bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties of crystalline La0.9Ca0.1MnO3: Comparison of bulk and nanometer-sized samples
Authors: Rozenberg E. , Jung G. , Auslender M. , Gorodetsky G. , Felner I. , Sominski E. , Gedanken A. , Mukovskii Ya. M.
Published: June 2006

ac and dc magnetic measurements have been employed to probe and compare magnetic ordering in bulk and nanometer-sized La0.9Ca0.1MnO3 single crystals. About the same cationic content was determined in both types of the samples. However, the magnetic ground state of the bulk crystal is characterized by a complex mixture of antiferromagnetically and ferromagnetically ordered phases, while the ground state of the nanosample seems to be ferromagnetic and coexisting with the superparamagnetic state at T<240K. The results are discussed in terms of the different randomness of indirect ferromagnetic exchange interactions mediated by the bound holes.
Lattice and spin dynamics in bcc Fe, 10at.% Be
Authors: Zhao P. , Cullen J. , Wuttig M. , Kang H. J. , Lynn J. W. , Lograsso T. A. , Moze O.
Published: June 2006

Body centered cubic Fe1−xBex alloys are known to display an enhanced tetragonal magnetostriction compared to Fe. In order to characterize the enhanced magnetoelasticity observed in this alloy system, we present detailed inelastic neutron scattering measurements of the phonon dispersion relations of a single crystal of bcc Fe, 10at.% Be along the high symmetry directions [100], [110], and [111] at room temperature. We observe in particular that the frequency of transverse phonons propagating along the [110] direction with a [11¯0] polarization at the zone boundary is reduced by 10% with respect to bcc Fe (the corresponding elastic shear constant c′=12(c11−c12) associated with this mode is approximately 70% that of pure Fe). The dispersion of spin waves has also been determined for energy transfers up to 40meV and is found to follow the isotropic dispersion relation E(q)=Dq2, with D∼200meV∕Å2 [for Fe, E(q)=Dq2, with D=280meV∕Å2].
Enhanced magnetic particle transport by integration of a magnetic flux guide: Experimental verification of simulated behavior
Authors: Wirix-Speetjens Roel , Fyen Wim , Boeck Jo De , Borghs Gustaaf
Published: June 2006

In the past, magnetic biosensors have shown to be promising alternatives for classical fluorescence-based microarrays, replacing the fluorescent label by a superparamagnetic particle. While on-chip detection of magnetic particles is firmly established, research groups continue to explore the unique ability of manipulating these particles by applying controlled magnetic forces. One of the challenging tasks in designing magnetic force generating structures remains the generation of large forces for a minimal current consumption. Previously, a simple transporting device for single magnetic particles has been demonstrated using a magnetic field that is generated by two tapered current carrying conductors [R. Wirix-Speetjens, W. Fyen, K. Xu, J. De Boeck, and G. Borghs, IEEE Trans. Magn. 41(10), 4128 (2005)]. We also developed a model to accurately predict the motion of a magnetic particle moving in the vicinity of a solid wall. Using this model, we now present a technique that enhances the magnetic force up to a factor of 3 using a magnetic flux guide. The larger magnetic force results in an average speed of the particle which increases with a factor of 3. These simulations show good agreement with experimental results.
Spin transport at interfaces in magnetic multilayers
Authors: Urazhdin S. , Loloee R. , Pratt W. P.
Published: June 2006

We report systematic measurements of resistance dependence on the angle between the magnetizations in magnetic multilayers at 4.2K, with varied configurations and thickness of one of the layers. Our results fall within a wide range of theoretical predictions based on the ballistic or diffusive transport models of the interface. We obtain a small but finite penetration depth of transverse spin current into the ferromagnets by using a diffusive transport model. We also show that the data for trilayers with the smallest thickness of one of the ferromagnetic layers are inconsistent with the existing models.
Structural and magnetothermal properties of the Gd5SbxGe4−x system
Authors: Chernyshov A. S. , Mudryk Ya. S. , Pecharsky V. K. , Gschneidner K. A.
Published: June 2006

The crystallographic and magnetic properties of the Gd5SbxGe4−x pseudobinary system were studied by x-ray powder diffraction at room temperature, and the heat capacity, magnetization, and electrical resistivity in the temperature interval 5–320K in applied dc magnetic fields between 0 and 100kOe. The Gd5Sb2.1Ge1.9 compound adopts the Tm5Sb2Si2-type structure (space group Cmca) and orders magnetically via a second order ferromagnetic-paramagnetic transition at 200K, whereas the Gd5SbxGe4−x compounds with x=0.7 and x=1 crystallize in the Sm5Ge4-type structure (space group Pnma) and exhibit first order phase transformations at 45 and 37K, respectively, and therefore, the giant magnetocaloric effect. The heat capacity and electrical resistivity measurements of Gd5Sb0.7Ge3.3 indicate a second order antiferromagnetic transition at 60K in fields 20kOe and lower.
Monte Carlo calculations of the magnetocaloric effect in RAl2 (R=Dy,Er)
Authors: Nóbrega E. P. , de Oliveira N. A. , von Ranke P. J. , Troper A.
Published: June 2006

In this work we calculate the magnetocaloric effect in the Laves phase compound RAl2 by using a model Hamiltonian of interacting spins where the spin-spin interaction is treated in the Monte Carlo simulation. The isothermal entropy change and the adiabatic temperature change upon magnetic field variations, for the compounds DyAl2 and ErAl2 are in good agreement with the available experimental data.
Temperature-driven band motion prior to the phase transition of an itinerant ferromagnet
Authors: Hindmarch A. T. , Marrows C. H. , Hickey B. J.
Published: June 2006

Tunneling magnetoresistance spectroscopy measurements have been performed on spin-valve magnetic tunnel junctions where the free magnetic electrode is a Cu38Ni62 alloy with a Curie temperature of around 240K. These measurements allow us to follow the temperature dependence of the energy of the bottom of a minority-spin band close to the Fermi energy, which is partly responsible for the tunneling conductance. The temperature dependence of the tunneling spin polarization of the CuNi electrode has also been extracted using the Julliere formula. We show that the tunneling spin polarization as a function of temperature can be related to the temperature-dependent magnetization using an extension of the commonly applied Stearns model that incorporates the motion of the band close to the Fermi level. This model reproduces the nonlinear relation between tunneling spin polarization and magnetization obtained for Cu38Ni62.
Superexchange coupling on oleylsarcosine-coated magnetite nanoparticles
Authors: Bakuzis A. F. , Pereira A. R. , Santos J. G. , Morais P. C.
Published: June 2006

Room temperature ferromagnetic resonance was used to investigate particle-particle interaction in magnetic fluid samples containing magnetite nanoparticles surface coated with dimercaptosuccinic acid (DMSA) or oleylsarcosine (OLEL). The DMSA sample showed a decrease of the magnetic resonance field (MRF) increasing the nanoparticle concentration (phi), whereas the OLEL sample showed the opposite behavior. The DMSA MRF concentration dependence was explained using a dipolar interaction model beyond the point dipole approximation. In addition, the magnetic resonance spectra of the OLEL sample showed an optical mode suggesting an antiferromagnetic superexchange coupling between magnetic nanoparticles forming dimers.
Investigation of tip-induced magnetic ripples on La0.7Sr0.3MnO3 surface
Authors: Chen Ji-Shiuan , Ma Yuan-Ron , Liou Yung , Yao Yeong Der
Published: June 2006

As demagnetized La1−xSrxMnO3 (LSMO) thin films are magnetized by a local magnetic field from a scanning magnetic tip without an external magnetic field, a magnetic ripple pattern appears on the LSMO surface. The magnetic ripple pattern, which consists of magnetic ripples with varying magnetic periods, is different from the conventional pattern magnetized by an external field. The magnetic ripples with longer magnetic periods have larger magnitude of magnetic moment. The magnitude linearly varies as a function of magnetic period. However, the magnitude of the remanent magnetization induced by the magnetic force microscopy tip is close to that induced by the external field.
Ru doping of the Mn site in La0.4Ca0.6MnO3 perovskite: Electron magnetic resonance study of electronic and magnetic ordering
Authors: Shames A. I. , Rozenberg E. , Auslender M. , Gorodetsky G. , Yakubovsky A. , Gudenko S. , Martin C. , Maignan A.
Published: June 2006

X -band (ν=9.4GHz) electron magnetic resonance (EMR) measurements were carried out in polycrystalline La0.4Ca0.6Mn1−xRuxO3(0⩽x⩽0.16) samples at 100K⩽T⩽550K, aiming to study magnetic/electronic ordering induced by Ru doping. EMR indicates that such doping modifies even the paramagnetic state of La0.4Ca0.6Mn1−xRuxO3 series: the linewidth of resonance signal increases with doping. The initial charge-ordered (CO) antiferromagnetic (AFM) ground state is also drastically modified by doping. At Ru contents x⩾0.04, the ferromagnetic (FM) EMR signal is observed below former TCO. It evidences that the CO transition transforms into the FM one. The magnetic ground state of La0.4Ca0.6Mn1−xRuxO3 remains definitely inhomogeneous due to the coexistence of FM and AFM phases up to, at least, x=0.10. The data obtained are compared with known ones for CaMn1−xRuxO3 system and discussed in the framework of the energy diagram model for Ru-doped manganites.
Structural, magnetic, and transport properties of (Zn,V)Te semiconductors
Authors: Wang Weigang , Ni Chaoying , Zhu Tao , Zhang Huiwu , Xiao John Q
Published: June 2006

Vanadium-doped ZnTe has been predicted to be one of the candidates for ferromagnetic semiconductors with a high Curie temperature [K. Sato and H. Katayama-Yoshida, Semicond. Sci. Technol. 17, 367 (2002)]. In this paper, we report the structural, magnetic, and transport properties of (Zn,V)Te films prepared by magnetron sputtering. Samples were fabricated on both GaAs and thermally oxidized silicon substrate at elevated temperature. Oriented sample (100) can be achieved on GaAs substrates and only polycrystalline samples are observed on Si substrates. X-ray diffraction (XRD) and transmission electron spectroscopy (TEM) show no magnetic precipitates in the (Zn,V)Te film. The magnetization measurement shows that the oriented sample is paramagnetic at 5 K, while films on Si substrate shows weak ferromagnetism at 5 K. The sign of magnetoresistance (MR=[R(H)-R(0)]∕R(0)) gradually changes from negative to positive with temperature, and positive MR at high temperatures shows H2 dependence, indicating ordinary MR effect. It is believed the observed negative MR corresponds to the ferromagnetic ordering at lower temperature.
Cylindrical magnetic shield made of a CFRP/amorphous magnetic tape/CFRP layered composite with built-in shaking coil
Authors: Sasada I. , Kimura T. , Takeda T. , Shimada M.
Published: June 2006

A transportable and rugged cylindrical magnetic shield (length 120 cm, inner diameter 36.5 cm, and weight 43 kg) is fabricated by compositing Co-based amorphous magnetic tapes and a toroidally wound copper-wire shaking coil with fiber-reinforced plastics (FRP). The innermost and the outermost part of the cylinder are made of carbon fiber-reinforced plastics (CFRP) for obtaining a rugged structure. The shielding factor evaluated for the transversally applied 10 Hz, 10μT magnetic field was better than 10 000 at the shaking condition of 400 Hz, 1.9A∕m, which requires only a 0.76VA shaking source.
Magnetic hardening in Fe3B∕Nd2Fe14B nanocomposite magnets induced by rapid thermal annealing
Authors: Shih J. C. , Saldanha A. J. , Suzuki K. , Shoji T. , Kato A. , Tajima S.
Published: June 2006

The decomposition behaviors of melt-spun amorphous Fe82−xNdxB18 (x=3-5.5) and Fe82−zNd5B18Mz (M=Ti, V, and Cr; z=1.5-5) alloys under a range of heating rates (0.042 to 8.3K∕s) have been investigated. The heating rate upon nanocrystallization has little effect on the structural and magnetic properties in both Fe79Nd3B18 and Fe77Nd5B18. In contrast, the Fe57 Mössbauer spectral area of Nd2Fe14B in Fe77.5Nd4.5B18 shows a clear increase with increasing heating rate, and the coercivity is enhanced. The coercivity of Fe77Nd5B18 doped with V and Cr is also enhanced to 200-430kA∕m when heated at a high rate of 3.3K∕s. Rapid thermal annealing is effective in enhancing magnetic hardness, in particular, when the metastability of Nd2Fe14B is moderately demoted.
Interface specific-resistance and scattering asymmetry of permalloy∕Al
Authors: Theodoropoulou N. , Sharma A. , Loloee R. , Pratt W. P. , Bass J. , Fert A. , Jaffres H.
Published: June 2006

Stimulated by observations by Garcia et al. [Bull. Am. Phys. Soc. 50, 237 (2005)] of much smaller magnetoresistances (MR) for Py∕Al∕Py nanopillars than for Py∕Cu∕Py, but only slightly larger switching currents Is for current-induced magnetization switching (CIMS), we have determined the specific resistance, (area A times resistance R), 2ARPy∕Al*, and the scattering asymmetry, γPy∕Al, at 4.2 K for interfaces between sputtered permalloy (Py) and aluminum (Al): 2ARPy∕Al*=8.5±1fΩm2 is an order of magnitude larger than the standard value of 2ARPy∕Cu*=1.0±0.1fΩm2, and γPy∕Al=0.025−0.01+0.045 is an order of magnitude smaller than γPy∕Cu=0.7±0.1. These two differences qualitatively account for the smaller MR but comparable Is with Al.
Large magnetoresistance (>600%) of a GaAs:MnAs granular thin film at room temperature
Authors: Yokoyama M. , Ogawa T. , Nazmul A. M. , Tanaka M.
Published: June 2006

A large positive magnetoresistance (MR) at room temperature was observed in a GaAs:MnAs granular thin film, in which MnAs nanoclusters were embedded in a GaAs matrix. Current-voltage characteristics and a MR effect of the GaAs:MnAs thin film were measured by a two-point-probe method. The MR ratio of the GaAs:MnAs granular thin film reached more than 600%, when a bias voltage of 110 V was applied to the film.
Giant Zeeman effects in colloidal diluted magnetic semiconductor quantum dots with homogeneous dopant speciation
Authors: Norberg Nick S. , Gamelin Daniel R.
Published: June 2006

Ligand field electronic absorption and magnetic circular dichroism (MCD) spectroscopies are used to probe Co2+ dopant speciation in ZnO, ZnSe, and CdS nanocrystals and confirm the high quality of these colloidal diluted magnetic semiconductor quantum dots (DMS-QDs). Measurements of the QD giant Zeeman splittings using MCD and Zeeman spectroscopies show no enhancement of N0(α−β) relative to bulk. MCD spectroscopy is also presented as an effective method for verifying the successful synthesis of colloidal DMS-QDs when doping cannot be confirmed by ligand field absorption, highly resolved electron paramagnetic resonance, or other rigorous dopant-specific spectroscopic means.
The A1 to L1 transformation in FePt and FeCuPt thin films: Determination of isothermal transformation kinetics from nonisothermal measurements
Authors: Berry D. C. , Barmak K.
Published: June 2006

Time–temperature-transformation diagrams describing the A1 to L10 transformation in 1μm thick FePt and FeCuPt alloy films are constructed from data obtained using nonisothermal differential scanning calorimetry in conjunction with a limited number of isothermal anneals. For the FePt alloys, an increase in Pt content from 45.6 to 52.5 at.% results in a >300× increase in the annealing time needed to reach a fraction transformed of 0.95 at 300 °C. Using geometric corrections, the results are extended to 10 nm thick films, which are found to transform approximately five times more slowly than thicker films.
Spin-spiral structures in free-standing Fe(110) monolayers
Authors: Nakamura Kohji , Mizuno Naoki , Akiyama Toru , Ito Tomonori , Freeman A. J.
Published: June 2006

Electronic and magnetic structures in spin-spiral structures of free-standing Fe(110) monolayers with lattice constants, a, matching those of bulk bcc Fe (2.87 Å) and W (3.16 Å), were investigated by means of first-principles film full-potential linearized augmented-plane-wave calculations including intra-atomic noncollinear magnetism. For a=2.87Å, the spin-spiral structures with wavelength around 7a are energetically favored over the collinear ferromagnetic state while those for a=3.16Å turn out to be less favorable. The formation of the spin-spiral structures are found to result from a Fermi-surface nesting that leads to an instability of the ferromagnetic state. In addition, the spin-orbit coupling is found to play an important role to determine the magnetization rotation. These results offer an important step in understanding complex noncollinear spin-spiral magnetism in thin films.
Cation occupancy determination in manganese zinc ferrites using Fourier transform infrared spectroscopy
Authors: Shultz M. D. , Carpenter E. E. , Morrison S. A. , Calvin S.
Published: June 2006

The magnetic and electric properties of ferrites are influenced by the cation distribution within the crystalline spinel lattice. Methods such as extended x-ray-absorption fine structure (EXAFS) have been used to determine cation occupancies within the crystalline structure of materials such as manganese zinc ferrite (MZFO); however, it is not practical to be used for daily analysis. Fourier transform infrared (FTIR) spectroscopy is another technique which has the potential to determine cation occupancy while offering speed and convenience. In the literature it has been demonstrated that in ferrite systems FTIR data can be correlated to cation percentages when comparing tetrahedral (Td) and octahedral (Oh) sites. FTIR spectra were collected on a series of MZFO nanoparticles in the range from 200 to 600cm−1 and two absorbance peaks were observed. The first absorption region shifted with changing sample composition as calculated from transmission EXAFS experiments and elemental analysis. The data was normalized to the maximum of the peak of interest and the shifts were correlated to cation occupancy.
Magnetic switching in epitaxial (110) La2∕3Ca1∕3MnO3 films
Authors: Infante I. C. , Hrabovský D. , Laukhin V. , Sánchez F. , Fontcuberta J.
Published: June 2006

We report on the magnetic anisotropy analysis of (110) La2∕3Ca1∕3MnO3 epitaxial films grown on (110) SrTiO3 substrates. We have measured the angular dependence of the longitudinal (ρxx) and transverse magnetoresistance (ρxy), with current along [001] direction, as a function of the angle θ between the current and the in-plane applied field. The measured ρxx(θ) and ρxy(θ) data reveal sharp variations that reflect the magnetic anisotropy of the system. We show that using a simple model for coherent rotation of magnetization, the shape of measured loops can be well reproduced and data analysis allows us to extract the anisotropy parameters. We will show that the system exhibits uniaxial anisotropy.
Thermal stability in spin-torque-driven magnetization dynamics
Authors: Serpico C. , Bertotti G. , Mayergoyz I. D. , d’Aquino M. , Bonin R.
Published: June 2006

In this article, thermal fluctuations in spin-torque-driven magnetization dynamics are described phenomenologically by introducing a Gaussian white noise term in the Landau-Lifshitz-Slonczewski equation. The ensuing stochastic magnetization dynamics is studied by considering the Fokker-Planck equation for the probability distribution of magnetization. The corresponding Fokker-Planck for the energy probability distribution is then derived in the limit of small fluctuations by averaging with respect to fast-time-scale precessional dynamics. By using this equation the stationary probability distribution of energy is analytically determined. This distribution has peaks around stable stationary states as well as around self-oscillatory regimes. On this basis, we define an effective potential barrier controlling switching between stable equilibrium states and self-oscillatory regimes.
Enhancement of the exchange-bias onset temperature in a columnar nanocrystalline Ni80Fe20∕Co3O4 thin film
Authors: van Lierop J. , Lin K.-W. , Guo Z.-Y. , Southern B. W.
Published: June 2006

Typically, exchange coupling can only occur when ferromagnetic spins couple to antiferromagnetic spins below the Néel temperature. We present results on a Ni80Fe20∕Co3O4 thin film that is composed of ∼10nm diameter nanocrystalline columns. Field cooling the film reveals low-temperature exchange-bias hysteresis loop shifts that are the same magnitude as those measured in a similar Ni80Fe20∕CoO system, although the bulk magnetocrystalline anisotropy is a factor of 5 smaller. The coercivity and exchange-bias loop shift exhibit the same temperature dependence with individual “blocking” temperatures. Most surprising is that the onset temperature of the exchange-bias is nearly four times higher than the bulk Néel temperature.
Origin of low coercivity of (Fe0.75B0.15Si0.10)100−xNbx (x=1–4) glassy alloys
Authors: Bitoh T. , Makino A. , Inoue A.
Published: June 2006

The density and the magnetization process of the melt-spun (Fe0.75B0.15Si0.10)100−xNbx (x=1–4) glassy alloys have been investigated to clarify the origin of low coercivity (Hc). Both Hc and the difference of the densities between the crystalline and glassy phases, which corresponds to the free volume in the glassy phase, decrease with increasing Nb content. An analysis of the magnetization process based on the law of approach to ferromagnetic saturation reveals that quasidislocation dipole (QDD)-type defects are the main sources of elastic stress. The results also suggest that the pinning force for magnetic domain walls generated by one QDD-type defect is independent of the Nb content, but the number density of QDDs decreases with increasing the Nb content. Therefore, it concluded that the origin of low Hc of the glassy alloys is the low number density of QDDs which corresponds to the low number density of the domain-wall pinning sites.
Hyperfine interactions in lutetium iron garnet
Authors: Chlan V. , Novák P. , Štěpánková H. , Englich J. , Kuriplach J. , Nižňanský D.
Published: June 2006

Nuclear Magnetic Resonance/Near Quadupole Resonace specra of Lu175 in lutetium iron garnet (LuIG) were measured in the range of 10–500MHz in zero external magnetic field at a temperature of 4.2K. Experimentally observed spectra had complicated structure and a theory was needed to interpret them. To this end we calculated the electronic structure of LuIG and from it the values of magnetic hyperfine fields and the components of electric-field-gradient tensor at the lutetium nuclei were determined. These parameters were used to simulate the theoretical spectra of Lu175 in LuIG. Simulated spectral lines of Lu175 at dodecahedral sublattice correspond reasonably well with the system of measured lines in the range of 10–200MHz. Several spectral lines in the range of 300–500MHz can be interpreted as the resonance of Lu175 at the octahedral sites that are nominally occupied by the ferric cations.
Investigation of magnetocrystalline anisotropy by planar Hall effect in GaMnAs epilayers grown on vicinal GaAs substrates
Authors: Lim W. L. , Liu X. , Dziatkowski K. , Ge Z. , Shen S. , Furdyna J. K. , Dobrowolska M.
Published: June 2006

An asymmetric shift of the Hall resistance in the presence of an in-plane magnetic field is observed in ferromagnetic GaMnAs epilayers grown on vicinal GaAs substrates, due to the superposition of both the planar Hall effect and the anomalous Hall effect (AHE). The asymmetric shift (i.e., the difference between the values of the Hall voltage observed at magnetic field of opposite sign) is a direct manifestation of the strength of the magnetocrystalline anisotropy, which confines the magnetization to the preferred crystalline plane, thus resulting in a nonzero component of the magnetization normal to the GaMnAs layer. This is confirmed by the observation that the asymmetry in the resistance is proportional to the saturated AHE resistance measured in perpendicular high field configuration.
Magneto-optical features and extraordinary light transmission through perforated metal films filled with liquid crystals
Authors: Strelniker Yakov M. , Stroud D. , Voznesenskaya A. O.
Published: June 2006

We calculate the effective dielectric tensor of a metal film penetrated by cylindrical holes filled with a nematic liquid crystal (NLC) whose director is parallel to the film and can be controlled by a static magnetic field whose direction can be rotated in an arbitrary direction in the plane of the film. We consider both randomly distributed holes (using a Maxwell-Garnett approximation) and a square lattice of holes (using a Fourier technique). Both the holes and the lattice constant of the square lattice are assumed small compared to the wavelength. The films are found to exhibit extraordinary light transmission at special frequencies, ωsp, related to the surface plasmon (SP) resonances of the composite film, which depends on the direction of the applied magnetic field.
High sensitivity and quantitative magnetic field measurements at 600°C
Authors: Yamamura Takuya , Nakamura Dai , Higashiwaki Masataka , Matsui Toshiaki , Sandhu Adarsh
Published: June 2006

High sensitivity micro-Hall sensors were fabricated using AlGaN∕GaN two-dimensional electron gas heterostructures grown by molecular beam epitaxy for high temperature operation. The room temperature electron mobility and sheet carrier concentration of the heterostructures were 850cm2∕Vs and 7.7×1012cm−2, respectively. The Hall voltage increased linearly with applied magnetic field up to 0.5T for all temperatures in the range of temperature from 20to600°C. A 100μm×100μm Hall device with a magnetic sensitivity of 0.35G∕(Hz)1∕2 at 600°C was used to measure the Curie temperature of NdFeB. The AlGaN∕GaN micro-Hall sensors will find a wide range of applications including high temperature scanning Hall microscopy, monitoring rotating parts in the engines of automobiles as well as space vehicles which are exposed to extreme changes in temperature and radiation.
Magnetic domains and magnetization reversal of ion-induced magnetically patterned Ruderman-Kittel-Kasuya-Yoshida-coupled Ni81Fe19∕Ru∕Co90Fe10 films
Authors: Fassbender J. , Bischoff L. , Mattheis R. , Fischer P.
Published: June 2006

Pure magnetic patterning by means of ion-beam irradiation of magnetic thin films and multilayers often results from a postdeposition local modification of the interface structure with only minor effects on the film topography. In the study presented here a 60keV fine-focused Co ion beam was used to change the coupling in a Ni81Fe19∕Ru∕Co90Fe10 structure from antiferromagnetic to ferromagnetic on a micron scale. Thereby an artificial structure with locally varying interlayer exchange coupling and therefore magnetization alignment is produced. High-resolution full-field x-ray microscopy is used to determine the magnetic domain configuration during the magnetization reversal process locally and layer resolved due to the element-specific contrast in circular x-ray dichroism. In the magnetically patterned structure there is, in addition to the locally varying interlayer exchange coupling across the Ru layer, also the direct exchange coupling within each ferromagnetic layer present. Therefore the magnetization reversal behavior of the irradiated stripes is largely influenced by the surrounding magnetic film.
Magnetic properties and magnetic-entropy change of MnFeP0.5As0.5−xSix(x=0–0.3) compounds
Authors: Dagula W. , Tegus O. , Li X. W. , Song L. , Brück E. , Cam Thanh D. T. , de Boer F. R. , Buschow K. H. J.
Published: June 2006

The effects of Si substitution for As on the magnetic and magnetocaloric properties of MnFeP0.5As0.5−xSix compounds have been investigated. The Si-substituted compounds MnFeP0.5As0.5−xSix with x=0, 0.1, 0.2, and 0.3 have been prepared by high-energy ball milling and solid-state reaction. X-ray diffraction shows that all the MnFeP0.5As0.5−xSix compounds crystallize in the Fe2P-type structure. Magnetic measurements show that the compounds are ferromagnetic with a nonlinear dependence of TC on Si content. All compounds exhibit a field-induced first-order magnetic phase transition. The magnetic-entropy change is derived from the magnetization data by using the Maxwell relations. The maximum magnetic-entropy change observed in this system reaches about 32J∕kgK for a field change from 0to2T for x=0.2, at temperature around 294K.
Tailoring the magnetic properties of CoFeNi alloys with variations in copper contents
Authors: Lee Jeong Oh , Kim Hyun Kyung , Kim Gyeung Ho , Jeung Won Young
Published: June 2006

CoFeNi alloys are some of the most studied soft magnetic materials because of their superior properties over FeNi alloys as write head core materials in hard disk drives. Pulsed electrodeposition was shown to be an interesting approach to vary the crystalline structure of the fcc-bcc mixed phase CoFeNi and CoFeNiCu films without changing the composition and the grain size by using a single bath. The permeability μ of CoFeNiCu films plated from bath composition exceeded 4.6×106. Coercivity Hc was 20–73A∕m. The high saturation magnetic flux Bs was 1.8T. The soft magnetic CoFeNiCu film prepared satisfies all the requirements needed for the preparation of magnetic recording heads, as all magnetic properties were improved in this direction.
Magnetocaloric effect in Gd5Si2Ge2∕Gd composite materials
Authors: Yue M. , Zhang J. , Zeng H. , Chen H. , Liu X. B.
Published: June 2006

Spark plasma sintering technique has been applied to synthesize composite Gdx(Gd5Si2Ge2)1−x (x=0.3, 0.5, and 0.7) with layer structure using high-purity gadolinium (Gd) metal and Gd5Si2Ge2 alloys. The magnetocaloric effect of the composites was studied by directly measuring adiabatic temperature change (ΔTad) with a magnetic-field change of 1.5T using a homemade magnetocaloric effect measuring apparatus. With increasing x from 0.3 to 0.7, ΔTad peak temperature shifted from 286to293K and the peak values of ΔTad slowly increased from 1.6to2.0K at a magnetic-field change of 1.5T. Meanwhile, the ΔTad peak of the composite broadened as Gd content was increased. For x=0.7, the composite showed a ΔTad ranging from 1.1to2.0K at a magnetic-field change of 1.5T in a temperature range of 260–300K, which adapted to work as a room-temperature refrigerant.
Package compatibility and substrate dependence of granular soft magnetic material CoFeHfO developed by reactive sputtering
Authors: Li Liangliang , Wang Shan X. , Hwang Kyu-Pyung , Min Yongki , Mao Ming , Schneider Thomas , Bubber Randhir
Published: June 2006

Integration of magnetic passive components into package has been attracting more interests recently, but efficient package-compatible magnetic materials are needed. We have developed a package-compatible granular material, CoFeHfO, on a printed circuit board by reactive sputtering and investigated the substrate dependence of its soft magnetic property. Atomic force microscopy and grazing incidence x-ray-scattering-diffraction spectra show that a rough substrate surface degrades the magnetic property of CoFeHfO thin films with almost the same crystal microstructure. With surface planarization by chemical-mechanical polishing, soft magnetic material CoFeHfO can be realized on the package substrate. This material is promising for future applications in package.
Comparison between the in-plane anisotropies and magnetostriction constants of thin epitaxial Fe films grown on GaAs and Ga0.8In0.2As substrates, with Cr overlayers
Authors: Morley N. A. , Gibbs M. R. J. , Ahmad E. , Will I. G. , Xu Y. B.
Published: June 2006

Thin epitaxial Fe films grown on GaAs(100) and Ga0.8In0.2As(100) substrates were investigated to determine how tuning the lattice constant mismatch between the Fe and the substrate may change the in-plane anisotropies and the magnetostriction. Two sets of Fe films were grown using molecular-beam epitaxy, each capped with a Cr overlayer. For each film, the in-plane anisotropy constants were determined from the normalized magnetization loops measured using a magneto-optic Kerr effect magnetometer. The lattice mismatch was found to give no contribution to the in-plane anisotropies. For all the films the magnetostriction constants, determined by the Villari method, were negative and became more negative as the Fe thickness decreased.
Effect of CrW underlayer on structural and magnetic properties of FePt thin films
Authors: Cao Jiangwei , Cai Jun , Liu Yan , Yang Zheng , Wei Fulin , Xia Ailin , Han Baoshan , Bai Jianmin
Published: June 2006

L 1 0 ordered FePt thin films with face-centered-tetragonal (001) texture have been prepared by magnetron sputtering on Cr100−xWx underlayer. The dependence of Cr100−xWx microstructure and FePt texture on the W content in the Cr underlayer was investigated. The addition of W element in Cr underlayer enhances the Cr (200) texture and increases the lattice constant of Cr, which is favorable for lowering the transformation temperature from fcc to fct phase because of the increase of the tensile stress along the FePt a axis. A good FePt (001) texture is obtained on the Cr85W15 underlayer with a substrate temperature of 400°C. The coercivity of FePt thin films on CrW underlayer is higher than on Cr underlayer and increases with increasing W content in the Cr underlayer because the formation of the CrW alloy inhibits the diffusion between FePt and CrW layer. A 5nm Pt intermediate layer was employed to suppress the diffusion between FePt and CrW underlayer further.
Nanostructured Mn–Al permanent magnets produced by mechanical milling
Authors: Zeng Qi , Baker Ian , Yan Zhi-cheng
Published: June 2006

Prealloyed powders of Mn54Al46 were mechanically milled, and the as-milled powders subsequently annealed at temperatures from 350to600°C to produce the ferromagnetic L10-structured τ phase. It was found that the magnetic properties are strongly dependent on both the fraction of τ phase and the grain size. Due to the nanostructure, a large coercivity, up to 4.8kOe, was obtained for Mn54Al46 powders annealed at 400°C for 10min. Both remanence curves and δM plots showed no exchange coupling between the τ-phase nanograins. The mechanism for the magnetization process was determined to be domain-wall pinning type.
Microstructural evolutions in NdFe10.5Mo1.5NX and Pr13Fe80B7 compounds during hydrogenation-disproportionation desorption recombination process
Authors: Han Jing-Zhi , Liu Shun-Quan , Du Hong-Lin , Wang Chang-Sheng , Yang Jin-Bo , Yang Ying-Chang
Published: June 2006

Microstructural changes of NdFe10.5Mo1.5 and Pr13Fe80B7 compounds during the solid-hydrogenation disproportionation desorption recombination process are investigated in this paper. It is found that the early disproportionated microstructure of NdFe10.5Mo1.5 and Pr13Fe80B7 alloys shows similar rodlike morphology. All the NdH2+X and PrH2+X rods have the same orientation and grow with a definite orientation related to the α-Fe matrix. However, it is different that Mo atoms are found to dissolve in the α-Fe matrix of the NdFe10.5Mo1.5 disproportionated products while the PrH2+X rods are enriched with B in the case of Pr13Fe80B7 alloys. No special crystallographic relationship between the recombined NdFe10.5Mo1.5 or Pr13Fe80B7 and its disproportionated products is observed. A preferred nucleation and growth of recombined Pr2Fe14B grains is found while that of recombined NdFe10.5Mo1.5 grains is not. Thus, the final hydrogenation-disproportionation desorption recombination (HDDR) NdFe10.5Mo1.5NX powder is isotropic while the HDDR Pr13Fe80B7 powder has a strong anisotropy under the same HDDR treatment conditions. In the end, the formation of anisotropy in the HDDR Pr13Fe80B7 and NdFe10.5Mo1.5NX powders is discussed.
Magnetic properties of a metal-organic antiferromagnet Mn(hfipbb)py(H2O)0.5
Authors: Yuen Tan , Lin C. L. , Pan Long , Huang Xiaoying , Li Jing
Published: June 2006

Mn ( hfipbb ) py ( H 2 O ) 0.5 [H2hfipbb=4, 4′-(hexafluoroisopropylidene)bis(benzoic acid), py=pyridine] is a recently discovered metal-organic coordination network. The crystal structure of this compound belongs to a triclinic space group P-1, and the lattice parameters are a=12.988Å, b=13.296Å, c=14.644Å, α=115.13°, β=95.61°, and γ=101.03°. Two crystallographically independent Mn atoms (Mn1 and Mn2) exist in this structure, and an alternate connection (–Mn1–Mn2–Mn1–Mn2–) through organic units along the x axis leads to a one-dimensional Mn2+ chain. Magnetic susceptibility M(T)∕H and isothermal magnetization M(H) were measured on single-crystal samples, as well as on powder samples of Mn(hfipbb)py(H2O)0.5. Antiferromagnetic ordering was observed below a transition temperature of TN=9.0K. High-temperature susceptibility data for powder samples were fitted to the Curie-Weiss law with θ=−30K and an effective moment of μeff=5.7μB, close to what is expected for a free Mn2+ ion. There is small but clear orientation dependence in the susceptibility data for single-crystal samples. The result of isothermal magnetization measured at 2K is consistent with the interpretation of an antiferromagnetic ground state, and a slope change was seen at a critical field of Hc=18kG, indicating a field-induced moment reorientation of the Mn2+ ions in this compound.
Improved synthesis and easy-axis alignment of L1-FePt nanoparticles
Authors: Jia Zhiyong , Kang Shishou , Shi Shifan , Nikles David E. , Harrell J. W. , Shamsuzzoha M.
Published: June 2006

A synthesis of partially ordered FePt nanoparticles has been developed. It involves the simultaneous reduction of iron acetate (or iron chloride) and platinum acetylacetonate. The high boiling point chemical hexadecylamine or trioctylamine was used as a solvent, and oleic acid or 1-adamantanecarboxylic acid was used as a surfactant. The reflux temperature of the mixture solutions ranged from 330to360°C, where disordered FePt particles can be partially transformed into the ordered L10 phase. Compared with previous results, x-ray-diffraction patterns of as-made samples prepared with the synthesis show a higher degree of chemical ordering. The composition of the FePt nanoparticles with the synthesis can be easily tuned. The room-temperature coercivity of as-made samples ranged from 1to4kOe, depending on the particle composition as well as the refluxing temperature during synthesis. The as-made particles were aligned in a 10kOe magnetic field, giving a parallel to perpendicular remanence ratio of about 1.6.
Investigation of artificial domains realized by local gallium focused ion-beam modification of Pt∕Co∕Pt trilayer structures
Authors: Aziz A. , Bending S. J. , Roberts H. , Crampin S. , Heard P. J. , Marrows C. H.
Published: June 2006

We present the results of experimental investigations of magnetic switching and magnetotransport in a generation of magnetic devices containing artificially patterned domains. Our devices are realized by locally reducing the coercive field of a perpendicularly magnetized Pt(3.5nm)∕Co(0.5nm)∕Pt(1.6nm) trilayer structure using a gallium focused ion beam. Artificial domain walls are created at the interfaces between dosed and undosed regions when an external magnetic field switches the former but not the latter. We have exploited this property to create stripelike domains with widths down to submicron length scales, separated by undosed regions. Using the extraordinary Hall effect to monitor the local magnetization we have investigated the reversal dynamics of these artificial domains by measuring major and minor hysteresis loops. The coercive field of regions irradiated with identical doses systematically increases as their size decreases. In the lower branch of minor loops, reversal is seen to occur via a few large Barkhausen events. Preliminary measurements of transport across domain walls reveal a positive domain-wall resistance, that does not change sign from 4.2to300K.
A two–dimensional model for the interaction between lubricant droplet on the slider surface and air flow within the head/disk interface of disk drives
Authors: Wu Lin
Published: June 2006

We numerically study the interaction phenomenon between a lubricant droplet located on the slider’s air bearing surface and the air flow within the head/disk interface of disk drives. A very strong interaction between the lubricant droplet motion and air flow is discovered for ultra-low-flying slider design. The lubricant droplet is driven to migrate towards the slider’s trailing edge by a net effect of air shearing, air bearing pressure gradient, and disjoining pressure gradient. The droplet simultaneously undergoes significant shape deformation. The moving and deforming droplet in turn modifies the effective air bearing surface profile and induces a corresponding air flow adjustment. For a simplified two-dimensional (2D) slider with a fixed flying attitude, our results show that the moving and deforming lubricant droplet induces significant air bearing force and pitch moment change. The interaction becomes stronger when the size of the droplet and the disk’s linear velocity are increased, and when the flying height and pitch angle of the slider are reduced. Our results indicate that a lubricant droplet contamination entering the air bearing surface may impose a non-negligible disturbance on the slider’s flying dynamics.
Recording performance of CoCrPtO perpendicular media with single-domain hard magnet-biased soft magnetic underlayers
Authors: Jung H. S. , Velu E. M. T. , Malhotra S. S. , Jiang W. , Bertero G.
Published: June 2006

Single-domain hard magnet-biased (HB) soft magnetic underlayers (SUL) with synthetic antiferromagnetically (SAF) coupled structure were successfully produced. Here, we describe the effect of HB SAF SUL on recording performance in a simple structure of Co86CrTa(40)∕Ru∕CoTaZr(t)∕interlayer(15)∕CoCrPtO(15nm). Radial anisotropy orientation of as-deposited CoTaZr films was induced at thickness ⩾60nm. As CoTaZr thickness increased from 60to195nm, media write-ability was significantly improved while magnetic properties of the CoCrPtO layer were slightly changed. Normalized media noise data are consistent with magnetic domain observation: Kerr images exhibited single magnetic domain, but magnetic force microscopy images detected strong magnetic ripple structure at 60nm. Less magnetic ripple was observed with increasing CoTaZr thickness. The magnetic ripples on CoTaZr, caused by exchange coupling with CoCrTa, clearly contributed to dc-erase noise. Media noise and signal-to-noise SNRme on 155nm thick CoTaZr were comparable with values obtained from the medium on conventional 120nm thick CoTaZr∕Ru∕CoTaZr.
Finite-element modeling and micromagnetic modeling of perpendicular writers
Authors: Heinonen Olle , Bozeman Steven P.
Published: June 2006

We compare finite-element modeling (FEM) and fully micromagnetic modeling results of four prototypical writers for perpendicular recording. In general, the agreement between the two models is quite good in the vicinity of saturated or near-saturated magnetic material, such as the pole tip, for quantities such as the magnetic field, the gradient of the magnetic field and the write width. However, in the vicinity of magnetic material far from saturation, e.g., return pole or trailing edge write shield, there can be large qualitative and quantitative differences.
Dynamics of laminated write elements
Authors: Heinonen Olle , Nazarov Alexey , Plumer Martin L.
Published: June 2006

One concern as storage technology moves to perpendicular recording is the remnant state of the writer top pole. In principal, a remnant state with a substantial magnetization density perpendicular to the recording medium can lead to the unwanted erasure of data. Also, it is desirable to have the writer reach a nonerasing remnant state as quickly as possible. One technique to reduce the magnetization in the remnant state is to laminate the pole tip with some nonmagnetic material [Y. Satoh, A. Ohtsubo, and Y. Shimada, IEEE Trans. Magn. 21, 1551 (1985); S. Wang et al., IEEE Trans. Magn. 30, 3897 (1994)]. We have performed fully micromagnetic simulations of write elements with eight, five, four, and two laminates coupled antiferromagnetically. Results are presented for recording fields, as well as for the decay of the magnetization to a remnant state. The two- and four-laminate write elements typically have a vortex induced in the pole tip, and this vortex tends to survive, even in the remnant state. This can give rise both to a slow decay as well as large remnant fields from the out-of-plane magnetization in the vortex. On the other hand, the magnetization of the eight-laminate pole tip decays by “scissoring” of the magnetization in the laminates, with a faster decay to the remnant state. However, locally large divergences of the magnetization density can give rise to “hot spots” with relatively large remnant fields.
Microfluidic magnetic separator using an array of soft magnetic elements
Authors: Smistrup Kristian , Lund-Olesen Torsten , Hansen Mikkel F. , Tang Peter T.
Published: June 2006

We present the design, fabrication, characterization, and demonstration of a new passive magnetic bead separator. The device operates in an effective state when magnetized by an external magnetic field of only 50mT, which is available from a tabletop electromagnet. We demonstrate the complete capture of 1.0μm fluorescent magnetic beads from a 7.5μL sample volume traveling at an average linear fluid velocity of 5mm∕s.
Conversion from Al to Al2O3 of subnanometer barriers for magnetic tunnel junctions monitored in real time
Authors: Fabrie C. G. C. H. M. , Kohlhepp J. T. , Swagten H. J. M. , Koopmans B. , de Jonge W. J. M.
Published: June 2006

In situ differential ellipsometry measurements are used to investigate the plasma oxidation dynamics of subnanometer Al layers in real time. An analysis of the measured oxidation rate allows us to monitor the conversion from Al to Al2O3 in real time and mark the onset of the CoFe electrode oxidation. In situ x-ray photoelectron spectroscopy (XPS) measurements of identical samples that were plasma oxidized for 3s are used to confirm the ellipsometry results. A linear relationship was found between the amount of Al2O3 determined from the XPS data and the amount of oxidized Al derived from the ellipsometry data. From this, we conclude that the conversion from Al to Al2O3 of subnanometer thin barriers for magnetic tunnel junctions can be observed by using the derivative of the ellipsometer signal.
Microwave absorption of integrated CoNbZr film on a coplanar waveguide
Authors: Kim Ki Hyeon , Yamaguchi Masahiro
Published: June 2006

The microwave power absorption and characteristic impedance of integrated CoNbZr magnetic films on coplanar waveguides have been investigated. The power absorption peaks of the CoNbZr films (50μm×2mm) with different film thickness, 0.5, 1, and 2μm, were observed at around 3.3, 4.5, and 5.8GHz, respectively. These peak frequencies were in good agreement with calculated ferromagnetic resonance frequencies including magnetic shape anisotropy effects. Compared with the coplanar waveguide without a magnetic film, the characteristic impedance of these integrated films at 1GHz (in passband frequency) was shown to be increased. This change resulted in the large increment of inductance up to 33% without any significant changes of the capacitance.
Ion beam synthesis of Fe nanoparticles in MgO and yttria-stabilized zirconia
Authors: Potzger K. , Reuther H. , Zhou Shengqiang , Mücklich A. , Grötzschel R. , Eichhorn F. , Liedke M. O. , Fassbender J. , Lichte H. , Lenk A.
Published: June 2006

To form embedded Fe nanoparticles, MgO(001) and YSZ(001) single crystals have been implanted at elevated temperatures with Fe ions at energies of 100keV and 110keV, respectively. The ion fluence was fixed at 6×1016cm−2. As a result, γ- and α-phase Fe nanoparticles were synthesized inside MgO and YSZ, respectively. A synthesis efficiency of 100% has been achieved for implantation at 1273K into YSZ. The ferromagnetic behavior of the α-Fe nanoparticles is reflected by a magnetic hyperfine field of 330kOe and a hysteretic magnetization reversal. Electron holography showed a fringing magnetic field around some, but not all of the particles.