bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of the resonance mode related to the random anisotropy in amorphous FeCoZr thin films
Authors: Ouahmane H. , Suran G.
Published: July 2002

The properties of a resonance mode, the existence of which is related to the random local anisotropy Kl, detected in amorphous FeCoZr thin films, are reported. The data are compared with those obtained on a-CoZr(R) R=rare earth films where the amount of Kl was an order of magnitude bigger. The overall trends, evolution of the nature of the mode from a longitudinal via a mixed to a pure transverse state are the same. The parameters of the mode are directly related to the value of Kl.
Simulations of the magnetic properties of thin film media with low coercivity grains
Authors: Walmsley N. S. , Chantrell R. W.
Published: July 2002

This article presents an extensive investigation of the effect of low coercivity (LC) grains on the remanence process in exchange coupled longitudinal thin film. In particular, it is shown that the inclusion of LC grains causes an increase in the slope of the magnetization curve in small negative fields leading essentially to a decrease in the stability of the written information. Switching field distributions and δI plots are used to illustrate the effect of LC grains on intergranular interactions.
First principles theory of spin waves in Fe, Co, and Ni
Authors: Brown R. H. , Nicholson D. M. C. , Wang Xindong , Schulthess T. C.
Published: July 2002

Using constrained local spin density functional theory it is possible to directly calculate the adiabatic magnon dispersion curve. Small amplitude magnons with wavelengths between 2 and 32 atomic layers were constructed and the energy change with respect to amplitude within the frozen potential approximation was calculated. The resulting dispersion curves give the spin wave stiffness for [111] face-centered-cubic Co and Ni in fair agreement with experiment. In Fe the stiffness was calculated along [100] and [110] directions. The two values of stiffness were found to be nearly equal to each other and roughly half the measured value. It was found that the calculated Fe stiffness did not change upon addition of gradient corrections to the local density approximation, indicating that the source of discrepancy is not likely a failure of the local density approximation. It is argued that the adiabatic approximation is more likely the source of discrepancy since the magnetic interactions in Fe are longer ranged than those in Co or Ni, thus making the dynamical retardation effect more important in Fe.
Magnetic structure in FeCr and FeCo
Authors: Qiu S. L. , Marcus P. M. , Moruzzi V. L.
Published: July 2002

The occurrence of magnetic phases in FeCr and FeCo in the CsCl structure has been studied by first-principles total-energy calculations with a sensitive and accurate method, using a four-atom unit cell. When both atoms in such binary compounds can be strongly magnetic, unusual structures are found. These materials have ferromagnetic (FM) and antiferromagnetic (AF) phases, but the equilibrium state for both is FM. However at 3% expansion of the lattice constant the ground state of FeCr becomes AF, whereas in FeCo the AF phase is never the ground state. The AF phase in both FeCr and FeCo has an unusual structure in that both the Fe and the Cr or Co sublattices are separately AF. In both the FM and AF phases at the equilibrium volume, the Fe moment is reduced in FeCr, but enhanced in FeCo from that in pure body-centered-cubic (bcc) Fe; also the Cr moment is increased from that in pure bcc Cr, while the Co moment is similar to the moment in hexagonal-dose-packed Co. In the FM phase of FeCr, but not in FeCo, the two Fe atoms in the four-atom unit cell have different moments, which have opposite signs at large volume.
Single-crystal yttrium iron garnet phase shifter at X band
Authors: How Hoton , Hu Wei , Vittoria Carmine , Kempel Leo C. , Trott Keith D.
Published: July 2002

A tunable phase shifter at X band using single-crystal yttrium iron garnet film material grown on GGG substrates is fabricated. The phase shifter is a fourth wavelength in the absence of a bias magnetic field. The phase can be tuned 120° by varying the bias magnetic field from 3440 to 3720 Oe. The resultant variation in insertion loss was 0.5 dB. Measurements compared very well with calculations.
Liquid coated melt-spun Nd–Fe–B powders for bonded magnets
Authors: Li D. , Gaiffi S. , Kirk D. , Young K. , Herchenroeder J. , Berwald T.
Published: July 2002

The liquid coating (LC) has been employed to apply epoxy and lubricant over the surface of rapidly solidified Nd–Fe–B powder particles. The LC led to an improvement of physical and magnetic properties for the powders and magnets compared to the dry blending and the encapsulation methods. The LC powders have excellent flowability and can be used for bonded magnets requiring very close tolerances; further bonded magnets made using this powder posses higher strength.
Effects of magnetic interactions on the distribution of energy barriers in the time dependence of magnetization of a magnetic thin film
Authors: Lee K. J. , Lee T. D.
Published: July 2002

Influence of the magnetic interactions on distribution of energy barrier and time dependent phenomena of magnetization are investigated by micromagnetic and Monte Carlo simulation. For the magnetic thin film with randomly distributed easy axes in the film plane, the shape of the density function of the energy barrier is significantly changed with the varying magnetic interactions. If the exchange or magnetostatic interaction is strong, the density function of energy barrier has a broad distribution, then magnetization decay with time shows a linear dependence on ln(t).
Highly oriented NiFe soft magnetic films on Si substrates
Authors: Gong Heng , Rao Maithri , Laughlin David E. , Lambeth David N.
Published: July 2002

Highly oriented NiFe thin films have been produced via sputter deposition on HF etched Si substrates. Cu and Ag are used as underlayers to induce the epitaxial growth of NiFe films. The orientation relationships between NiFe, Cu, Ag, and Si have been determined by x-ray diffraction measurements and transmission electron microscopy. Magnetic properties have also been characterized.
Band alignment at organic-inorganic semiconductor interfaces: α-NPD and CuPc on InP(110)
Authors: Chassé T. , Wu C.-I. , Hill I. G. , Kahn A.
Published: July 2002

We present a photoemission study of the electronic properties of organic-inorganic semiconductor heterojunctions formed between the two hole transport materials, N,N′-diphenyl-N,N′-bis(1-naphthyl)-1-1′biphenyl-4,4″diamine (α-NPD) and copper-phthalocyanine (CuPc), and InP(110). The highest occupied molecular orbital of α-NPD (CuPc) is found to be 0.2 eV below (0.2 eV above) the InP valence band maximum, leading to a staggered (nested) energy level configuration. The α-NPD/InP and CuPc/InP interfaces exhibit 0.4 and 0.65 eV interface dipole barriers, respectively, that indicate a displacement of negative charge from the organic film to the inorganic substrate. This charge displacement is found to be consistent with the relative ionization energies and electron affinities of the materials.
Exchange coupling of radio frequency sputtered NiMn/NiFe and NiFe/NiMn bilayers
Authors: Qian Zhenghong , Sivertsen John M. , Judy Jack H. , Everitt Brenda A. , Mao Sining , Murdock Edward S.
Published: July 2002

Exchange coupling of radio frequency sputtered NiMn/NiFe (NiMn on top) and NiFe/NiMn (NiMn at bottom) bilayers have been investigated. It was found that the exchange coupling field, Hex, is not only directly related with the annealing temperature and time, but also is greatly influenced by the thin film deposition conditions. It was demonstrated that successful antiferromagnetic-ferromagnetic bilayer preparation should avoid interfacial contamination, which could destroy the spin coupling at the interface. The NiFe/NiMn bilayers show a high exchange coupling field [307 Oe for NiFe(200 Å)/NiMn(500 Å)] bilayer with a high blocking temperature around 430 °C. Most important is that the coupling field was able to sustain its strength up to almost 270 °C before starting to decrease. X-ray diffraction reveals that the diffraction intensity of NiMn in as-deposited bilayers does not seem important to achieve a high exchange coupling field. Furthermore, the NiMn thickness dependence of the magnetic properties of NiMn/NiFe bilayer and the NiFe thickness dependence of magnetic properties of NiFe/NiMn bilayers have been investigated and explored.
Metastable permalloy monoxide based spin valves and pseudo-spin valves
Authors: Perera P. , Ayala A. G. , Gutierrez C. J.
Published: July 2002

We report the reactive magnetron sputter deposition of a metastable antiferromagnetic oxide, (Ni81Fe19)O or permalloy monoxide (PyO), suitable for exchange biasing permalloy (Ni81Fe19 or Py) film layers at room temperature or for manipulating metallic Py film coercivities. Examples are presented demonstrating how PyO can be incorporated in Py/Cu/Py-based exchange biased spin valves (SV) or nonexchange biased pseudo-spin valves (PSV) using the same metallic Py target for fabricating both the PyO pinning layer and the Py metallic layers. The presence of a Ti seed layer beneath the PSV or SV film structures and the oxidized silicon substrate is shown to have an insignificant effect on the film magnetic properties, demonstrating the feasible use of Ti as an adhesion or diffusion barrier layer in hybridized microelectronic devices based on silicon. Glancing incidence parallel beam x-ray diffraction data are presented supporting the existence of the antiferromagnetic monoxide rocksalt phase for the PyO. In addition, vibrating sample magnetometry and four point probe magnetoresistance analysis data are presented for the SV and PSV films.
Energy transfer processes in Yb3+ and Tm3+ ion-doped fluoride crystals
Authors: Mita Yoh , Ide Takeshi , Togashi Masahiro , Yamamoto Hajime
Published: July 2002

Energy transfer processes from Yb3+ to Tm3+ ions have been investigated in various fluoride microcrystals to examine the application limit of a simple rate equation model and to obtain methods for characterizing the host materials as to energy transfer. It has been shown that the energy transfer coefficients from donor Yb3+ to acceptor Tm3+ ions differ by nearly one order of magnitude even for fluoride lattices that have similar luminescence characteristics. The energy transfer coefficients increase monotonically with Yb3+ concentration at low Yb3+ concentrations, while they take nearly constant values at high Yb3+ concentrations. The present experimental results were compared with computer simulation results as well as related analyses. It is shown that the apparently complicated behaviors are consistently explained by a microscopic model. As an example of the application of the present results, the optimization of the infrared emission of Tm3+ ions is shown.
Magnetization reversal process in polycrystalline ordered Fe–Pt(001) thin films
Authors: Suzuki Toshio , Honda Naoki , Ouchi Kazuhiro
Published: July 2002

Magnetization reversal processes in Fe–Pt(001) thin films prepared by a high-pressure sputter deposition method were studied. Samples were classified in four types of domain patterns. Type I, with maze-like domain patterns, has a mixing mode of nucleation and wall motion for magnetization reversal. While, type II, with large island domain patterns, shows wall motion in its magnetization reversal. Type III has small island domain patterns, and type IV has fine discrete domain patterns showing rotational modes with inclined M–H loops. Type IV is expected to be one of the candidates for future ultrahigh-density magnetic recording media with high resolution and low noise.
Magnetization switching in small ferromagnetic particles: Nucleation and coherent rotation
Authors: Nowak U. , Hinzke D.
Published: July 2002

The mechanisms of thermally activated magnetization switching in small ferromagnetic particles driven by an external magnetic field are investigated. For low uniaxial anisotropy the spins rotate coherently while for sufficiently large uniaxial anisotropy they behave Ising-like, i.e., the switching then is due to nucleation. The crossover from coherent rotation to nucleation is studied for the classical three-dimensional Heisenberg model with uniaxial anisotropy by Monte Carlo simulations. From the temperature dependence of the metastable lifetime the energy barrier of a switching process can be determined. For the case of infinite anisotropy we compare numerical results from simulations of the Ising model with theoretical results for energy barriers for both, single- and multidroplet nucleation. The simulated barriers are in agreement with the theoretical predictions.
Investigation of ion beam deposited spin valve interface structure by 59Co nuclear magnetic resonance
Authors: Jȩdryka Ewa , Bailey William E. , Wójcik Marek , Nadolski Stefan , Wang Shan X.
Published: July 2002

59Co nuclear magnetic resonance was used to study the bulk and interface microstructure in the unpinned Co layer in a series of highly (111)-textured ion beam deposited spin valves. The intent of the study is to determine the degree of Co interface intermixing and any possible variation of the Co layer microstructure as a result of weakening (111) texture of the NiFe/Co/Cu/Co/NiFe/FeMn film stack. We found that the interfaces are diffused over ∼2 monolayers on both sides of the Co layer, involving an equivalent of about 3 Å of Co per interface and vary only slightly with deteriorating texture. The main structural change is the drop of perfect fcc stacking in the Co layer.
Thickness dependence of giant magnetoresistance effect in granular Cu–Co thin films
Authors: Małkiński L. M. , Wang J.-Q. , Seip C. T. , Wiemann J. , Wiley J. B.
Published: July 2002

This work investigates the magnetic and transport properties of Cu–Co thin films with a special reference to their dependence on the film thickness. Such dependencies of the giant magnetoresistance (GMR) effect in silver-based magnetic alloys, such as Ag–Fe, Ag–Co, and Ag–FeNi films, have recently been found, and they were interpreted within the framework of surface spin-flipping scattering. This article reports on similar thickness dependence in the Cu-based alloy, although the spin-orbit interaction in Cu films is much weaker than in Ag films. A reduction of the GMR in the thinnest samples by a factor of 6, compared to the value of as-deposited bulk samples (8.6% in 50 kOe and at 5 K), was accompanied by an increase in resistivity by no more than 50%. A novel vapor-mixing technique of simultaneous sputtering from two sources was used to deposit Cu80Co20 granular thin films of the 20% nominal Co volume fraction. The thickness of the films, ranging from 8 to 400 nm, was measured by the small-angle x-ray reflectivity method. The average size of the Co particles ranging from 2.5 to 3 nm was determined from the superparamagnetic behavior of the Cu–Co granular films.
The effect of Co addition on the saturation magnetization of Fe16N2
Authors: Jiang E. Y. , Wang H. Y. , Ma Z. W.
Published: July 2002

The effects of Co addition on the structure and the saturation magnetization of Fe16N2 were investigated. Enhancement of the formation of Fe16N2 phase by Co addition was observed. Films with 5–25 at % Co contents deposited at proper conditions exhibit a high saturation magnetization up to the range of 2.5–2.7 T. The saturation magnetization of (Fe, Co)16N2 alloys phase is expected to be 2.8–2.9 T, which is as large as that of Fe16N2. This demonstrates that proper Co addition does not induce notable changes in the high saturation magnetization of the Fe16N2.
Dependence of the magnetic and magnetoelastic properties of (TbFe2)1−xBx melt-spun alloys on x
Authors: Jerems F. , Greenough R. D.
Published: July 2002

Rare earth–iron alloys containing highly anisotropic rare earth ions exhibit huge values of magnetostriction in the crystalline compounds with large values still maintained in the amorphous counterparts (for amorphous (TbFe2)87B13 λs was found to be 620 ppm at 77 K and 1.6 T). Melt-spun ribbons have a high potential for applications due to their softer magnetic properties and dimensions (∼25 μm thick) allowing lower applied fields and higher operating frequencies. Melt-spun ribbons of TbFe2 containing between 3 and 14 at. % boron as the glass former were prepared and exhibit an x-ray amorphous structure for x⩾7 at. % B. Their magnetic and magnetostrictive properties are discussed in terms of the boron concentration. For the amorphous alloys little variations in these properties are observed whereas for x<7 at. % significant changes take place due to a nanocrystalline structure. By applying a two-sublattice mean-field model to the M(T) data, the intrasublattice and intersublattice exchange parameters have been obtained and are compared with previous results on crystalline TbFe2. The results are consistent with the differences in Curie temperatures.
Magnetic anisotropy engineering in in-plane magnetized ultrathin ferromagnetic films (invited)
Authors: Bland J. A. C. , Hope S. , Choi B. , Bode P.
Published: July 2002

We have studied the effect of depositing submonolayer quantities of Cu onto the CO exposed Co/Cu(110) system at room temperature using the magneto-optic Kerr effect. Cu overlayers are found to completely reverse the in-plane 90° easy axis switch caused by the CO adsorption, for all Co thicknesses studied up to 40 ML. The Cu reverses the sign of the effective in-plane uniaxial anisotropy KUeff thereby switching the easy axis from the [1-10] to the [001] direction. Two modes of switching are observed depending on the magnitude of the cubic magnetocrystalline anisotropy constant K1 which is in turn dependent on the thickness of the Co films. For sufficiently thick Co films (dCo>15 ML), the easy axis is found to shift gradually from the [1-10] to the [001] direction due to the competition between the cubic and effective uniaxial anisotropy contributions. Therefore, we are able to controllably engineer the direction of the easy axis in this system as a function of Cu overlayer thickness. For thin Co films (dCu<15 ML) K1 tends to zero as revealed by BLS measurements of Hillebrands et al. and the easy axis switch is abrupt. We have engineered an experimental realization of an isotropic two-dimensional XY magnet by depositing submonolayer coverages of Cu onto a CO exposed 5 ML Co/Cu(110) film with a zero cubic anisotropy component K1 at room temperature. For a Cu coverage of 1.02 ML, the uniaxial anisotropy component vanishes also, and we observe a corresponding loss of ferromagnetic order at remanence. Further Cu deposition restores the uniaxial anisotropy and the magnetic order. Therefore we have directly observed the stabilization of ferromagnetic order by magnetic anisotropy in an ultrathin magnetic film, as theoretically predicted.
Temperature dependence of magnetization at Fe/MnFe2 interface
Authors: Islam M. N. , Siu I. L. , Walker J. C.
Published: July 2002

Mössbauer spectroscopy is used to extract depth sensitive information near the surface of an Fe film in Fe/MnF2 bilayers. We find that the hyperfine field at the surface has a quasilinear temperature dependence. For layers deeper into the film, the quasilinear temperature dependence diminishes and deep enough into the films, the hyperfine field goes like T3/2 as expected for bulk. We interpret this behavior as evidence of surface spin wave modes created by a perpendicular surface anisotropy, as previously predicted.
Magnetic properties of RFe11.3Nb0.7 compounds (R=rare earth)
Authors: Wang J. L. , Yang F. M. , Fuquan B. , Wang F. W. , Tang N. , Brück E. , de Boer F. R.
Published: July 2002

Structural and magnetic properties of RFe11.3Nb0.7 compounds with rare-earth elements (R=Y, Sm, Gd, Tb, Dy, Ho, and Er) have been investigated. The Curie temperature increases for R=Sm–Gd, then decreases from R=Gd to Er. In the compound with R=Tb, with increasing temperature, a spin reorientation from an easy magnetization direction in the plane to an easy cone occurs at 365 K. In the compound with R=Er, a spin reorientation from easy plane to easy axis is found at about 40 K. Two spin reorientations take place in the compound with R=Dy, from easy plane to a complex structure at 125 K and from complex structure to easy axis at 210 K. At room temperature, the easy magnetization direction is along the c axis for R=Y, Sm, Gd, Dy, Ho, and Er, and in the plane for R=Tb. Studies of the magnetic anisotropy in YFe11.3Nb0.7 and GdFe11.3Nb0.7 point out that the Fe sublattice anisotropy is of easy axis type. In HoFe11.3Nb0.7, a first-order magnetization process takes place below 150 K when an external magnetic field is applied along the hard magnetization direction. The exchange-interaction constants JR–Fe decreases with increasing atomic number of R, as is generally found in rare-earth transition-metal compounds.
A study on the possibility of using nontextured polished substrates for longitudinal thin film recording media
Authors: Lo Yu-Yun , Lin Yusin , Chen Chris C. , Wang Chien-Min
Published: July 2002

The use of NiAl seedlayer before depositing the underlayer on a (nontextured) polished substrate was studied. Same sputtering conditions were used on a (circumferentially) textured substrate for the purpose of comparison. The static magnetic properties measured by the vibrating sample magnetometer show very close Hc, Mrδ, and S* between them; and the magnetic recording performances measured by the Guzik tester show they are comparable. The “twice around modulation” verified by signal envelope test disappears on both of them. From this result, it is believed that the circumferential texturing is probably no longer needed when the NiAl seedlayer is added before depositing the underlayer.
Pressure dependence of the ferromagnetic to antiferromagnetic transition in Fe3(Ga1−xAlx)4 with x=0.0 and 0.1
Authors: Duijn H. G. M. , Brück E. , Buschow K. H. J. , de Boer F. R. , Prokeš K. , Sechovský V.
Published: July 2002

The ferromagnetic to antiferromagnetic transition in Fe3Ga4 is studied by means of ac-susceptibility measurements under chemical and external hydrostatic pressure. Substitution of Al for Ga results in an increase of the ferromagnetic to antiferromagnetic transition temperature (T0) of 4.1(4) K/at. % Al. Application of hydrostatic pressures up to 7 kbar also yields a positive effect: dT0/dp=3.4(4) K/kbar. The external-pressure-induced increase of T0 in Fe3(Ga0.9Al0.1)4 is considerably weaker: dT0/dp=0.93(10) K/kbar. Thermal-expansion measurements reveal that the volume change at the ferromagnetic to antiferromagnetic transition ΔV/V amounts to only 0.02%. We believe that the volume effect in conjunction with a shift in the Fermi level drives the ferromagnetic to antiferromagnetic transition. The details of the band structure at the Fermi surface determine the magnetic properties and may give rise to the strong pressure dependence of T0.
Magnetoelasticity of Cr–Ga alloy single crystals at high pressures
Authors: Prinsloo A. R. E. , Alberts H. L. , Smit P.
Published: July 2002

Measurements are reported of the pressure dependences of the elastic constants of Cr+0.16 at. % Ga and Cr+0.88 at. % Ga alloy single crystals through the Néel temperature of both crystals and through the incommensurate–commensurate transition temperature of the latter crystal. The long-wavelength acoustic-mode Grüneisen parameters, γp, which quantify the lattice vibrational anharmonicity, are calculated from the measurements. Both alloys show, depending on the temperature, unusually large positive and negative values of γp which are ascribed to strong coupling of the spin-density wave to the acoustic phonons. The nature of these interactions differs for the two alloys.
Structural development in the early stages of annealing of sol–gel prepared lead zirconate titanate thin films
Authors: Huang Z. , Zhang Q. , Whatmore R. W.
Published: July 2002

Lead zirconate titanate (PZT) thin films on platinized silicon were fabricated and their structural development upon annealing was characterized by x-ray diffraction and transmission electron microscopy (TEM). The amount of a transient intermetallic phase Pt3Pb was found initially to increase with annealing time and to decay after reaching a maximum. The kinetic process of growth and decay was simulated by using the Avrami equation. The Avrami coefficient n and growth rate constant k were determined by comparing the experimental results and the simulated curves, from which activation energies of 40 and 145 kJ/mol were obtained for the growth and decay of the intermetallic Pt3Pb phase, respectively. The perovskite PZT was found by using TEM to nucleate epitaxially on top of the Pt3Pb phase. Evidence is presented that the Pt3Pb phase plays a major role in determining the crystallite’s orientation at the nucleation stage of the perovskite PZT. This depends strongly on the annealing temperature and the orientation changes little during the following growth process.
Effect of nitrogen on the band structure of GaInNAs alloys
Authors: Shan W. , Walukiewicz W. , Ager J. W. , Haller E. E. , Geisz J. F. , Friedman D. J. , Olson J. M. , Kurtz Sarah R.
Published: July 2002

We show that incorporation of nitrogen in Ga1−xInxAs to form Ga1−xInxNyAs1−y alloys leads to a splitting of the conduction band into two nonparabolic subbands. The splitting can be described in terms of an anticrossing interaction between a narrow band of localized nitrogen states and the extended conduction-band states of the semiconductor matrix. The downward shift of the lower subband edge accounts for the N-induced reduction of the fundamental band-gap energy. An analysis of the relationship between the subband splitting and the band-gap reduction demonstrates that the energetic location of the valence band is nearly independent of the N content in Ga1−xInxNyAs1−y alloys.
Analysis of neutron diffraction spectra acquired in situ during stress-induced transformations in superelastic NiTi
Authors: Vaidyanathan R. , Bourke M. A. M. , Dunand D. C.
Published: July 2002

Neutron diffraction spectra were obtained during various stages of a reversible stress-induced austenite to martensite phase transformation in superelastic NiTi. This was accomplished by neutron diffraction measurements on bulk polycrystalline NiTi samples simultaneously subjected to mechanical loading. Analysis of the data was carried out using individual lattice plane (hkl) reflections as well as by Rietveld refinement. In the Rietveld procedure, strains in austenite were described in terms of an isotropic (hkl independent) and an anisotropic (hkl dependent) component. At higher stresses, austenite lattice plane reflections exhibited nonlinear and dissimilar elastic responses which may be attributed to the transformation. The texture evolution is significant in both austenite and martensite phases during the transformation and two approaches were used to describe this evolving texture, i.e., an ellipsoidal model due to March–Dollase and a generalized spherical-harmonic approach. The respective predictions of the phase fraction evolution as a function of applied stress were compared. A methodology is thus established to quantify the discrete phase strains, phase volume fractions, and texture during such transformations.
Electroabsorption spectroscopy on tris-(8-hydroxyquinoline) aluminum-based light emitting diodes
Authors: Rohlfing Frank , Yamada Toshiki , Tsutsui Tetsuo
Published: July 2002

We determined the electric-field distribution in organic light emitting diode LED structures fabricated with 4,4′-bis [N-(1-naphthyl)-N-phenylamino]-biphenyl (α-NPD) as hole-transport material and tris-(8-hydroxyquinoline) aluminum (Alq) as electron-transport and emissive material. The electric-field distribution was obtained from an investigation of the linear and the nonlinear Stark effect of the materials when employed in organic LEDs using electroabsorption spectroscopy. We measured the electric-field distribution as a function of the applied voltage in the forward and in the reverse direction. Whilst the average electric fields in the α-NPD and the Alq layers are equal in the reverse direction, the field in the Alq layer is considerably larger than that in the α-NPD layer in the forward direction, and the factor by which these fields differ changes with increasing voltage, in particular in the vicinity of the turn-on voltage. We discuss the electric-field distribution in terms of the charge injection and charge transport in devices as well as the possibility of charge accumulation at the α-NPD/Alq interface.
Angle-resolved ultraviolet photoelectron spectroscopy of In-[perylene-3,4,9,10-tetracarboxylic dianhydride] system
Authors: Azuma Yasushi , Akatsuka Shinichiro , Okudaira Koji K. , Harada Yoshiya , Ueno Nobuo
Published: July 2002

The In-[perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)] system, obtained by the sequential evaporation of PTCDA and In on cleaved MoS2 surfaces, was measured by means of angle-resolved ultraviolet photoelectron spectroscopy. The results indicate that the four In atoms react with one PTCDA molecule. Using a model compound of the reaction product, In4PTCDA, the quantitative analysis of the take-off angle (θ) dependence of the photoelectron intensity from the new band shows that the band originates from the π state involving In 5pz atomic orbitals, and the In4PTCDA molecules lie tilted at the averaged tilt angle of the molecular plane β≅10°.
Phase transformation and conductivity in nanocrystal PbS under pressure
Authors: Jiang J. Z. , Gerward L. , Secco R. , Frost D. , Olsen J. S. , Truckenbrodt J.
Published: July 2002

The grain-size effect on the phase transition induced by pressure in PbS was studied by in situ high-pressure electrical resistance and synchrotron radiation x-ray powder diffraction measurements. The mean transition pressure of the B1-to-B16 phase transformation was found to be 6.3±1.3 GPa in 8±1 nm PbS while it is 3.1±0.7 GPa for 10 μm PbS. The resistivity of the B16 PbS phase decreases exponentially with pressure in both samples at ambient temperature. They follow R∝exp(−CP), where C=−0.64 GPa−1 for 10 μm PbS and C=−0.34 GPa−1 for 8±1 nm PbS. These results are discussed in terms of a decrease of energy band gap with increasing pressure.
Chemical order induced by He+ ion irradiation in FePt (001) films
Authors: Ravelosona D. , Chappert C. , Mathet V. , Bernas H.
Published: July 2002

We show that partial chemical ordering can be obtained at moderate processing temperatures by using postgrowth ion bombardment. This was demonstrated both on disordered (S∼0) and partially ordered (S∼0.4) sputtered FePt(001) films in which the order parameter S was increased up to 0.3 and 0.6, respectively. X-ray diffraction measurements indicate that the high crystalline quality of the films is not modified as irradiation proceeds. The changes on the magnetic hysteresis loops are compatible with the expected perpendicular magnetic anisotropy increase. This novel method could have a great impact on the current race toward high anisotropy materials to increase magnetic recording density.
Magnetic properties of epitaxial NiFe/Cu/Co spin-valve structures on GaAs(001)
Authors: Lew W. S. , Samad A. , Li S. P. , Lopez-Diaz L. , Cheng G. X. , Bland J. A. C.
Published: July 2002

Cu(50 Å)/NiFe(60 Å)/Cu(60 Å)/Co(20 Å) epitaxial spin-valve structures were grown on GaAs(001) substrates by molecular-beam epitaxy at room temperature. In situ reflection high-energy electron diffraction measurements indicate the stabilization of the bcc-Co(001) phase on 1×1 unreconstructed GaAs(001) for thicknesses up to 20 Å and the epitaxial growth of the fcc-Cu(001) spacer layer and fcc-FeNi(001) top magnetic layer. Magneto-optical Kerr effect and Brillouin light-scattering measurements of the composite structure showed that a fourfold cubic anisotropy is present but a twofold anisotropy also occurs directed along the 〈110〉 axes. The easy cubic axes are directed along the 〈100〉 axes, which implies that the cubic anisotropy constant Kl for bcc-Co is positive. The magnetic anisotropy of the bcc-Co layer has a striking influence on the magnetoresistance characteristics which were found to be angular dependent. A simulation of this mixed anisotropy behavior yields quantitative agreement with the experimental results.
Ultrafine magnetic cyanide particles
Authors: Ng C. W. , Ding J. , Chow P. Y. , Gan L. M. , Quek C. H.
Published: July 2002

Cobalt– and nickel–iron hexacyanide powders were synthesized by the microemulsion method using CoCl2 or NiCl2 and K3FeIII (CN)6. The resultant powders K0.2Co1.4[Fe(CN)6].6.5H2O and K0.8Ni1.1[Fe(CN)6].4.5H2O were single phase with a mean particle size in the range of 5–10 nm. Curie temperatures of the cobalt– and nickel–iron cyanide powders were estimated to be 14 and 28 K, respectively, using Curie–Weiss law. The coercivity was measured to be 1.8 kOe for nanoscaled Co–Fe cyanide particles. High coercivity of 4.0 kOe was achieved in the coprecipitated Ni–Fe cyanide powder. Superparamagnetic behavior was observed in the microemulsion-derived Ni–Fe cyanide particles. It has been found that a heat treatment at 150 °C led to a presence of a soft magnetic phase and a strong reduction of magnetic anisotropy.
Noncollinear magnetism of Cr and Mn monolayers on Cu(111)
Authors: Kurz Ph. , Bihlmayer G. , Blügel S.
Published: July 2002

Cr and Mn monolayers on a triangular lattice are prototypical examples of frustrated spin systems in two dimensions. Collinear and noncollinear magnetic structures of these monolayers on Cu(111) substrate are investigated on the basis of first-principles total-energy calculations using the full-potential linearized augmented plane-wave method extended by the vector spin-density description for the interstitial and vacuum region. The search for the magnetic minimum-energy configurations included unit cells with one, two, and three atoms. For Cr the minimal energy was found for a 120° spin configuration in a (∛×∛)R30° unit cell, which is in agreement with the classical nearest-neighbor Heisenberg model with antiferromagnetic exchange interaction. The same behavior is expected for Mn, but a surprising result was found: the minimal energy was found for a collinear row-wise antiferromagnetic structure.
Coercitivity and its temperature dependence in NdFeB thin films with Cr, Mo, Ti, or Ta buffer layers
Authors: Jiang H. , O’Shea M. J.
Published: July 2002

NdFeB thin films of the form A(20 nm)/NdFeB(d nm)/A(20 nm) were prepared by magnetron sputtering on a Si(100) substrate. The hard Nd2Fe14B phase is formed by a postanneal in vacuum. The buffer layers A used are Cr, Mo, Ta, Ti, and NdFeB layer thickness used are 540, 180, 90, and 54 nm. We have found several different combinations of anneal temperature, buffer layer, and NdFeB film thickness d that lead to large coercivity, as high as 17.0 kOe, and energy product, as high as 10.3 MG Oe. The temperature dependence of coercivity was analyzed using a modified Brown’s equation and we find that the microstructural parameter αK and the effective demagnetization factor Ne change with the buffer material and anneal temperature. Possible magnetic reversal mechanisms are discussed in light of these results.
Magnetic properties of thin film and granular Dy50Fe50 as a function of size
Authors: O’Shea M. J. , Jiang H. , Perera P. , Hamdeh H. H.
Published: July 2002

Thin amorphous Dy50Fe50/A layers are prepared by sputtering to understand the influence of the spacer layer A on magnetic properties in the DyFe thickness regime where size effects are also important. The spacer layer A in this work is either Ti or Ca and we compare to our earlier work involving a spacer layer of Mo. The Dy50Fe50 layer is amorphous and Mössbauer spectroscopy indicates that two types of Fe site are present. Finite size effects manifest themselves below a size of 10 nm in a reduction of magnetic ordering temperature TC and coercivity HC. For equal values of d, the reduction of TC and HC is larger for the system with a Ti or Mo spacer layer as compared to the Ca spacer layer. We argue that both size and the structure of the interface are important in lowering HC and TC. The temperature dependence of coercivity is also studied and suggests that magnetic reversal via domain wall movement occurs in our thinnest films.
Disk wear as a result of low frequency HDI resonance
Authors: Wang Larry Y. , Sullivan Mike , Cheng Tai , Chao Jim
Published: July 2002

Spinstand level testing has demonstrated a failure mechanism that may go undetected using standard strain gage and acoustic emission methods of data capture. Since normally static friction is higher than dynamic friction, dynamic friction measurements are often ignored, filtered, or sampled at a much lower data rate than static friction measurements. In this study, dynamic friction peak values significantly higher than the static friction were recorded during take-off of Pico heads on laser-textured media. Furthermore, data collected using an optical surface analyzer (OSA) showed a greater degree of wear on disks exhibiting high dynamic friction. FFT was employed to analyze the signal modulation of the high dynamic friction event. Resonance at a frequency of approximately 1050 Hz was found to be associated with the high dynamic friction. Experiments were designed to reveal factors that influence this resonance occurrence. The factors identified that contribute to this resonance were natural frequency of the head load arm, disk bump pitch, and lubricant thickness. The head/disk interface system is believed to be excited by an improper bump pitch if the lubricant layer is not thick enough to reduce the friction value.
Composition and diffusion of nitrogenated carbon into the magnetic layer
Authors: Tomcik B. , Osipowicz T. , Huan C. H.
Published: July 2002

A series of dc sputter deposited amorphous carbon nitride films were characterized by micro-Raman spectroscopy. Films were deposited on silicon, CoCrPt/CrV/glass and a CoCrPtTa/CrV/glass substrate. A direct correlation was found between the nitrogen content in a film, measured by Rutherford backscattering spectroscopy, and the Raman C≡N peak intensity. A frequency downshift of the Raman G band was observed for very thin films. It reflects not only the film structure but also the contribution from the vibration spectrum of the film-substrate interface. From the integrated intensity of the carbon band and a Raman shift it is possible to determine the thickness of the carbon overcoat as well as evaluate the carbon diffusion into the magnetic layer. A secondary ion mass spectroscopy carbon depth profile analysis provided additional proof of carbon diffusion into the magnetic layer.
A nonlinear dynamics theory for modeling slider air bearing in hard disk drives
Authors: Sheng Gang , Liu Bo , Hua Wei
Published: July 2002

A nonlinear dynamics theory is presented for modeling air bearing slider systems. The nonlinear dynamic coefficients are acquired by fitting the database of the discrete linear dynamic coefficients. The linear dynamic coefficients for an air bearing slider around steady flying state are calculated by using a Reynolds-equation-based perturbation method. A nonlinear analysis shows that the natural frequencies of the system decrease with the increase of slider vibration amplitude, and that the softening feature of the system bends the resonance to lower frequency and complicates the system vibrations. The analysis correlates with experimental results.
Temperature dependent phenomena in La1−xSrxMnO3 films studied by magnetic force microscopy
Authors: Soh Yeong-Ah , Aeppli G. , Mathur N. D. , Blamire M. G.
Published: July 2002

Magnetic domain structure of La1−xSrxMnO3 films was studied using magnetic force microscopy (MFM). Evolution of the magnetic patterns was monitored as a function of temperature by using a variable temperature sample stage. The magnetic contrast in the MFM images decreases as the temperature is raised and vanishes as the system approaches the Tc of the film. At temperatures above the Tc of the film, local ferromagnetic regions with a higher Tc are detected around the grain boundaries. We attribute this variation in the local Tc to the local variation of strain in the film.
Microstructure and magneto-optical properties of CoFe1.9RE0.1O4 nanocrystalline films on quartz substrates
Authors: Cheng Fu-Xiang , Jia Jiang-Tao , Liao Chun-Sheng , Xu Zhi-Gang , Zhou Biao , Yan Chun-Hua , Chen Liang-Yao , Zhao Hai-Bin
Published: July 2002

A novel family of composited oxides, Co–RE ferrites (RE=rare earth), has been fabricated on quartz substrates by a sol-gel method. The studies on the microstructure and magneto-optical effects of the Co–RE ferrite films were carried out. It has been found that the doping of Co ferrite with Yb or Lu ion notably enhance the magneto-optical rotations in the spectral range of 350–420 nm, which made them very promising to be used for magneto-optical recording at short wavelengths in the future.
Patterning magnetic films by ion beam irradiation
Authors: Terris B. D. , Weller D. , Folks L. , Baglin J. E. E. , Kellock A. J. , Rothuizen H. , Vettiger P.
Published: July 2002

We have used ion beam irradiation through a silicon stencil mask to alter the magnetic properties of Co/Pt multilayer and FePt chemically-ordered superlattice films. In both systems, ion irradiation disorders the as-grown films which results in a reduction of the magnetic anisotropy. Regularly spaced micrometer-sized regions of magnetically altered material have been produced over areas of a square millimeter. These magnetic structures have been observed by magnetic force microscopy. By stepping the mask during irradiation, features at twice the spatial frequency of the mask holes have been produced. Such patterned magnetic films are of interest for application in high-density magnetic recording.
Exchange-dominated surface spin waves in ferromagnetic and antiferromagnetic films
Authors: Milton Pereira J. , Cottam M. G.
Published: July 2002

Theoretical results are presented for the localized surface spin waves in thin magnetic films in the exchange-dominated regime. The method is based on a spin-wave operator and Green-function technique that utilizes special properties of tridiagonal and pentadiagonal matrices, and two applications are described here. One is to study the effects of finite film thickness in coupling the modes localized near the two surfaces of an antiferromagnet with a simple cubic structure for the magnetic ions, and numerical examples are given for ultrathin films. The second application is to consider the surface spin waves in ferromagnetic films with body-centered cubic structure and (111) surfaces. Its relevance to recent experimental data for localized modes in epitaxial W/Ni/W films is discussed.
Electrical and optical properties of pyrolytically electrostatic sprayed fluorine-doped tin–oxide: Dependence on substrate–temperature and substrate–nozzle distance
Authors: Zaouk D. , Zaatar Y. , Khoury A. , Llinares C. , Charles J.-P. , Bechara J.
Published: July 2002

Tin–oxide (SnO2) thin films were prepared by a modified spray technique called electrostatic spray pyrolysis. Their electrical and optical properties dependence on fluorine concentration, substrate temperature Ts, and the substrate–nozzle distance Dsn was studied. Dsn and Ts seem to be interrelated for the optimization of good quality fluorine-doped SnO2 films. Films of about 9×10−4 Ω cm resistivity and high visible 85% transparency were obtained for a substrate temperature of 550 °C, a 6 cm substrate nozzle distance, and 80% of hydrofluorhydric acid HF in the starting solution. These data are discussed in light of the kinetics reaction.
Unpinned behavior of the surface Fermi level of GaN detected by photoreflectance spectroscopy
Authors: Behn U. , Thamm A. , Brandt O. , Grahn H. T.
Published: July 2002

The photoreflectance signal from GaN films is sensitive to the ambient medium. A large decrease in the photoreflectance amplitude is observed, when the ambient medium is changed from air to vacuum. This effect is attributed to ultraviolet-light-induced desorption of oxygen from the sample surface leading to a reduction of the surface barrier height. The effect is absent, when a thin Ti layer is deposited on top of the GaN film. A simple model is used to demonstrate that the surface photovoltage can be strongly reduced with a decrease of the surface barrier height.
Quasistatic measurements for hysteresis modeling
Authors: Wulf Marc De , Dupré Luc , Melkebeek Jan
Published: July 2002

In order to validate and test the correctness of hysteresis models used in the simulation of soft magnetic materials (electrical steel), one has to dispose of experimental data describing the hysteresis behavior of the material e.g., measurements under slow time varying excitation conditions in order to reduce the dynamic effects to a strict minimum. Based on measured loops (1–5 Hz) on nonoriented 3% SiFe alloys, and starting from the statistical loss theory of Bertotti, where the total applied field is subdivided into a hysteresis, a classical and an excess field, one can obtain the dc loop of the material by eliminating the remaining dynamic effects in the lamination. A comparison between three types of measurements is made, namely, hysteresis loops obtained by extrapolating from dynamic measurements using the statistical loss theory, second loops measured under slow time varying induction (0,1 Hz)—the influence of the used frequency (0,1–5 Hz) and the used excitation wave form (constant dH/dt…constant dH/dt) is examined—and third measured loops obtained from a static (ballistic-like) method. An improvement of the quasistatic measurement procedure is proposed, and implemented in the data-acquisition software for the determination of the material Everett function.
High speed characteristics of thin film write heads at deep submicron track width
Authors: Mao Chris Y. , Zhu Jian-Gang , White Robert M.
Published: July 2002

This article presents a micromagnetic study of the dynamic magnetic switching process in the pole tip region of stitched-pole thin film write heads. The impacts of track width reduction and pole material saturation moment on the high frequency performance of the heads have been investigated. It is found that the magnetic switching process of the pole tip region at low recording frequencies can be characterized by three stages: the nucleation of a vortex (or vortices), followed by the motion of the vortex (or vortices), and finally the annihilation of the vortex (or vortices). At high frequencies, however, a residual vortex (or vortices) will always remain in the pole tips, resulting in lower head field amplitude. Frequency roll-off characteristics of the head field response have been calculated. The roll off is the result of residual vortex (or vortices), and the vortex moving speed limits the operational frequency range of the head. Reducing the track width lowers the head field 3 dB roll-off frequency. The simulation also finds that the use of 45/55 NiFe, which has significantly higher moment than permalloy, results in higher roll-off frequency as compared to permalloy.
Kondo resonance behavior of heavy fermion f-electron materials (invited)
Authors: Allen J. W. , Gweon G.-H. , Schek H. T. , Liu L.-Z. , Tjeng L. H. , Park J.-H. , Ellis W. P. , Chen C. T. , Gunnarsson O. , Jepsen O. , Andersen O. K. , Dalichaouch Y. , Maple M. B.
Published: July 2002

The Kondo properties of the impurity Anderson model provide a theoretical framework for relating thermodynamic and angle integrated electron spectroscopy data in many heavy fermion materials. We describe the success and the challenges of this approach, summarize a detailed analysis of CeSi2, and give a perspective on the relation to the lattice Anderson model.