bluuebunny/crossref_metadata_2025 huggingface dataset:
Deposition of perpendicular magnetic recording Co–Cr layers with nanosize domains using a plasma enhanced type of sputtering apparatus
Authors: Kadokura S. , Naoe M.
Published: July 2002

Co–Cr thin films for perpendicular magnetic recording layers were deposited using a new type of facing targets sputtering apparatus by optimizing the film thickness tF, the substrate temperature Ts, and the sputtering Ar pressure PAr. The Co76Cr24 films with tF of 50 nm were deposited on glass disks at Ts of 230 °C and PAr of 0.03 Pa. These films were composed of highly c-axis oriented hcp crystallites, in which isolated ferromagnetic areas with lower Cr content CCr were uniformly distributed in the paramagnetic host matrix with higher CCr. The diameter of grains was 5–20 nm with voidless grain bounderies and the diameter of lower CCr areas was as small as 3–5 nm. The perpendicular coercivities Hc⊥ in initial growth regions, the whole film and surface regions were 1100, 1900, and 2700 Oe, respectively. Transmission electron microscope images of these specimens showed that ferromagnetic areas of highly c-axis oriented hcp crystallites with large uniaxial magnetic anisotropy constant are particulate-like. Consequently, the deposition of Co–Cr thin films with much higher Hc⊥ from the initial growth region to that of a surface may be the key technology for preparing perpendicular magnetic recording layers at ultrahigh density above 20 Gbit/in.2
Magnetoresistance in glass-coated Fe–Ni–Cu microwires
Authors: Wang K.-Y. , Feng L. , O’Connor C. J. , Tang J. , Chen D.-X. , Vazquez M. , Hernando A.
Published: July 2002

Glass-coated Fe–Ni–Cu microwires were prepared by Taylor’s technique. X-ray diffraction data show patterns corresponding to fcc Cu. Negative magnetoresistance has been observed, which reaches 8.15% at 77 K and 6.35% at 300 K in magnetic field of 9.0 T. There is no significant difference between I⊥H and I∥H configurations. Both dc and low frequency ac (f<1 kHz) measurements exhibit essentially the same values of magnetoresistance. The observed magnetoresistance in the Fe–Ni–Cu microwires is of the same origin found in the granular giant magnetoresistance materials and is distinguishable from the giant magnetoimpedance commonly seen in soft magnetic microwires.
Inverse magnetoresistance in Fe/Si ion beam sputtered sandwiches
Authors: Dinia A. , Guth M. , Schmerber G. , Ounadjela K.
Published: July 2002

A series of Fe/Si sandwiches have been prepared by ion beam sputtering at room temperature onto glass substrate with the following nomenclature: Glass/Si20 nm/Fe5/6 nm/Fe5 nm/Ru2 nm. Magnetization measurements have been performed at 300 K and show no evidence of antiferromagnetic exchange coupling. However, the magnetoresistance curves recorded at 300 K are very interesting and show an inverse magnetoresistance for sandwiches with Si spacer layer thicknesses between 1.2 and 1.5 nm. The resistance is smaller at zero field than at saturation. This inverse magnetoresistance is due to the superparamagnetic interfaces and finds its origin in the difference of the electronic nature of the Fe/Si interfaces and Fe/Ru interfaces. Fe1−xSix iron silicide at Fe/Si interfaces has a scattering spin asymmetry ratio (α=ρ↓/ρ↑) larger than one, whereas, Fe with Ru impurities at the Fe/Ru interfaces presents a scattering spin asymmetry ratio smaller than one.
Low-temperature magnetization and thermoremanence of CoCl2⋅H2O
Authors: DeFotis G. C. , King H. A. , Bergman J. S. , Fuller Z. J. , Branch C. S. , Hammann J.
Published: July 2002

Reported here are field-cooled (FC) and zero-field-cooled (ZFC) magnetizations (MFC and MZFC, respectively) in smaller and larger fields than used in previous work, and thermoremanent magnetization data (TRM) for various temperatures and wait times. For fields of 12.8 and 0.1 G a separation between MFC and MZFC develops near 9 K, well below the 16.1 K magnetization maximum or the ∼14 K antiferromagnetic transition; thus, reentrant behavior occurs as for the higher fields used previously. Maxima in MZFC(T) are observed at 7.2 and 8.0 K for 12.8 and 0.1 G, respectively. Similar measurements in fields of from 3.0 to 15.5 kG show an evolution in the form of MFC(T) and MZFC(T); the separation between these develops at somewhat higher temperatures than 9 K and no maximum appears in MZFC. The field dependence of (MIRR/H)MAX, where MIRR=MFC−MZFC, is determined and shows a change in regime between 2 and 3 kG. The TRM as a function of time is measured for temperatures of 1.6, 4.3, and 5.8 K, with wait times ranging from 10 to 500 min. The relaxation rate is quite small, consistent with glassy dynamics with a wide distribution of relaxation times, and increases with increasing temperature. Remarkably, however, aging effects are absent even at 5.8 K, although this is 69% of the splitting temperature between MFC and MZFC. An explanation may reside in randomized antiferromagnetic couplings between chemical chains which are individually ordered ferromagnetically, and in the formation of a structure of almost independent clusters.
Spin dynamics and energy gap of a Fe dimer from susceptibility and 1H nuclear magnetic resonance
Authors: Lascialfari A. , Tabak F. , Abbati G. L. , Borsa F. , Corti M. , Gatteschi D.
Published: July 2002

The iron(III) S=5/2 dimer [Fe(OMe)(dbm)2]2 (in short Fe2) has a nonmagnetic S=0 ground state. The separation between the singlet ground state and the first excited (triplet) state is determined from susceptibility measurements to be about 22 K; for a dimer this value is equal to the antiferromagnetic exchange constant J. Proton nuclear magnetic resonance measurements were performed on Fe2. The nuclear spin-lattice relaxation rate (NSLR) was studied as a function of temperature at 31 and 67 MHz and as a function of the resonance frequency (10–67 MHz) at T=295 K. At room temperature the 1H NSLR is independent of frequency contrary to the strong dependence found in planar ring compounds like Fe6 and ferric wheel (Fe10). The temperature dependence of the proton NSLR shows an exponential decrease on lowering the temperature from which we estimate a gap value about double the value obtained from the uniform susceptibility, a result which is unexpected if the NSLR were simply proportional to the concentration of dimers in the triplet excited state.
Preparation of soft, anisotropic sendust films in the as-deposited state
Authors: Dodd P. M. , Atkinson R. , Salter I. W. , Araghi M. S. , Gamble H. S.
Published: July 2002

FeSiAlN films have been prepared by N2 reactive deposition from a sendust target by rf magnetron sputtering. Films show excellent magnetic properties in the as-deposited state with well-defined in-plane uniaxial anisotropy, which is highly desirable from a device perspective. Coercivity values of less than 0.5 Oe along the hard-axis direction were measured in 200 nm thick films. Magnetic properties were found to vary with nitrogen and argon flow rate ratio with optimum magnetic properties being produced using 0.2%–1.0% N2 in the sputter gas. Films sputtered in pure Ar showed high coercivity and grains appear to cluster together. The nitrided films by comparison had a drastically reduced coercivity, smaller grain size, and no grain clustering was present. Coercivity was found to increase with film thickness and anisotropy was less pronounced in films thicker than 500 nm. Cross-sectional transmission electron microscopy of thick sendust films showed a clear change in growth morphology with a columnar microstructure being formed above 500 nm.
The effect of oxygen on magnetic properties and corrosion resistance of Fe–N thin films
Authors: Xu Dong , Cai Bingchu , Chen Xuidong , Ding Guifu , Zhang Mingsheng
Published: July 2002

The effect of oxygen and heat treatment on magnetic properties and corrosion resistance of Fe–N thin films sputter-deposited under various N2+O2 partial pressure were investigated. All the as sputtered films have a single phase of α-Fe only, except where a high N2+O2 partial pressure was used. After annealing at 200–500 °C, the structure and magnetic properties of Fe–N–O films were changed. Under suitable conditions the magnetic properties of Fe–N–O films were found to have Hc of 0.5 Oe and 4πMs around 20 kG. It is also demonstrated that the oxygen has improved the corrosion resistance and thermal stability of Fe–N thin film.
Magnetostriction and soft magnetic properties of (Co1−xFex)–Al–O granular films with high electrical resistivity
Authors: Ohnuma S. , Kobayashi N. , Masumoto T. , Mitani S. , Fujimori H.
Published: July 2002

We have investigated the magnetic properties of (Co1−xFex)–Al–O granular thin films prepared by a reactive sputtering method in an atmosphere of O2+Ar. The coercivity and electrical resistivity of the films are almost independent of x, but with increasing x the anisotropy field decreases linearly and the saturation induction has a broad maximum of 20 kG around x=0.7. The granular films show the same general tendency as bulk Co–Fe alloys in the compositional dependence of magnetostriction (λ). The magnitude of λ varies with increasing annealing temperature. Using a film with x=0.08 as the core of a spiral-wound inductor gave a quality factor Q=25 at a frequency of 300 MHz.
Effect of nitrogen on the properties of sputter deposited NiFeRe films
Authors: Al-Jibouri A. , O’Kane W. , Peranjapie A. , Schwartz P.
Published: July 2002

Bias layers for soft adjacent biased magnetoresistance (MR) heads require low coercivity, high permeability magnetic materials that can be magnetized easily by a current in the adjacent MRE layer. While the advantage of (SAL) MR heads include the ability to adjust the bias field by optimizing the bias current, a major disadvantage of this biasing technique is arises from electrical shunting due to the finite electrical resistivity of the SAL material. The introduction of N2 in the deposition ambient was found to increase the electrical resistivity, and decrease both anisotropy and saturation magnetization of the films. The increase in resistivity was attributed primarily to a decrease in the grain size of the films. As a result a series of NiFeRe films for SAL biased MR heads were deposited by radio frequency diode sputtering in a series of N2 containing ambient atmospheres.
Observation of ferromagnetic resonance in the time domain
Authors: Hicken R. J. , Wu J.
Published: July 2002

Optical pump–probe spectroscopy has been used to observe damped ferromagnetic resonance (FMR) oscillations in thin film Fe samples. The FMR was pumped by magnetic field pulses generated by an optically triggered photoconductive switch, and probed by means of time resolved measurements of the magneto-optical Kerr rotation. The photoconductive switch structure consisted of a parallel wire transmission line, of 125 μm track width and separation, defined on a semi-insulating GaAs substrate. The biased transmission line was optically gated at one end so that a current pulse propagated along the transmission line to where the sample had been overlaid. The magnetic field associated with the current pulse is spatially nonuniform. By focusing the probe beam on the sample at different points above the transmission line the effect of the orientation of the pump field has been studied. The gyroscopic motion of the magnetization has been modeled by solving the Landau–Lifshitz–Gilbert equation and the magneto-optical response of the sample has been calculated by taking account of both the longitudinal and polar Kerr effects. The calculated and measured magneto-optical Kerr rotations are found to be in reasonable agreement.
Study of magnetization reversal mechanism of very thin film with perpendicular magnetic anisotropy by means of the anomalous Hall effect
Authors: Nakagawa Shigeki , Takayama Kazuhisa , Sato Atsushi , Naoe Masahiko
Published: July 2002

In this study, magnetization reversal of a Co–Cr very thin film with rectangular area of 1.0×1.0 cm2 was observed by means of the anomalous Hall effect. The amplitude of the Hall voltage VH took the maximum and minimum values when magnetic field was applied perpendicular and parallel to the film plane, respectively. The hysteresis loop observed in perpendicular direction exhibited the largest lean for the film deposited at substrate temperature Ts of 100 °C. It was found that for the film with a large perpendicular magnetic anisotropy constant, VH is independent to the angle of applied field. The Hall loop of the Co–Cr film 150 Å thick revealed its shape more similar to a Kerr loop than a vibrating sample magnetometer loop. The VH–H measurement is useful to evaluate the magnetization process of very thin films without the perturbation of the magnetization component from the substrates and the specimen folder in the measurement system especially for the case of obliquely applied magnetic field condition.
Magnetic reversal of tapered permalloy bars with holes in the center
Authors: Merton C. , Skidmore G. D. , Schmidt J. , Dahlberg E. D. , Wan H. , Pant B.
Published: July 2002

The magnetic reversal mechanism of tapered permalloy bars with holes in the center was studied using a Magnetic Force Microscope with in situ magnetic field capability. The samples studied were lithographically patterned from a 20-nm-thick NiFe film using a subtractive process to create tapered bars 18 wide×348 μm long. The easy axis of the permalloy is parallel to the long axis of the bar. In the center of the tapered bar was either a 10, 5, or 3 μm diameter hole. The remnant state after saturation parallel to the long axis of the bar is a large domain magnetized along the saturating field direction except near the hole. The magnetization at the edge of the hole can be explained by considering edge pinning and the last direction of a saturating magnetic field. An inplane magnetic field parallel to the long axis of the bar reverses the magnetization by domain nucleation at the edge of the hole. After the bar has reversed, the same type of wall structure is seen as in the remnant state. As the magnetic field is increased further, the magnetization rotates away from parallel to the edge of the hole, as seen by the emergence of surface poles along the hole edge.
Effects of Co substitution on magnetic properties of Pr3(Fe1−xCox)27.5Ti1.5 (x=0–0.3)
Authors: Shah V. R. , Markandeyulu G. , Rama Rao K. V. S. , Huang M. Q. , Sirisha K. , McHenry M. E.
Published: July 2002

X-ray diffraction carried out on random and oriented samples of Pr3(Fe1−xCox)27.5Ti1.5 (x=0, 0.1, 0.2, 0.3) showed that the easy magnetization direction is near the b axis for x=0, 0.2, and 0.3 and is almost along the b axis for x=0.1. Magnetic hysteresis data taken on oriented samples showed that the anisotropy field (HA) varies from 12 kOe for x=0 to 25 kOe for x=0.3 at 300 K. At 10 K, HA increases from 55 kOe for x=0.1 to 70 kOe for x=0.3. An indication of spin reorientation transition has been observed at ∼250 K in x=0.3.
Magnetic properties of Fe/Tb multilayers with large Fe layer thickness
Authors: Freitag A. E. , Chowdhury A. R.
Published: July 2002

Fe/Tb multilayers that display significant perpendicular magnetic anisotropy (PMA) up to an Fe layer thickness of 55 Å have been fabricated and examined for the first time (to the best knowledge of the authors). Two series of Fe/Tb multilayer samples with a wide range of Fe layer thickness ranging between 8 and 55 Å and with constant Tb layer thickness of 6.5 and 11.5 Å were fabricated by planar magnetron sputtering. The magnetic and structural properties of these samples were examined using x-ray diffraction, Mössbauer spectroscopy, and torque magnetometry. Mössbauer spectra show PMA of the Fe magnetic moments for samples that consist of Fe layers and mixed interfaces only. The formation of an unmixed Tb layer starting at about 12 Å Tb layer thickness leads to parallel alignment of the Fe magnetic moments. PMA in such multilayers is induced by a mixed interface and maintained by the exchange interaction between adjacent Fe layers. The interfaces that induce PMA in Fe/Tb multilayers are very close in composition to that of TbFe2 for which maximum PMA was found in thin amorphous Fe–Tb films.
Highly oriented perpendicular Co-alloy media on Si(111) substrates
Authors: Gong Heng , Rao Maithri , Laughlin David E. , Lambeth David N.
Published: July 2002

CoCrPt/Ti/Ag films with the easy axes of the hexagonal-closed-pack Co grains perpendicular to the film plane were epitaxially grown on HF-etched Si(111) single crystal substrates by rf sputter deposition. The orientation relationship was determined by x-ray pole figure measurements and transmission electron microscopy to be CoCrPt(0001)[101̄0]∥Ti(0001)[101̄0]∥Ag(111)[112̄]∥Si(111)[112̄]. The magnetic properties of the CoCrPt films were greatly improved by introducing these single crystal templates. Rocking curve measurement showed a greatly improved c-axis orientation of the cobalt alloy. Highly oriented, high coercivity properties for perpendicular recording have been obtained.
Effects of CoCrZr seed layer on noise properties and microstructure of CoCrPt media
Authors: Kanbe T. , Tamai I. , Takahashi Y. , Tanahashi K. , Ishikawa A. , Hosoe Y.
Published: July 2002

We have developed a nonmagnetic (CoCr30)Zrx [x=7, 10, 14 at. %] seed layer for CoCrPt glass media and have compared its structural and noise properties to those of the media with a Ta/Zr dual seed layer, which have lower media noise than the media with a Cr seed layer. The media with a (CoCr30)Zr10 seed layer had lower media noise than that with the Ta/Zr dual seed layer, which is attributed to reduced grain size in the magnetic layer. However, the media noise increased drastically owing to a 78% increase of the grain size in the magnetic layer when the Zr content in the seed layer increased from 10 to 14 at. %. The transmission electron microscope analysis indicates that the (CoCr30)Zr10 seed layer has a nanocrystalline structure, while (CoCr30)Zr14 was almost amorphous. This would be the main reason of the drastic change in the grain size of the magnetic layer. The microstructure of the CoCrZr seed layer is very sensitive to the Zr content and strongly affects the microstructure of the magnetic layer and thereby media noise.
Effect of inter-granular exchange coupling on read/write properties in thin film recording media affected by thermal fluctuation
Authors: Nakatani Y. , Hayashi N. , Uesaka Y. , Fukushima H.
Published: July 2002

The effect of thermal fluctuation and inter-granular exchange coupling on longitudinal and perpendicular magnetic recording media is investigated by computer simulation. It is found from the calculation of magnetic characteristics that the change in Hc due to thermal fluctuation can be suppressed by inter-granular exchange interaction in perpendicular recording media, but it can not be suppressed in longitudinal recording media. It is found from the calculation of read/write characteristics that magnetization states recorded in longitudinal recording media are affected by thermal fluctuation sooner with the increase in the inter-granular exchange coupling, while the magnetization states recorded in perpendicular recording media is found to become less sensitive to thermal effect when the inter-granular exchange coupling is increased.
Magnetostrictive bending of an anisotropic free crystal substrate: Analytical and numerical solutions
Authors: Farber P. , Hörmann M. , Bischoff M. , Kronmüller H.
Published: July 2002

A model to calculate the effective elastic modulus of a single crystal cantilever used as a substrate for magnetostrictive measurements of thin films is given. Calculations are presented for Si (110), sapphire (11̄00) (M plane) and (12̄10) (A plane) cantilevers. Numerical calculations using the finite element method for sapphire show a very high accuracy of the proposed model.
Isotropic dielectric functions of highly disordered AlxGa1−xInP (0⩽x⩽1) lattice matched to GaAs
Authors: Schubert M. , Woollam J. A. , Leibiger G. , Rheinländer B. , Pietzonka I. , Saß T. , Gottschalch V.
Published: July 2002

Determination of the complex dielectric function and the critical-point energies of (AlxGa1−x)0.51In0.49P, over the full range of composition x and for photon energies E from 0.75 to 5 eV is reported from variable angle of incidence spectroscopic ellipsometry. Native-oxide effects on the (AlxGa1−x)0.51In0.49P optical functions are removed numerically. The highly disordered state of the metalorganic vapor-phase epitaxy grown samples is analyzed by transmission electron microscopy. Optical anisotropy investigations revealed that the order-induced optical birefringence is negligible throughout. The augmentation of A. D. Rakić and M. L. Majewski [J. Appl. Phys. 80, 5909 (1996)] to Adachi’s critical-point model, i.e., consideration of Gaussian-like broadening function instead of Lorentzian broadening, is used for calculation of the isotropic (AlxGa1−x)0.51In0.49P dielectric function ∈. The optical functions spectra consistently match the experimental data, whereas previously reported model dielectric functions fail to reproduce the correct absorption behavior of the quaternary, especially near the fundamental band-to-band transition. The results are compared to those presented previously, and influence of spontaneous chemical ordering is discussed.
A quantitative analysis of stress-induced leakage currents and extraction of trap properties in 6.8 nm ultrathin silicon dioxide films
Authors: Endoh Tetsuo , Chiba Takao , Sakuraba Hiroshi , Lenski Markus , Masuoka Fujio
Published: July 2002

An analytical model for the quantitative analysis of stress-induced leakage currents (SILC) in ultrathin silicon dioxide films is described, which enables the extraction of trap parameters, e.g., trap site location. Assuming a two-step trap-assisted inelastic tunneling mechanism, the conduction of electrons through the silicon dioxide film proceeds as follows: First, electrons tunnel from the cathode into neutral trap sites followed by an energy relaxation into the lowest available energy state of these trap sites. Finally, the electrons reach the anode by a direct tunneling process. We applied this model to the SILC characteristics of a stressed 6.8 nm ultrathin silicon dioxide film. The following parameters could be deduced: The trap sites are located at 4.47 nm relative to the cathode interface with a trapped sheet charge density of |6.54×10−8| C/cm2, and a trap state energy of 2.3 eV relative to the conduction band edge of the silicon dioxide.
Micromagnetics simulation of nanoshaped iron elements: Comparison with experiment
Authors: Dao N. , Homer S. R. , Whittenburg S. L.
Published: July 2002

A micromagnetics simulation has been conducted on nanostructured magnetic elements of iron in order to investigate the effect of the shape of the element on magnetic properties, such as domain formation and hysteresis loops. These results are compared with recent experimental studies. The results display an impressive agreement with both the experimentally observed magnetic domains in individual particles as well as the shape of the hysteresis loops. The simulation results then explain features in the hysteresis loops in terms of vortice formation and motion.
Transparent stacked organic light emitting devices. II. Device performance and applications to displays
Authors: Gu G. , Parthasarathy G. , Tian P. , Burrows P. E. , Forrest S. R.
Published: July 2002

Vertical stacking of organic light emitting devices (OLEDs) that emit the three primary colors is shown to be a means for achieving efficient and bright full-color displays. In Paper I, we addressed stacked OLED (SOLED) design and fabrication principles to optimize emission colors, operating voltage, and efficiency. Here, we present results on two different (metal-containing and metal-free cathode) SOLED structures that exhibit performance suitable for many full-color display applications. The operating voltages at 10 mA/cm2 (corresponding to video display brightnesses) are 6.8, 8.5, and 12.1 V for the red (R), green (G), and blue (B) elements of the metal-containing SOLED, respectively. The respective subpixel luminous efficiencies are 0.53, 1.44, and 1.52 cd/A, and the Commission Internationale de L’Éclairage (CIE) chromaticity coordinates are (0.72, 0.28), (0.42, 0.56), and (0.20, 0.22). In the high transparency metal-free SOLED, an insulating layer was inserted between the two upper subpixels to allow for independent grounding of all color emitters in the stack. At operating voltages of 12–14 V, video display brightnesses were achieved with luminous efficiencies of 0.35, 1.36, and 1.05 cd/A for the R, G, and B subpixels, respectively. The respective CIE coordinates for R, G, and B emissions are (0.72, 0.28), (0.26, 0.63), and (0.17, 0.28) in the normal viewing direction, shifting inperceptibly as the viewing angle is increased to as large as 60°. Finally, we discuss addressing schemes of SOLED displays, and compare them with other strategies for achieving full-color, OLED-based displays.
Memory effect and temperature behavior in spin valves with and without antiferromagnetic subsystems
Authors: Li Y. F. , Yu R. H. , Dimitrov D. V. , Xiao John Q.
Published: July 2002

Temperature behavior and memory effect in standard spin valves (SV) and SVs with synthetic antiferromagnetic (Co/Ru/Co) (SV-SAF) subsystems have been studied. SV-SAFs show much better temperature stability. Memory effect refers to the phenomenon that the exchange bias can be altered at temperatures (TR’s) much lower than the blocking temperature (TB), and these temperatures (TR’s) are imprinted into SVs. The memory effect greatly deteriorates the magnetoresistance behaviors in SV. Our results suggest that the memory effect is caused by a distribution of local blocking temperatures (Tb’s). The magnetization state in the pinned layer is critical in determining the temperature behavior of HE and magnetoresistance. By partially reversing the magnetization in the pinned ferromagnetic (FM) layers, we are able to separate the temperature dependencies of the local exchange bias (He) associated with regions consisting of different Tb’s. Two features have been observed: (1) the local exchange bias (He) with a narrow Tb distribution has a weak temperature dependence; (2) the simple algebraic sum of local He’s nearly reproduce the total HE with the difference between these two quantities representing the domain wall energy in the FM layer. On the other hand, SV-SAFs show strong resistance to memory effects because of two factors; the strong exchange coupling through the Ru layer, and the net magnetic moment of Co/Ru/Co layers in SV-SAF being close to zero. The former makes the two SV-SAF FM layers behave coherently, while the latter makes the interaction between the SV-SAF and the external field negligibly small.
Grain-size effect on pressure-induced semiconductor-to-metal transition in ZnS
Authors: Jiang J. Z. , Gerward L. , Frost D. , Secco R. , Peyronneau J. , Olsen J. S.
Published: July 2002

The grain-size effect on the semiconductor-to-metal transition in ZnS has been investigated by in situ high-pressure electrical resistance and optical measurements. It is found that the grain-size effect can elevate the transition pressure of ZnS in a larger pressure range. On the basis of the results obtained and results reported in the literature, we demonstrate that the dangers of using the transition pressures of the II–VI compounds as pressure calibrators without a detailed knowledge of their grain-size effects on the transition pressures cannot be overstressed.
Depth profile of the implantation-enhanced intermixing of Ga+ focused ion beam in AlAs/GaAs quantum wells
Authors: Eshlaghi Soheyla , Meier C. , Suter Dieter , Reuter D. , Wieck A. D.
Published: July 2002

The implantation-induced intermixing depth profile for 100 keV Ga+ ions was determined by photoluminescence measurements on a series of samples containing quantum wells at variable depth from the surface but identical thickness. They were uniformly implanted and subsequently a rapid thermal annealing was applied. The measured maximum of the intermixing occurred at a depth of about 70 nm, significantly deeper than theoretical predictions. These results are important for achieving sufficient intermixing with a low implantation dose, thereby optimizing crystal quality and lateral resolution.
Emitter-base bias dependence of the collector current ideality factor in abrupt Pnp AlGaAs/GaAs heterojunction bipolar transistors
Authors: Ekbote S. , Cahay M. , Roenker K.
Published: July 2002

Starting with the 4×4 Luttinger–Kohn Hamiltonian and making use of the axial approximation, we calculate the emitter current as a function of the applied forward emitter-base bias for a typical Pnp AlGaAs/GaAs single heterojunction bipolar transistor (HBT). While including the effects of emitter series resistance and recombination in the quasi-neutral base and emitter-base space-charge region, we then calculate the collector current density versus emitter to base bias and find it to be in excellent agreement with the experimental results for a Al0.4Ga0.6As/GaAs Pnp HBT recently reported in the literature. For that structure, the collector current ideality factor is found to increase from 1.1 at low forward bias VEB to 3.0 at large applied emitter-base forward bias approaching the built-in potential. Experimental values are equal to 1.2 and 2.25 at low and large VEB, respectively.
Ballistic electron emission microscopy of Au/n-ZnSe contacts and local density of states spectroscopy
Authors: Chahboun A. , Coratger R. , Ajustron F. , Beauvillain J. , Dharmadasa I. M. , Samantilleke A. P.
Published: July 2002

Ballistic electron emission microscopy (BEEM) has been used to investigate the Au/n-ZnSe contact at high voltage. A statistical barrier height value of 1.63±0.05 eV is obtained. The metal–insulator–semiconductor structure is invoked to explain domains of low electron transmission. Features appear in BEEM spectra at higher voltages and can be attributed to the density of empty states in the semiconductor. Impact ionization effects are observed when the electron kinetic energy exceeds the band-gap energy.
Magnetoresistance of La0.5Sr0.5MnO3 nanoparticle compact
Authors: Wang Zhi-Hong , Ji Tian-Hao , Wang Yi-Qian , Chen Xin , Li Run-Wei , Cai Jian-Wang , Sun Ji-Rong , Shen Bao-Gen , Yan Chun-Hua
Published: July 2002

Magnetization, resistance, and current–voltage (I–V) measurements have been performed in La0.5Sr0.5MnO3 compact prepared by pressing sol-gel nanoparticles (46 nm) at 723 K with a high pressure (4 GPa). The pressed compound orders ferromagnetically at 340 K (TC) and has a substantial drop in the thermomagnetic curve below 158 K (TDP). After undergoing a metal–to–semiconductor transition at 140 K (TMS), the compound reenters into a strong semiconducting state below 60 K, demonstrating a charge localized behavior induced by the small grain rather than the magnetic disorder which is related with the frozen spin clusters below TDP. Instead of showing a feature near TMS, the magnetoresistance (MR) ratio increases almost linearly with decreasing temperature. The large low field MR corresponding to the sharp rise of magnetization is obtained at 5 K and, evidenced as the spin polarized intergrain tunneling (SPIT) effect by the nolinear I–V curve. Although La0.5Sr0.5MnO3 has a relatively high TC, the SPIT MR decays rapidly from 17.6% (5 K, 0.3 T) to 7.6% (150 K, 0.3 T), indicating that if trying to put the low field sensitivity of SPIT MR into application at room temperature, the selected compound having a higher TC seems to be a prerequisite.
Magnetically based sensorless switched reluctance drive for general purpose applications
Authors: Al-Bahadly Ibrahim H.
Published: July 2002

Shaft position transducers are commonly used to provide rotor position information for commutation of the switched reluctance (SR) motor and for excitation control. However, in low cost applications such as fans and pumps, particularly at low power levels, the shaft position sensor is too costly. Therefore, a simple sensorless position drive system is preferred. It is the aim of this article to present a simple sensorless rotor position measurement for a SR using the magnetization data of the motor windings. The proposed method is based on estimating a particular rotor position on a phase by phase basis and measuring flux linkage and current when the estimated position is reached. By comparing the measured flux linkage with the prestored flux linkage corresponding to the particular position for the measured current, the angular difference between the estimated position and the particular position can be calculated. The proposed sensorless SR drive system has been tested in the laboratory and its output performance was compared to the output of commercial system based on an optical sensor.
Transport properties of R6Fe11Al3 compounds (R=La,Nd)
Authors: Wang Fangwei , Zhang Panlin , Shen Bao-gen , Yan Qiwei , Gong Huayang
Published: July 2002

The different temperature-dependent resistivity has been observed in the compounds R6Fe11Al3 (R=La,Nd) with tetragonal Nd6Fe13Si type structure: ρ=1.0×10−5+4.85×10−6 T0.2Ω m for R=La and ρ=1.0×10−5+7.62×10−7 T0.5Ω m for R=Nd, respectively, while the residual resistivity has a same value. About 4% negative magnetoresistance is obtained in Nd6Fe11Al3 at 5 K in a field of 6 T, but no magnetoresistance in La6Fe11Al3.
Effect of CoFe composition of the spin-valvelike ferromagnetic tunnel junction
Authors: Kikuchi H. , Sato M. , Kobayashi K.
Published: July 2002

The magnetoresistance (MR) ratio of a ferromagnetic tunnel junction with a spin-valvelike structure of NiFe/CoFex/Al–O/CoFex/NiFe/IrMn/Al is dependent upon CoFe composition. MR ratio increases with increasing Fe content, and shows a maximum of 42% for Fe content 26 at. % after annealing at 225 °C. Before annealing, the bias voltage dependence depend on Fe content, however, the bias voltage dependence did not depend on Fe content after annealing. We think that the increasing defect states in the barrier layer with the increasing Fe content in CoFex layer cause the degradation of the bias voltage dependence. After annealing, the defect states of samples decrease to same level, and the bias voltage dependencies of samples are improved and become same.
Comparison of oxidation methods for magnetic tunnel junction material
Authors: Chen E. Y. , Whig R. , Slaughter J. M. , Cronk D. , Goggin J. , Steiner G. , Tehrani S.
Published: July 2002

Advances in reducing the resistance and enhancing the magnetoresistance (MR%) of the magnetic tunnel junction (MTJ) material has made it useful for magnetoresistive random access memory as well as magnetic field sensing applications. One of the most important aspects for producing the MTJ material is the method used for forming the tunnel barrier, and its impact on the properties of MTJ such as resistance and area product (RA), MR%, and RA uniformity across a large area. We have explored forming the aluminum oxide tunnel barrier with air; reactive sputtering; plasma oxidation with plasma source; plasma oxidation with power introduced from the target side; and plasma oxidation with power introduced from the substrate side. Our results show that all techniques can be made to work. Plasma oxidation is favored due to its simplicity and manufacturing compatibility. It was also discovered that different oxidation methods used in this study caused little difference in MTJ resistance uniformity. The latter is mainly determined by the Al metal-thickness uniformity. Modeling based on Simmons’ theory supports our experimental finding. This illustrates the importance in improving Al metal-film uniformity for producing MTJ with ultra-uniform resistance.
Magnetic anisotropy of Co/Cu(001) caused by Cu coverage
Authors: Gavrilenko V. I. , Wu Ruqian
Published: July 2002

Magnetocrystalline anisotropy energies of the Co/Cu(001) and Cu/Co/Cu(001) systems are studied using the full potential linearized augmented plane wave method. We systematically compare the results obtained by using the generalized gradient approximation (GGA) for the exchange-correlation energy/potential and the local density approximation (LDA) methods. The GGA MCA energy differ remarkably from the LDA data even for the same structural input.
The surface terminal layer and composition of the colossal magnetoresistance perovskite: La0.65Pb0.35MnO3
Authors: Borca C. N. , Ristoiu Delia , Xu Q. L. , Liou S.-H. , Adenwalla S. , Dowben P. A.
Published: July 2002

The composition in the surface region of the colossal magnetoresistance perovskite manganite materials, La0.65Pb0.35MnO3 has been studied using angle resolved x-ray photoemission spectroscopy. The results are consistent with a Mn–O terminal layer and Pb segregation to the near-surface region. This is similar to the behavior exhibited by La0.65Ca0.35MnO3 and La0.65Sr0.35MnO3. The O–Mn–O terminal layer appears to be close to the Mn3+ valence state.
A study of interface dynamics for stiction-free slider and super-smooth disk
Authors: Zhu Yao-Long , Liu Bo , Hua Wei , Sheng Gang , Yamamoto Takayuki
Published: July 2002

This paper reports results of experimental investigations into the head–disk interface dynamics for the combination of the stiction free slider with super-smooth disk and the influences of disk roughness and lubricant thickness on the flying performance of stiction-free slider. The experiments were carried out with an optical head–disk interaction tester with which the tribologically interface used in the tester is still identical to the actual disk drive case The results indicate that the pad height on the air-bearing surface of the slider is one of the key parameters that determines the take-off and landing velocity of the slider. The flying performance of the slider strongly depends on the lubricant thickness when the disk speed is around the take-off velocity.
A study of dynamic friction at the head–disk interface
Authors: Tang Huan , Wang Li-Ping , Gui Jing , Kuo David
Published: July 2002

With its precisely controlled contact geometry, the head–disk interface with laser zone texture affords a model system for the study of dynamic friction. By using two types of head sliders, i.e., the conventional slider and the padded slider, and a matrix of hard disks with a wide range of laser zone texture parameters, head–disk contacts involving a small number as well as a large number of bumps are realized. A rich variety of dynamic friction behavior is observed with respect to bump height and bump density dependence. A satisfactory explanation of these friction behaviors requires that both the deformational component and the adhesive component of friction be considered on equal footings.
Hard disk lubricant conformation and distribution via angle-resolved ESCA
Authors: Karplus M. A. , Waltman R. J. , Pocker D. J.
Published: July 2002

Lubricant distribution on test disks for hard drives has been examined with angle-resolved ESCA. The lubricant partitions itself into thin, presumably monolayer, areas and thicker patches largely impenetrable to the substrate photoelectrons. These thicker regions are at least three times as thick as the monolayer and may correspond to the trilayers detected by surface energy and ellipsometric surface diffusion measurements. Detailed examination of layering within the lubricant shows significant perfluoropolyether (Zdol) backbone and a discernible excess of ether oxygen adjacent to the overcoat surface. The latter results indicate that the inverted-U conformation sometimes sketched for bonded lubricants is an exaggeration for the system examined here. The analysis models include a two-tiered overlayer structure (thin and thick) and a two-slab structure for revealing subtle layering within the thin regions. Current office spreadsheets provide adequate visualization and optimization capability for performing these analyses.
Origin of line broadening in Co-substituted NiZnCu ferrites
Authors: Byun Tae Young , Byeon Soon Cheon , Hong Kug Sun , Kim Chang Kyung
Published: July 2002

A systematic variation in linewidth with Co concentration at the X band (9.38 GHz) was observed in polycrystalline Co-substituted NiZnCu ferrites. Also, the temperature dependence of the linewidth and complex permeability were measured for two different Co concentrations. The linewidth shows a minimum with Co concentration. The contribution of porosity, magnetic anisotropy, and eddy current to line broadening was calculated. The line broadening due to eddy current was negligible and the line broadening due to porosity and magnetic anisotropy explain well the variation of linewidth with Co concentration. The temperature at which the linewidth increases rapidly increases with Co concentration. This temperature is consistent with the temperature of the second maximum peak in the temperature dependence of permeability. Therefore, the rapid increase in linewidth with temperature is attributed to the rapid increase in magnetocrystalline anisotropy of divalent cobalt ions.
Achieving optimum loop shapes in quaternary Pr–Co alloys
Authors: Branagan D. J. , Kramer M. J. , Tang Yali , McCallum R. W.
Published: July 2002

The magnetic properties and microstructures of a quaternary Pr–Co–Ti–C alloy were investigated. After heat treating at 800 °C, the quaternary alloy developed high coercivity (16.7 kOe) and high energy product (8.6 MGOe). Hysteretic loop shapes exhibiting single-phase magnetic character were achieved which was a problem which previously plagued development of Pr–Co alloys. The optimum microstructure contained 75–100 nm Pr1Co5 hard magnetic grains, 75–100 nm Pr1Co2 second phases, and <10 nm TiC grain boundary precipitates. The important factors in achieving optimum loop shapes in Pr–Co alloys were examined in detail.
Epitaxial nanomagnets with intrinsic uniaxial in-plane magnetic anisotropy
Authors: Zölfl M. , Kreuzer S. , Weiss D. , Bayreuther G.
Published: July 2002

High quality epitaxial Fe films were grown on GaAs(001) by molecular beam epitaxy and magnetron sputtering. Two-dimensional arrays of circular dots with 200 nm diameter and 500 nm period were made by interferometric lithography and ion beam etching. Large area patterning (about 1 cm2) allows integral magnetic measurements with an alternating gradient magnetometer. The magnetic behavior of thick patterned films is dominated by the demagnetizing field. Ultrathin continuous films and dot arrays of these show a strong uniaxial in-plane magnetic anisotropy with the easy axis in [110] direction which is fully conserved during the patterning process. This means that two stable remanent single domain states exist in ultrathin Fe(001) sub-μm dots on GaAs(001) because (i) the magnetostatic energy is not important due to the small aspect ratio, and (ii) the Fe/GaAs(001) interface creates a strong uniaxial in-plane magnetic anisotropy. Nanomagnets with these properties seem very attractive for high density memory elements.
High frequency effects in perpendicular recording media
Authors: Greaves S. J. , Muraoka H. , Sugita Y. , Nakamura Y.
Published: July 2002

Simulations of perpendicular recording media were carried out to determine the effect of switching speed limitations upon recording performance. Simulations of hysteresis loops at various applied field sweep rates show that the onset of a switching speed limited increase in coercivity occurs for sweep rates in excess of 2×1013 Oe/s. Switching speeds of individual grains were found to be around 18 to 38 ps, depending on the medium thickness and the magnetization state of surrounding grains. Recording simulations show that for media thicknesses of up to 180 Å, writing frequencies of 5 Gbit/s are feasible before loss of output occurs.
Designing a giant magnetoresistance field sensor via inferences from a giant magnetoresistance hysteresis model
Authors: Sablik M. J. , Beech R. S. , Tondra M.
Published: July 2002

By using a model for giant magnetoresistance (GMR) hysteresis and a model for Barkhausen noise, a magnetic hysteresis model is used to map the effects of magnetic hysteresis on GMR and on accompanying magnetic noise in a GMR magnetic field sensor. Two magnetic noise sources potentially exist in the field sensor: (1) the GMR multilayer material and (2) permalloy field concentrators. The GMR material typically shows a coercivity at Hc≅1 kA/m, much larger than Hc=0.012 kA/m of permalloy. Because permalloy has a very large maximum permeability, it is a much larger magnetic noise source than the GMR material, and would greatly affect sensor operation if operated near H=0. By operating with a bias field well above 1 kA/m, one can operate away from both noise sources. Because the increasing and decreasing arms of the magnetic hysteresis tail of the GMR material are each approximately proportional to |H|1/2 over a large field range, the model shows that increasing and decreasing portions of the GMR vs H hysteresis curve turn out to be linear, parallel to each other, for the operating field region. If the GMR curve is linear in a region away from Hc, a bias field operation in this range would mean that the sensor would not only be nearly noiseless (save for Johnson noise) but also would exhibit linear change in field under an applied field H and could easily be calibrated to measure H. Thus, the modeling points the way to low noise GMR field sensor design. In practice, it is found that biasing at fields halfway down the GMR curve does indeed produce a much quieter measurement than near zero bias field.
Micromagnetic simulation of a flux guide for a read head with sub-100 nm resolution
Authors: Abelmann Leon , Zhu Jian-Gang , Bain James A. , Ramstöck Klaus , Lodder Cock
Published: July 2002

Large scale 3D micromagnetic simulations are performed on single pole read heads with pole tip cross sections of 45×45 and 100×200 nm. It is shown that tips with these dimensions have a much higher output than predicted by an analytical theory using the reciprocity theorem. The larger of these tips still behaves in a relatively soft manner and has an output waveform shape very close to the one predicted by the analytical model. The response of the small tip however is hysteretic.
Optical properties of ZnS1−xSex alloys fabricated by plasma-induced isoelectronic substitution
Authors: Rujkorakarn Rong , Nelson Art J.
Published: July 2002

Nonequilibrium growth of thin-film ternary ZnS1−xSex semiconductor alloys was accomplished using physical vapor deposition with simultaneous electron cyclotron resonance H2S plasma activation. Substrate temperature, gas flow, and plasma power determine the ZnS1−xSex alloy composition and structure. Integrated optical transmission spectra for the ZnS1−xSex semiconductor alloys as a function of H2S plasma power are presented. Using the α2 vs hν plots for the various ZnS1−xSex films, the optical band gap Eg is extrapolated from each curve. This methodology yields the values of the band gap as a function of stoichiometry. We observe that the plasma induced isoelectronic substitution of S into the ZnSe lattice increases the band gap. This study shows that plasma-induced isoelectronic substitution is technologically feasible and useful for fabricating ternary II–VI alloys under nonequilibrium conditions.
Magnetic properties of BaFe12−2xZnxZrxO19 particles
Authors: Wei F. L. , Fang H. C. , Ong C. K. , Wang C. S. , Yang Z.
Published: July 2002

ZnZr doped barium ferrite single domain particles BaFe12−2xZnxZrxO19 with 0⩽x⩽0.8 were prepared by the chemical coprecipitation method. With increasing doping concentration x, the magnetocrystalline anisotropy and thus the coercivity was drastically decreased. This was mainly due to the substitution of Fe3+ ions in the magnetoplumbite structure and strongly affected by the selective occupation of nonmagnetic cations on sublattice sites. Compared with coercivity, the zero-field saturation magnetization decreased much slower. The particle size decreased with x, while both of the lattice parameters “a” and “c” increased. The high-field differential susceptibility showed an increase with increasing doping concentration x, revealing the breakdown of the magnetic collinear structure and subsequently increased fraction of surface canted spins.