bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferromagnetic hysteresis and aftereffect in polycrystalline TDAE-C60
Authors: Dunsch L. , Eckert D. , Fröhner J. , Bartl A. , Müller K.-H.
Published: July 2002

The microscopic origin of ferromagnetic ordering as well as the existence of hysteresis in TDAE-C60 are contradictorily discussed in the literature. At 1.7 K the zero-field magnetization, M(0), extrapolated from the demagnetization curve of a TDAE-C60 powder, is only a small fraction of the saturation magnetization Ms≈1.2 A m2/kg (or emu/g) measured at a field of 4 MA/m. The small value of M(0)/Ms may be due to (i) a large amount of small superparamagnetic particles and/or (ii) alignment of a canted magnetic structure at high field. After leaving TDAE-C60 powder in a sealed quartz tube with He for eight weeks this ratio increased from about 8% to 65% but Ms remained unchanged. This observation points to agglomeration of superparamagnetic clusters increasing the contribution to the ferromagnetic behavior. Typical extrinsic magnetic quantities describing a ferromagnetic material, such as remanence Mr, coercivity HcJ and viscosity S, have also been measured. For temperatures 10, 5, and 1.7 K typical values of Mr and HcJ are 30, 90, 200 μT, and 50, 110, and 200 A/m, respectively. The values of coercivity have the order of magnitude of those of low-carbon steel (at room temperature). After leaving a pressed TDAE-C60 sample in a sealed quartz tube with He for six weeks Mr increased and HcJ decreased, both by about 30%. The samples show a logarithmic time-dependence of magnetization ΔM=−S ln(1+t/t0) with large values of the viscosity S. In the remanent state (at H=0) the measured values of S/Mr are 0.025, 0.021, and 0.019 for T=10, 5, and 2.5 K, respectively.
Effect of strong magnetic fields on the characteristics of bilayer lipid membranes
Authors: Suda T. , Ueno S.
Published: July 2002

To clarify the effects of strong magnetic fields on biological membranes, changes in the capacitance of a black membrane, which is an artificially formed lipid bilayer membrane, were observed under strong magnetic fields up to 8 T. The effects of dc electric fields on a black membrane were also investigated. The membrane was suspended across a 0.8 mm diam hole in a teflon vessel immersed in a phosphate buffer solution. The capacitance of the membranes was increased through the application of magnetic fields perpendicular to the membranes. When a 4 T magnetic field was applied to the membrane, the capacitance change reached 96%. The capacitance of the membranes varied according to the size of the outer vessel in which the teflon vessel was placed. It is thought that the changes in the capacitance of the membrane were caused by the difference between the hydrostatic pressure on the outer and the inner sides of the teflon vessel. This difference in hydrostatic pressure was due to changes in the surface of the solution caused by the effect of a magnetic-field gradient on the solution. No effects except those due to mechanical deformation due to changes in hydrostatic pressure were observed on the lipid bilayer membrane from static magnetic fields up to 8 T.
Magnetic thermometry in the aseptic processing of foods containing particulates (abstract)
Authors: Ghiron Kenneth , Litchfield Bruce
Published: July 2002

Aseptic processing of foods has many advantages over canning, including higher efficiency, lighter packaging, better taste, and higher nutritional value. Aseptic processing is different from canning where the food and container are sterilized together. Instead, a thin stream of food is heated and the packaging is independently sterilized before the food is placed in the package. However, no aseptic processes have been successfully filed with the FDA for foods containing sizable solid particles because of uncertainties in the thermal sterilization of the particles (e.g., soup). We have demonstrated that by inserting small paramagnetic particles in the interior of the simulated and real food particles, the local temperature can be measured. With this information, any questions about the adequate sterilization of the particles can be resolved. The measurements were done by directing the food stream through a magnetic field and sensing the voltages induced in a pickup coil by the motion of the magnetized particles. Details of the equipment design and data analysis will be discussed along with an introduction to the aseptic processing of foods.
Observation of magnons by light scattering in epitaxial CoFe/Mn/CoFe trilayers
Authors: Tschopp S. , Robins G. , Stamps R. L. , Sooryakumar R. , Filipkowski M. E. , Gutierrez C. J. , Prinz G. A.
Published: July 2002

We report on Brillouin scattering measurements on a CoFe/Mn/CoFe trilayer film characterized by unusually large biquadratic coupling. The magnetic field dependence of the exchange coupled in- and out-of-phase magnons as well as their in-plane directional dependence are determined. The saturation magnetization of the trilayer was measured independently through superconducting quantum interference device magnetometry. The spin wave data is well represented by a generalization of the model that takes into account the antiferromagnetic order in the Mn layer.
Transverse susceptibility of magnetic inks
Authors: Potanin Andrei A. , Shrauti Suresh M. , Arnold David W. , Lane Alan M.
Published: July 2002

The transverse susceptibility, χt, of a suspension of single-domain ferromagnetic particles in a viscous fluid is calculated. The yield stress is introduced to describe the structure formation. Magnetic interactions are taken into account through the mean-field model. Calculations are compared to experiments in which a dc field, H, is slowly increased. The experiments were performed on a model iron oxide dispersion. The function χt(H) goes through a maximum which decreases and shifts to a higher field when the pigment concentration is increased. This is attributed to an increase of the yield stress and the mean-field interaction parameter in our model.
Occurrence of self-organized criticality in ordered magnetic systems
Authors: Chubykalo O. , González J. , González J. M.
Published: July 2002

We analyze the collective behavior of a simple polycrystalline micromagnetic systems. More concretely, we have evaluated, for both textured and isotropic systems, the distribution of sizes of the collective demagnetization events (avalanches) as a function of the total size of the system and for different values of the exchange energy-to-anisotropy energy ratio. It is concluded that, when the structural and magnetic lengths characteristic of the system are of the same order of magnitude, this distribution is, in the case of small size systems, scaleable whereas it is independent of the total size of the system for larger values of that parameter. This result is attributed to the occurrence of quasisimultaneous avalanche nucleation and excludes the occurrence of criticality.
Exchange coupling and electronic structure of La1−xCaxMnO3: Effect of lattice distortion, canting, and doping (abstract)
Authors: Mryasov O. N. , Sabiryanov R. F. , Freeman A. J. , Jaswal S. S.
Published: July 2002

The influence of lattice distortion, canting of magnetic moments, and doping on the exchange coupling and the electronic structure of La1−xCaxMnO3 was studied using a generalization of the linear muffin-tin orbital (LMTO) method for noncollinear magnetic ordering1 and the LMTO–Green function technique in single-site approximation.2 Jahn–Teller type lattice distortions (f), including rotation and tilting of the oxygen octahedra, were varied from the ideal orthorhombic phase (f=0) to the observed structure3 (f=1). The canting angle (Θ) is considered also as a simulation parameter which is varied from Θ=0° ferromagnetic (FM) phase to Θ=180° antiferromagnetic (AFM). The effect of doping was simulated for x=1.,0.5,0 ordered alloys. We found that (i) doping and change of the magnetic ordering (from FM to AFM) promotes the competition between positive eg and negative t2g contributions to the exchange coupling between ferromagnetic sheets (J⊥); (ii) the J⊥ exchange is strongly of non-Heisenberg type, the bilinear contribution changes sign from positive to negative at f∼0.75; (iii) the metal–semiconductor transitions occur for Θ⩾120° and for distortions f⩾0.6.
Magnetization process in a two-phase exchange-coupled system: A microscopic study
Authors: Ryan D. H. , Feutrill E. H. , Ding J.
Published: July 2002

The magnetization process in an exchange-coupled α-Fe+Nd2Fe14B nanocomposite has been studied by Mössbauer spectroscopy. Measurements in fields of up to 2 T confirm that the magnetization of the soft phase is strongly coupled to that of the hard phase. Analysis of magnetization curves and magic-angle spectra of saturated samples shows that the remanence is dominated by the hard phase.
Magnetic separation using a switchable system of permanent magnets
Authors: Watson J. H. P. , Beharrell P. A.
Published: July 2002

In high gradient magnetic separation, the separator consists of a ferromagnetic matrix which is energized by an external field source. The aim of this work is to develop a viable magnetic separation system utilizing permanent magnets as the field source. The use of such a source has several advantages over an electromagnetic or superconducting system, mainly obviating the need for power supplies or cryogenic cooling. However, the periodic requirement of filter cleaning dictates that the field source must be switchable in order to facilitate filtrate removal. Hence, permanent magnets have not been widely used. The solution presented here is to employ a novel arrangement of permanent magnets which permits the flux density in the matrix to be switched between distinct maximum and minimum levels. Hence, optimum capture is carried out with the field at maximum, then cleaning is accomplished by washing the filter with the field at minimum. The early work has centered on a simple configuration of this system which has been incorporated into a separator which demonstrated that the basic principles were sound. More sophisticated configurations have been developed and their designs are being optimized by means of computer-aided design. One such system is currently being built, providing an operating field as high as 0.35 T, with a low field of less than one mT. It is anticipated that subsequent work will provide the basis for a large operating volume, self-contained and fully reusable magnetic separation system.
Analysis of a spherical permanent magnet actuator
Authors: Wang J. , Jewell G. W. , Howe D.
Published: July 2002

This paper describes a new form of actuator with a spherical permanent magnet rotor and a simple winding arrangement, which is capable of a high specific torque by utilizing a rare-earth permanent magnet. The magnetic-field distribution is established using an analytical technique formulated in spherical coordinates, and the results are validated by finite element analysis. The analytical field solution allows the prediction of the actuator torque and back emf in closed forms. In turn, these facilitate the characterization of the actuator and provide a firm basis for design optimization, system dynamic modeling, and closed-loop control law development.
Improvement of thermal stability and magnetoresistance recovery of Tb25Co75 biased spin-valve heads
Authors: Oliveira N. J. , Ferreira J. L. , Pinheiro J. , Fernandes A. M. , Redon O. , Li S. X. , ten Berge P. , Plaskett T. S. , Freitas P. P.
Published: July 2002

The thermal stability of TbCo exchange biased spin valve sensors has been extended to 230 °C, by using a Co pinned layer rather than NiFe. Magnetoresistance (MR) remains essentially stable up to annealing temperatures TA of 230 °C and degrades to 1% at TA=240 °C. Providing TA does not exceed 230 °C, any loss in the MR signal can be fully recovered by applying a field perpendicular to the film plane. This improved thermal stability allows processing at higher temperatures. The unidirectional exchange in the TbCo/Co interface becomes uniaxial for TA>100 °C. Even though the unidirectional character was not recovered by any field/anneal treatment, uniaxial anisotropy above 120 Oe is maintained for TA=260 °C. Devices were fabricated using a process with a maximum temperature of 180 °C. No MR loss is found during process in test structures at wafer level. A prototype 10-μm-track width spin valve tape head for QIC applications gave a maximum output of 2.3 mVpp at 20 kfci.
Spin dynamics study of the critical dynamics of the anisotropic three-dimensional Heisenberg antiferromagnet (abstract)
Authors: Bunker Alex , Chen Kun , Landau D. P.
Published: July 2002

Using Monte Carlo and spin-dynamics techniques,1 we studied the dynamic behavior of the body-centered-cubic classical Heisenberg antiferromagnet with single site anisotropy at the critical temperature. In order that we may directly compare our results to experiment, we performed the simulation with the anisotropy term set to match the degree of anisotropy found23 in both FeF2 (strong anisotropy) and MnF2 (weak anisotropy). Through the determination and analysis of the form of the neutron scattering function S(q,ω) at Tc we have studied the critical dynamics. We have compared our results to simulations1 for the isotropic case, and to experimental results23 and theory45 for the anisotropic case. We have found, in agreement with theory, an intense purely diffusive longitudinal component and a suppressed propogative transverse component. We were able to determine the transverse relaxation rate, Γ⊥, at the limit q→0 since at this limit Γ⊥→ωm, the characteristic frequency, which can be measured by the simulation.1 Γ⊥ was found to be noncritical in agreement with theory and experiment. We were able to make a quantitative comparison to experimental results of Γ⊥(0) for both FeF2 and MnF2.
Effect of thermal fluctuation on read/write properties of longitudinal and perpendicular recording media (abstract)
Authors: Nakatani Y. , Hayashi N. , Uesaka Y. , Fukushima H.
Published: July 2002

The read/write properties of longitudinal and perpendicular recording media affected by thermal fluctuation has been investigated by computer simulation. The write process was simulated based on the Langevin equation.1 The magnetization distributions resulting from thermal fluctuation after the writing were calculated based on the Monte Carlo method2 to obtain the output signals. The material parameters, Ms=400 emu/cm3, Ku=2×106 erg/cm3, and α=1, were used. No exchange interaction was assumed between particles. The temperature of 300 K was used. The calculation region was 6000 Å×12 000 Å, and the film thickness was 187.5 Å. The particle size was varied from 93.8 to 375.0 Å. Eight cycles of signals were recorded using a ring head (6 Gbit/in.2). Figures 1 and 2 show the effect of in-plane particle size on the signal-to-noise ratio 109 s after the recording for the longitudinal and the perpendicular media, respectively. The ratio increased when the particle size is decreased in both cases, but decreased in the longitudinal media when the particle size is less than 120 Å. The write field H0 (the field center in the gap) was varied from 6000 to 9000 Oe.
Anisotropy in the electrical resistivity of Ca-substituted yttrium iron garnet thin films
Authors: Turpin G. B. , Bornfreund R. E. , Wigen P. E. , Lehmann-Szweykowska A.
Published: July 2002

The existence of an in-plane anisotropy in the room-temperature electrical resistivity of an (011)-oriented liquid-phase-epitaxy-grown Ca0.14:yttrium iron garnet (YIG) film has been observed. The resistivity determined along the [01̄1] crystal direction was found to be consistently larger than that along the [100] direction by a factor of 1.47±0.07, which is within 4% of the square root of 2. These results suggest that charge conduction may in fact be occurring entirely along the easy 〈100〉 directions regardless of the crystal orientation of the applied electric field. The observed preference for a conduction path along the [100] direction is discussed in terms of linear chains of alternating {Y}–O–(Fe)–O–{Y} ions which are known to extend through the entire macroscopic length of the YIG crystal.
Large anisotropic magnetoresistance in ternary NiFeX films for magnetoresistive heads (abstract)
Authors: Komuro M. , Kawato Y. , Fuyama M. , Tajima Y. , Tadokoro S. , Imagawa T.
Published: July 2002

Highly sensitive magnetoresistive heads are required for magnetic disk drives with large areal density. Films with large anisotropic magnetoresistance are among the promising candidates for this purpose. In this work, the effect of third elements, X (Au, Pt, Ag, Cu, Pd, Co, Ru, ZrO2), to Ni80Fe20 alloy on anisotropic magnetoresistivity (Δρ) and other magnetic properties is examined with varying third element composition. Ternary films were deposited by rf sputtering on Ta seed layers. The thicknesses of ternary films were 5–20 nm which were determined by the x-ray reflectivity method. The value of Δρ for ternary films increases when Au, Pt, Ag, Co, and ZrO2 are added. On the other hand, Δρ decreases when Ru is added. Considering the application for the magnetoresistive (MR) head, low ρ0, low Hk, and low Bs are required except for large Δρ. The value of Δρ for Ni74Fe19Au7 film with the thickness of 10 nm is 0.65 μΩ cm which is 20% larger than that for Ni80Fe20. The values of Hk, λ, and Bs for Ni74Fe19Au7 are 4.8 Oe, 1×10−7, and 0.92 T, respectively. Therefore, NiFeAu ternary films are suitable for the MR head. Relative output for the Ni74Fe19Au7 head, calculated by an equation using the above results, is 23% larger than that for the Ni80Fe20 head. Furthermore, the higher output was confirmed by evaluation of fabricated heads.
Microstrip transmission line tapers on ferrites
Authors: Albuquerque M. R. M. L. , d’Assunção A. G. , Lima F.
Published: July 2002

The spectral domain approach is employed to perform a theoretical investigation of tapered microstrip lines on magnetized ferrite substrates. A linear variation of the conducting strip width along the direction of propagation is considered. The analysis takes into account the effects of the applied dc magnetic bias field in the transmission characteristics of these structures. The properties of the taper are determined by a model based on a segmentation of the considered line into uniform microstrip line subsections. Normalized phase constants and characteristic impedances are obtained by using the Hertz vector potentials method and Galerkin numerical technique. Numerical results are presented to show the taper input parameters as a function of the load impedance, geometrical dimensions, operating frequency, and ferrite parameters, considering the orientation and magnitude changes of the biasing magnetic-field H0. The results agree fairly well with those available in the literature for tapered microstrip lines on isotropic dielectric substrates.
Charge and spin current flows in spin transistors and similar devices (abstract)
Authors: Hershfield S. , Beck G.
Published: July 2002

During the last few years, there has been considerable interest in devices of the spin transistor geometry such as those of M. Johnson. These devices consist of current flowing from a ferromagnet to a paramagnet, with voltage probes placed perpendicular to the current flow in the paramagnet. First theoretical calculations require anomalously large spin polarizations in order to explain the magnitude of the observed effect. To obtain a more detailed understanding of this and similar experiments, we have solved a set of coupled drift-diffusion equations for spin-up and spin-down electrons in two and three dimensions. This allows us to obtain the spin current, the charge current, and the electrochemical potentials for both spins of electrons in the same geometry as the actual experiments. As expected we can see the separation of spin and charge currents in these devices. More importantly, for large voltage probes the potential is not constant across the part of the voltage probe touching the sample. The actual voltage measured depends in detail on how the spin current and charge currents relax within the voltage probes. This may explain some of the discrepancy in understanding the spin transistor experiments. We have also examined a number of other nonplanar geometries. In several of them we are able to realize a spin-current source in which there is a net flow of magnetization, but no net charge current.
Control of preferred orientation and magnetic property of (PtMnSb+Mn2Sb) two-phase films fabricated by solid state reactions in thin multilayered films (abstract)
Authors: Nakayama Tadachika , Matsui Toshiyuki , Morii Kenji
Published: July 2002

Although the ferromagnetic Heusler type (B1b) PtMnSb phase exhibits a large magneto-optical Kerr rotation effect, it is usually hard to obtain the perpendicular magnetic anisotropy in this film because of its small crystalline anisotropy. On the contrary, the ferrimagnetic phase of Mn2Sb, whose crystal structure is the Cu2Sb type (C38), shows uniaxial magneto-optical anisotropy above 240 K, but its magneto-optical Kerr rotation effect is not so large. Accordingly, if the films consisting of these two phases (PtMnSb+Mn2Sb) are produced under texture control, one could find many interesting properties for the applications of film. Recently, we have successively fabricated this kind of two-phase films by solid-state reactions of Pt/Mn/Sb multilayers. However, the texture control, which is important for obtaining the perpendicular anisotropy, has been still remained as an unsolved problem. In this work, we have focused our attention on the possibility to control the preferred orientation of the Mn2Sb phase by changing the stacking pattern of multilayers, deposition conditions and postdeposition treatments. The two-phase films consisting both PtMnSb and Mn2Sb were prepared by annealing the Pt/Mn/Sb multilayer having the stacking pattern [{Pt(1.0 nm)/Mn(2.5 nm)/Sb(2.5 nm)}1/{Pt(0.0 nm)/Mn(2.5 nm)/Sb(2.5 nm)}2]20. Whereas, the single phase of PtMnSb was obtained after annealing the multilayer of [Pt(1.2 nm)/Mn(2.4 nm)/Sb(2.4 nm)]60. The difference in the phase evolution may be ascribed to the microstructure developed near the interfaces by interdiffusion. Hereby, we have prepared the Mn/Sb bilayer and observed in detail the interdiffused area by transmission electron microscopy.
Exchange field and Hc dependence on the ferromagnetic material in exchange couples with CoO (abstract)
Authors: Takano Kentaro , Berkowitz A. E.
Published: July 2002

As recording density increases, magnetoresistive (MR) sensors are becoming increasingly important in read heads. NixCo(1−x)O is receiving technological attention for biasing magnetoresistive sensors as a robust alternative to FeMn. The interfacial exchange coupling between a ferromagnetic (FM) layer and an antiferromagnetic (AFM) is observed as an exchange field and an enhanced coercive field of the FM layer. The AFM/FM coupling is sensitive to the interfacial structure and the AFM and FM magnetic parameters. In this work, we deposited various FM layers on similar 300 Å CoO base layers to study the dependence of the FM exchange integral parameter J on the exchange HE and coercive HC fields. CoO was selected as the AFM material because (i) its simple spin and crystal structures facilitate the structural characterization and modeling of its magnetic properties, and (ii) it’s modest Néel temperature of 300 K facilitates the use of a superconducting quantum interference device for the magnetic measurements at temperatures ranging from 5 to 400 K. The 300 Å CoO films were reactively sputtered on silicon substrates and capped with various 300 Å FM films, Ni, Co, Fe, and permalloy (Ni81Fe19). The 300 Å CoO base layer films were polycrystalline with columnar grains. The CoO deposition conditions were reproduced to ensure similar structural and magnetic interfacial AF environments. The observed HE temperature dependence cannot be explained by current theoretical models. The temperature dependence of the exchange fields have the common features (i) a blocking temperature Tb=300 K, which corresponds to the bulk Néel temperature of CoO, (ii) a rise in the exchange field with decreasing temperature, (iii) an intermediate temperature region of constant HE (plateau value), and (iv) a second region of linearly increasing HE with decreasing temperatures down to 0 K. The plateau value of the HE decreased inversely with increasing FM magnetization as predicted by theory. The low-temperature increase of HE is more significant in the FM with higher exchange integral J values. The crossover temperature from the plateau to the low-temperature rise in HE appears to be dependent on FM’s J value. The increase in the interfacial coupling strength could suggest the magnetic ordering of a secondary phase localized at the interfacial atoms. The temperature dependence of HC enhancement does not share the nonlinear temperature behavior of HE. For T<300 K, HC increases linearly with decreasing temperatures down to 10 K. Although the HC enhancement may have magnetoelastic contributions, the disappearance of the linear enhancement at 300 K, the Néel temperature of CoO, indicates that the dominant mechanism is the interfacial magnetic coupling.
Improvement of magnetic properties and intergranular microstructure of Nd–Fe–B magnets by intergranular addition of MgO oxide
Authors: Chen Zhongmin , Yan Aru , Wang Xiaotian , Hadjipanayis G. C.
Published: July 2002

In this work we have studied in detail the effect of MgO on magnetic properties and intergranular microstructure. We have found that both coercivity and thermal stability can be remarkably enhanced by the intergranular addition of MgO. For Nd22Fe71B7 magnets with 2 wt % MgO addition, the coercivity at room temperature and 180 °C are enhanced from 17.0 and 3.2 kOe to 22.1 and 5.2 kOe, respectively, and the reversible and irreversible flux loss from room temperature to 180 °C is reduced from 25.4% and 5.2% to 20.5% and 0.5%, respectively. Microstructural studies reveal that a new intergranular Nd–O–Fe–Mg phase with a composition close to Nd70O23Fe3Mg2 appears in the magnets with MgO addition. The improvement of magnetic properties by the MgO addition is believed to be due to the appearance of a Nd–O–Fe–Mg intergranular phase, which probably hinders the propagation of the domain walls between Nd2Fe14B grains. It is further found that the addition of Mg or O alone into the intergranular regions of the magnets does not lead to the formation of this Nd–O–Fe–Mg intergranular phase, and thus, cannot substantially improve the coercivity and the thermal stability of the magnets.
Formation of a Schottky barrier between eutectic Ga,In and thiophene oligomers
Authors: Lous E. J. , Blom P. W. M. , Molenkamp L. W. , de Leeuw D. M.
Published: July 2002

The formation of a Schottky barrier between an eutectic (Ga,In) alloy and a highly doped thiophene oligomer is followed as a function of time using current density–voltage and capacitance–voltage measurements. Within 1 h, the diode characteristics change from almost nonrectifying, leaky behavior into a rectification ratio of 104 with a considerably reduced leakage current. Measurements and energy band diagram calculations show that the depletion width increases with time due to a decrease in the ionizable acceptor density of the semiconductor at the Schottky interface. This is probably caused by a chemical reaction between the in-diffusing metals and the doped oligomer.
Simultaneous measurement of six layers in a silicon on insulator film stack using spectrophotometry and beam profile reflectometry
Authors: Leng J. M. , Sidorowich J. J. , Yoon Y. D. , Opsal J. , Lee B. H. , Cha G. , Moon J. , Lee S. I.
Published: July 2002

We performed simultaneous measurements of all the layer thicknesses in six layer silicon on oxide film structures. Visible-near-infrared spectrophotometry was combined with beam profile reflectometry to produce enough information to discriminate between potential solutions; the spectrometer or beam profile reflectometer alone is insufficient to solve such a complicated film stack. Development of a robust measurement recipe required a new global optimization method working in parameter spaces of up to 12 parameters. The recipe obtained was applied to a 50 site mapping of the wafer. We found excellent agreement between our optical measurement results and scanning electron micrograph data for all thicknesses.
Crystal structure and magnetic ordering of Pr in (Pb0.5Cu0.5)2(Ba0.5Sr0.5)2PrCu2O8
Authors: Lin Y.-C. , Chuang W. Y. , Li W.-H. , Lee K. C. , Lynn J. W. , Yang C. L. , Ku H. C.
Published: July 2002

The crystal structure of polycrystalline PbBaSrPrCu3O8 was studied using high resolution neutron diffraction. Rietveld refinement of the diffraction pattern shows that the compound crystallizes into the Tl2Ba2YCu2O8 2212-type structure. The Pb and Cu atoms in the two (Pb,Cu)O layers are randomly mixed to form two (Pb0.5Cu0.5)O layers, and the Ba and Sr atoms are also randomly mixed to form two (Ba0.5Sr0.5)O layers, resulting in (Pb0.5Cu0.5)2(Ba0.5Sr0.5)2PrCu2O8. The magnetic ordering of the Pr ions was also studied using magnetic neutron diffraction and ac susceptibility measurements. At low temperatures, magnetic peaks presumably originating from the Pr spin ordering were observed at the {1/2 1/2 1/2 1/2}, {1/2 1/2 3/2}, and {1/2 1/2 5/2} positions. The Pr spins order at TN≈9 K with the moment direction along the c axis and the nearest-neighbor spins coupled antiferromagnetically. A cusp associated with the antiferromagnetic ordering at TN is also clearly observed in ac susceptibility measurements.
Submicron-scale film morphology effects on media noise of CoCrTa thin films on smooth substrates
Authors: Gao C. , Zhang B. , Malmhäll R. , Richter H. J. , Grannen K. , Rauch G. C.
Published: July 2002

The effect of submicron-scale morphology on media signal-to-noise ratio (SNR) has been evaluated for Cr/CoCrTa thin films deposited on super-smooth Al/NiP substrates. Two types of morphology and topography variations were studied. First, the underlayer X was made either smooth or rough in the submicron scale, and the subsequent Cr and magnetic layers deposition replicated the topography of layer X. For the second case, two different buffer layers were deposited with flat and smooth topography in the submicron scale. The subsequently deposited Cr/CoCrTa layers are either morphologically homogeneous or inhomogeneous. In both cases SNR measurements show a dramatic dependence on the morphology. It is concluded that the submicron-scale morphology variation was a profound contributor to the difference in media SNR. To make high-performance ultrahigh-density media, morphology homogeneity in the submicron-scale is essential.
Enhanced plasma radiation source: Tandem-puff, pinch-on-wire plasma
Authors: Wessel F. J. , Coleman P. L. , Loter N. , Ney P. , Rahman H. U. , Rauch J. , Thompson J.
Published: July 2002

We describe experiments for a neon tandem-puff Z pinch modified with a small-diameter, high-Z wire target (i.e., pinch-on-wire). The radiative yield for photon energies in the range of 1–100 keV is measured. With a copper-wire target the integral yield (J) between 0.9 and 1.5 keV increases by a factor of 1.5 compared to the pinch without a target; the yield is unchanged or slightly increased for higher-Z wires. The high-energy integral yield, above 6 keV, increases by a factor of 2 or more with a copper target and as much as a factor of 5 with a tungsten target. This behavior cannot be accounted for by simple hydrodynamic compression of a hot plasma and suggests yield enhancement by a nonthermal mechanism.
Magnetization reversal in bicrystal media
Authors: Dova P. , O’Grady K. , Morales M. P. , Doerner M. F.
Published: July 2002

Intergranular interactions and time dependence effects have been studied in CoCrPt/Cr thin films with two different Cr concentrations and different physical grain sizes. The samples have a bicrystal structure in which Co alloy grains, grown onto a Cr underlayer have subgrains with orthogonal c-axes. It was found via the ΔI method that exchange coupling was predominant in all the films along the circumferential direction. The samples with higher Cr concentration exhibited lower exchange coupling as indicated by the value of d(ΔI)max/dH which was found to correlate with the integrated medium noise. The study of the time dependence effects revealed that higher Cr concentration caused a reduction in activation volumes indicating a higher degree of segregation in the grain boundaries of the films. A correlation is reported between the activation volumes and the domain images of the samples in the ac demagnetized state.
Influence of Nd magnetic subsystem on spin-reorientation phase transition in Nd2CuO4 at low temperature
Authors: Knigavko A. N. , Huang H. L. , Sobolev V. L.
Published: July 2002

Acoustic measurements on Nd2CuO4 single crystals have recently revealed a ferroelastic phase transition at about Tc=5 K. In view of the strong magnetoelastic coupling in the compound it was attributed to an additional reorientation of Cu spins. In the present report it is shown that this transition can be successfully described if one takes the Nd magnetic subsystem into account explicitly. This approach requires treating a phenomenological Hamiltonian within invariants of the fourth order in spins only, which is natural for a tetragonal symmetry of the system. Complementary information about the strength of Nd–Nd interactions has been derived.
Ferro/antiferromagnetic interactions and the Fermi density of states: A thermopower study
Authors: Fontcuberta J. , Seffar A. , Hernando A. , Gómez-Sal J. C. , Rojo J. M.
Published: July 2002

Thermopower and magnetic moment measurements in the series GdPt1−xCux, GdNi1−xCux, and NdNi1−xCux are reported. The experimentally estimated Fermi density of states is shown to be highly correlated with the onset of antiferro to ferromagnetic transition in the series. This supports an earlier prediction [J. Appl. Phys. 79, 4815 (1996)] of the coupling sign of a periodic array of localized magnetic moments.
Coercivity of ultrathin films with in-plane magnetization
Authors: Hyman R. A. , Stiles M. D. , Tang Lei-Han , Zangwill A.
Published: July 2002

We report numerical and analytic results for a model of coercivity and magnetization reversal in an array of square monolayer-height magnetic islands on a monolayer of magnetic material with in-plane magnetization. Reversal nucleates at step edges where local two-fold anisotropy is present in addition to the intrinsic four-fold anisotropy of the (001) flat surface of a cubic crystal. Simple analytic formulas for the coercive field are derived that agree well with numerical simulations.
Nonuniform domain magnetization in CoFeSiB amorphous ribbons
Authors: Chen D.-X. , Muñoz J. L. , Vázquez M.
Published: July 2002

The low field ac susceptibility, χ=χ′−jχ′′, and domain structures of as-cast, stress relieved, and field annealed CoFeSiB amorphous ribbons are studied in the remanence state. An eddy current loss analysis is made based on a model which combines the contributions of domain wall displacements (DWD) and domain magnetization rotations (DMR). It is found that although having similar longitudinal bar domain structures, χ of the field annealed ribbon is due to DWD, but it is dominated by DMR for the first two, which indicates a nonuniform magnetization in the domains.
Finite element method for stationary and static electromagnetic fields
Authors: Lager Ioan Ernest , Mur Gerrit
Published: July 2002

A finite element method is described for computing static and stationary electric and magnetic fields directly in terms of the electric and magnetic field strength. The conditions at interfaces between different media and on the outer boundary are modeled pointwise exactly. The error in modeling the curl and divergence equations that correspond to interface free subdomains is minimized by means of a weighted residuals method. In order to be able to satisfy the conditions at interfaces between different media, use is made of a combination of nodal and edge elements. The validity of our approach is illustrated by solving a problem that has practical value for close contact magnetic recording. The numerical results are compared with analytical solutions that are available for this model.
Charge-density wave and magnetic phase diagram of chromium alloys
Authors: Fishman R. S. , Jiang X. W.
Published: July 2002

The magnetic phase diagrams of all dilute Cr alloys can be explained by a simple theoretical model with coupled spin- and charge-density waves and a finite electron reservoir. If the charge-density wave and electron reservoir are sufficiently large, then the paramagnetic to commensurate spin-density wave transition becomes strongly first order, as found in Cr1−xFex and Cr1−xSix alloys. The observed discontinuity of the slope dTN/dx at the triple point and the bending of the configuration interaction phase boundary are also natural consequences of this model.
Magnetic properties of the Pr1−xLaxMnGe system
Authors: Saha Shibaji , Ali Naushad
Published: July 2002

Magnetization, electrical resistivity, and thermal expansion measurements were carried out on a polycrystalline Pr1−xLaxMnGe system (for x=0.0–0.7) to study its magnetic properties particularly the high magnetic ordering temperature of the Pr sublattice. PrMnGe is known to be antiferromagnetic with TN=415 K. It orders ferromagnetically at 150 K and again becomes antiferromagnetic below 80 K. We have found that the ferromagnetic ordering temperature (T2) and the magnetization decrease with increasing La concentration in Pr1−xLaxMnGe. The low-temperature antiferromagnetic ordering temperature (T1) is also found to decrease with increasing La concentration. The small Pr–Pr contact distance (which may occur due to a low affinity of lanthanide and Mn elements) is thought to be responsible for the high ordering temperature of Pr moments. Resistivity data have clearly indicated the antiferro- to ferromagnetic (T2) and the ferro- to antiferromagnetic (T1) transitions. Thermal expansivity data suggest the T1 transition to be of first order and the T2 transition to be of second order.
Magnetic properties of Hubbard clusters: Noncollinear spins in N-atom clusters
Authors: Ojeda-López M. A. , Dorantes-Dávila J. , Pastor G. M.
Published: July 2002

The ground-state magnetic properties of clusters with N-atomic sites are studied by solving the single-band Hubbard Hamiltonian in the unrestricted Hartree–Fock approximation. Three-dimensional arrangements of spins are considered in the solution. Results for stability and magnetic order, as a function of the Coulomb interaction strength U/t, and number of electrons ν, are presented for all the clusters with N=3, 4, and for the set of N=13 fcc-, hcp-, icosahedral-, and bcc-like clusters. In most cases, for band fillings (ν) close to half-band |ν/N−1|⩽0.2−0.4, it is found that the antiferromagneticlike noncollinear spin solutions yield the smallest energy for U/t larger than a critical value (0<(U/t)c⩽6).
Properties of polycrystalline (Nd1−xGdx)1.85Ce0.15CuO4−y compounds
Authors: Jardim R. F. , Westphal C. H. , Becerra C. C. , Paduan-Filho A.
Published: July 2002

We have studied the structural, magnetic, and transport properties of polycrystalline (Nd1−xGdx)1.85Ce0.15CuO4−y; x=0.0, 0.05, 0.10, 0.25, and 0.50; produced under different atmospheres and cooling rates after the reduction process. From x-ray analysis the T′-structure is preserved for all samples studied. We also found that quenched samples in argon atmosphere exhibit superconductivity below ∼22 K. The temperature dependence of the electrical resistivity ρ(T) displays a striking double resistive superconducting transition with no evidence of a zero resistance state down to 1.5 K. The electrical resistivity has a ≈20% drop at the upper critical temperature Tci followed by a plateau down to a lower temperature Tcj. While Tci is both weakly dependent on the Gd content and external applied magnetic field, the behavior of ρ(T) at low temperatures is strongly sensitive to the Gd concentration, excitation current, and applied magnetic fields. Also, the behavior of ρ(T) below ≈3 K is almost field independent. The magnetic susceptibility data χ(T) reveal superconductivity below Tci and a reentrantlike behavior at low temperatures where the magnitude of χ(T) increases rapidly with decreasing temperature. These observations are similar to those observed in granular Ga films close to the nonmetallic side of the superconductor-insulator transition. We argue that these compounds can be understood within the framework of a superconducting granular model.
Mössbauer study of Ba ferrite sputtered films with large saturation magnetization and perpendicular magnetic anisotropy constant (abstract)
Authors: Noma K. , Matsushita N. , Nakagawa S. , Naoe M.
Published: July 2002

The magnetic hyperfine structures of Ba ferrite sputtered films composed of BaM ferrite (BaO⋅6Fe2O3) crystallites with perfect c-axis orientation were investigated using conversion electron Mössbauer spectroscopy (CEMS). The films deposited by sputtering the targets with a little Ba-excessive composition of BaO⋅5.5Fe2O3 and the mixture of Ar and O2 as sputtering gas (specimen A) exhibited the saturation magnetization 4πMs of 4.7 kG and the perpendicular magnetic anisotropy constant Ku1 of 2.4×105 J/m3. On the other hand, the films deposited by sputtering the targets with a little Fe-excessive composition of BaO⋅6.5Fe2O3 and the mixture of Xe, Ar, and O2 (specimen B) exhibited large 4πMs of 5.1 kG and Ku1 of 3.3×105 J/m3, where the 4πMs and Ku1 of the single crystal of BaM ferrite are 4.8 kG and 3.3×105 J/m3, respectively. The CEMS measurements were carried out at a room temperature with the c-axis parallel to the γ-ray direction. The ratio in intensity of absorption lines indicated that the direction on magnetic spins in the both films were perpendicular to film plane. The intensity of the sextets corresponding to Fe ions in trigonal bipyramid position 2b was relative large for the specimen B. These results were correlated to the formation of excessive S blocks among BaM crystallites observed in the x-ray diffraction diagram of specimen B and the change of spin distributions and superexchange interactions in R-block of BaM crystallites.
Giant Faraday magneto-optical effects induced by Mn2+ in Zn1−xMnxSe
Authors: Zheng Yu-Xiang , Zhou Shi-Ming , Chen Liang-Yao , Dai Ning , Wang Jie , Jin Cai-Xia
Published: July 2002

Zn 1−x Mn x Se films were grown by molecular-beam epitaxy on (100)-oriented GaAs, with Mn mole fraction varying from 0.06 to 0.22. All samples were characterized by x-ray diffraction. The Faraday rotations of Zn1−xMnxSe films was measured with polar Kerr apparatus in the 1.5–3.5 eV photon energy range at room temperature and 10 kG magnetic field. The Faraday spectra show two rotation peaks located at about 2.45 and 2.6 eV for all samples, and another peak located at about 2.74 eV appears for higher composition (x>0.14) samples. The Mn2+ transitions shift toward the red with increasing Mn mole fraction. The Faraday rotations related to the interband transitions were not observed. The three Faraday rotations were due to the Mn2+ d–d* multiplet transitions: A16(S6)→T24(G4) (∼2.45 eV); A16(S6)→A14(G4) E4(G4) (∼2.6 eV); and A16(S6)→T14(P4) (∼2.72 eV), respectively.
Transient thermoelectric effect with tunable pulsed laser: Experiment and computer simulations for p-GaAs
Authors: Sasaki Minoru , Ueda Tomoh , Tanioka Makoto , Mukai Hirokazu , Inoue Masasi
Published: July 2002

A photoinduced “transient thermoelectric effect” (TTE) has been measured for a p-GaAs crystal using a tunable pulsed laser, over the laser energy range 0.93–1.80 eV, laser intensity 0.2–130 mJ/cm2, time range 1 ns–1 ms, and temperature range 4.2–50 K, with special attention to native defects of EL2 centers, whose ground state (EL20) and excited state (EL2ex) are located, respectively, at 0.76 and 1.80 eV above the top of the valence band (their energy difference σex=1.04 eV). After laser irradiation at one end of the sample, a TTE voltage is induced within a rising time τr (1.0–1.5 μs) due to hole diffusion, followed by exponential decay with multiple decay times τ1–τ5 that depend on the laser energy, its intensity, and the temperature. The decay time τ1 is assigned to relate to photoexcited electron diffusion in the conduction band and others τ2–τ5 with electron recombinations with photogenerated holes in the valence band via EL2 centers in p-GaAs, for which a rough evaluation of the capture cross section is made. Based on the experimental data, we have discussed the photoinduced carrier generation/recombination processes in three laser energy ranges with the two boundaries σex and the band-gap energy Eg (=1.50 eV); regions I (E<σex), II (σex⩽E<Eg), and III (E⩾Eg). For these three energy regions, we have carried out computer simulations for the photoinduced TTE voltage profiles by solving one-dimensional transport equations for photogenerated electrons and holes, in qualitative agreement with the observations.
Influence of an inhomogeneous spatial distribution of defects on the constant photocurrent method
Authors: Zhang Qing , Adriaenssens Guy J.
Published: July 2002

The constant photocurrent method has been widely used in hydrogenated amorphous silicon as an efficient way of determining the optical absorption coefficient in the low-absorption region, and of estimating the defect density in the band gap. However, while the analysis is generally carried out on the assumption of uniform material parameters throughout the sample the experimental situation may fail to approximate that model. We therefore examine the influence on the resolved defect density of an inhomogeneous spatial distribution of defects, and of surface recombination, by means of a steady-state diffusion equation for photoexcited carriers. Differences by as much as a factor of 2 are observed within the range of possible experimental circumstances.
Magnetic properties and Kerr rotation of amorphous FeCoTbNd films
Authors: Kim Jai-Young , Hoffmann Horst
Published: July 2002

Amorphous FeCoTb films with perpendicular anisotropy have been sputtered from FeCo, Tb, and Nd targets onto glass substrates, mounted on a rotating substrate holder. The composition of the films, the magnetic properties, and the Kerr rotation depend as well on the distance between the substrates and the rotation axis as on the angular velocity of the substrate holder. A model of anisotropic short range order is given, which results from a layered structure due to the sequential sputtering from the different targets.
Orientation dependence of coupling and interlayer moments in Fe/Cr multilayers (abstract)
Authors: Harp G. R. , Tomaz M. A. , Antel W. J. , O’Brien W. L.
Published: July 2002

The relationship between interlayer coupling and interlayer d-electron magnetic moments is studied using magnetometry and x-ray magnetic circular dichroism in Fe/Cr multilayers. Multilayers are simultaneously prepared with growth axes along different crystallographic orientations to determine the orientation dependence of these effects. It is found that the oscillatory exchange coupling is orientation dependent in the low thickness regime but surprisingly, the induced Cr d-electron magnetic moments are not orientation dependent. Similar results are found in the Fe/V multilayer system. This is evidence for the importance of sp band derived coupling in the low thickness regime.