bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Zn ion on magnetic properties of Fe3O4 magnetic colloids (abstract)
Authors: Lin C. H. , Kuo P. C. , Pan J. L. , Huang D. R.
Published: July 2002

The effects of Zn ion on magnetic properties Fe3O4 magnetic colloids were investigated in this study. Fe3O4 magnetic colloids were produced by the chemical coprecipitation method, i.e., mixing an acidic solution containing FeCl2⋅4H2O, FeCl3⋅6H2O, ZnCl2⋅4H2O, with a NaOH alkali solution at 70 °C, and then centrifuging them from the mixed solution. Various reaction times, solution pH values, and Zn ion contents were also used. Fe3O4 magnetic fluid was obtained by adding ammonium oleate into the mixed solution, precipitating the colloids from the solution, neutralizing the colloids by hydrochloric acid, and dispersing the colloids in n-hexane. XRD, EDX, TEM, and VSM were used to determine the structure, chemical compositions, particle sizes, and magnetic properties of the colloids and the magnetic fluid. The spinel colloids was easily form at a higher pH value in solutions where the pH value ranged from 7 to 12. Fe3O4 colloids were completely formed within the first minute of mixing and the particle size of Fe3O4 colloids did not increase with time after the first minute.

The lattice parameter of Fe3O4 colloids increased linearly with the Zn ion content because the diameter of Zn ion is larger than that of Fe ions. The particle size of Fe3O4 colloids was found to be 10 nm by TEM. For an initially fixed Zn content of 8 wt % in solutions, the Zn content in the Fe3O4 colloids ranged from 3.32 wt % at pH=5 to a maximum value of 7.85 wt % at pH=10. Later, it reduced to 7.51 wt % at pH=12 because Zn ion has the lowest solubility at pH=10. At 8 wt % of zinc ion in the solution, the σs of the Fe3O4 colloid increase sharply from 0 at pH=3 to 92 emu/g at pH=8 and then reach a maximum value of 94 at pH=10. The σs value and Hc value of the Fe3O4 colloid were found significantly improved by adding a suitable amount of Zn ions, e.g., ranging from 70 emu/g and 48 Oe at Zn=0 wt % to a maximum 94 emu/g and 50 Oe at Zn=7.14 wt %. Later they reduced to 70 emu/g and 44 Oe at Zn=12.52 wt % when prepared at pH=10. The σs value of the magnetic fluid was found linearly proportional to the colloid content in the magnetic fluid. For a colloid containing 7.51 wt % of Zn ion, the σs value of the magnetic fluid is 9.8 emu/g at 25 wt % of colloid.
Effect of structural irregularity on propagation properties of optical waves in discontinuous magneto-optical media with one-dimensional quasirandom aray structures
Authors: Inoue Mitsuteru , Yamamoto Takeshi , Isamoto Keiji , Fujii Toshitaka
Published: July 2002

To elucidate the effect of structural irregularity on propagation properties of optical waves in discontinuous magneto-optical media, theoretical analysis was carried out by employing random matrix technique and a model with one-dimensional quasirandom array structure. The analysis revealed that the effect of structural irregularity was so significant that the dispersion curves of optical waves varied considerably depending on the media structures. However, no matter how the medium structure varies irregularly, dispersion curves of waves always exist within the confines between those of the half (0...01...1) and the alternate (0101...01) structures. This fact suggests that the effect of structural irregularity becomes less significant when the discontinuous media have fine discrete structures, where the dispersion curves of the half and the alternate structures are very close.
Nonhomogeneous magnetization reversal in 2D Ising clusters
Authors: García-Pablos D. , García-Mochales P. , García N. , Serena P. A.
Published: July 2002

We have performed Monte Carlo simulations on 2D circular Ising clusters, studying the distribution of the magnetization within the cluster as well as the magnetization reversal process when an applied external field is suddenly changed. We have shown that for highly anisotropic systems (the Ising-like limit), the magnetization reversal process is not uniform in a wide range of temperatures. Spins having a lower coordination at cluster edges drive the reversal process, acting as nucleation centers. We have found that there is a connection between the roughness transition temperature and the differences in the time evolution patterns of the magnetization. Our simulations agree with experimental results on magnetization reversal of single domain particles.
Oxygen dependence of the Josephson weak link effect, specific heat, and the transition temperature of YBa2Cu3Ox
Authors: Glenis S. , Choi G. , Lin C. L. , Mihalisin T. , Wang X. Q.
Published: July 2002

We have measured χ(T) for oxygen-annealed YBa2Cu3Ox samples and observed a glass-like behavior at low magnetic fields which can be explained in terms of a Josephson weak link effect. The glass transition temperature Tg depends on the oxygen annealing temperature and sample pellet pressure. Tg disappears when a sample was powdered after receiving an oxygen anneal, indicating that the Josephson weak link effect occurs between intergranular boundaries. In addition, Tc shifts from 93 K for the air-sintered samples to 90 K for the oxygen-annealed materials. Under vacuum annealing, Tg disappears and Tc first shifts back to 93 K. Prolonged vacuum annealing or vacuum annealing at higher temperatures depresses Tc to below 90 K. The temperature dependence of the specific heat shows a single anomaly for samples sintered in air or annealed under high vacuum. But a double-peak specific heat anomaly occurs for the oxygen-annealed samples.
Simple function for a complex domain configuration
Authors: Arrott A. S. , Lee J.-G.
Published: July 2002

A complex domain configuration found in an iron whisker can be generated by a function with three parameters. The configuration is generated by passing a current along the axis of a {100} whisker with a square cross section. It has four domains in which the magnetization circulates about a central domain magnetized along the z axis. There are four {110} 90° walls and four {100} 90° walls separating these domains. Two of the parameters are known a priori from micromagnetics: a1 describes type I 90° walls between two domains with in-plane magnetization; and a2 describes type II 90° walls between the domains with in-plane magnetization and the central domain with the magnetization out of the plane. The third parameter h, which determines the width of the central domain, is adjustable to minimize the total micromagnetic energy in response to magnetic fields. The magnetization pattern is generated from a vector potential A(x,y)ẑ. Calculating Ms curl A(x,y)ẑ produces Mx and My. Then Mz is found from M2x+M2y+M2z=M2s. The potential has four parts: A(x,y)=Ax+Az+Ah+Ac, where Ax and Ay are the same function (with x and y interchanged) used to create the in-plane domains and the type I walls, Ah generates the type II walls, and Ac describes the outer corners. The resulting magnetization is divergence free. The analytic functions are convenient for calculation of the magnetic response to applied fields.
Radio frequency ion beam deposition of diamond-like carbon for sliders and heads
Authors: Wang Lien-Chang , Halada Gary , Gambino Richard J. , Hayes Alan , DiStefano Sal
Published: July 2002

Diamond-like carbon prepared by direct ion beam deposition from a filamentless rf ion source has been found to have properties suitable for protective coatings on sliders and heads. One advantage of the rf inductively coupled plasma source used in this study is that it can be operated reliably for hundreds of hours with high concentrations of hydrocarbon gas. We have studied deposition from argon-CH4 mixtures with 28% to 100% CH4 and beam energies mainly in the 100 to 400 eV range. X-ray photoemission spectra analysis shows that films prepared with pure CH4 have less sp3 (diamond-like) bonding than films prepared from mixtures with argon.
Comparison of tribological performance of pure carbon and carbon-nitrogen coated thin film head sliders
Authors: Wang Geng , Silversten John M. , Judy Jack H. , Chen Ga-Lane
Published: July 2002

The wear performance of pure carbon and carbon nitrogen (C:N) coated thin film head sliders was evaluated by continuous drag testing (CDT). Comparison was made in light of protection of these two various carbon films. By studying the air bearing surfaces of the heads under atomic force microscopy (AFM) and secondary electron microscopy (SEM), it was found that during the CDT test, the head may fail before the disk fails and the area of Al2O3 is the most possible place where wear begins. There were small amounts of material transferred from head slider to disk, although no evidence of opposite transfer was found.
First principles determination of magnetocrystalline anisotropy for surfaces and interfaces using a torque method (abstract)
Authors: Wang Xindog , Freeman A. J. , Wu R. , Wang D. S.
Published: July 2002

Perpendicular magnetic alignment is vital for high density magneto-optical recording materials. Despite the tremendous theoretical/computional advances made during the last few decades, the determination of magnetocrystalline anistropy (MCA) from first principles still remains a great challenge for complex systems. We will describe our recently proposed torque method for the first principles determination of MCA. In the usual first principles methods, one calculates the band energies associated with two magnetization directions and substracts one from the other. Within this approach, one has the difficulty of getting rid of the random fluctuations arising from the two different Fermi surfaces due to different magnetization directions. We show that to accurately determine the spin-orbit induced uniaxial ansisotropy energy for surfaces/interfaces, calculation of the torque at a specific angle is sufficient and one avoids the complexities associated with two Fermi surfaces by employing the Feynman-Hellman theorem. In the k-space integrations, we used both linear and quadratic interpolation schemes and convergence is assured when these two schemes agree to the accuracy desired. Examples, including Fe and Co multilayer systems, will be presented to demonstrate the efficiency and precision of this method. Detailed comparisons with previously proposed state-tracing method by Wang et al. are also made and discussed.
On the γ-like surface of α-Ce: Theory (abstract)
Authors: Hjortstam O. , Trygg J. , Johansson B. , Eriksson O. , Wills J. M.
Published: July 2002

We have shown theoretically, by means of a full-potential LMTO method in a slab geometry, that the topmost surface layer of α-Ce is γ-like. The calculations are fully relativistic and include all electrons. Also an orbital correction to the f-electron states is included to allow for f localization. For the topmost layer the spin moment is found to be 0.70 μB for the f electrons and 0.08 μB for the d-electron states while the orbital moment from the f electrons is found to be −1.07 μB. These moments correspond well to the moments calculated for bulk γ-Ce which are 0.63, 0.07, and −0.87 μB, respectively. The subsurface and lower lying layers are calculated to have spin and orbital moments close to zero. We therefore conclude that the topmost layer on the α-Ce surface is γ-like while the subsurface and lower lying layers are similar to bulk α-Ce. Our findings explain recent photoemission experiments on this material and provide a theoretical foundation for the interpretation of these experiments. The fact that our theory assumes that α-Ce has delocalized f electrons, and the agreement with the interpretation of photoemission experiments, gives support that the Mott transition model for the α→γ phase transition is correct.
Experimental analysis of the effects of tape thickness on magnetic recording
Authors: Friedmann A. , Wei D. , Bertram H. N. , Wolf J. K. , Swanson R. , Jeffers F.
Published: July 2002

Advances in magnetic tape recording have produced media with magnetic layers as thin as 0.1 μm. In this article, a metal particulate tape with a magnetic layer thickness of ∼0.37 μm is compared to a standard thick media tape with a magnetic layer thickness of ∼4 μm. Measurements of the isolated pulse are made and shown to compare well with micromagnetic simulations. The replay voltage versus current is measured with a 4 μm track width, shielded magnetoresistive head at various densities. The thin tape shows better high density response at high currents than the thick tape. The simulations show that the transitions are sharper on the thin tape due to both the reduction in thickness, and an improvement in the particle orientation. The better oriented particles yield narrower pulses, thereby improving the high frequency response of the tape. Frequency response measurements are also taken with the magnetoresistive head, which yield a signal to noise ratio of ≳20 dB at 200 kfci. Last, overwrite performance versus current is compared for the two tapes plus a metal-evaporated (ME) tape with a 0.2 μm thick layer. A significant improvement in overwrite is seen on the ME tape.
Computer simulation of ultrahigh-density perpendicular magnetic recording
Authors: Yoshida K. , Hara M. , Hirayama Y. , Sugita Y.
Published: July 2002

The possibility of ultrahigh-density recording higher than 10 Gb/in.2 with perpendicular magnetic recording is investigated by computer simulation for a ring-type head and single-layer medium combination. A nucleation model is used as a media model because it incorporates a nucleation site, which causes irreversible magnetization switching. Fundamental read–write characteristics are found to be entirely different from those of longitudinal recording. Recorded magnetization strongly depends on head field strength; the maximum magnetization appears around the head field strength of media coercivity, and beyond this the recorded magnetization decreases abruptly. Spacing loss in the recording process also depends on head field strength and recording density. However, saturation recording can be attained even at an ultrahigh recording density of 600 kFCI with a spacing of 30 nm. Also, a higher signal-to-noise ratio than in longitudinal recording can be obtained by introducing weak intergrain exchange interaction with a relatively large grain size in the media film. This suggests that perpendicular magnetic recording is stable in thermal fluctuation. © 1996 American Institute of Physics.
Prediction of the limitations placed on magnetoresistive head servo systems by track edge writing for various pole tip geometries
Authors: Davidson R. , Simmons R. , Charap S.
Published: July 2002

The typical configuration for inductive write/magnetoresistive read heads used in hard disk applications involves a shared pole (shield) between the write transducer and the read transducer. The shared pole forms the leading pole of the write portion of the head. The write track width is primarily determined by the width of the trailing pole, however, the leading pole geometry has an important influence on track-edge writing effects and, therefore, on embedded servo system performance. This effect is simulated for shared pole, trimmed pole, and, for comparison, conventional inductive head pole geometries. The merits of each geometry and impact of side writing on servo is discussed.
Effect of sputtering condition on dynamic characteristics and microstructures of magneto-optical 5.25 in. SiN/TbFeCo/SiN/Al disks for 532 nm recording media
Authors: Ro M. D. , Cho B. I. , Kim M. J. , Kim S. S. , Ahn Y. M. , Lee K. G. , Gill B. L.
Published: July 2002

A systematic study of the effect of sputtering conditions, for each layer of the magneto-optical SiN 500 Å/TbFeCo 200 Å/SiN 200 Å/Al 600 Å disks, such as power and Ar gas flow rate on the noise levels (NL) and carrier-to-noise ratio (CNR) was performed for the 532 nm high density storage media in this work. The NL dropped to its minimum value of −71.3 dB as the sputtering power for the first SiN increased from 0.5 to 1.5 kW. With a further increase in sputtering power to 2.5 kW, it sharply increased to −64.5 dB. This was ascribed to the smooth and dense surface of the first layer at 1.5 kW, as was observed in the atomic forces microscopy images. The spherical, isotropic, fine grains with a diameter of about 0.2–0.7 μm at 1.5 kW were found, while the longitudinal, directional granular features with a length of 2.5 μm were seen at 2.5 kW. The highest CNR of 46.3 dB was observed at 0.6 kW with a constant sputtering Ar gas flow rate of 25 sccm for the magneto-optical layer. The sputtering conditions for other layers are as follows: 1.5 kW with sputter Ar/N2 gas flow rate of 30 sccm/11 sccm for the first and third SiN layer, and 0.6 kW with 25 sccm of Ar for the Al reflection layer. This is due to the smooth surface morphologies of the magneto-optical layer at this optimum sputtering pressure, as previously reported in similar research. To obtain a high readout signal, the phase compensation for the elliptic laser beam has been considered.
Parametrical interaction of magnetostatic volume waves in a space-time periodic magnetic field
Authors: Fetisov Y. K. , Ostrovskaya N. V. , Popkov A. F.
Published: July 2002

The theory describing parametrical interaction of magnetostatic backward volume waves (MSBVW) in a space-time periodic magnetic field was developed. Forward and backward scattering of MSBVW propagating in a 20-μm-thick yttrium-iron-garnet film at a central frequency of 3 GHz was observed. A space-time periodic magnetic field with a spatial period of 500 μm, a frequency in the range 20–150 MHz, and a magnitude up to 10 Oe was created by ac current passing through a meander line placed on the film surface. An interaction bandwidth of 20 MHz and an efficiency of up to 10% have been obtained in accordance with theoretical predictions.
Experimental determination of an effective demagnetization factor for nonellipsoidal geometries
Authors: Zheng Guobao , Pardavi-Horvath M. , Huang Xiaohua , Keszei B. , Vandlik J.
Published: July 2002

For a nonellipsoidal magnetic sample, the internal magnetic field Hint(r) is inhomogeneous even when a uniform external magnetic field Happ is applied to it. In such a case the elements of the demagnetizing tensor become position-dependent, N=N(r). The knowledge of the local demagnetization tensor is important for the analysis and design of devices using finite size and shape magnetic elements. The demagnetizing tensor elements can be calculated analytically and/or numerically, however, often a quick check of the extent of the inhomogeneity of the magnetization distribution of a sample, or a single approximate value of the demagnetizing factor for the given non-ellipsoidal geometry, would be satisfactory. Therefore a method to define and measure an effective demagnetizing tensor element Neff for rectangular and circular shapes has been developed. Experiments, performed on 2×4 mm2 yttrium iron garnet samples up to 220 μm thickness, show that the analytical approximation can be used to define an Neff. But even for a length/thickness ratio of 200, the thin film approximation still is in an error of 3.7%.
An efficient design to reduce the flux leakage of a spindle motor
Authors: Ying T. F. , Chen C. M. , Liao C. P. , Wu M. D. , Huang D. R.
Published: July 2002

A small dc brushless spindle motor with small magnetic flux leakage must be used for a CD-ROM drive application because the magnetic flux leakage may affect the magnetic and electric control circuit of the pickup head. This paper presents a motor design that efficiently reduces magnetic flux leakage by using a pair of yokes on the rotor magnet. Using these yokes at a distance of 2.0 mm reduced the magnetic flux leakage from 344 to 29 G along the radial direction and from 117 to 10 G along the axial direction. After shielding for the magnetic flux leakage, the dynamic performance of the motor cannot be affected. The torque of the CD-ROM spindle motor can be controlled at the same range for shielded and unshielded spindle motors.
Mössbauer-effect study of face-centered-cubic-like Fe on Cu(001) (invited) (abstract)
Authors: Keune W. , Schatz A. , Ellerbrock R. D. , Fuest A. , Wilmers K. , Brand R. A.
Published: July 2002

More than 30 years ago, Weiss has postulated the existence of two different magnetic fcc-Fe states [high-spin (HS)/high atomic volume or low-spin (LS)/low atomic volume] in order to explain the Invar effect in fcc-Fe alloys. Such metastable states may be stabilized by epitaxial growth of ultrathin Fe films on Cu(001) under suitable conditions which depend on film thickness and growth temperature. In situ conversion-electron Mössbauer spectroscopy, combined with low-energy electron diffraction, reflection high-energy electron diffraction, and Auger electron spectroscopy, on ∼3- and ∼7-ML-thick 57Fe films grown in ultrahigh vacuum at 300 K reveals a thickness-dependent transition from a HS ferromagnetic (FM) state with an anisotropically expanded fcc (fct-like) structure (c/a≳1) to a LS antiferromagnetic (AFM) isotropic fcc state. In contrast, the stability of the HS fct-like phase is extended to at least 7 ML in films grown at low T (90 K) and annealed to 300 K. The HS-FM phase in 7 ML films is rather stable against annealing up to 500 K; annealing at 570 K leads to a HS–LS transformation which is correlated with abrupt surface segregation of Cu. By placing 2-ML-thick isotopically enriched 57Fe-probe layers into a 300 K grown natural Fe film of 7 ML total thickness we could obtain a magnetic depth profile along the film-normal direction: while the LS-AFM state (with TN∼70 K) was found at the film center and a paramagnetic Fe–Cu alloy at the Fe/Cu interface, Fe surface atoms were observed to be in a HS-FM state with a noncubic atomic environment. Only today can we begin to understand the complex behavior of fcc-Fe/Cu(001).
Giant magnetoresistance properties in multilayered Co-Ag/Cu granular alloys
Authors: Iijima Makoto , Shimizu Yutaka , Kojima Naomi , Tanaka Atsushi , Kobayashi Kazuo
Published: July 2002

In this article, we introduce a novel Co-rich Co-Ag/Cu granular alloy structure with increased magnetic sensitivity, and report on our study of the relationship of giant magnetoresistance (GMR) and magnetic properties to annealing temperature and Cu thickness in sputtered Co66-Ag34/Cu multilayered films. We heat treated Co-Ag/Cu films with Cu spacer thickness ranging from 15 to 50 Å up to 500 °C, and found that the MR ratio loosely depends on both the Cu spacer thickness and the annealing temperature, peaking at 7.6% with a 25 Å Cu layer and an annealing temperature of 280 °C. Based on the magnetic properties we observed, as well as x-ray studies, we found that Cu spacers at least 25 Å thick are able to separate the Co-Ag magnetic layers. Our data also indicated that the annealing treatment changed the coupling of magnetic layers from ferromagnetic to antiferromagnetic. The high thermal stability and the high magnetic sensitivity suggest potential use of our novel multilayered structure in applications as magnetic sensors.
Growth and magnetic properties of FexNi1−x ultrathin films on Cu(100)
Authors: Schumann F. O. , Wu S. Z. , Mankey G. J. , Willis R. F.
Published: July 2002

We have investigated ultrathin FexNi1−x films grown epitaxially on Cu(100) with different stochiometry. With the surface magneto-optic Kerr effect (SMOKE) we measured the variation of the Curie temperature TC as a function of the film thickness n in monolayers (ML). Using the results of our previous investigations on finite-size scaling (Huang et al.), we are able to extrapolate the value TC(∞) for samples with different Fe content. In particular, alloy films with Fe concentrations close to 65% remain ferromagnetic. This is in contrast to bulk Fe65Ni35, which shows a collapse of long range order, which is the so-called invar effect associated with a fcc to bcc structural transition. Growing these alloy films on a Cu(100) substrate forces them to adapt the Cu lattice spacing, thereby suppressing the structural relaxation.
Data storage based on proximal probe techniques (invited) (abstract)
Authors: Mamin H. J. , Terris B. D. , Rugar D.
Published: July 2002

Recently, there has been considerable interest in examining the feasibility of using proximal probe techniques as the basis for a data storage device. These techniques, derived from the scanning tunneling microscope (STM) and atomic force microscope (AFM), provide a potential pathway to reaching the ultrahigh densities needed in the decades ahead. While these techniques offer high areal density, a number of formidable technical challenges must be met, however, in order to produce a device with realistic data rate, error rate, and overall reliability. In this talk we will review some of the approaches that have been taken, including those based on the STM, the AFM, and near-field optics. We will focus on the efforts in our laboratory to demonstrate realistic data rates at reasonably high densities using thermomechanical writing with an AFM tip, and near-field recording with a solid immersion lens. The prospects for parallel tip arrays and issues of overall implementation will also be addressed.
Bit-shift performance investigations at different skew angles and for different media orientations
Authors: Hu S. B. , Liu B. , Lee C. S.
Published: July 2002

Bit-shift performance was investigated at different skew angles and for media with different orientation. Results indicate that the bit-shift value increases as the skew angle increases for both planar orientated media and near-isotropic media. As the skew angle increases, the off-track capability, described by the bit shift at different off-track distances, decreases and the bit-shift profile becomes asymmetric. Comparison of normalized bit-shift values (normalized according to the bit shift at 0° skew angle) shows that the bit shift of the near-isotropic media is not as sensitive to skew angle variation as the media with strong orientation.
Mechanically ground Fe73.5Cu1Nb3Si13.5B9: A soft magnetic material in powdered form
Authors: Giri Anit K. , García Tello P. , González J. , González J. M.
Published: July 2002

We report on the preparation, by high energy ball milling and starting from an amorphous melt–spun material, of powdered samples exhibiting, after suitable thermal treatments, saturation coercive forces of the order of a few tens of mOe.
Effect of cutting techniques on local magnetic characteristics of SIFE (abstract)
Authors: Philips D. A. , Dupre L. R. , Eloot K. , Melkebeek J. A.
Published: July 2002

In this article the effect of cutting techniques on the local magnetic characterization of nonoriented motor lamination iron is presented. Starting from the same material (0.3% Si, 0.3% Al, finally annealed condition), rings have been cut using three different techniques: spark erosion, laser cutting, and punching. First a classical measurement has been performed on stacks of ten identical rings, using a measurement winding applied uniformly along the circumference of the ring. In this way, the average BH loops under quasistatic conditions have been obtained, and are used as a reference further on. It is found that the cutting techniques have a considerable impact on these average magnetic characteristics. In a second step, local measurement windings have been wound on single rings. The quasistatic BH loops have then been measured as a function of the position along the circumference of the ring, with B still the average induction over the entire magnetic cross section. A systematic fluctuation of typically 5% around the reference loop has been observed for all three materials, which cannot be attributed to measurement errors. In a third step, quastistatic local BH-loops have been measured at different radial positions. A dedicated measurement technique has been used, allowing the measurement of the local flux between two points 1 mm apart. No variation of the BH loops with the radial position has been observed in case of the material cut using spark erosion. This result is in agreement with the very low mechanical impact of the cutting technique. In case of the material cut with a laser, a considerable variation of the BH-loops with the radial position has been observed. This proves that the heat affected zone extends several mm inside the material. For the punched material again no variation with the radial position could be observed. This shows that the impact of the punching is confined to a region <1 mm wide, close to the edge.
High coercivity of melt–spun Sm2Fe15Al2C1.5 compound
Authors: Zhang Jun-Xian , Cheng Zhao-Hua , Shen Bao-Gen
Published: July 2002

The magnetic hardening of melt–spun Sm2Fe17Cx was studied and the coercivity of 4.6 kOe for Sm2Fe17C1.5 alloys was reported a few years ago. Recently, we have succeeded in preparing single-phase compounds of Sm2(Fe, M)17Cx (M=Ga, Al, or Si) with high carbon concentration by arc melting. It was found that the substitution of Ga or Al not only facilitated the formation of high carbon concentration rare-earth iron compounds with a 2:17-type structure, but also was very effective in raising the value of the anisotropy field. For example, the sample of Sm2Fe15Al2C1.5 has a saturation magnetization of 110.2 emu/g, a Curie temperature of 576 K, and an anisotropy field of 111 kOe. It is known that melt spinning is an effective means to obtain high coercivity of magnetically hard materials. In this work, the hard magnetic properties of melt–spun Sm2Fe15Al2C1.5 alloys were investigated. It was found that the value of coercivity depends strongly on the quenching rates and an optimum coercivity of 9.4 kOe was obtained at the quenching rate of 20 m/s. X-ray diffraction patterns indicate that the as-quenched ribbons have a phase of the Th2Zn17-type structure. The high coercivity of these as-quenched ribbons originates from the excellent intrinsic magnetic properties of Sm2Fe15Al2C1.5. It can be concluded that the substitution of Al is very effective in raising the coercivity of melt–spun Sm2Fe15Al2C1.5 ribbons.
Investigation of the spin-Peierls phase diagram of CuGeO3: Far-infrared electron spin resonance in high field
Authors: Palme W. , Ambert G. , Boucher J. P. , Dhalenne G. , Revcolevschi A.
Published: July 2002

Electron spin resonance on single crystals of the spin-Peierls compound CuGeO3 has been performed in magnetic fields up to 17 T in the temperature range 1.8–20 K. Using far-infrared laser frequencies of 245 and 525 GHz we could observe resonance conditions in the three different magnetic phases, i.e., the uniform, the dimerized, and the incommensurate phases for a magnetic field applied parallel to the a axis of the crystal. So for the first time data on electron spin dynamics in the incommensurate phase are reported for fields far from the transition to the dimerised phase. Striking effects concerning the g factor, linewidth, and hysteresis are observed.
Variable texture NiOFe2O3 ferrite films prepared by pulsed laser deposition
Authors: Samarasekara P. , Rani R. , Cadieu F. J. , Shaheen S. A.
Published: July 2002

Pulsed laser deposition using bulk NiOFe2O3 targets onto heated substrates has been used to synthesize single phase Ni spinel ferrite films onto various substrates. Flowing oxygen has been used during the deposition to maintain the oxygen stoichiometry. Ni ferrite films have been deposited onto C-, R-, and A-plane sapphire, polycrystalline Al2O3, and fused silica. Single-crystal (111) oriented NiOFe2O3 films have been made onto C-plane sapphire for substrate temperatures of greater than 900 °C. Polycrystalline highly (400) textured Ni ferrite films have been made onto R-plane sapphire with I(400)/I(311)=6.15. Films made onto A-plane sapphire, polycrystalline alumina, and fused silica showed only moderate texturing. The coercive force of the (111) oriented NiOFe2O3 was 120 Oe perpendicular to the film plane and 95 Oe in plane.
A re-interpretation of the existence of a spectrum of activation energies for the microstructural changes in Al 1% Si lines
Authors: Stulens H. , Knuyt G. , De Ceuninck W. , De Schepper L. , Stals L.
Published: July 2002

During the first thermal treatment after deposition and/or passivation of Al-based interconnects, a marked decrease in the electrical resistance can be observed. This resistance decrease cannot be described in terms of a single rate constant. Precipitation of the alloyed elements is probably the responsible atomic process. In a previous article, a spectrum of activation energies was extracted in order to characterize this decay. Recent research has shown that the presence of an activation energy spectrum is, mathematically, completely equivalent with a spectrum of pre-exponential factors. Since for precipitation–dissolution, the pre-exponential factor is a function of the distribution and geometry of the precipitates, the use of a spectrum of pre-exponential factors is for this specific case probably physically more relevant. The technique introduced for the determination of the spectrum of activation energies is still valid in case of the presence of a spectrum of pre-exponential factors.
Carbon incorporation for strain compensation during solid phase epitaxial recrystallization of SiGe on Si at 500–600 °C
Authors: Antonell M. J. , Jones K. S. , Haynes T. E.
Published: July 2002

Transmission electron microscopy has been combined with time-resolved reflectivity and ion channeling to study the effects of carbon doping on solid-phase epitaxial regrowth (SPER) of strained 2000 Å, Si0.88Ge0.12Si alloy layers grown by molecular-beam epitaxy (MBE). Relative to the undoped layers, carbon incorporation in the MBE grown SiGe layers prior to regrowth at moderate temperatures (500–700 °C) has three main effects on SPER. These include a reduction in SPER rate, a delay in the onset of strain-relieving defect formation, and a sharpening of the amorphous/crystalline (a/c) interface, i.e., promotion of a two-dimensional (planar) growth front. These results suggest that C incorporated during SPER reduces the lattice-mismatch strain.
Influence of ion energy flux on structure and optical properties of a-C:H thin films
Authors: Lee Jung H. , Lee Young H. , Farouk Bakhtier
Published: July 2002

The effects of ion energy flux (IEF) on the structure and optical properties of a-C:H thin films are investigated. The films are deposited in a 13.56 MHz, rf driven asymmetric plasma reactor at 25 °C from a gas mixture of styrene and hydrogen. In situ impedance analysis is used to determine the IEF on the film surface. IEF is shown to be linearly proportional to power/pressure ratio. The film structure and properties evaluated by Raman spectra, Rutherford backscattering spectrometer, and ellipsometry reveal that the sp2 carbon fraction, density, dielectric constant, and refractive index of the film increase with increasing IEF, while the hydrogen content decreases. The absorption coefficient of the film increases with increasing IEF possibly due to increased graphitization. The disorder in the films appears to be reduced with increasing IEF.
Anisotropy of permeability at 10 Oe in textured soft magnetic materials
Authors: Birsan M. , Szpunar J. A.
Published: July 2002

In this article, we propose and deduce analytical formulas which describe the anisotropy of the permeability at 10 Oe in textured soft magnetic materials. The material texture is represented using the orientation distribution function. The property is compared to experimental data obtained from two grain oriented 3% Si–Fe samples of different texture quality.
Weak ferromagnetic resonance of Gd2CuO4 small particles
Authors: Mira J. , Rivas J. , Butera A. , Tovar M. , Vázquez Vázquez C. , Mahía J. , López-Quintela M. A. , Oseroff S. B.
Published: July 2002

Microwave-absorption measurements have been performed in Gd2CuO4 particles of controlled size. We have measured the microwave absorption associated with a magnetic resonance of the weak-ferromagnetic component of the magnetization. The onset temperature of this signal, related to the appearance of weak ferromagnetism, is depressed when the particle size is decreased. A simultaneous depression of the Néel temperature is suggested as the origin of the observed dependence, due to the limitation on the two-dimensional correlation length imposed by the particle size.
Optical properties of ultrathin GaAs/AlAs quantum well structures with an electric field
Authors: Erdoğan M. U. , Sankaran V. , Kim K. W. , Stroscio M. A. , Iafrate G. J.
Published: July 2002

A theoretical study of the optical properties of GaAs/AlAs quantum well structures in the presence of an electric field is presented. In the first part of the article, interband transitions from the valence band to the conduction band are studied near the type-I to type-II transition point. In the second part, the effect of the electric field on intersubband transitions within the conduction band is considered. The band structure is calculated using a second-nearest-neighbor empirical sp3 tight binding method including spin–orbit effects. Interband and intersubband transition energies, optical matrix elements, and absorption coefficients are given as functions of the electric field. It is shown that the optical properties of these structures can be modified significantly with field near the anticrossing point.
Space-charge-limited currents in amorphous semiconductors with correlated defects
Authors: Schauer František , Nešpůrek Stanislav , Valerián Hynek
Published: July 2002

Model calculations of space-charge-limited currents for a semiconductor containing correlated defects exhibiting amphoteric electronic states are presented. The filling of such states by charge-carrier injection is as follows: (1) the states with a positive correlation energy are filled in two separate steps involving one electron each, (2) the states with a negative correlation energy are filled in a concentrated step involving two electrons. These features are reflected in space-charge-limited current characteristics and their temperature dependencies.
Strain and quantum confinement energies in n-type modulation-doped lattice-mismatched InAsP quantum-well wires
Authors: Hammersberg J. , Notomi M. , Weman H. , Lundström T. , Potemski M. , Sugiura H. , Okamoto M. , Tamamura T.
Published: July 2002

Low-temperature luminescence and magnetoluminescence experiments have been performed on n-type modulation-doped lattice-mismatched InAsxP1−x/InP quantum-well wires. From these experiments we can obtain information about the conduction-band subband structure, the electron effective mass, and consequently the conduction-band density of states. The doping level is high enough to populate several subbands in the conduction band which become observable in the luminescence spectra. The low-temperature luminescence spectra contain a distinct signature of the Fermi level at the high-energy slope. The zero-field wire luminescence exhibits an energy blue shift due to lateral quantum confinement within the wire and strain energy enlargement of the optical band gap. We have determined the separate energy contributions to the blue shift by high-field magnetoluminescence experiments. We have also calculated the (nonuniform) strain distribution and the strain-induced band shift within the wires. The theoretical results agree well with the experimental data. The information obtained on the subband structure and the electron effective mass can be used to estimate the length of the space-charge region in the doped area and the 1D carrier concentration in the quantum-well wires, without using any electrical contacts.
Conversion of evanescent into propagating light in near-field scanning optical microscopy
Authors: Fukuzawa Kenji , Kuwano Hiroki
Published: July 2002

Conversion of evanescent light into propagating light (as needed in near-field scanning optical microscopy) is analyzed by means of a photocantilever. The photocantilever is a silicon cantilever with a pn junction photodiode on its tip. The photocantilever tip converts evanescent light from a sample into propagating light. Theoretical values given by scattering and transmission models are compared with our experimental values. The scattering model gives results that are closer to the experimental values than does the transmission model. This indicates that the nonpropagating evanescent light is converted into scattered light at the photocantilever tip, and that the scattered light is collected by the photodiode.
Electrically detected magnetic resonance in a-Si:H/a-Ge:H multilayers
Authors: Graeff C. F. O. , Stutzmann M. , Miyazaki S.
Published: July 2002

The transport and recombination properties of hydrogenated amorphous silicon/hydrogenated amorphous germanium (a-Si:H/a-Ge:H) multilayers have been investigated as a function of the a-Ge:H well width by electrically detected magnetic resonance (EDMR). For a-Ge:H layers thicker than 4 nm, the EDMR signal is positive in sign, or enhancing, and composed of two components. It is observed in the dark as well as under illumination, and assigned to hopping through defects perpendicular to the multilayer planes. For the samples with a-Ge:H layer thinner than 4 nm, the EDMR signal is negative in sign, or quenched, and observed only under illumination. The quenched signal is also composed of two components, and is assigned to the recombination of the photocreated carriers in the a-Si:H layer, as well as in the interface. The results indicate that the good photoconductivity in the infrared observed in such multilayers is explained by transfer of carriers from the a-Ge:H well to the a-Si:H layer.
Optical attenuation in planar waveguides of unidirectionally oriented copolyester film
Authors: Bai S. J. , Spry R. J. , Alexander M. D. , Barkley J. R.
Published: July 2002

The in-plane optical loss was correlated with molecular orientation in a unidirectionally stretched poly(ethylene terephthalate-co-isophthalate) copolyester film. X-ray scattering was applied to ascertain the anisotropic and amorphous natures of the stretched film. The film was adhered onto a silicon wafer to fabricate a planar waveguide. Multiple TE and TM propagation modes were obtained on the planar waveguide using a prism coupler at 632.8 nm yielding in-plane refractive indices of 1.6545 and 1.5464, parallel and transverse to the stretch direction, respectively. For each waveguide mode, a propagation streak was generated and registered on photographic film. The in-plane linear attenuation coefficient, α∥≡{ln[I(O)/I(x∥)]}/x∥, was derived from the propagation streak. The optical path of each mode was determined and used to normalize α∥. For the TE modes, α∥ increased with the mode number and was highly anisotropic, i.e., α∥ (parallel to the stretch direction)≤α∥ (transverse to the stretch direction). However, for the TM modes, α∥ was found to be a constant smaller than those of the TE modes, and was independent of mode number as well as molecular orientation. The bulk α∥ was extrapolated to remove the surface loss contributions for the planar waveguide. Dipole interaction between the stretched copolyester, surface irregularities, and the TE or TM polarization was analyzed to delineate the in-plane optical loss behavior.
A new technique for studying the Fano factor and the mean energy per ion pair in counting gases
Authors: Pansky A. , Breskin A. , Chechik R.
Published: July 2002

A new method is presented for deriving the Fano factor, F, and the mean energy per ion pair, Wi, in counting gases. It is based on the technique of individual counting of single ionization electrons induced in low-pressure gas samples by soft x-ray photons. A correlation of the experimental data with a detailed simulation of the electron deposition and counting process permits the extraction of the Fano factor and the mean energy per ion pair values. We present data of F and Wi for C2H6 and Ar/C2H6 over the energy range of 100–1500 eV. The energy dependence of these parameters reflects the atomic level structure of the gases. We discuss in detail the accuracy of this technique and its advantages and limitations. Ways are proposed for improving the technique and for broadening the energy range.
Buried layer formation in silicon by laser radiation
Authors: Medvid’ A. , Madzhulis I. , Kaupužs J. , Blūms J.
Published: July 2002

The effect of CO2 laser radiation on the spatial distribution and state of oxygen or nitrogen atoms, implanted in silicon wafers, is investigated experimentally. Infrared spectroscopy of the implanted and irradiated samples showed the formation of a new phase inside the silicon. Auger spectrometry of the implanted oxygen atom distribution function showed a decrease in its width by 6%, and a shift of the distribution maximum toward the irradiated surface of the wafer by 0.25 of the initial half-width. A stochastic model describing the process of buried layer formation from interacting impurities in the presence of a temperature gradient is proposed. A nonlinear diffusion equation is derived and the results obtained within this model are in qualitative agreement with our experiments. The possibility of forming buried layers in Si, i.e., SiO2 or Si3N4, as well as controlling their thickness and depth of location by means of CO2 laser irradiation is shown both experimentally and theoretically.
Reply to ‘‘Comment on three-dimensional analysis of a heat-spreading phenomenon in phase-locked arrays of oxide-isolated diode lasers’’ [J. Appl. Phys. 79, 9402 (1996)]
Authors: Nakwaski Wl/odzimierz
Published: July 2002

A short reply to the Comment by A. D. Sadovnikov on ‘‘Three-dimensional analysis of a heat-spreading phenomenon in phase-locked arrays of oxide-isolated diode lasers’’ is presented.
Comment on ‘‘Three-dimensional analysis of a heat-spreading phenomenon in phase-locked arrays of oxide-isolated diode lasers’’ [J. Appl. Phys. 67, 2711 (1990)]
Authors: Sadovnikov A. D.
Published: July 2002

A correction to the expression [W. Nakwaski, J. Appl. Phys. 67, 2711 (1990)] for the three-dimensional temperature distribution in the heat sink of a laser is presented. It is also extended to the case of an odd number of laser chips.
Exciton luminescence in Ge–Ge1−xSix multiple-quantum-well structures
Authors: Orlov L. K. , Aleshkin V. Ya. , Kalugin N. G. , Bekin N. A. , Kuznetsov O. A. , Dietrich B. , Bacquet G. , Leotin J. , Brousseau M. , Hassen F.
Published: July 2002

Photoluminescence spectra of quasi-2D excitons in Ge–Ge1−xSix multiple-quantum-well structures (MQWS) on Ge (111) substrates are investigated. The properties of the energy spectra for electrons and holes in strained nanometer Ge layers are discussed on the basis of experimental measurements and theoretical estimations. We found experimentally the Ge band gap in Ge–Ge1−xSix MQWS and its dependence on a layer thickness, and also the binding energy of quasi-2D excitons in strained nanometer Ge layers. It was shown that the no-phonon transitions intensity increases with a decrease in a quantum-well width by enhanced scattering on the short-range component of the potential perturbation near the interfaces and in the barriers.
Application of amorphous Cu–Zr binary alloy as a diffusion barrier in Cu/Si contact systems
Authors: Takeyama Mayumi , Kagomi Shinya , Noya Atsushi , Sakanishi Kouichirou , Sasaki Katsutaka
Published: July 2002

Thermally stable Cu/Si contact systems using an amorphous binary alloy of Cu0.6Zr0.4 with a relatively low resistivity of ∼150 μΩ cm as a diffusion barrier have been developed. The application of the stable compound ZrN in the Zr/Cu/Cu–Zr/ZrN/Si contact system effectively suppresses the interfacial reactions up to a temperature of 550 °C, which is higher than the crystallization temperature of the Cu–Zr amorphous alloy, ∼500 °C. By designing the contact system with the Cu-containing amorphous alloy Cu–Zr and the stable barrier compound ZrN, also a compound of a constituent material of the amorphous alloy, we can obtain an effective diffusion barrier in the Cu/Si contact system.