bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of the Zn-phosphate coating on magnetic properties of Fe73.5Cu1Nb3Si15.5B7 nanocrystalline alloy powder cores
Authors: Jang D. H. , Noh T. H. , Choi G. B. , Kim Y. B. , Kim K. Y.
Published: June 2006

The effects of Zn-phosphate coating on the magnetic properties of Fe73.5Cu1Nb3Si15.5B7 nanocrystalline alloy powder cores have been investigated. The Zn-phosphate coating provided good electrical insulation between the magnetic particles through formation of an oxide and other compounds on their surfaces. The consolidated magnetic cores with powders treated in the solution of pH=1.3 acidity exhibited a permeability of 45, persisting up to about 2 MHz and a core loss of 500mW∕cm3 at the frequency of 50 kHz under the induction of Bm=0.1T. Furthermore, 62% permeability at 50 Oe of dc bias field was obtained. From these results, it was considered that the Zn-phosphate coating could be an effective method to form an efficient insulating coat even for small-sized Fe73.5Cu1Nb3Si15.5B7 nanocrystalline alloy powders.
Magnetic and electronic properties of the iron-containing polyoxotungstate [Fe4(H2O)10(β-SbW9O33)2]6−
Authors: Prinz M. , Takács A. F. , Schnack J. , Balasz I. , Burzo E. , Kortz U. , Kuepper K. , Neumann M.
Published: June 2006

The magnetic and x-ray photoelectron spectroscopy (XPS) studies on the transition metal substituted, dimeric polyoxotungstate [Fe4(H2O)10(β-SbW9O33)2]6− are reported. The magnetic data were analyzed by using an isotropic Heisenberg Hamiltonian. The ground state of the frustrated molecule has a total spin of S=2. The XPS Fe 2p spectra suggest a 2+ formal valence state. The deviation from the contained Fe3+ ions can be explained by charge-transfer effects.
Design of permanent magnet brushless motors with asymmetric air gap for electric vehicles
Authors: Chau K. T. , Cui Wei , Jiang J. Z. , Wang Zheng
Published: June 2006

This paper proposes a cost-effective approach to design permanent magnet brushless dc motors for electric vehicles. The key is to shape the pole arc in such a way that the air gap length is at a maximum at the leading edge of each rotor pole arc and at a minimum at the trailing edge of the same pole arc, hence resulting in an asymmetric air gap. Thus, for a specified rotational direction, the distortion of air gap flux density and hence the torque ripple can be significantly suppressed. Also, with the use of advanced conduction angle control, the motor can achieve a wide speed range. The proposed motor drive is designed and implemented for a low-voltage battery-powered electric motorcycle.
Comparison of the differential equation accommodation model with experiment
Authors: Yanik Levent , Yarimbiyik A. Emre , Della Torre Edward
Published: June 2006

A differential equation accommodation model, which we previously presented based upon the Preisach model, has been modified so that changing the accommodation constant, β, does not affect the major loop. This has the dual advantage that identification of the model parameters is easier and also ensures that an accommodating minor loop does not go outside the major loop. The modified model permits detailed comparison with experiment. There was a remarkable agreement between the model and previously published experimental data.
Laser-induced ultrafast spin dynamics in epitaxial Co∕Mn exchange-coupled bilayers
Authors: Dalla Longa F. , Kohlhepp J. T. , de Jonge W. J. M. , Koopmans B.
Published: June 2006

The spin dynamic response to femtosecond laser excitation in epitaxial Co/fct-Mn(001) exchange-coupled bilayers is studied. Damped oscillations in the polar Kerr rotation transients, representing a precessional motion of the magnetization vector, are observed for an atomically flat Co∕Mn interface, when a magnetic field is applied perpendicular to the exchange bias direction. The absence of a measurable ultrafast demagnetization in the first picosecond after laser excitation proves that the precession is launched by a laser-induced subpicosecond quenching of the exchange coupling. The exact value of the damping parameter varies within the range 0.05⩽α⩽0.2, depending on the detailed structure of the sample.
Magnetoresistance in La- and Ca-doped YBa2Cu3O7−δ
Authors: Qian B. , Xing J. H. , Wu X. S. , Jiang S. S. , Gao J.
Published: June 2006

We studied the microstructures, electronic, and magnetic properties on La-doped and La- and Ca-codoped YBa2Cu3O7−δ (YBCO). The superconducting transition temperature remains unchanged up to 10% for La-doped YBCO. The competition between electrons and holons was assumed according to the variation of Tc0 in La and Ca codopings in YBCO. The magnetoresistance (MR) effect is about 8%, which is observed obviously near the critical temperature and is independent of the content of La in La-doped YBCO. MR increases up to about 40% with the incorporation of Ca in La-doped YBCO. We present here possible explanations for the magnetoresistance effect in polycrystalline samples based on the microstructure and the increase of oxygen vacancies at grain-boundary interface.
Vortex domain wall depinning by polarized current in submicron half-ring wires
Authors: Chen Y. S. , Cheng K. W. , Yu C. , Lee S. F. , Chen D. C. , Wu S. H. , Lin M. T. , Liou Y. , Wu K. T. , Yao Y. D.
Published: June 2006

Domain wall pinning force in the junctions (corners), with different shapes of square, semicircle, or triangle, of half-ring in-series wires is considered to study the current injection induced wall movements. This geometry has less thermal activation at the region of domain wall nucleation in contrast to notch structures. The wires with square corners have the largest domain pinning force to resist polarized current-induced magnetization reversal, judging from the largest slope in the current-field dependence (ΔI∕ΔH=0.274).
Tunneling spectroscopy in CoFeB∕MgO∕CoFeB magnetic tunnel junctions
Authors: Ono Kazunaga , Daibou Tadaomi , Ahn Sung-Jin , Sakuraba Yuya , Miyakoshi Takefumi , Morita Tadashi , Kikuchi Yukio , Oogane Mikihiko , Ando Yasuo , Miyazaki Terunobu
Published: June 2006

The d2V∕dI2-V measurements were used to investigate the tunneling mechanism in CoFeB∕MgO∕CoFeB magnetic tunnel junctions (MTJs), which showed a giant tunnel magnetoresistance ratio up to 200% at room temperature. The d2V∕dI2-V spectra of CoFeB∕MgO∕CoFeB junctions resemble those of single-crystal Fe(001)∕MgO(001)∕Fe(001) MTJs. Broad peaks appeared around ±600mV in spectra for antiparallel magnetic configurations. A complex structure was apparent in the spectra for parallel configurations. We inferred that giant tunnel magnetoresistance observed in CoFeB∕MgO∕CoFeB junctions originates in coherent tunneling between the Δ1 bands of crystallized CoFeB electrodes.
The effects of small metal additions (Co,Cu,Ga,Mn,Al,Bi,Sn) on the magnetocaloric properties of the Gd5Ge2Si2 alloy
Authors: Shull R. D. , Provenzano V. , Shapiro A. J. , Fu A. , Lufaso M. W. , Karapetrova J. , Kletetschka G. , Mikula V.
Published: June 2006

The structural and magnetic properties of arc-melted and homogenized (1300°C, 1h) alloys of Gd5Ge1.9Si2X0.1(X=Cu, Co, Ga, Mn, Al, Bi, or Sn) were investigated by powder x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and magnetometry. The addition of Cu, Ga, Mn, and Al completely eliminated the large hysteresis losses present in the undoped Gd5Ge2Si2 alloy between 270 and 330K, broadened the magnetic entropy change ΔSm peak, and shifted its peak value from 275 to 305K similar to that observed earlier for Gd5Ge1.9Si2Fe0.1. The addition of Bi or Sn had a negligible effect on either the alloy hysteresis losses or the characteristics of the ΔSm vs T peak. The microstructure of the alloy doped with Cu, Co, Ga, Mn, or Al consisted of a majority phase (depleted of silicon) and a minor intergranular phase (rich in silicon and of the corresponding metal additive). For Bi or Sn doping, the microstructure consisted of only the Gd5Ge2Si2 phase. Low temperature x-ray diffraction data on an Fe-doped sample showed the same spectra at 245 and 300K, consistent with the majority phase possessing an orthorhombic structure. Refrigeration capacity calculations show that Gd5Ge1.9Si2X0.1(X=Fe,Cu,Co,Ga,Mn,orAl) alloys are superior magnetic refrigerants compared to the undoped Gd5Ge2Si2 alloy.
Spin-polarized scanning tunneling microscopy and spectroscopy study of c(2×2) reconstructed Cr(001) thin film surfaces
Authors: Oka Hirofumi , Sueoka Kazuhisa
Published: June 2006

Spin dependent electronic properties of c(2×2) Cr(001) thin film surfaces grown on MgO(001) substrates are investigated by means of spin-polarized scanning tunneling microscopy and spectroscopy. An averaged dI∕dV spectrum obtained on the c(2×2) Cr(001) thin film surfaces exhibits a surface state around +0.1eV above the Fermi level. The intensity of the surface state peak in the spectra measured on (001) terraces is alternately varied whenever a monatomic step is crossed. Therefore, the shifted surface state as well as an original one on (1×1) Cr(001) surfaces has spin-polarized feature.
Tuning of MgO barrier magnetic tunnel junction bias current for picotesla magnetic field detection
Authors: Ferreira R. , Wisniowski P. , Freitas P. P. , Langer J. , Ocker B. , Maass W.
Published: June 2006

Two sets of low resistance MgO junctions were patterned into junctions with areas from 1 to 24μm2. By properly choosing the operating conditions the background noise can be placed at the level of equivalent fields of ∼10−11 and ∼10−12T∕Hz0.5 calculated for 30 Oe linear range junctions of types 1 (150Ωμm2, tunnel magnetoresistance (TMR)=150%) and 2 (30Ωμm2, TMR=100%), respectively. Such room temperature sensitivities can only be achieved at frequencies where the 1∕f noise contribution is negligible. From the 1∕f noise Hooge constant (αH=2.66×10−9μm2 at R×A∼150Ωμm2 and αH=1.24×10−9μm2 at R×A∼30Ωμm2) the 1∕f noise corner in the optimum biasing conditions is predicted to be located between 10 and 70 MHz, depending on junction area and resistance.
Conceptual material design for magnetic tunneling junction cap layer for high magnetoresistance ratio
Authors: Nagamine M. , Nagase T. , Nishiyama K. , Yoshikawa M. , Amano M. , Asao Y. , Ikegawa S. , Yoda H. , Honjo H. , Mori K. , Ishiwata N. , Tahara S.
Published: June 2006

A conceptual material design for magnetic tunneling junction cap layer realizing a steep NiFe∕AlOx interface is proposed. Tunnel magneto resistance stack of cap∕NiFe∕AlOx∕CoFe∕Ru∕CoFe∕PtMn∕Ta∕∕sub was prepared. Maximum magnetoresistance (MR) ratios of nonmagnetic-NiFeZr, Zr, Ta, Ru, and Rh caps at 0 V were 55%, 28%, 50%, 43%, and 42%, respectively. The decrease of MR ratio and the increase of resistance area product RA with Ru cap compared to Ta cap correlate with the partial oxidation of the NiFe∕AlOx interface occurring in additional postannealing, which was confirmed by focused-ion-beam–transmission-electron-microscope–energy-dispersive-x-ray-fluorescence observation. Since standard electrode potential is Ta<Fe<Ni<Ru, it is supposed that NiFe with Ru cap is positively charged, the NiFe∕AlOx interface is easily oxidized during annealing by negatively charged oxidizing species, and increase of RA and decrease of MR ratio occur. RA with Rh cap was even higher than that with Ru cap, consistent with the higher electrode potential of Rh than that of Ru. On the other hand, as the electrode potential of Ta is lower than NiFe, we think that NiFe with Ta cap is negatively charged, the oxidation of the NiFe∕AlOx interface is suppressed, and the lower RA and higher MR ratio than those with Ru cap are obtained. Since the electrode potential of Zr is still lower than Ta, we expected an even higher MR ratio with Zr cap. However, magnetism and magnetostriction of Zr∕NiFe∕AlOx∕∕sub sample changed significantly at first and saturated rapidly in sequential postannealing processes, indicating that the diffusion of Zr to NiFe proceeds at the beginning and saturates promptly. Therefore, we introduced nonmagnetic-NiFeZr alloy cap and the highest MR ratio of 55% was realized, without suffering from the diffusion of Zr. The highest MR ratio with nonmagnetic-NiFeZr cap is consistent with the lowest electrode potential of Zr, and we believe that nonmagnetic-NiFeZr cap realizes a steep NiFe∕AlOx interface without the oxidation of NiFe.
Electronic nature of layered oxysulfide Sr2−xCaxCu2CoO2S2 with CoO2 planes
Authors: Ito K. , Endo T. , Kubodera T. , Kamihara Y. , Matoba M. , Kitô H.
Published: June 2006

We have studied the electronic nature of the layered oxysulfide Sr2−xCaxCu2CoO2S2 which has strongly correlated CoO2 square planes. These materials exhibit narrow-gap semiconducting behavior and the conduction mechanism depends on the temperature. Valence band x-ray photoemission spectroscopy spectra show that Ca doping and the production of Sr defects cause the generation of a quasiparticle band near the Fermi level. These phenomena suggest that the materials are changing from correlated semiconductors to bad metals.
Magnetic configurations and magnetization reversal in the Co rings prepared by capillary force lithography
Authors: Kim Sarah , Jeong Jong-Ryul , Kim Sang-Hyun , Shin Sung-Chul , Yang Seung-Man
Published: June 2006

In this work, we have successfully fabricated micro- and nanosized magnetic elements by using capillary force lithography, which combines the essential feature of nanoimprint lithography. The magnetic configurations and magnetization reversal mechanism in elliptical Co elements with an aspect ratio of 1.75:1 were investigated using the magneto-optical microscope magnetometer and micromagnetic simulation. The magnetization reversal mechanism was found to take place by the formation and annihilation of two vortices in both the elliptical dot and ring patterns with an external field applied along the major axis. It was also observed that the two vortices evolved with mirror symmetry and center of inversion symmetry for the case of elliptical ring and dot patterns, respectively.
Three-dimensional hysteresis of soft magnetic composite
Authors: Lin Z. W. , Zhu J. G. , Guo Y. G. , Wang X. L. , Ding S. Y.
Published: June 2006

Hysteresis phenomenon is one of the important characteristics of soft magnetic materials. A three-dimensional (3D) magnetic property measurement system has been developed. This system can effectively control the locus of the time-varying magnetic flux density vector B and measure the corresponding magnetic field strength vector H in a cubic sample of soft magnetic material. The sample involved in this study is a soft magnetic composite sample made of highly pure iron powder. This paper investigates the B and H loci in 3D space and the power loss when the B loci are controlled to become circles and ellipses lying in three orthogonal planes. It is found that the B and H loci lie in the same magnetization plane, but the H loci and losses depend strongly on the orientation, position, and process of magnetization. On the other hand, the H vectors evolve into a unique locus pattern, and the power losses approach a unique value when the B vectors evolve into the same loci through either a series of small circles or ellipses.
Design and implementation of a magnetically suspended microrobotic pick-and-place system
Authors: Shameli Ehsan , Craig David G. , Khamesee Mir Behrad
Published: June 2006

Micromanipulation is an emerging technology in such diverse areas as precision engineering, microfabrication, and microsurgery. Each of these areas impose certain technological constraints and requirements in fabrication, actuation, and control. This paper performs a review on the latest technologies of microrobotic actuation techniques and suggests a suitable technique for the actuation of a magnetically levitated microrobot. The microrobot, suspended in an externally produced magnetic field, consists of a gripper attached to a series of permanent magnets and is capable of simple pick and place tasks. A number of electromagnets produce the external magnetic field and three laser sensors feedback the position of the levitated microrobot. Through finite element analysis, performance of the levitation system was investigated, and simulations and experiments were carried out to demonstrate the practical capabilities of the proposed system.
Enhancement of writing margin for low switching toggle magnetic random access memories using multilayer synthetic antiferromagnetic structures
Authors: Fukumoto Yoshiyuki , Suzuki Tetsuhiro , Mori Kaoru , Honjo Hiroaki , Igarashi Chuji , Ohshima Norikazu , Miura Sadahiko , Ishiwata Nobuyuki , Tahara Shuichi , Asao Yoshiaki , Yoda Hiroaki
Published: June 2006

We developed synthetic antiferromagnets (SAFs) with a multilayer structure where more than three magnetic layers were coupled in an antiparallel configuration for use as a free layer of toggle magnetic random access memories, with the aim of reducing the switching field. The SAFs consisted of a magnetic layer of NiFe∕CoFe with a spacer layer of Ru and were deposited on the Al-oxide barrier layer in magnetic tunnel junctions. Conventional bilayer SAFs did not realize a large writing margin with a low spin flop field (Hflop). On the other hand, multilayer SAFs increased the saturation field (Hs) significantly with increases in both the number of magnetic layers (N) and the antiferromagnetic coupling (AFC) strength between the inner magnetic layers while maintaining a low Hflop. This is because strong AFCs involved in the inner magnetic layers and weak AFCs of the outer magnetic layers determine Hs and Hflop of these, respectively. To control an AFC of each spacer layer, we chose an appropriate thickness for each Ru layer in the multilayer SAFs according to the Ru crystalline structure that was responsible for its AFC strength.
Vortex dynamics in patterned ferromagnetic ellipses
Authors: Buchanan Kristen S. , Roy Pierre E. , Fradin Frank Y. , Guslienko Konstantin Yu. , Grimsditch Marcos , Bader Sam D. , Novosad Val
Published: June 2006

The dynamics of individual magnetic vortices and vortex pairs confined in lithographically defined ferromagnetic ellipses were measured using a microwave reflection technique. Resonance frequencies were detected in the subgigahertz range for Ni80Fe20 (Permalloy) ellipses ranging in size from 3 by 1.5μm to 1 by 0.5μm, 40nm in thickness. Micromagnetic simulations indicate that the single mode observed for one vortex is a translational mode and that the two eigenmodes associated with a vortex pair correspond to coupled translational modes of vortices with parallel or antiparallel core polarizations. The single-vortex resonance scales inversely with the ellipse size, in agreement with the simulations and analytical theory.
Stability enhancement of nanopillar structure for spin transfer magnetization switching using IrMn buffer layer
Authors: Lee J. C. , Chun M. G. , Park W. H. , You C.-Y. , Choe S.-B. , Yung W. Y. , Kim K. Y.
Published: June 2006

We report here the effect of ultrathin IrMn buffer layer on the magnetic and spin transport properties of spintronic structure for current-induced magnetization switching. The insertion of the ultrathin (∼1nm) IrMn buffer layer drastically enhanced the coercive field of the fixed ferromagnetic layer from 36 to 215Oe. Interestingly, the ultrathin IrMn buffer layer even enhanced the magnetoresistance ratio about 30%, and consequently the spin polarization effect was enhanced by reducing the critical current density of magnetization switching from 3.13×108 to 1.16×108A∕cm2.
Analytical determination of the surface energy of sub-5nm head-disk interfaces accounting for multilayer effects
Authors: Suh Allison Y. , Polycarpou Andreas A.
Published: June 2006

In this work, a five-layer HDI configuration was employed to derive a simple way to relate the multilayer Hamaker constant to an effective surface energy of the HDI. Specifically, the five layers of the HDI include two layers on the slider [diamondlike carbon (DLC) overcoat, Al2O3–TiC] and two layers on the disk (lubricant, DLC overcoat) as well as the air gap (or flying height). Following the formulation for two equivalent homogeneous surfaces, one can derive the effective surface energy of the five-layer model. To investigate the effect of the topmost layer thicknesses of the slider and disk on the surface energy, they were first varied from 2 to 5nm and from 0.5 to 2nm, respectively. It was found that the surface energy depends largely on the disk lubricant thickness while it has little dependence on the slider DLC thickness. Lubricant pickup by the slider and its effect on the surface energy was also investigated and it was found that the overall surface energy of the interface is lower when there is lubricant pickup.
R
-dependent magnetic and structural properties in RMn2O5 with R=Y,Er,Ho,Dy,andTb
Authors: Han Tai-Chun , Lin Jauyn Grace
Published: June 2006

We have synthesized a series of orthorhombic RMn2O5 with R=Y,Er,Ho,Dy,andTb, and employed the techniques of x-ray powder diffraction and dc magnetic susceptibility in order to systematically study their R-dependent structural and magnetic properties. It is found that in spite of the similarity in the crystalline structures of these five samples, only YMn2O5 and ErMn2O5 show canted antiferromagnetic transitions at 45K. Particularly for YMn2O5, the magnetization saturates at relatively low field (∼5kOe) compared with that of the others (>20kOe), suggesting that the magnetic moments of R-ions contribute significantly to the net moment of the system.
Magnetic cell manipulation utilizing magnetic particles and diamagnetic collagen fibers
Authors: Iwasaka M. , Kurakane T. , Kimura T. , Kimura F. , Ueno S.
Published: June 2006

This paper reports a method of controlling the orientation of adherent fibroblastic cells (osteoblasts) by utilizing a ferromagnetic particle chain and a diamagnetic collagen under exposure to magnetic fields. A cell culture medium with cells and magnetic particles (γ-Fe2O3) was mixed with a collagen solution and incubated for 24h. During the first 3h of incubation, the medium in the cell culture dish was exposed to magnetic fields of up to 8T. The exposure caused the aggregation of magnetic particles (MPs), which formed chains in parallel with the magnetic field and at the same time oriented the polymerized collagen fibers perpendicular to the magnetic field. A lattice pattern of MP chains and collagen fibers was observed on the bottom of the culture flask. After 24h of incubation, the spindlelike cells had become oriented in parallel with the MP chains or the collagen fibers. The results indicate the possibility of a technique of cellular manipulation with MP-collagen hybrid that could be used to control cellular orientation.
Intermartensitic transformations in Ni2Mn1−xCoxGa Heusler alloys
Authors: Khan Mahmud , Stadler Shane , Ali Naushad
Published: June 2006

Ni 2 MnGa that possesses a Heusler L21 structure undergoes a martensitic transformation from the parent cubic (austenitic) phase to a low temperature complex tetragonal structure at TM=202K and has a Curie temperature of TC=376K. Some research groups have observed an intermartensitic transformation at a temperature TI<TM, in Ni2MnGa single crystals. In this work detailed studies on the influence of substitution in the Mn subsystem by magnetic Co on the intermartensitic transformation properties of Ni2Mn1−xCoxGa compounds have been done by magnetization (5–400K) and thermal expansion (80–300K) measurements. The samples Ni2Mn0.92Co.08Ga, Ni2Mn0.91Co.09Ga, and Ni2Mn0.90Co.10Ga were studied. The intermartensitic transformation is observed in all of these alloys. As the Co concentration increases, the transformation becomes more pronounced and the temperature range for which the alloys stay in the intermartensitic state decreases as Co concentration increases. Similarities were observed between the magnetization and thermal expansion curves. The results are discussed in terms of the internal stress produced as a result of the Co substitution.
Magnetization switching in nanopillars with FePt alloys by spin-polarized current
Authors: Seki T. , Mitani S. , Yakushiji K. , Takanashi K.
Published: June 2006

FePt ∕ Au ∕ FePt nanopillars with current-perpendicular-to-plane geometries were fabricated, and current induced magnetization switching was demonstrated. Resistance measured with sweeping current showed the resistance change due to the change of the magnetization alignment of the two FePt layers, which was interpreted as the magnetization switching by spin-polarized current. The critical current density for the magnetization switching of the FePt layer with a uniaxial magnetic anisotropy of 2×106ergs∕cm3 was of the order of 108A∕cm2.
Vibration based electromagnetic micropower generator on silicon
Authors: Kulkarni Santosh , Roy Saibal , O’Donnell Terence , Beeby Steve , Tudor John
Published: June 2006

This paper discusses the theory, design and simulation of electromagnetic micropower generators with electroplated micromagnets. The power generators are fabricated using standard microelectromechanical system processing techniques. Electromagnetic two-dimensional finite element anlysis simulations are used to determine voltage and power that can be generated from different designs. This paper reports a maximum voltage and power of 55mV and 70μW for the first design, incorporating microfabricated two-layer Cu coils on a Si paddle vibrating between two sets of oppositely polarized electroplated Co50Pt50 face centered tetragonal phase hard magnets. A peak voltage and power of 950mV and 85μW are obtained for the second design, which includes electroplated Ni45Fe55 as a soft magnetic layer underneath the hard magnets. The volume of the device is about 30mm3.
Evolution of the magnetic properties and magnetic structures along the RmMIn3m+2 (R=Ce, Nd, Gd, Tb; M=Rh, Ir; and m=1,2) series of intermetallic compounds
Authors: Pagliuso P. G. , Garcia D. J. , Miranda E. , Granado E. , Lora Serrano R. , Giles C. , Duque J. G. S. , Urbano R. R. , Rettori C. , Thompson J. D. , Hundley M. F. , Sarrao J. L.
Published: June 2006

We discuss the evolution of the magnetic properties and magnetic structures along the series of intermetallic compounds RmMIn3m+2 (R=Ce, Nd, Gd, Tb; M=Rh, Ir; and m=1,2). The m=1,2 are, respectively, the single layer and bilayer tetragonal derivatives of their cubic RIn3 relatives. Using a mean field model including an isotropic first-neighbors Ruderman-Kittel-Kasuya-Yoshida interaction (K) and the tetragonal crystalline electrical field (CEF), we demonstrated that, for realistic values of K and CEF parameters, one can qualitatively describe the direction of the ordered moments and the behavior of the ordering temperature for these series. The particular case, where the rare-earth ordered moments lie in the ab plane or are tilted from the c axis and TN can be reduced by tuning the CEF parameters, revealed an interesting kind of frustration that may be relevant to the physical properties of complex classes of materials such as the RmMIn3m+2 (M=Rh, Ir, and Co; m=1,2) heavy-fermion superconductors.
Magnetism of Cu2CdB2O6: Quantum spin system having a nearly singlet state and antiferromagnetic long-range order
Authors: Hase Masashi , Kohno Masanori , Kitazawa Hideaki , Suzuki Osamu , Ozawa Kiyoshi , Kido Giyuu , Imai Motoharu , Hu Xiao
Published: June 2006

A 1∕2 magnetization plateau in magnetic fields above 23T and antiferromagnetic (AF) long-range order (AFLRO) in low fields were observed in Cu2CdB2O6. Experimental results are consistent with quantum Monte Carlo results for an expected spin system. Two kinds of Cu sites [Cu(1) and Cu(2)] are located adjacent to each other. Spins on the Cu(1) sites are in a nearly spin-singlet state and a finite energy is necessary to break the nearly spin-singlet state. Spins on the Cu(2) sites are almost polarized in the 1∕2 plateau region, whereas they form AFLRO in low fields. Therefore, the nearly spin-singlet state and AFLRO coexist adjacently in low fields, but exchange interaction between the Cu(1) and Cu(2) spins is not negligible.
Stability of magnetization states in submicron Permalloy disks
Authors: Jausovec Ana Vanessa , Xiong Gang , Cowburn Russell P.
Published: June 2006

The switching behavior of Permalloy (Ni81Fe19) disks with dimensions close to the experimentally determined phase boundary separating the single domain and vortex ground states was investigated. The disks fabricated with electron beam lithography and thermal evaporation had diameters ranging from 100to330nm. The remanence curve, measured with a magneto-optical Kerr magnetometer and decaying sinusoidal field pulses with different sweeping amplitudes, revealed the presence of three different remanence states at different magnetic field regimes in all the disk sizes that were investigated. At low fields a vortex state was observed, which was replaced with a metastable state in fields above the metastable nucleation field (HNM) and then finally a single domain state at fields above the metastable annihilation field (HAM). Further investigation revealed that once the vortex state was established it could not be destroyed even if field pulses above HNM were applied.
Magneto-optical properties of wider gap II-VI ZnMnTe and ZnMnCoTe films
Authors: Imamura M. , Okada A. , Yamaguchi T.
Published: June 2006

In CdMnTe and CdMnCoTe films, Mn shifts the absorption edge toward higher energies. However, this gap shift occurs at around 2.1eV because the band gap of the combination of CdTe (1.53eV) and wideband gap MnTe (2.9eV) is small. In order to widen the gap of AII1−xMnxBVI alloys and effectively use LDs that work at shorter wavelengths for Faraday rotation, we have studied ZnMnTe and ZnMnCoTe films, whose parent materials are wideband gap ZnTe (2.28eV) and MnTe. The relationship between the quantity (αhν)2 and the optical energy for Cd0.65Mn0.35Te and data on Zn0.75Mn0.25Te and Zn0.79Mn0.20Co0.01Te films showed that the direct gap energy of the Cd0.65Mn0.35Te film is roughly 2.25eV and the gap of Zn0.75Mn0.25Te and Zn0.79Mn0.20Co0.01Te (∼2.4eV) is 0.15eV (∼40nm) larger than that of Cd0.65Mn0.35Te. The increase is due to the combination of wideband gap ZnTe and MnTe. Transparency and Faraday rotation are observed for Zn1−xMnxTe and Zn1−x−yMnxCoyTe films.
Phase transformation-induced coercivity mechanism in rare earth sintered magnets
Authors: Menushenkov Vladimir
Published: June 2006

The phase transformation-induced coercivity mechanism in SmCo5±x sintered magnets is proposed based on the phase transformations according to the hypothetic Sm–Co phase diagram. The phase transformations are supposed to modify the surface of principal phase grains. The precipitation of the SmCo5−x phases in Sm-rich magnets and the Sm2Co17 phase in Co-rich magnets at grain boundaries of the principal SmCo5 phase leads to the smoothing out of the grain surface and, thus, coercivity increases.
An integrated microfluidic cell for detection, manipulation, and sorting of single micron-sized magnetic beads
Authors: Jiang Z. , Llandro J. , Mitrelias T. , Bland J. A. C.
Published: June 2006

A lab-on-a-chip integrated microfluidic cell has been developed for magnetic biosensing, which is comprised of anisotropic magnetoresistance (AMR) sensors optimized for the detection of single magnetic beads and electrodes to manipulate and sort the beads, integrated into a microfluidic channel. The device is designed to read out the real-time signal from 9μm diameter magnetic beads moving over AMR sensors patterned into 18×4.5μm rectangles and 10μm diameter rings and arranged in Wheatstone bridges. The beads are moved over the sensors along a 75×75μm wide channel patterned in SU8. Beads of different magnetic moments can be sorted through a magnetostatic sorting gate into different branches of the microfluidic channel using a magnetic field gradient applied by lithographically defined 120nm thick Cu striplines carrying 0.2A current.
Influence of reference layer stability on the switching performance of sub-micron-sized magnetic tunnel junctions
Authors: Klostermann Ulrich , Park Chanro , Raberg Wolfgang , Dahmani Faiz , Ruehrig Manfred
Published: June 2006

Arrays of sub-micron-sized, magnetic tunnel junctions are patterned and the switching field (Hc) of the free layer (FL) and its distribution (σ) are measured by Kerr magnetometry. A correlation of Hc and σ with the magnetic stiffness (stability against external magnetic fields) of the reference system (RS) is observed. For simple pinned RSs the stiffness is varied by different materials (CoFe vs CoFeB) and its thicknesses, while for artificial antiferromagnetic pinned systems the thickness of the exchange coupling layer of Ruthenium is modified. It is shown that less stiffness causes a lower Hc and larger σ. This effect is assumed to be due to magnetic mirror charges induced in RS by the magnetic dipoles of the patterned FL elements. These mirror charges screen the dipole stray field of the FL resulting in lower effective shape anisotropy, which goes along with reduced switching fields. Micromagnetic simulations performed for different pinning strengths of a single layer RS clearly support this observation. From high field measurements perpendicular to the unidirectional exchange anisotropy of the RS, an order parameter λ can be extracted quantifying the stiffness (∼1∕λ). λ is found to be linearly correlated to σ and Hc.
Inspection of pole tip diamondlike carbon wear due to heater-induced head-disc contact
Authors: Song Dion , Kvitek Richard , Schnur Deborah
Published: June 2006

Heater-induced head-disc contacts can cause highly localized wear of the pole tip. We found that scanning electron microscopy and low beam-current focused ion beam imaging are suited at providing a map of the entire pole tip surface and quickly identify the location and shape of heater-induced wear. For longitudinal heads, the imaging can reveal detailed structure near the writer gap. By measuring the topography near the pole tip using atomic force microscopy (AFM), one can retrieve quantitative wear information. Using unburnished parts as controls, the accuracy of the AFM method reported here is about 1nm. We found transmission electron microscopy and Auger electron spectroscopy to be less effective in quantifying wear.
The magnetic and magnetoresistance properties of ultrathin magnetite films grown on MgO substrate
Authors: Zhou Y. , McEvoy Ciaran , Ramos R. , Shvets I. V.
Published: June 2006

We report on the properties of ultrathin (2, 4, 6, and 8nm) epitaxial films of magnetite, Fe3O4, grown on MgO (100). Atomic force microscopy image and V-I curves suggest that the films at this thickness are still continuous. The resistivity versus temperature results imply that the conductivity mechanism in all these films is similar. The resistivity of 4nm thick film is much greater than that of 6 and 8nm films. The films show ferrimagnetic instead of reported superparamagnetic behavior. The dead layer formed by Mg diffusion between MgO substrate and magnetite films and also the dead layer on the top uncapped film could be the possible reasons for the anomalous resistivity and magnetic properties of the ultrathin films. The effect of the “dead layer” in the thinner film is relatively greater than the one in the thicker film and should lead to a lower magnetoresistance.
Magnetic properties of ultrathin Co∕Ge(111) film with oxygen surfactant
Authors: Chang H. W. , Tsay J. S. , Chiou Y. L. , Huang K. T. , Chan W. Y. , Yao Y. D.
Published: June 2006

Magnetic properties of ultrathin Co∕Ge(111) films with oxygen surfactant have been investigated using surface magneto-optic Kerr effect technique. As the oxygen exposure increases, their magnetic properties could be significantly modified. As the thickness of Co films increases to above 6 ML (monolayer), pure cobalt islands start to accumulate on the surface and the amount of oxygen on the surface layers increases with increasing oxygen exposure time. Series experiments of different sequences of oxygen exposure and Co deposition have been performed. From the results of slight chemical shift and depth profiling measurements, one can conclude that oxygen plays a role as a surfactant. The adsorbed oxygen influences the electronic density of states of Co and leads to the changes of the magnetic properties. The appearance of the O∕Co∕Ge interface could modify the stress anisotropy, and as a result the coercivity of 30 ML Co∕Ge(111) increases from 730to810Oe with 500L of oxygen exposure.
Cobalt-Al2O3-silicon tunnel contacts for electrical spin injection into silicon
Authors: Min B. C. , Lodder J. C. , Jansen R. , Motohashi K.
Published: June 2006

The resistance of Co–Al2O3–Si tunnel contacts for electrical spin injection from a ferromagnet into silicon is investigated. The contacts form a substantial Schottky barrier, 0.7eV, which plays a dominant role in the electronic transport. On Si with a low doping concentration (∼1015cm−3), the contact resistance is affected by the Al2O3 tunnel barrier only in the forward bias. In the reverse bias (the spin injection condition), the Schottky barrier results in a very high contact resistance, ∼102Ωm2. While the contact resistance is improved to ∼10−2Ωm2 using Si with a high doping concentration (∼5×1019cm−3), it is still about five to six orders of magnitude higher than the value needed for resistance matching to silicon.
Energy surface model and magnetization switching for exchange coupled magnetic particles
Authors: Gao Kai-Zhong , Fernandez-de-Castro Juan
Published: June 2006

This paper describes the energy surface model for two exchange coupled magnetic particles and a study of the critical switching field in this coupled system. It is shown that for static switching, the total energy is continuously reduced during the reversal process. The critical switching fields versus applied field angle can be directly obtained from the energy surface model. The results are in good agreement with micromagnetic simulation. For a fast dynamic switching with small damping, the critical switching field may be further reduced. In addition, it is shown that an increase in either Ms or the grain volume of the soft particle will lead to a further reduction of the switching field. This is primarily due to an increase in the Zeeman energy that changes during the reversal.
A quantitative model of signal to noise ratio as function of magnetic spacing
Authors: Zhang Kezhao
Published: June 2006

A quantitative model has been developed to study the relationship between the signal to noise ratio (SNR) and the magnetic spacing. The effects of the reading and writing processes, the linear density, and the noise mix (the ratio of the media noise power and the electronic noise power) on the SNR are studied, as a function of the magnetic spacing. The model demonstrates that magnetic spacing reduction effectively improves SNR and that the writing process contributes more to the SNR at low linear density, while the reading process contributes more at higher linear density.
Co magnetism and the order of the magnetic transition in Er1−xGdxCo2 Laves phases
Authors: Liu X. B. , Altounian Z.
Published: June 2006

Co itinerant magnetism and the order of the magnetic transition in Er1−xGdxCo2 cubic Laves phases have been studied by magnetic measurements and a first principle density functional theory (DFT) calculation. The saturation magnetization (at 5K), derived from M−1∕H plot with a maximum field of 6T, decreases almost linearly with increasing Gd content. The derived Co magnetic moments, however, remain almost unchanged and range from 1.0to1.1μB∕Co. The first order magnetic transition at TC persists for x⩽0.1, as evidenced by thermomagnetic curves, M(T), and Arrott plots around TC. The total energy, Et, and magnetic moments are calculated as a function of lattice constant, a. In ErCo2, Et(a) shows two minima, corresponding to a low and a high spin state of Co, respectively. The Co sublattice is at a metastable high spin ferromagnetic state in ErCo2, which is responsible for the first order magnetic transition at TC. The replacement of Er by Gd eliminates the double minimum feature of Et(a) and drives the magnetic state of the Co sublattice to a stable state. The DFT calculation successfully explains the change in the order of the magnetic transition when the Gd content is increased in Er1−xGdxCo2.
Oxygen content of La1−xSrxMnO3−y thin films and its relation to electric-magnetic properties
Authors: Sakai Joe , Ito Nobuaki , Imai Syozo
Published: June 2006

It is known that the electric and magnetic properties of typical double-exchange materials La1−xSrxMnO3−y (LSMO) are strongly affected by oxygen nonstoichiometry y, as well as by divalent ion doping level x. In the present study, we fabricated LSMO (x=0.4) thin films on SrTiO3 (STO) (001) and LaAlO3 (LAO) (001) under various pressures of oxygen ambient pO2, and evaluated their oxygen content 3−y using non-Rutherford elastic resonance spectroscopy. The change of their electric and magnetic properties was also measured and discussed. It was revealed that the oxygen content 3−y does not increase monotonically as pO2 increases. Curie temperature TC and insulator-metal transition temperature TIM were correlated with 3−y for the films on STO. The film on LAO of a quite high pO2 showed ferromagnetism and a metallic conductivity, unlike the films of lower pO2’s. The ferromagnetism is attributed to c∕a axis ratio closer to that of the bulk.
Relaxation effects in interacting nanostructured particulate systems
Authors: Cimpoesu Dorin , Stancu Alexandru , Spinu Leonard
Published: June 2006

In this paper we have systematically studied the effect of interparticle dipolar interaction on the magnetic relaxation of a system of interacting uniaxial, single domain spherical particles lying in a regularly network formed within one layer. We have generated structured samples, with narrow distributions of the dimension and orientation of the particles, and we have analyzed the evolution of the interaction field distribution (IFD) during the magnetic relaxation at different temperatures. It is shown that IFD is state dependent and that the magnetic viscosity does not monotonically increase with the temperature.
Incomplete switching of media magnetization in perpendicular magnetic recording
Authors: Xue Jianhua , Zhou Yuming , Zhong Lieping , Fernandez-de-Castro Juan
Published: June 2006

Incomplete magnetization switching may take place between two recorded transitions in perpendicular magnetic recording. These write process issues were studied with a micromagnetic model. The relatively poor effective field from the central part of the perpendicular writer is unable to reverse the media grains properly. Consequently, media dc noise will increase as the incomplete switching becomes more severe. An expression for the effective field heff was proposed to easily discover those cases. The incompletely switched magnetization observed in the static footprint could also be partially transferred into the dynamic write process. The calculated media signal-to-noise ratio on a pseudorandom sequence could be reduced by as much as 3dB (compared to the fully switched case). On the other hand, transition quality does not become worse with a smaller heff. This insensitivity to the transition quality was caused by the magnetostatic field from the opposite magnetization polarity on the other side of the recorded bit.
Ferromagnetic resonance study of the exchange bias field in NiFe∕FeMn∕NiFe trilayers
Authors: Nascimento V. P. , Baggio Saitovitch E. , Pelegrini F. , Figueiredo L. C. , Biondo A. , Passamani E. C.
Published: June 2006

The ferromagnetic resonance (FMR) technique is used to study the exchange bias field in asymmetrical NiFe∕FeMn∕NiFe trilayers produced by dc magnetron sputtering under different working pressures. The FMR spectra give evidence of two resonance modes attributed to the two asymmetrical noninteracting NiFe layers. The study of the in-plane angular dependence of the absorption field allows the measurement of the exchange bias field at both bottom ferromagnetic (FM)∕antiferromagnetic (AFM) and top AFM∕FM interfaces.
On the calculation of exchange interactions in metals
Authors: Antropov V. P. , van Schilfgaarde M. , Brink S. , Xu J. L.
Published: June 2006

We describe techniques to determine magnetic exchange parameters using modern band structure methods. The analytical and numerical implementations of the linear-response method are discussed. The applications of the presented technique have been done for 3d ferromagnets. Our results point out difficulties in defining a pairwise exchange coupling for itinerant magnets, while for systems with localized moments the traditional adiabatic approach is mostly valid.
Tunnel magnetoresistance in MgO-barrier magnetic tunnel junctions with bcc-CoFe(B) and fcc-CoFe free layers
Authors: Ikeda S. , Hayakawa J. , Lee Y. M. , Tanikawa T. , Matsukura F. , Ohno H.
Published: June 2006

We have investigated the spin tunneling transport in magnetic tunnel junctions (MTJs) with Co40Fe40B20, Co50Fe50, and Co90Fe10 free layers which were deposited on the lower electrode consisting of the same Co40Fe40B20 reference layer/MgO barrier. The tunnel magnetoresistance (TMR) ratio depends critically on the choice of the free layer; the TMR ratios up to 355% were obtained for the MTJs with Co40Fe40B20 free layers and up to 277% with Co50Fe50 free layers, both of which have highly (001)-oriented bcc structures. No high TMR ratio was observed for the MTJs with Co90Fe10 free layer having a polycrystalline fcc structure.
Magnetic minor hysteresis loops of compressively deformed transition-metal single crystals
Authors: Kobayashi Satoru , Takahashi Seiki , Kamada Yasuhiro , Kikuchi Hiroaki , Ara Katsuyuki
Published: June 2006

Magnetic minor hysteresis loops of compressively deformed Ni single crystals have been analyzed. We confirmed universal simple relations between magnetic parameters of minor loops, which are independent of dislocation density, crystal orientation, and the symmetry of crystal. The magnetic properties deduced from the relations are more sensitive to dislocations than those of the major hysteresis loop. Present results clearly show the great capability of minor loops for nondestructive evaluation of degradation in ferromagnetic materials.
Metastable state before magnetization reversal in single-domain elongated thin films
Authors: Lai Jun-Yang , Wei Zung-Hang , Lai Mei-Feng , Chang Ching-Ray , Wu J. C. , Lo I. C.
Published: June 2006

A metastable state for the elongated Permalloy elements is found to exist within a short field range before magnetization reversal. From the micromagnetic simulation it exhibits a wavelike structure, and the corresponding magnetic pole density distribution shows a pattern with periodic spots along the boundary. We also use magnetic force microscopy imaging and magnetoresistance measurement, which measures the nucleation field and coercive field, to study the noncoherent magnetization reversal properties of Permalloy ellipse with long axis, short axis, and thicknesses of 18μm, 1μm, and 45nm, respectively. The metastable state before switching is found to be repeatable.
Recording studies of perpendicular media leading to 230Gb∕in2
Authors: Xiao M. , Do H. , Weresin W. , Dai Q. , Ikeda Y. , Takano K. , Moser A. , Lengsfield B. , Berger A. , Schabes M. , Nayak V. , Supper N. , Rosen H. , Marchon B. , Minardi M. , Heinz B.
Published: June 2006

Two media, A and B, are discussed to illustrate the media requirements and properties for the 230Gb∕in2 demonstration. A and B had similar layer structures except that the recording layers had different oxide compositions and that the exchange break layer thicknesses were 21 and 13nm, respectively. They had similar coercivity and intrinsic switching field but showed large difference in writability. Consequently, even though they achieved similar performance for heads down to a track width of 150nm, medium A could not be saturated adequately for heads with a track width of 120nm. On the other hand, medium B possessed the desirable properties for high density recording and formed the base for the media that were used in the 230Gb∕in2 demonstration.