of characteristic energies of the double wells, and thus does not contradict the assumption of Arrhenius relaxation dynamics based on Maxwell-Boltzmann statistics.
Photon-induced magnetization changes in single-molecule magnets (invited)
Authors: Bal M. , Friedman Jonathan R. , Rumberger E. M. , Shah S. , Hendrickson D. N. , Avraham N. , Myasoedov Y. , Shtrikman H. , Zeldov E.
Published: June 2006

Microwave radiation applied to single-molecule magnets can induce large magnetization changes when the radiation is resonant with transitions between spin levels. These changes are interpreted as due to resonant heating of the sample by the microwaves. Pulsed-radiation studies show that the magnetization continues to decrease after the radiation has been turned off with a rate that is consistent with the spin’s characteristic relaxation rate. The measured rate increases with pulse duration and microwave power, indicating that greater absorbed radiation energy results in a higher sample temperature. We also performed numerical simulations that qualitatively reproduce many of the experimental results. Our results indicate that experiments aimed at measuring the magnetization dynamics between two levels resonant with the radiation must be done much faster than the ⩾20μs time scales probed in these experiments.
Magnetic field analysis of laminated core by using homogenization method
Authors: Muto H. , Takahashi Y. , Wakao S. , Fujiwara K. , Kameari A.
Published: June 2006

This paper describes an approach to efficient modeling of the microscopic structure of magnetic materials in the nonlinear magnetostatic field analysis of a laminated core. When the ordinary finite element method is applied, large memory and computational cost are required due to the huge number of elements generated by detailed modeling of a laminated core. In order to overcome the above difficulties, we introduce the homogenization method, which is widely used in continuum mechanics, into the magnetic field computation and expand the method into the nonlinear analysis. Furthermore, the specialized homogenization method for a laminated core is carried out to verify the above homogenization method in the electromagnetism. Some numerical results are also presented to demonstrate the effectiveness of the proposed method.
Microstructure and magnetic properties of electrodeposited CoPtP alloys
Authors: Park Ho Dong , Lee Kwan Hyi , Kim Gyeung Ho , Jeung Won Young
Published: June 2006

CoPtP alloys have been grown by electrochemical process in an external magnetic field in order to enhance the perpendicular magnetic properties. The coercivity and squareness of the alloys were improved as the external magnetic field was increased. The alloys have a mosaic microstructure consisting of grains with size in the range of 10–15nm. The grains are separated by highly well defined 1–2nm grain boundaries. The alloys exhibit a columnar microstructure with a hcp [002] fiber texture. The films exhibit significant perpendicular magnetic anisotropy and permanent magnetic properties in the perpendicular direction, with coercivity of up to 6.1kOe and squareness of up to 0.9.
Analysis of 60nm diam spin dependent tunneling memory cells with thermally assisted writing
Authors: Pohm A. V. , Daughton J. M. , Deak J. G.
Published: June 2006

An analysis has been performed for spin dependent tunneling memory cells with a 5nm thick pinned, storage magnetic layer with a 60nm diam and with a saturation magnetization of 1000emu∕cm3. In reading, the required pinning fields plus anisotropy fields for the cases of with and without error correction were found to be 79 and 108Oe. The required total fields for writing for the cases with and without error correction were calculated to be 93 and 129Oe. The write current needed to provide the total, effective, 129Oe write field was calculated to be 1.1mA for the assumed word line structure. The needed heating current through the tunnel cell was calculated to be 41μA assuming a tunnel junction and an added resistive layer. A multiple sample read mode with an autozero step and a word read field requires word read currents of 2.50 and 2.75mA. The multisample, autozero mode has wider margins. If the semiconductor selection matrix can be placed underneath the cells, the calculated cell is 0.022μm2.
Fabrication of Mn-doped ZnO diluted magnetic semiconductor nanostructures by chemical vapor deposition
Authors: Liu J. J. , Yu M. H. , Zhou W. L.
Published: June 2006

Mn-doped ZnO diluted magnetic semiconductor (DMS) nanostructures were prepared by direct reaction of zinc metal and manganese chloride powder under oxygen environment using chemical vapor deposition method. Several kinds of nanostructures including nanorod, bowl, and cage were obtained at different deposition temperature zones. The morphologies and crystal structures of the as-synthesized nanostructures were characterized using field-emission scanning electron microscopy, transmission electron microscopy, and x-ray diffraction spectroscopy. Superconducting quantum interference device measurement shows that the doped nanorods exhibited low-temperature ferromagnetism at 5K with Curie temperature around 37K, whereas the DMS nanocrystalline bowl/cage structures have room-temperature ferromagnetic behavior.
Theoretical calculation of magnetic structure variation in Pr5Ni2Si3
Authors: Song S. H. , Snyder J. E. , Jiles D. C.
Published: June 2006

The variation of magnetization with temperature of the Pr5Ni2Si3 compound was calculated using a nearest neighbor exchange interaction approximation. Pr atoms, which are the only element in this compound with a net magnetic moment, were classified into three types based on the number of nearest neighbor exchange interactions. The expected magnetization versus temperature curve for each type of Pr atom was calculated using the Brillouin function, as well as the average magnetization versus temperature curve for the entire unit cell. The results show that the “corner” atoms exhibit very different behavior from that of the other types of Pr atoms on the “center” or “edge” sites. This is due to the broken symmetry in exchange interaction at the corner site due to interactions with atoms from outside the unit cell that are in closer proximity than atoms within the unit cell. This is considered to be the cause of a second magnetic phase transition observed at a lower temperature than the Curie temperature.
Transition parameter evolution during decay
Authors: Valcu Bogdan , Richter H. J.
Published: June 2006

Time-domain analysis of the transition noise is applied to playback wave forms captured during thermal decay of perpendicular media. The transition parameter is extracted for each wave form and its time dependence is obtained. The experimental data show that the transition parameter remains constant with time.
Vortex dynamics in coupled ferromagnetic multilayer structures
Authors: Chou Kang Wei , Puzic Aleksandar , Stoll Hermann , Schütz Gisela , Van Waeyenberge Bartel , Tyliszczak Tolek , Rott Karsten , Reiss Günter , Brückl Hubert , Neudecker Ingo , Weiss Dieter , Back Christian H.
Published: June 2006

Magnetization dynamics in ferromagnetic multilayer structures was studied by time-resolved transmission x-ray microscopy. A square-shaped 1×1μm2 trilayer structure consisting of Co(20nm)∕Cu(10nm)∕Permalloy Ni80Fe20(20nm) was investigated. Each ferromagnetic layer showed a Landau-like domain configuration with a single vortex. A gyrotropic vortex motion was excited by an in-plane magnetic field alternating at a frequency of 250 MHz. The movement of the magnetic vortex in each individual magnetic layer was imaged by taking advantage of the element specificity of the x-ray magnetic circular dichroism. A 180° phase shift between the gyrotropic vortex motion in the Permalloy and the Co layer was observed. This phase shift can be ascribed to the magnetic coupling between the layers.
The effect of doping level and sintering temperature on Jc(H) performance in nano-SiC doped and pure MgB2 wires
Authors: Shcherbakova O. , Dou S. X. , Soltanian S. , Wexler D. , Bhatia M. , Sumption M. , Collings E. W.
Published: June 2006

Nanoscale SiC doped Fe∕MgB2 wire samples were prepared by an in situ reaction technique using SiC doping levels of 0, 5, 10, and 15 wt %. Samples were heat treated at different temperatures using different temperature profiles. The effects of doping level and sintering temperature on superconducting properties of wire samples were investigated. The important finding of this study was that the enhancement in Jc(H) by nano-SiC doping can be achieved at different field regions by appropriate compromising of the doping level and sintering temperature.
Crystal structure and physical properties of Gd3Co4Sn13 intermetallic antiferromagnet
Authors: Pires M. A. , Ferreira L. Mendonça , Duque J. G. S. , Urbano R. R. , Agüero O. , Torriani I. , Rettori C. , Bittar E. M. , Pagliuso P. G.
Published: June 2006

We have synthesized single crystalline samples of Gd3Co4Sn13 intermetallic compound using a Sn-flux method. This compound crystallizes with a cubic Yb3Co4Sn13-type structure, space group Pm-3n, which has 40 atoms per unit cell. Measurements of the magnetic susceptibility, heat capacity, electrical resistivity, and electron spin resonance (ESR) revealed that Gd3Co4Sn13 is a metallic Curie-Weiss paramagnet at high temperature and presents an antiferromagnetic ordering below TN=14.5K. In the paramagnetic state, a single Gd3+ ESR line with a nearly temperature independent g∼2.005(2) is observed, and its linewidth follows a Korringa-like behavior as a function of temperature. From the Korringa rate (ΔH∕ΔT∼4Oe∕K) and g-shift (Δg∼0.012) obtained from the ESR experiments combined with the magnetic susceptibility and specific heat data for Gd3Co4Sn13, we have extracted the exchange parameters between the Gd3+ local moments and the conduction-electrons (c-e) in this compound. This exchange parameter Jfs≈10meV was found to be c-e wave-vector independent and the electronic structure of Gd3Co4Sn13 has a single band character.
Combined effects of magnetic fields and temperature changes on 1-aminonaphthalene-8-sulfonic acid fluorescence in red blood cell ghost cell membrane
Authors: Iwasaka M. , Yaoita M. , Iwasawa T. , Ueno S.
Published: June 2006

In the present study, we performed an experiment to clarify the possible effects of magnetic fields of up to 8 T on cell membrane fluidity by using red blood cell ghosts and a fluorescence dye, 1-aminonaphthalene-8-sulfonic acid (ANS). The time course of ANS emission at 480 nm under the influence of a magnetic field at 5 T was observed. The effects of multiple rapid temperature changes and magnetic fields were investigated. The emission intensity at 480 nm increased when the temperature of the cell holder was increased from 20 to 38–46 °C for 15 min. A change in temperature exhibited an increase in the fluidity of the lipid molecules in the cell membrane and increased the population of ANS molecules emitting light at 480 nm in the cell membrane, which is hydrophobic. A discontinuous change in fluorescence at 38–40 °C was exhibited under exposure to a magnetic field at 5 T, while the temperature dependency was continuous without exposure to the magnetic field. In addition, under exposure to the magnetic field, the fluorescence during a decrease in temperature from 38 to 20 °C remained at a level close to the fluorescence during an increase in temperature. The results indicated that the fluidity of the molecules in the cell membrane was decelerated by exposure to magnetic fields at 5 T. We speculated that the magnetic orientation in a part of the lipid membrane disturbed the release of ANS molecules from a hydrophobic region of the membrane.
Ferrite losses of cores with square wave voltage and dc bias
Authors: Van den Bossche Alex P. , Valchev Vencislav Cekov , Van de Sype David M. , Vandenbossche Lode P.
Published: June 2006

Ferrite material properties may vary depending on the grade and manufacturer: there are differences between batches and also the production process may change in time. On the other hand, in power applications, the usual voltage wave forms are closer to square wave than to sine wave, and moreover they contain a dc bias component that can easily more than double the ferrite losses. Therefore, in loss critical applications it is good to be able to both test and model the losses of the actual ferrite cores under the same conditions as in the actual power application. In this paper, experiments were carried out at different induction levels and dc bias currents. Losses were measured at frequencies of 20, 100, and 500 kHz on a ferrite core with Ferroxcube 3F3 material, a Mn–Zn ferrite. We observe that mainly the lower frequencies are sensitive to dc bias. A model including wide ranges in amplitude, frequency, and also dc bias is proposed. In this model, the losses are separated in three terms: a hysteresis dependent term, an additional loss term depending on dc bias, and a high frequency term.
High frequency properties of polymer composites consisting of aligned Fe flakes
Authors: Zhang Xiaokai , Ekiert Thomas , Unruh Karl M. , Xiao John Q. , Golt Michael , Wu Ruixin
Published: June 2006

We have successfully fabricated composites consisting of aligned Fe flakes embedded in a polymer matrix. Similarly high values of permeability and permittivity have been achieved, resulting in potentially significant improvements in device miniaturization, impedance matching, and bandwidth. Various effective medium theory models fail to give accurate values of permeability and permittivity of flake/polymer composites, indicating that modifications are needed for flake shape inclusions.
Relation between interface stress in the seed layer and the orientation ratio of longitudinal media
Authors: Ono Takuya , Kawada Yasuyuki , Ataka Toyoji , Soma Ken-ichiro
Published: June 2006

The orientation ratio (OR) is a key issue to achieve high density in longitudinal recording media. Recent recording media have seed layers which exclusively promote small grain growth of the recording layer. In this paper, the effect of seed layers on OR was investigated by the use of various seed materials deposited twice. OR tends to decrease as the thickness of the seed layer is increased; however, the degree of decrease is quite different with seed material. A seed material with small Young’s modulus is preferable for a large OR. These results suggest that OR depends on the interface stress which is relieved as seed layer thickness is increased. Moreover, the relation between the stress in the seed layer and OR was also considered with a multilayer model.
Drive integration in perpendicular recording (invited)
Authors: Guarisco Davide , Li Zhaohui , Higgins Bill E. , Saito Kaz , Wu Yan , LeFebvre Andrew
Published: June 2006

This paper reports on the progress in perpendicular drive integration. In the first part, an experiment comparing the effect of magnetic spacing variation between longitudinal and perpendicular recordings is discussed. First, it is shown that the Wallace equation applies to perpendicular recording provided that the density of the recorded signal is sufficiently high. Using a thermal actuator, the effect of separately changing the read and write magnetic spacings of longitudinal and perpendicular head and media is compared. It is shown that the bit error rate is more sensitive to write space variations versus read space variations. However, the dependence is similar between longitudinal and perpendicular components. In the second part, two types of single-head, 95mm, 7200rpm desktop perpendicular drives (40 and 80Gbyte capacity) are presented. They both achieve good bit error rate and off-track capability in all zones. The thermal decay rate of the 40Gbyte drive was measured and compared to a similar longitudinal drive. It was found that the decay rate is much smaller in the case of the perpendicular drive in the range of −6–+80°C. The thermal decay rate of the two perpendicular drives was compared at ambient temperature and found to be equally small. Finally, a measurement of the bit error rate of the 40Gbyte perpendicular drive over the same temperature range demonstrates that the drive operates well in this temperature range.
Magnetization switching induced by in-plane current with low density in Pt∕Co∕Pt sandwich
Authors: Lin W. W. , Sang H. , Liu D. , Jiang Z. S. , Hu A. , Wu X. S. , Xiao G.
Published: June 2006

We have observed that the extraordinary Hall resistance of Pt∕Co∕Pt sandwich with perpendicular magnetic anisotropy changes from positive to negative drastically as the current density increases in an applied field, indicating the magnetization switching induced by the current. There exists a critical current density that changes for the different applied field with the order of current density of 104A∕cm2, which is much lower than that reported in literatures on the current-induced magnetization switching. The results of the extraordinary Hall effect of the sample in different in-plane current density show that the magnetization-switching field decreases with the increment of current density when the current density is larger than 104A∕cm2.
Study of parallel and perpendicular exchange biases in FePt–FeMn multilayers
Authors: Phuoc Nguyen N. , Suzuki Takao
Published: June 2006

A systematic investigation of parallel and perpendicular exchange biases in [FePt∕FeMn]10 multilayers deposited onto MgO(100) substrates by ion beam sputter-deposition system is performed. The thickness (FeMn) dependences of exchange bias field and blocking temperature are discussed. The blocking temperature increases with the increase of FeMn thickness and becomes nearly constant as the FeMn thickness is beyond a critical value. Of interest is the blocking temperature of the parallel exchange bias which is higher than that of the perpendicular one. Also, the angular dependence of parallel and perpendicular exchange biases is investigated.
Observation of nitrogen polarization in Fe–N using soft x-ray magnetic circular dichroism
Authors: Sánchez-Hanke C. , Gonzalez-Arrabal R. , Prieto J. E. , Andrzejewska E. , Gordillo N. , Boerma D. O. , Loloee R. , Skuza J. , Lukaszew R. A.
Published: June 2006

X-ray magnetic circular dichroism (XMCD) measurements were performed on epitaxial iron nitride thin films at the nitrogen K and at the Fe LIII and LII absorption edges. The iron nitride samples measured with XMCD consist primarily of γ′ phase with no observed enhancement on their magnetic moment as compared to that of pure Fe. The XMCD difference signal between left and right elliptically polarized x rays shows a small effect in the 10−5 range at the N edge, indicative of the possible polarization of nitrogen in the γ′ Fe–N samples. XMCD spectra collected with higher energy resolution reveal the presence of multiple components in the Fe LIII absorption edge that are related to different environments for the Fe atoms, i.e., near neighbors or next near neighbors to the N sites. Finally element specific hysteresis loops were also recorded at the N and Fe absorption edges using the difference signal in various incident beam angle geometries.
X-ray absorption spectroscopy studies on magnetic tunnel junctions with AlO and AlN tunnel barriers
Authors: Mun B. S. , Moon J. C. , Hong S. W. , Kang K. S. , Kim K. , Kim T. W. , Ju H. L.
Published: June 2006

X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) measurements of the optimized magnetic tunnel junctions (MTJs) with AlO and AlN barriers have been performed to study the chemical structures of the barrier and the underlying layer. These MTJs with AlO and AlN barriers exhibited increased tunneling magnetoresistance (TMR) after annealing at 200°C from 27% to 45% and from 25% to 33%, respectively. Surprisingly, the XPS and XAS measurements confirmed that both the as-grown and the annealed MTJs had metallic Co and Fe at the interface between the barrier and the underlying CoFe layer. After annealing, under-stoichiometric AlOx and AlNx phases in MTJs with AlO and AlN barriers partially transformed into stoichiometric Al2O3 and AlN phases, respectively. Thus the increase in TMR after annealing for MTJs with clean interface between the barrier and the underlying layer is believed due to the anion redistribution inside the barrier layer, not from back diffusion from pinned magnetic layer to barrier layer.
Inverse magnetoresistance caused by nano-nitride-layer doping at the inner interfaces in the sandwich of Co∕Cu∕Co
Authors: Zhao Z. C. , Wang H. , Xiao S. Q. , Huang D. , Gu Y. Z. , Xia Y. X. , Jin Q. Y. , Zha C. L. , Wu X. S.
Published: June 2006

The influence of a nano-nitride-layer (NNL) doped at different interfaces in the structure of Cu∕Co∕Cu∕Co∕Cu on magnetoresistance (MR) is investigated. As the NNL is doped at the inner interfaces of the core Co∕Cu∕Co sandwich, an inverse MR is observed. This contrasts sharply with that doping at the two outer interfaces between the core sandwich (Co∕Cu∕Co) and the buffer or/and the capping layers. The result arises from the negative spin asymmetry induced by the NNL doping under different interfacial circumstances. Moreover, the MR value increases in magnitude as temperature is decreased from room temperature to 4.2K.
Ferromagnetic properties of anatase Ti1−xFexO2−δ thin films
Authors: Kim Kwang Joo , Park Young Ran , Ahn Geun Young , Kim Chul Sung , Park Jae Yun
Published: June 2006

The effects of Fe doping on the magnetic and electronic properties of reduced TiO2−δ thin films have been investigated. Anatase Ti1−xFexO2−δ films exhibit a ferromagnetic behavior at room temperature for a certain range of Fe doping. Conversion electron Mössbauer spectroscopy measurements indicate that Fe2+ and Fe3+ ions coexist in the Fe-doped films, substituting the octahedral Ti4+ sites. The contribution of possible Fe3O4 clusters to the observed ferromagnetism is not likely to happen. The Ti1−xFexO2−δ films exhibit a p-type character by Hall effect measurements but the observed ferromagnetism turns out to be independent of the hole concentration. The observed ferromagnetism in the Ti1−xFexO2−δ films can be explained in terms of a direct ferromagnetic coupling between two neighboring Fe3+ ions via an electron trapped in oxygen vacancy nearby.
Nanostructure calculation of CoAg core-shell clusters
Authors: Dorfbauer F. , Schrefl T. , Kirschner M. , Hrkac G. , Suess D. , Ertl O. , Fidler J.
Published: June 2006

Detailed studies of the structure of magnetic nanoclusters are crucial for understanding their magnetic properties. We have investigated the structure of CoxAg1−x nanoparticles by means of molecular dynamics simulations utilizing the embedded atom method. Starting from a completely random distribution of Co and Ag atoms, the clusters were heated up to 1300K and subsequently cooled down. The size of the resulting particles was 2.8nm (864 atoms). A clear segregation of the Ag atoms on the surface of the Co core was obtained.
Interfacial and annealing effects on magnetic properties of CoFeB thin films
Authors: Wang Yung-Hung , Chen Wei-Chuan , Yang Shan-Yi , Shen Kuei-Hung , Park Chando , Kao Ming-Jer , Tsai Ming-Jinn
Published: June 2006

The interfacial and annealing effects on magnetic properties of CoFeB thin films with Ta and Ru interfaces were investigated. It is found that the thickness of magnetically dead layer of as-deposited CoFeB film strongly depends on the interfaces. After annealing above 150°C boron atoms seem to diffuse out of CoFeB film and the effective saturation magnetization of CoFeB film increases with annealing temperature and annealing time. In addition, CoFeB film with Ta interfaces remains amorphous while that with Ru interfaces starts to crystallize during the annealing above 250°C. Furthermore, the annealing-induced anisotropy field of CoFeB film can be modified by using different seed and capping materials.
Electroplated CoFe thin films for electromagnetic microactuators
Authors: Bedenbecker Matthias , Gatzen Hans H.
Published: June 2006

To replace NiFe alloys used as flux guides in magnetic microelectromechanical systems, electroplated CoFe thin films were examined. The films were deposited using pulse plating. The results show a strong influence of the reverse current Ireverse on the deposition rate and the saturation flux density Bs. The relative permeability μr is influenced both by the forward current Iforward and by reverse current Ireverse. Based on the examinations an optimized deposition was performed. A film thickness of 15μm was reached during a deposition time of 1h. This film exhibited a saturation flux density Bs of 1.4T, a coercivity Hc of 1130kA∕m, and a relative permeability μr of 290. At this thickness, no delamination occurred and the film showed only minor signs of corrosion, a phenomenon CoFe films are typically prone to.
L
1
FePt–MgO perpendicular thin film deposited by alternating sputtering at elevated temperature
Authors: Peng Yingguo , Zhu Jian-Gang , Laughlin David E.
Published: June 2006

FePt – MgO two phase thin films have been obtained by an alternating sputtering method at elevated temperatures. It is found that the L10 FePt grains grow in a columnar manner through the thickness of the film and possess a (001) perpendicular texture promoted by the (200)-textured crystalline MgO underlayer. The amorphous MgO in the two phase mixture forms uniform separation walls between FePt grains. The microstructure is similar to that of Co-alloy/oxide granular media.
Critical phenomenon in soft magnetic properties of giant magnetostrictive materials: Computer simulation
Authors: Fukunaga Hirotoshi , Yamaguchi Takayuki
Published: June 2006

Dependence of magnetostrictive and magnetic properties on grain size was calculated numerically for an isotropic giant magnetostrictive material. The model magnet assumed is composed of 8000 cubic (Tb0.3Dy0.7)Fe2 grains. The direction of magnetization and the magnetostriction of each grain was determined for a given applied field under the consideration of the anisotropy, exchange, magnetoelastic, elastic, and Zeeman energies. Subsequently, the hysteresis loop and the magnetostriction versus applied field curve was obtained by varying the applied field. With decreasing the grain size D, the coercivity Hc and dλ∕dH, where λ is the magnetostriction, decreased abruptly at D=25nm. This improvement in soft magnetic properties exceeded the expected improvement from Herzer’s calculation, in which Hc was proportional to D6. In order to study the significant improvement in detail, we calculated magnetic and magnetostrictive properties with varying magnetostriction and anisotropy constants. Resultantly, it was clarified that the critical phenomenon occurs when the total of elastic and magnetoelastic energies exceed the magnetic anisotropy energy in magnitude.
Micromagnetic simulation of small-angle neutron scattering from magnetic recording media
Authors: Ogrin F. Y. , Lee S. L. , Wismayer M. , Thomson T. , Dewhurst C. D. , Cubitt R. , Weekes S. M.
Published: June 2006

A micromagnetic simulation of the magnetic morphology of CoCrPtB based longitudinal recording media is used to model small-angle neutron scattering data and provide a quantitative description of the local flux density in these nanostructured magnetic materials. The model addresses several aspects of the experimental measurements and, in particular, explains an unusual increase in scattering along the applied field direction for certain values of the scattering vector q. The increased scattering along the field direction results in a change of the phase of the angular variation of the scattering by 90∘. This 90∘ change in scattering phase arises naturally from the influence of stray fields when modeling the media as a heterogeneous alloy consisting of grains with a high saturation magnetization core and a permeable shell.
First principles study on the electronic structure and effective exchange interaction of Y(Co1−xCux)5
Authors: Sakuma Akimasa
Published: June 2006

In order to investigate the enhancement mechanism of coercivity of SmCo5 due to partial substitution of Co atoms by Cu atoms, we calculate, by the first principles band calculation, the magnetic parameters such as magnetic moments and exchange constants of Y(Co1−xCux)5 for 0≦x≦1. The moments and the Curie temperatures estimated from the exchange constants decrease almost linearly with the Cu concentration x and are in quantitative agreement with the measured values. It is proposed that the decrease of effective exchange interactions between R ions by the partial substitution of Co atoms by Cu atoms is responsible for the high coercivity of this system.
Characterization of surface and interface structure of YBa2Cu3O7−δ-based trilayer with La0.67Ca0.33MnO3 spacer
Authors: Tan W. S. , Cai H. L. , Liu J. S. , Wu X. S. , Jiang S. S. , Wu Z. H. , Jia Q. J. , Gao J.
Published: June 2006

Thin YBa2Cu3O7−δ∕La0.67Ca0.33MnO3∕YBa2Cu3O7−δ (YBCO/LCMO/YBCO) trilayers on (001)-oriented SrTiO3 (STO) substrates were fabricated by magnetron sputtering technique. The trilayers are well c-axis oriented confirmed by x-ray diffraction. The surface and interface structure of the trilayers were investigated by grazing incident x-ray reflectivity. The results showed that there exists diffusion at the YBCO/LCMO interfaces with the diffusion length of several nanometers. The root-mean-square (rms) roughness of surface and interface in the trilayers varied with the thickness of YBCO layer. The rms roughness of surface was consistent with observation by atomic force microscopy. A further analysis indicated that the rms roughness was correlative to the misfit strain relaxation in film.
Reconstruction of local magnetic properties of steel sheets by needle probe methods using space mapping techniques
Authors: Crevecoeur G. , Dupre L. , Vandenbossche L. , Van de Walle R.
Published: June 2006

Cutting stresses introduced by punching influence the magnetic characteristics of electrical steels. A nondestructive experimental method used for measuring flux distributions in laminations is the needle probe method. The probe signals can be simulated by solving the two-dimensional nonlinear diffusion equation for the magnetic field in combination with a proper Preisach model. The Preisach parameters in several subregions of the steel sheet which best fit the input probe signals are obtained by solving the inverse problem. The method used for minimizing the cost function is the space mapping technique. This technique combines the fine model, which uses the finite element method, with a semianalytical coarse model, which reduces the nonlinear problem to a linear problem.
Magnetism and electronic structure of binuclear manganese complexes in ortho-quinone ligand and polymer environments
Authors: Rakhimov R. R. , Arrington S. A. , Hwang J. S. , Prokof’ev A. I. , Alexandrov I. A. , Aleksandrov A. I.
Published: June 2006

By means of mechanochemical synthesis we obtained a coordination polymer containing binuclear manganese complexes with organic catechol∕ortho-quinone ligands. The reaction system contained polystyrene, manganese acetylacetonate, and donor-acceptor mixture catechol∕ortho-quinone. Electron paramagnetic resonance (EPR) and infrared spectroscopic data show that the binuclear manganese complex is covalently linked to the chain of polystyrene. Theoretical EPR spectrum analysis revealed a triplet state of the complex with two nonequivalent manganese ions coupled to each other by spin exchange. The type of magnetic coupling between manganese ions in this system is similar to the one in manganese based inorganic magnetic materials.