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Enhancement of exchange field (Hex) and thermal stability of the textured CoFe/IrMn with Os/Cu buffer layer and Os diffusion barrier layer were studied. As revealed by x-ray Diffraction (XRD), an Os (0002) surface mesh was observed to form on Cu (100)/Si (100). The growth of CoFe (111)/IrMn (111) on such a template is parallel to the Os (0002). With the Os/Cu buffer layer, the CoFe/IrMn presents an enhancement of 70 Oe on Hex larger than that without Os/Cu. The Hex of the textured sample was 230 Oe at room temperature and it was increased to 330 Oe after 250 °C annealing. When the temperature reached 350 °C, Hex vanished. The increment of the temperature at which the textured and the nontextured sample obtaining their maximum Hex and the vanishing temperature of Hex were 50 and 75 °C, respectively. Furthermore, the CoFe/Os (d)/IrMn slowed down the Hex degradation. The sample with d=0.3 nm obtained its maximum Hex at 250 °C and vanished when it reached 400 °C. The combination of CoFe/IrMn with Os/Cu buffer layer and Os barrier layer made the Hex higher and also better thermal stability. [ABSTRACT FROM AUTHOR]

The magnetization reversal behavior in half-ring NiFe structures and the influence of IrMn exchange bias layer was studied in this experiment. Two-step switching behavior, as in the ring shape, was observed when external field was in the short axis for single half-ring films. For NiFe–IrMn double layer structures, the unidirection anisotropy could be controlled by field cooling the samples. The exchange field strength did not follow a cosine curve when the external field was rotated in the sample plane. It could be attributed to the competition between the shape and the exchange anisotropies. When the strength of exchange field was strong, a single-step switching was observed. Two-step switching was retained for weaker exchange coupling. [ABSTRACT FROM AUTHOR]

Single layer CoPt thin films with thicknesses from 30 to 100 nm were sputtered on glass substrates. A preannealing at 250 °C for 80 min was applied to the samples, before ordering treatment at 700 °C for 10 min. This preannealing process resulted in a 33%–65% decrease in coercivity and 23%–55% decrease in volume fraction of order phase f0. Results of morphology investigation showed that the preannealing increases the surface roughness, which mainly results from the elimination of defects. Structural results further suggest that the eliminated defects are mostly low dimensional, such as dislocations or vacancies. It can thus be concluded that those low dimensional imperfections in the CoPt films play an enhancing role in ordering transformation process. [ABSTRACT FROM AUTHOR]

The magnetic properties and microstructure of ultrathin Co films grown on a Si(111)-7×7 surface were investigated. The experimental results observed by surface magneto-optic Kerr effect (SMOKE) and scanning tunneling microscopy show that the surface morphological evolution of x ML (monolayer) Co/Si(111) films is strongly related to their magnetic properties. Due to the formation of a CoSi2 layer, no magnetic signal could be detected by SMOKE for x=2.1. Both longitudinal and polar hysteresis loops appear for 4.2–8.5 ML Co/Si(111) films because of their rougher surfaces. When the Co thickness is increased to 11 ML, a magnetic hysteresis loop only occurs in the longitudinal configuration, which can be attributed to the contribution of volume anisotropy. After annealing an 11 ML Co/Si(111) film at 400 and 500 K, the surface becomes rougher, inducing magnetic anisotropy on the polar configuration. When the annealing temperature was increased to 600 K, however, the Co could react with Si to form a nonmagnetic cobalt silicide compound, and consequently, the hysteresis loops disappeared. [ABSTRACT FROM AUTHOR]

The aim of this paper was to design a micromagnetic bearing (MMB) motor for small form factor optical drives. A MMB motor was developed with inner and outer magnetic-ring stack structure of high permeability. These rings were arranged on the shaft above the permanent magnet of the rotor and the stator. The magnetic force between the MMB, the permanent magnet, and the stator induced the magnetic coupling effect that generated the demon friction torque loss. However, the loss was controlled well under 1.93×10-4 N m by the proposed approach, so that the good stable system was achieved. After suppressing the loss caused by the magnetic coupling effect, the shaft can be rotated without any frictional contacts in radial direction, the running current was around 0.18 A, and the maximum speed was around 1850 rpm. It shows that the MMB demonstrates the lower friction torque loss in comparison with the conventional microball bearing (MBB). Moreover, the radial vibration of our device is 21% lower than the conventional MBB type. To verify the performance of the provided system, both the computer simulation and the experiment were performed. [ABSTRACT FROM AUTHOR]

The uses of Os as an antidiffusion and buffer layer in IrMn exchange coupled CoFe film were investigated. For the purpose of antidiffusion, the inserted Os layer showed a distinct improvement of S>0.9, with HC slightly increasing by 1.6 times for the CoFe/Os/MnOs multilayer after 400 °C annealing, even though the Os thickness was as thin as 0.3 nm. Furthermore, with a 0.3 nm Os barrier, the 350 °C annealed CoFe/Os/IrMn/CoFe showed almost the same magnetic behavior as the as-deposited state, while the Hex of the upper part of the CoFe/Os/IrMn changed from 100 to 190 Oe. In addition, as a buffer layer, the Os buffer layer could enhance the diffraction peak intensities of IrMn(111)/Os(002) and CoFe (111), and the Hex of CoFe/IrMn was proportional to the Os thickness. A 120 Oe of Hex was achieved by using an 11 nm Os buffer layer in a CoFe 10 nm/IrMn 15 nm bottom type film. These results show that Os has the potential to be an antidiffusion and buffer layer in a magnetic multilayer. [ABSTRACT FROM AUTHOR]

With the rapid development of automation techniques, the claw-poled stepping motors are widely used, especially in optical scanners. Most research on stepping motors has concentrated on electrical properties, but a few papers have reported on the performance in relation to the magnetic-field distribution. The purpose of this study is to analyze the effect of the shape of the stator tooth and to search for the optimal parameters using a magnetic-circuit simulation technique. Through numerical calculations, the optimal performance conditions can be obtained by varying the ratio between the two bases of the trapezoid teeth between 1/5 and 1/3, and varying the ratio between the heights of individual teeth in relation to the separation between the two yokes from 11/15 to 13/15. [ABSTRACT FROM AUTHOR]

Magnetization reversal phenomena in submicron half-ring patterned wires with different corner structures have been investigated. The wires with corner structures of rectangular, semicircle, and triangular shapes were connected in series by two or five half-rings. The variation of domain structures with magnetic field is illustrated by electron transport measurements, simulation, and magnetic force microscopy (MFM) images. The switching behavior depends on the corner structures connecting the half-ring structures. These results are consistent with the domain pattern and magnetic phase shift observation provided by the MFM measurements. [ABSTRACT FROM AUTHOR]

Domain wall pinning force in the junctions (corners), with different shapes of square, semicircle, or triangle, of half-ring in-series wires is considered to study the current injection induced wall movements. This geometry has less thermal activation at the region of domain wall nucleation in contrast to notch structures. The wires with square corners have the largest domain pinning force to resist polarized current-induced magnetization reversal, judging from the largest slope in the current-field dependence (ΔI/ΔH=0.274). [ABSTRACT FROM AUTHOR]

Magnetic properties and crystal structure of the Fe49-xCoxPt51 (x=0.0,0.7,1.3,2.2) thin films deposited on a quartz substrate heated at 500 °C were investigated. A significantly enhanced energy product of 18.4 MG Oe (87% larger than that of the binary film) was obtained in the x=1.3 sample. This improvement can be attributed to the well exchange coupling between the Ll0 and the residual disordered FePt regions. Unlike the common exchange spring (coupled) magnets or films showing a well defined two-phase structure, the chemical ordering of Fe–Co–Pt films changes continuously from the ordered regions to the disordered regions. We consider that this continuous change of chemical ordering enhances exchange coupling. Furthermore, the addition of cobalt also accompanied the decrease of crystal domain (subgrain) size in FePt grains. The fine-grain dispersion also can be a reason for the high energy product. [ABSTRACT FROM AUTHOR]

In this study, we investigated the electron transport properties of interface between a ferromagnet and a superconductor with flowing current perpendicular to plan (CPP) at 4.2 K in Fe/Nb multilayers. The CPP resistance increased linearly with layer thickness and with bilayer number. We extracted the unit area resistance value of one pair of interface for superconducting and normal Fe/Nb by using a series resistor model. Hence, we can quantitatively analyze the interface resistance between Fe and Nb in the diffusive regime. [ABSTRACT FROM AUTHOR]

Magnetic properties of ultrathin Co/Ge(111) films with oxygen surfactant have been investigated using surface magneto-optic Kerr effect technique. As the oxygen exposure increases, their magnetic properties could be significantly modified. As the thickness of Co films increases to above 6 ML (monolayer), pure cobalt islands start to accumulate on the surface and the amount of oxygen on the surface layers increases with increasing oxygen exposure time. Series experiments of different sequences of oxygen exposure and Co deposition have been performed. From the results of slight chemical shift and depth profiling measurements, one can conclude that oxygen plays a role as a surfactant. The adsorbed oxygen influences the electronic density of states of Co and leads to the changes of the magnetic properties. The appearance of the O/Co/Ge interface could modify the stress anisotropy, and as a result the coercivity of 30 ML Co/Ge(111) increases from 730 to 810 Oe with 500 L of oxygen exposure. [ABSTRACT FROM AUTHOR]

The magnetoimpedance (MZ) effect of the pseudo-spin-valve transistor (PSVT) was investigated at room temperature in the frequency ranged from 100 Hz to 15 MHz. The PSVT can be regarded as a complex combination of resistors, inductors, and capacitors, while the impedance (Z) consists of a real part, the resistance (R), and an imaginary part, the reactance (X). Besides, all these components exhibit magnetic hysteresis. It is due to the frequency dependent behavior that R does not reach a minimum at the resonant frequency (fr). The frequency dependences of MZ and MX ratios cross zero at fx=6.5 MHz and at fr=3.65 MHz, respectively. The shape of magnetoreactance (MX) loop is reverse to the magnetoresistance (MR) loop; furthermore, MX ratio changes sign from negative at fr to positive at f>fr. The MZ loop also reverses shape and sign after crossing fx. For instance, the MZ loop with a ratio of 0.077% at 6 MHz switches to -0.086% and -0.125% at 7 and 8 MHz, respectively. [ABSTRACT FROM AUTHOR]

An innovative damping induced by magnetic force was designed successfully for a totally passive magnetic bearing motor. A magnetic ring of high permeability and an annular-shaped rubber pad were mounted on the stator 0.55 mm below the permanent magnet of the rotor. Computer simulations were compared with experimental measurements to decide on the material and configuration of the critical components. The natural frequencies for lateral and rotational modes of the rotor are around 22 Hz measured by impulse method. Both the magnetic bearing motor with and without magnetic damping are rotated at a rated speed of 3840 rpm, which is far above the first critical speed of 1305 rpm. Without magnetic damping, the natural damping ratio in the radial direction of the rotor is 0.0655. After damping, it increases to 0.1401.We have demonstrated by both experimental measurement and theoretical calculation that the antishock performance is significantly improved by the innovative damping technology in a passive magnetic bearing motor. [ABSTRACT FROM AUTHOR]

Face-centered-tetragonal L10 Fe/Pt multilayers have been prepared by molecular-beam epitaxy on MgO (001) substrates at 500 °C. An ultrathin MgO layer, 1, 3, and 5 nm in thickness, respectively, was inserted into the middle of Fe/Pt multilayers by using an e-beam evaporation without introducing any oxygen source. The insertion of MgO layer effectively reduced the average grain size and the size of magnetic domains. Out-of-plane coercivity of the FePt films decreased with increasing thickness of the MgO insert layer. It was found through the studies of angular dependent coercivity that upon MgO insertion the decrease in coercivity is originated from the weakening of domain-wall motion, while domain rotation is enhanced depicting a decoupling of intergrain interaction. [ABSTRACT FROM AUTHOR]

Tetragonal L10 ordered Fe/Pt multilayers were prepared by molecular-beam epitaxy on Pt-buffered MgO(001) substrates at 500 °C. An ultrathin Ag (0.5 nm) layer was symmetrically inserted into [Fe/Pt] bilayers with different periods to introduce defects or pinning sites at the interfaces of Ag and Fe/Pt bilayers. The effects of Ag pinning layers in the Fe/Pt multilayers have been studied. The insertion of Ag pinning layers effectively reduced the size of magnetic domains. The distribution of angular dependent coercivity of Fe/Pt multilayers with inserted Ag pinning layers between zero and ten periods, indicates a tendency of the domain-wall motion behavior to be weakened but nucleation mode enhanced. [ABSTRACT FROM AUTHOR]

Hot-filament chemical vapor deposition, using a mixture of methane and hydrogen, is used to grow micrometer-long multiwall carbon nanotubes (MWNTs) on 1-μm-diametric iron dots with thicknesses of 54, 40, and 20 nm. Bunches of MWNTs grow on the nanosized thin-film iron dots, and thicker iron dots have more MWNTs, because the nanosized thin-film iron dot behaves as a thin film with many catalyst nanoparticles rather than as a catalyst surface. Therefore, the thickness of the nanosized thin-film iron dot strongly dominates the MWNT growth. However, the MWNTs growing on the iron dots are 1 μm long and ∼90 nm wide, indicating that the length and diameter of the MWNT are independent of the size and thickness of the iron dot. In addition, the effect of the applied electrical field on the growth of MWNTs is presented. [ABSTRACT FROM AUTHOR]

Magnetic properties of Co films (<2 nm) with Ag buffer layers (<0.7 nm) grown on Ge(100) at room temperature and 200 K were studied by surface magneto-optical Kerr effect. Without the buffer, the films reveal in-plane magnetic anisotropy even Co and Ge forms nonmagnetic interfacial alloys. The hysteresis due to intercalation of Ag can be detected at thinner Co thicknesses. The buffer can effectively cutoff the intermixing of Co and Ge. As the thickness of Ag is reduced, out-of-plane magnetic anisotropy due to the interface interactions between Co/Ag and Co/Ge was discovered and was only at 200 K. [ABSTRACT FROM AUTHOR]

A spin transistor consisting of a metallic pseudo-spin-valve emitter, a copper base, and a p-n junction collector was prepared on a Si(100) wafer. This spin transistor can provide high magnetocurrent output, high magnetocurrent variation, and high transfer ratio. The common collector configuration with an emitter bias of 5.12 V at 77 K gives a large magnetocurrent variation of more than 95.5 μA in the collector, and the change is more than 3400% with a transfer ratio of 2.59310-3. At room temperature, these changes go down to 98.3 μA and 55.3%, respectively, and the transfer ratio rises to 5.98310-3. The high performance of this spin-valve transistor is due to the use of a p-n junction as an energy barrier to select spin electrons. [ABSTRACT FROM AUTHOR]

We have studied the current induced domain wall motion by using patterned U geometry. The observation of two magnetic states of the U-pattern was evidenced. One is the vortex domain wall at the center of semicircular arc in U-pattern and the other is the continuous magnetic state without wall. We investigated the influence of the positive and negative dc current injection on domain wall motion before switching field with density on the order of ~107 A/cm2. The critical current varied dramatically as the bias field is close to the switching field and only gradually as the field is far away from the switching field. [ABSTRACT FROM AUTHOR]

We report here the resistance of Co/NbxTi1-x multilayers, for x=0.4 and 0.6, with current flowing perpendicular to the layer plane at 4.2 K. When NbTi films are sandwiched between Co, we found that there are critical thicknesses of 20 nm for x=0.4 and 27 nm for x=0.6, below which no superconducting transition could be found. Using a series resistor model, we extracted the unit area resistance of one pair of Co/NbTi interfaces and compared with the pure Nb case we have reported. The influence of mean free paths and superconducting coherence lengths is analyzed. [ABSTRACT FROM AUTHOR]

Hot-filament chemical vapor deposition, using a mixture of methane and hydrogen, is used to grow multiwall carbon nanotubes (MWNTs) on 54-nm-thick iron dots with diameters of 970, 770, 340, and 140 nm. The size effect of the nanosized thin-film iron dot is presented on the MWNT growth. More MWNTs grow on larger iron dots. However, the diameters of the MWNTs that grow on iron dots with average diameters of ∼120 nm are independent of the sizes of the iron dots. An approach to growing MWNTs on the nanosized thin-film iron dots is described. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Pure phase of [Co3(pyz)(HPO4)2F2] crystal powder was successfully synthesized. The structure consisted of neutral sheets of [Co3(HPO4)2F2], which were pillared through pyrazine ligand to form three-dimensional frameworks. Below 20 K, the magnetic hysteresis loops showed a ferromagnetic part superimposed with an antiferromagnetic (AF) part. With increasing field magnitude, the AF part showed sharp steps at 5 kOe. Micromagnetic simulation, taking into account the Co ions as AF coupled sublattices and as suggested by the negative Weiss temperature extrapolated by the inverse susceptibility versus temperature behavior, explained the hysteresis loops the temperature dependence qualitatively. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetic properties of one monolayer (ML) Ni/1 ML Co/Pt(111) film upon thermal annealing were investigated. Increases in polar Kerr rotation correspond to the topmost Ni layer incorporated with the second Co layer on Pt, and the further alloying of Co-Pt during the annealing. Interestingly, Curie temperature shifted dramatically to 325 K when the film was annealed at 830 K. The alloy formation of Ni-Pt and top-layer enrichment of Pt may be the main reason causing the great shift of Curie temperature. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We studied the structure and magnetic properties of molecular-beam epitaxy grown 300 Å thick Fe/Pt multilayers with different bilayer thickness and annealing temperature. The Fe/Pt multilayers were deposited on 100 Å thick Pt buffer layers at 100 °C on Al2O3 (0001) substrates. The structure of as-deposited Fe/Pt films was fcc(111). While the postannealing temperature >=400 °C, an additional FePt(100) orientation was observed. A large coercivity range, namely, 200–16 000 Oe can be tuned by varying the bilayer thickness and annealing temperature. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Patterned Permalloy submicron-size structures have been fabricated by e-beam lithography in the shape of a ring with a tip. A tip was intentionally added into the ring as a geometrical defect to interrupt the continuity of the magnetization, which aligns along the ring, in order to pin the domain wall. Magnetic switching and reversal process have been measured by the magnetoresistance measurement. The switching field about 260 Oe was obtained. At the remanent state, there was a 0.21% difference in the magnetoresistance between the angles of 90° and 0° that was equivalent to the domain wall magnetoresistance. By applying an external field, the domain wall moved along the ring under a lower field (100 Oe), which is smaller than the switching field. A drop (0.24%) in the resistance between the angle of 70°–120° has been observed that means the domain wall was moving into the voltage measuring region during the rotation. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetoresistance in NiFe-Al-NiFe single-electron tunneling device has been studied at temperatures between 0.066 and 0.8 K and in magnetic fields up to 3 T. The competition effect among the superconducting, the Coulomb blockade, and the magnetic tunneling has been experimentally investigated. An enhancement effect of the tunneling magnetoresistance due to the superconductivity of the Al island has been observed in the nonlinear range of the current-voltage I - V characteristics. The superconducting critical magnetic fields obtained from the magnetoresistance curves are roughly decreased from 1.5±0.1 to 1.3±0.1 T, and 1.2±0.1 T for temperature increasing from 66 to 400 mK, and 800 mK, respectively. For Al island in its normal state, the resistance of the NiFe-Al-NiFe single-electron tunneling device is roughly 40 kΩ and is insensitive to the current variation. However, in general, the resistance increases with decreasing the current for the central Al island in its superconducting state. [ABSTRACT FROM AUTHOR]

We have investigated the magnetization reversal process of the disk-, ring-, and center dot ring-patterned Ni[SUB80]Fe[SUB20] wires. For the fields applied perpendicular to the wire direction, interesting shape dependent magnetoresistance (MR) ratios were found. The MR ratios were varied from 0.8%, 0.65%, and 0.4% at room temperature and 1.7%, 1.5%, and 1.1% at 10 K for the disk-, ring-, and center dot ring-patterned wires. For the same wires, the switching field is reduced from -170, -110, and -90 Oe at room temperature to -140, -70, and -20 Oe at 10 K. These results were due to the shape anisotropy and domain-wall motion. The anisotropy MR (AMR) ratios measured at 10 K of the disk-, ring-, and center dot ring-patterned wires were 1.9 ± 0.1%, 1.7 ± 0.1%, and 1.3 ± 0.1%, respectively, it is almost even the same (1.1 ± 0.1%) at room temperature. We have observed that the center dot reduces the MR ratio and increases magnetic saturation field of the Ni[SUB80]Fe[SUB20] wires. [ABSTRACT FROM AUTHOR]

The thickness and magnetic field dependence of resistance in Co/Nb multilayers with current perpendicular to plane geometry were measured at 4.2 K. When the number of bilayers increased, the resistance increased linearly. This linear behavior enables us to use a series resistance model to analyze our data for the thicknesses we used, 20 and 80 nm for Nb. When sandwiched between Co, Nb is a normal metal when thinner than 30 nm, otherwise it is superconducting. Assuming bulk resistivities for normal Nb and Co, we got unit area resistance values of 6.3 and 3.5 fΩm[SUP2] for superconducting and normal Nb/Co interfaces. There was no magnetoresistance observed, at a resolution of about 0.1%. The applicability of a diffusive regime model is discussed. [ABSTRACT FROM AUTHOR]

Face-centered-cubic Ag(100) submicrometer islands on an RCA-cleaned Si(100) substrate were fabricated by molecular beam epitaxy; a 500 Å Fe thin film was then grown onto Ag films at 100 °C. We experimentally demonstrate that the magnetic behavior of Fe films is strongly dependent on the thickness and morphology of the Ag underlayer. The Ag film, in order to reduce the surface free energy, forms isolated three-dimensional square islands with {111} sidewall on the Si(100) substrate. The average height, grain size and surface roughness of these Ag islands were tuned by varying the deposition thickness of the Ag film. The in-plane easy axis of the Fe film was rotated 45° while the thickness of the Ag underlayer reaches 100 Å and the Ag rough surface provides a source of domain wall pinning. [ABSTRACT FROM AUTHOR]

The influences of an Ag buffer layer on the magnetic properties of ultrathin Co/Ge(111) films grown at ambient temperature were studied using the surface magneto-optic Kerr effect technique. Due to the intermixing of Co adatoms and Ge(111) substrate, a nonferromagnetic layer forms at the initial stage of the deposition for Co/Ge(111) films. We demonstrate experimentally that the ferromagnetic inactive layer can be reduced by introducing an Ag buffer layer and the orientation of the easy axis of magnetization remains unchanged. Three magnetic phases have been resolved for Co/Ag/Ge(111) films with a Ag thickness less than 6 monolayers. In the phase diagram, the boundary between ferromagnetic and nonmagnetic regions shifts to a lower Co thickness from 10 to 5 monolayers as the thickness of the Ag layer increases from 0 to 6 monolayers. [ABSTRACT FROM AUTHOR]

We study the structure and perpendicular magnetism of molecular beam epitaxy grown (FePt)[SUB1-x]Mn[SUBx] films with doping concentration x = 0, 1%, 2%, 3%, 4%, and 5%. The (FePt)[SUB1-x]Mn[SUBx] films were made by multilayers growth of [Fe/Pt/Mn]×N at 100 °C and annealed at 600 °C. X-ray diffraction scans indicate that relatively better L1[SUB0] ordered structure for low Mn doping (x < 2%). The (001) and (003) superstructure peaks decrease with the increase of the Mn doping for x&ges;2%, and a significant (111) peak appears for x > 3%. The perpendicular magnetic anisotropy effect of the (FePt)[SUB1-x]Mn[SUBx] films tends to decrease with the increase of Mn doping for x > 1% However, the x = 1% doped films possess slightly better perpendicular magnetic anisotropy effect than the zero doped film. The perpendicular magnetic anisotropy constant are of about 1.3 × 10[SUP7] and 1.6 × 10[SUP7]erg/cm[SUP3] for x = 0% and x = 1%, respectively. [ABSTRACT FROM AUTHOR]

FeTaCN films were deposited on quartz substrates by cosputtering of Fe and TaC targets at room temperature with different N[SUB2] flow rate ratios in the sputtering gas. The as-deposited films were postannealed in vacuum for 30 min at various temperatures. The effects of annealing temperature on the N[SUB2] flow rate ratio and film thickness on the magnetic properties and microstructure of the film were investigated. X-ray diffraction and transmission electron microscopy analyses show that the as-deposited FeTaCN film has a nanocrystalline structure or mixing phases of nanocrystalline and amorphous. Nanocrystalline as-deposited film with good soft magnetic properties (in-plane coercivity Hc&par;= 1∼2 Oe and 4πMs=12-14kG) can be obtained by controlling the N[SUB2] flow rate ratio and film thickness. The soft magnetic properties can be improved by postannealing the as-deposited film at 200-300 °C as the N[SUB2] flow rate ratio is higher than 5 vol %. For the Fe[SUB71.03Ta[SUB 6.1]C[SUB 7.2]N[SUB 15.67] film, the Hc&par; value decreases as the film thickness is increased when the annealing temperature is lower than 400 °C. After annealing at 300 °C, its Hc&par; is about 3.57 Oe as the film thickness is 50 nm and Hc&par; will decrease to 0.18 Oe as the film thickness is increased to 1000 nm. [ABSTRACT FROM AUTHOR]

Micron size NiFe wire having a patterned shape of semicircle in series was fabricated. Magnetoresistance of the wire has been studied from 10 to 300 K. Domain wall resistivity is nearly independent of the temperature; however, the domain wall switching field decreases relatively rapidly with increasing temperature. We have observed experimentally two distinct domain structures at the corners of the NiFe semicircle-ring patterned wire at remanence after longitudinal and transverse saturation fields. We can explain successfully the magnetization reversal process on the magnetoresistance loops by the contribution from anisotropic magnetoresistance and magnetic domain configuration. [ABSTRACT FROM AUTHOR]

Through the proper design of submicron permalloy (Ni[SUB80]Fe[SUB20]) wires, domain wall magnetoresistance is investigated. A positive contribution to magnetoresistance (MR) was found for domain walls in these wires after extracting the anisotropic MR effect. Some theoretical models are used to discuss our results. [ABSTRACT FROM AUTHOR]

Four different magnetization configurations of micron- and submicron-sized permalloy square frames are investigated by numerical simulations and experiments. Beside the pure conventional 90° Neel type wall with zero net magnetic pole, we also obtain numerically another high energy domain wall with positive or negative net magnetic poles in the corner. These three kinds of domain walls constitute four different patterns in square frames. We compare the magnetic pole density distributions derived from the spin configurations of simulation results with the images taken by magnetic force microscopy, and find reasonable agreement between them. [ABSTRACT FROM AUTHOR]

Magnetoresistance (MR) in Co-Al-Co and Al-Co-Al double tunneling junctions has been studied at temperatures between 65 and 750 mK and in magnetic fields up to 3 T. The electrical resistance decreases with increasing temperature. In the low magnetic field region, the electrical resistance hysteresis behavior is attributed to a typical TMR for ferromagnetic Co and insulator Al[sub 2]O[sub 3] elements. In the high magnetic field region, a sharp resistance variation roughly near 2.0 T for the Co-Al-Co system and 1.75 T for the Al-Co-Al system has been observed and is attributed to the electron tunneling effect. From the current-voltage and dI/dV characteristics, the superconductivity energy gap is roughly 0.5 meV in the Co-Al-Co system and roughly 0.3 meV in the Al-Co-Al system; and magnetic tunneling energy is roughly 0.01 meV in the Co-Al-Co system and roughly 0.06 meV in the Al-Co-Al system. [ABSTRACT FROM AUTHOR]

Magnetic properties of cobalt films grown on Ge(111) and Si(111) substrates were investigated. On a Ge(lll) substrate, cobalt films possess an in-plane anisotropy. On a Si(lll) substrate, ultrathin cobalt films (3-9 monolayers), which were deposited at 300 K, exhibited a canted easy axis. The different orientations of the easy axis of magnetizations are attributed to the different roughness of the film/substrate interfaces. Interaction between Co layers and the substrates produces intermixed compound layers that are nonmagnetic. The thickness of this compound layer is 3.8 monolayers for Co/Ge(111), and 2.1 monolayers for Co/Si(111). A series of annealing experiments showed that the onset temperature of the disappearance of the magnetism for Co films is lower on Ge than that on Si substrate. For cobalt film, this onset temperature is 300 K on Ge(lll) and 575 K on Si(lll). [ABSTRACT FROM AUTHOR]

Cobalt films have been grown on yttria-stabilized cubic zirconia (YSZ) (100) and (110) substrates by molecular beam epitaxy. Both hcp(0001) and fcc(111) twin structures and fcc(110) films have been successfully fabricated on the YSZ(100) and (110), respectively. For the Co on YSZ(100) case, the Co films possess either hcp(0001) or fcc(111) crystals with in-plane 30° rotation. For the Co on YSZ(110) case, the structural relationship is YSZ(110)[100] Co(110)[1-10]. All the films display an isotropiclike magnetic anisotropy with the coercivity increasing abruptly above its martensitic transition temperature. The coercivity decreases with increasing the thickness of Co films from 100 Å to 500 Å; and increases as the deposited temperature above 500 °C. Co films grown on YSZ(100) are in favor of the layer by layer growth, and Co films grown on YSZ(110) are in favor of the island . [ABSTRACT FROM AUTHOR]

Exchange anisotropy for a PtMn/Ni[sub 80]Fe[sub 20] bilayer grown on a Mo(001) step surface is studied. The PtMn/Ni[sub 80]Fe[sub 20] bilayers were mainly grown as a (110) quad-crystal structure mixed with a minor (001) component. The PtMn/Ni[sub 80]Fe[sub 20] bilayers show a unidirectional exchange anisotropy with exchange field up to about 190 Oe with easy axis parallel to the underlying Mo step-edge direction. The azimuthal distribution of the exchange field is explained by interplay of a step-induced unidirectional anisotropy and crystalline-induced anisotropy. [ABSTRACT FROM AUTHOR]

A detailed study of the interface properties as well as the thermal stability has been done for the Co/Al-O/CoFe/NiFe magnetic tunnel junction, by using high resolution transmission electron microscopy equipped with energy dispersive x-ray spectrum. The Al behaves more stable against thermal annealing compared with the Fe, Co, Ni, and O elements. The reduction of the tunnel magnetoresistance ratio for the low annealing temperature (200 °C) may be caused by the spin flip scattering at oxide ion, rather than by the change in magnetic properties. The annealing at higher temperatures (300 °C and 400 °C) results in a strong interdiffusion, and in turn the disappearance of the magnetoresistance due to the shortcut of the junction. [ABSTRACT FROM AUTHOR]

Thickness dependence on the domain wall resistivity of zig zag thin permalloy wires was studied from 10 to 300 K. The maximum domain wall resistivity was obtained in wire with 100-nm-film thickness. The multidomain state resistivity was 14.29 µΩ cm, while single-domain state resistivity was 14.36 µΩ cm at 10 K. The ratio of domain wall magnetoresistance was measured to be 0.034%, 0.112%, and 0.258%, and the magnetic field where the domain wall started to switch was measured as -70, -40, and +80 Oe for wires with thicknesses of 20, 40, and 100 nm, respectively, at 250 K. Domain wall resistivity was nearly independent of temperature for wire with 40-nm-film thickness but varied significantly with temperature for 100-nm-thick wire between 10 and 300 K. [ABSTRACT FROM AUTHOR]

The multilayer granular structure has been developed and has proved to be a promising candidate for extremely high-density magnetic recording. Recently, the properties of friction and wear of the structure have been studied and the in-situ nanoscale protection concept has been proposed. In this paper, two series of CoCrPt-C multilayer samples with various interlayer carbon concentration and with/without carbon overcoat (top layer) are compared, having been prepared by using facing target sputtering (FTS) and normal dc sputtering (DCS), respectively. The corrosion resistance of the sample is investigated using environmental and electrochemical methods. Optical microscopy and time-of-flight secondary ion mass spectrometry are used to characterize the corrosion test samples. For the samples prepared by FTS, both top and interlayer carbon can provide protection for the media. In terms of the samples prepared by DCS, the carbon layer may increase the porous density during the corrosion process. It is concluded that the sp³/sp² ratio of the carbon is the most important consideration in nanoscale protection for the granular thin film media. Raman spectroscopy results further confirm the conclusion. [ABSTRACT FROM AUTHOR]

The influences of random disorder in the barrier on tunnel conductance (TC) and magnetoresistance (TMR) in ferromagnet (FM)/insulator (semiconductor) (I(S))/FM junctions are investigated theoretically taking into account spin-orbit (SO) interaction. The TMR decreases significantly due to the spin-flip scattering (SF) caused by the SO interaction. We have found that the SF scattering is much stronger for anti-parallel configuration of magnetization and the TMR can even be inverted when the SF scattering is beyond some critical value. The numerical calculations are performed within the single-orbital tight-binding model using the recursive Green's function method based on the extended Landauer-Bfittiker formula. [ABSTRACT FROM AUTHOR]

The magnetic properties of ultrathin Ag/Co/Cu(111) films have been investigated using the surface magneto-optical Kerr effect technique. Along polar direction with a harder axis of magnetization, Ag overlayer-induced oscillation of the coercive force shows a strong in-plane anisotropy for complete Ag atomic layers. It is consistent with the enhanced longitudinal Kerr intensity. A more significant change of the magnetic properties for a thinner film was observed and this should be attributed to a larger ratio of the magnetic-nonmagnetic interface to the volume. The relatively easy axis of the magnetization is along the longitudinal direction for the Ag/Co/Cu(111) system. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Numerical solutions of Brown's Fokker-Planck equation are used to analyze the response of a superparamagnetic particle to an ac applied field. The nature of the response is governed by the rate of intrawell relaxation processes: At low driving frequencies they maintain the system close to a quasistationary state, and the response is Markovian. By contrast, probability redistribution effects taking place at high frequencies lead to a non-Markovian response mode which displays memory phenomena. The high frequency limiting cycles are analyzed in detail, and the transition to conventional low frequency hysteresis loops is discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The orientation of the magnetization and the occurrence of interfacial ferromagnetic inactive layers for ultrathin Co films grown on Ge(111) and Ge(100) surfaces have been studied using the in situ surface magneto-optic Kerr effect. On a Ge(111) substrate, cobalt films (<=28 monolayers) with in-plane easy axis of magnetization have been observed; however, on a Ge(100) substrate, ultrathin Co films (14-16 monolayers) with canted out-of-plane easy axis of magnetization were measured. The ferromagnetic inactive layers were formed due to the intermixing of Co and Ge and lowering the Curie temperature by reducing Co film thickness. The Co-Ge compound inactive layers were 3.8 monolayers thick for Co films grown on Ge(111) and 6.2 monolayers thick for Co films deposited on Ge(100). This is attributed to the difference of the density of surface atoms on Ge(111) and Ge(100). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A series of NbTi single thin films, Co/NbTi/Co trilayers, and multilayers are made by dc sputtering to investigate the superconductive dimensional crossover between two-dimensions (2D) and three dimensions. From the temperature dependence of the upper critical fields measured resistively, we see a nonlinear changing to linear dependence of H[sub c2](T) from 60 to 80 nm of NbTi thickness for trilayers. Insertion of 0.6 nm thick Co between 30 nm NbTi films also shows 2D behavior, which suggests confinement of the superconducting wave function within individual layers. Magnetic field response is measured to study the interplay between the superconductor and ferromagnet. We inferred a magnetic penetration depth of ∼35 nm into NbTi. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]