bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscoelastic liquid bearing modeling via lattice Boltzmann method
Authors: Kim Woo Tae , Chen Haigang , Jhon Myung S.
Published: June 2006

As the need for higher areal recording density in hard disk drives (HDDs) requires continuous reduction of the fly height in head-disk interface, the tribological issues become critical during operation. In viscoelastic liquid bearing (VLB) technology, thin liquid films instead of air bearing are used for lubrication. In this paper, we developed a computational tool based on lattice Boltzmann method (LBM), which is accurate, fast, robust, and highly parallelizable, for the accurate modeling of a non-Newtonian ultrathin liquid film undergoing extremely high shear rates. We adopted truncated power-law and the Bird-Carreau models to take into account the shear rate dependent viscosity via the relaxation time in our LBM scheme. After the feasibility study of the pressure driven microchannel, the pressure and flow fields under the model slider were calculated for different constitutive relationships. Together with the order of magnitude analyses, our LBM simulations, using a physically realistic viscoelastic constitutive equation, will provide accurate predictions on VLB drive used in HDDs.
Structural and magnetic properties of LaMn1−xFexO3 (<x<1.0)
Authors: Zhou X.-D. , Pederson L. R. , Cai Q. , Yang J. , Scarfino B. J. , Kim M. , Yelon W. B. , James W. J. , Anderson H. U. , Wang C.
Published: June 2006

Electronic, structural, and magnetic properties of Mn-doped lanthanum ferrites were studied by neutron diffraction, superconducting quantum interference device, and impedance spectroscopy. Neutron diffraction refinements were performed with the constraint of full La occupancy, which showed the presence of excess oxygen when x<0.4. Mixed valent Mn cations and cation vacancies, therefore, exist in all the samples. The samples with x>0.7 are magnetically ordered at room temperature with orthorhombic symmetry (Pbnm). When x<0.3 the structure is rhombohedral and magnetically disordered above 16K. The majority carriers, electron holes, correspond to high oxidation states of Mn. The carrier concentration is determined from the Seebeck coefficients, and is a function of temperature and Fe concentration. The measurements of conductivity and Seebeck coefficients show polaron hopping at elevated temperatures.
Thin film SmCo magnets for use in electromagnetic microactuators
Authors: Budde Thomas , Gatzen Hans H.
Published: June 2006

Efficient magnetic microactuators require a deposition and patterning of a permanent magnetic material. A material that can be deposited in the range of up to a couple of 10μm is sputtered SmCo. For the fabrication of magnetic microactuators, alternative substrate materials besides silicon are of great interest. Therefore, alumina-ceramic as well as B270-glass substrates were included in the investigation. A maximum energy product of 90kJ∕m3 was achieved for rather thick layers of 30μm deposited on glass or ceramic substrates. The latter substrates were found to be suitable for the deposition of SmCo layers up to a thickness of 50μm. Furthermore, the SmCo exhibits isotropic magnetic properties, thus a magnetization of the permanent magnetic layer can be performed in plane as well as perpendicular to the film plane. For the patterning of these thick SmCo layers ion beam etching and wet chemical etching were examined. For both methods, the suitability of patterning thick SmCo layers could be demonstrated. For the integration of a SmCo permanent magnet in a magnetic microactuator, the two technologies for deposition and patterning of the SmCo layer had to be combined. Two linear microactuators are presented utilizing different integration methods of the SmCo component as well as direction of magnetization.
Thermoelectrical study of ferromagnetic nanowire structures
Authors: Serrano-Guisan Santiago , Gravier Laurent , Abid Mohamed , Ansermet J.-Ph.
Published: June 2006

The mixed effects of heat and charge transports have been studied at room temperature for Ni∕Cu and Co∕Cu multilayers with currents perpendicular to the interfaces as well as Ni and Co homogeneous nanowires. In order to carry out this analysis, magnetothermogalvanic voltage (MTGV) measurements have been performed. The method consists in monitoring an alternating voltage response that arises when an oscillation of the temperature of the nanostructure is applied and a steady current crosses the nanostructure. Different responses were observed for thicknesses of the ferromagnetic layer larger or shorter than the spin diffusion length. Qualitatively different MTGV profiles were also observed for Ni and Co homogeneous nanowires. These results demonstrate the importance of spin relaxation processes produced in ferromagnetic/nonferromagnetic (FM/NF) interfaces as well as in FM layers for the MTGV response.
Effect of nano-patterning on anisotropy of Cu∕Ni∕Cu nanolines
Authors: Lyons E. S. , O’Handley Robert C. , Ross C. A.
Published: June 2006

Cu ∕ Ni ∕ Cu films grown epitaxially on Si have shown perpendicular magnetic anisotropy over a wide range of Ni thicknesses. Using interferometric lithography and ion milling, epitaxial and polycrystalline Cu∕Ni∕Cu films were patterned into large area arrays of parallel lines with widths of 100 and 200nm. The effect of patterning on the anisotropy of Cu∕Ni∕Cu with tNi=6.9 and 20.6nm was determined from M-H loops measured by vibrating sample magnetometry. The nanolines show significantly reduced tendency toward perpendicular magnetization and increased energy favoring magnetization across the linewidth. These results are interpreted in terms of magnetoelastic energy changes due to relaxation of misfit strain upon patterning and shape anisotropy.
Pulsed laser deposited epitaxial Sm–Co thin films with uniaxial magnetic texture
Authors: Singh A. , Neu V. , Tamm R. , Rao K. , Faehler S. , Skrotzki W. , Schultz L. , Holzapfel B.
Published: June 2006

Sm–Co thin films have been grown epitaxially with pulsed laser deposition on Cr buffered MgO(110) substrates. The buffer microstructure plays a significant role in controlling the growth and hence the magnetic properties of the Sm–Co film. High deposition temperatures of the Cr buffer result in a rough and discontinuous microstructure, thereby resulting in an x-ray amorphous or nanocrystalline Sm–Co layer, as has been confirmed by transmission electron microscopy studies. By lowering the buffer deposition temperature from 700to300°C, the roughness decreases from 5to0.6nm. Sm–Co films grow epitaxially on these low temperature buffers with the epitaxial relation MgO(110)[001]∥Cr(211)011∥SmCo(100)[001] which implies a single in-plane orientation of the c axis along the MgO[001] direction. The strong in-plane crystallographic texture seen in the pole figure measurements leads to a very pronounced magnetic texture, quantified by a remanence ratio JrMgO[110]∕JrMgO[001] as low as 0.08 and a high remanence of 0.84T along with a high coercivity of 3T when measured along the easy axis.
Extracting the intrinsic switching field distribution in perpendicular media: A comparative analysis
Authors: Winklhofer Michael , Zimanyi Gergely T.
Published: June 2006

We introduce a method based on the first-order-reversal-curve (FORC) diagram to extract the intrinsic (microscopic) switching-field distribution (SFD) of perpendicular recording media (PRM). To demonstrate the viability of the method, we micromagnetically simulated FORCs for PRM with known SFD. The extracted SFD is compared with the SFD obtained by means of two different methods that are based on recoil loops, too, which, however, rely on mean-field approximations and assumptions on the shape of the SFD. The FORC method turns out to be the most accurate algorithm over the technologically relevant range of magnetic quality factors Q, where the other methods overestimate the width of the SFD.
Design a linear motor absorber
Authors: Chang Chi-Shen , Liu Tzong-Shi , Lin Shir-Kuan
Published: June 2006

This paper raises a valid method to design a linear motor which serves as active dynamic vibration absorber to reduce disk drives vibration at multiple speeds. A better linear motor performance, such as lower consumption energy and higher electrical efficiency, can be achieved by tuning the diameter of a winding coil, the thickness of the magnet, and the winding spaces in a linear motor absorber.
Hopping percolation transition in granular ferromagnets
Authors: Strelniker Yakov M. , Havlin Shlomo , Berkovits Richard , Frydman Aviad
Published: June 2006

We present computer simulations of the magnetotransport properties of two-dimensional and three-dimensional granular ferromagnets using a random resistor network in which the conductivity, σ, between pairs of neighboring grains depends upon the intergrain distance [σ∝exp(−κr), where κ is a measure of disorder and r is a random number, 0⩽r⩽1] and the relative magnetic orientations. We study the resistance (R) distribution function, P(R), and find that in both the weak disorder regime L∕κν>1 (not sensitive to the removal of any single bond) and the strong disorder regime L∕κν<1 (very sensitive to such a removal) the distribution depends only on L∕κν and can be well approximated by a log-normal function with dispersion bκν∕L, where b is a coefficient which depends on the type of the lattice and ν is the critical exponent of the percolation correlation length.
Static ionic displacements in Fe–Ni alloys from first principles
Authors: Liot F. , Simak S. I. , Abrikosov I. A.
Published: June 2006

Static local displacements of ions in disordered face-centered cubic Fe50Ni50 alloy are studied from first principles in the framework of the density functional theory. The disordered alloy is modeled using a 64 atom supercell constructed as a special quasirandom structure. Fully relaxed atomic positions inside the supercell are calculated by means of projected augmented wave method as implemented in Vienna ab initio simulation package. According to our calculation, the relative changes of mean nearest neighbor interatomic distances due to local lattice relaxations are relatively small (⩽0.6%), in agreement with experiment. At the same time, we predict that for all types of pairs, Fe–Fe, Fe–Ni, and Ni–Ni, the dispersion of the nearest neighbor interatomic distances is rather large, and the individual changes of distances between certain pairs of atoms due to local lattice relaxations can be one order of magnitude larger than the mean values for the corresponding pair of atoms.
Activation barriers of submicron magnetoresistive random access memory cells with single and synthetic antiferromagnet free layers
Authors: Hwang Injun , Kim Kwang-Seok , Cho Y. J. , Kim K. W. , Kim Taewan
Published: June 2006

Thermally activated magnetization reversals of submicron sized magnetic tunnel junctions with NiFe single and NiFe∕Ru∕NiFe synthetic antiferromagnet (SAF) free layers are investigated by varying the pulse durations and current amplitudes in switching pulse measurements. The measured data show good agreement with the switching probability predicted by the Arrhenius-Neel theory and switching behaviors with a single activation energy barrier. Estimated activation barriers for magnetization reversals are higher for magnetic tunnel junctions (MTJs) with SAF free layers than MTJs with single free layers. It is believed that the high activation barrier is achieved by the larger magnetic volume of SAF layers.
Quantum effects in small-capacitance high temperature superconducting tunneling junctions
Authors: Alvarez G. A. , Iguchi I. , Wang X. L. , Dou S. X. , Yao Q. W.
Published: June 2006

We investigated the effects of single electron charging energy in high temperature superconductors. Various phenomena originating from Coulomb blockade were observable in superconducting tunnel junctions. High quality tunneling junctions were fabricated from c-axis oriented NdBa2Cu3O7−δ∕PrBa2Cu3O7−δ∕NdBa2Cu3O7−δ thin film multilayers by the pulsed laser deposition method. The current-voltage characteristics (CVCs) show a Coulomb gap for Cooper pair tunneling when the charging energy exceeds the Josephson coupling energy. We found a regime in which the CVCs exhibit sharply defined Coulomb steps due to single electron dynamics and nonlinear tunneling rates. From the obtained Coulomb staircase, the tunneling resistance shows a quantum effect: It is modulated by the tunneling current in the form h∕4e2RT∼[sin(πI∕I0)2∕(πI∕I0)]. We suggest an interpretation involving the quantum resistance h∕e2 and the competition between the charging, Josephson, and thermal energies of the system. Our results give a perspective on a solid-state quantum system with considerable interest for direct application in quantum computing.
A soft magnetic underlayer with negative uniaxial magnetocrystalline anisotropy for suppression of spike noise and wide adjacent track erasure in perpendicular recording media
Authors: Hashimoto Atsushi , Saito Shin , Takahashi Migaku
Published: June 2006

The suppression of spike noise and wide adjacent track erasure (WATE) are important technical issues in the development of a perpendicular recording medium (PRM). As a solution to both of these problems, this paper presents a type of soft magnetic underlayer (SUL) with negative uniaxial perpendicular magnetic anisotropy. The magnetic anisotropy is achieved by employing a material with negative uniaxial magnetocrystalline anisotropy (Kugrain). WATE is suppressed in the SUL by realizing wide distribution of magnetic flux below the edge of the return yoke, while spike noise is eliminated by ensuring the formation of a Néel wall instead of a Bloch wall in SUL domains. CoIr with the disordered hcp structure is selected as a negative Kugrain material, and c-plane-oriented CoIr films with various Ir contents are prepared for experimental evaluation. Among the films tested, the CoIr film with 22at.% Ir is found to provide the minimum Kugrain value of −6×106ergs∕cm3. Under a field applied parallel to the film plane, this film exhibits soft magnetic properties, attributable to the high crystallographic symmetry of the c-plane sheet texture. A PRM fabricated using the CoIr SUL is confirmed to display substantially lower spike noise and WATE compared to conventional structures.
Conduction noise attenuation by Fe3O4 thin films attached on microstrip line
Authors: Kim Sun-Tae , Ryu Gi-Bong , Kim Sung-Soo
Published: June 2006

Fe 3 O 4 thin films are prepared by reactive sputtering and their magnetic, electric, and noise absorbing properties are investigated with the aim of thin film noise absorbers in gigahertz frequencies. Fe3O4 thin films were deposited on the glass substrate by reactive sputtering. It is found that the precise control of the oxygen partial pressure is the most critical to obtain the single-phase Fe3O4 thin film. The vibrating sample magnetometer measurement indicates that the saturation magnetization is 400emu∕cm3 and the coercive force is about 200Oe. A microstrip line (with a characteristic impedance of 50Ω) was used for the measurement of noise attenuation. Attaching the thin film on the microstrip line, the S11 parameter is increased from −60dB (without a film) to about −15dB (with a film). The S21 parameter is reduced to about −3dB (about 50% in power) in the frequency range of 1–6GHz, which is due to the magnetic loss of the Fe3O4 films. Power absorption (defined by the ratio of power loss to input power) increases with frequency and saturates to maximum value (about 0.5) in the frequency region of 4–6GHz. It can thus be suggested that the Fe3O4 thin film is one of the high potential materials for noise suppressors in gigahertz frequencies.
Uniform MgB2 thin films grown on Si(111) and Al2O3(0001) substrates prepared by e-beam evaporation and in situ annealing methods
Authors: Zhang Yi Bing , Zhu Hong Mei , Zhou Shi Ping , Ding Shi Ying , Lin Zhi Wei , Zhu Jian Guo
Published: June 2006

Mg B 2 superconducting thin films on Si(111) and Al2O3(0001) substrates were prepared by high vacuum e-beam evaporation and two-step in situ annealing techniques. The precursor films [B(100Å)∕Mg(151Å)]6∕Al2O3 (or Si) were deposited at room temperature and 1×10−7mbar of background vacuum, then annealed in situ at 630°C for 30min in an argon atmosphere of 150Pa. The atomic force microscopy image showed that the films were uniform with grain sizes of about 100nm. An extremely sharp superconducting transition with a width of 0.1K and a zero-resistance temperature of 30.3K was obtained, indicating a film of high uniformity and purity in its phase with perfect connection between the MgB2 grains.
Investigation of dynamic and static magnetic properties of Fe(001)∕ZnSe by simultaneous measurement of ferromagnetic resonance, magneto-optical Kerr effect, and non-time-resolved magneto-optical Kerr effect detected ferromagnetic resonance
Authors: Möller Marc , Spoddig Detlef , Meckenstock Ralf
Published: June 2006

The dynamic magnetic response and the switching behavior of Fe(001)∕ZnSe was measured simultaneously in conventional ferromagnetic resonance (FMR), magneto-optical Kerr effect (MOKE), and non-time-resolved Kerr detected FMR (MOKE-FMR) in a dedicated setup through the full hysteretic cycle. Fe(001)∕ZnSe exhibits a double stepped magnetization reversal, if the external magnetic field is applied along a hard magnetic axis. The switching fields lie within the line- width of the low field ferromagnetic resonance line. After field reversal FMR spectra show small, but noticeable, changes in intensity. These changes are more pronounced in the MOKE-FMR spectra, which show a different intensity distribution due to the different signal generation. Simultaneous measurements of FMR and MOKE prove the changes to coincide with the switching fields. At higher microwave powers of about 1W the FMR linewidth becomes dependent upon the direction of the external field sweep. On sweeping down the linewidth is larger than on sweeping up, indicating foldover. This interpretation is confirmed by numerical simulations of the Landau-Lifshitz-Gilbert equation.
Influence of partial substitution of Ce on the Curie temperature and magnetic entropy change in itinerant-electron metamagnetic La(FexSi1−x)13 compounds
Authors: Fujita A. , Fujieda S. , Fukamichi K.
Published: June 2006

In La(FexSi1−x)13, the partial substitution of Ce for La results in the decrease of the Curie temperature TC, and the isothermal entropy change ΔSm becomes larger with decreasing TC. The increase of ΔSm with decreasing TC is also confirmed by applying hydrostatic pressure, although the increment of ΔSm is not so large. Accordingly, another effect addition to the reduction of volume due to the small ionic radius of Ce should be considered for the enhancement of ΔSm. From the fitted isothermal magnetization curves, it is evident that the partial substitution of Ce enhances the thermal variation of the forth-order coefficient B(T) in the Landau expansion of the Gibbs free energy, being consistent with the increase of ΔSm. Therefore, it is concluded that the change in the band structure also contributes the enhancement of ΔSm.
Measurements of large high-performance permanent magnet with superconducting magnet
Authors: Kato S. , Shinagawa H. , Kido G.
Published: June 2006

A magnetometer with a cryogen-free superconducting magnet was developed. Sample magnetization is calculated from the induced voltage of a pickup coil under alternating magnetic fields. The sample is fixed in the superconducting magnet and the structure of the equipment is simple. When a large high-performance permanent magnet is tested, a strong magnetic force is applied on the sample. In our system, because the structure is simple, it is easy to prepare a stout sample holder that can keep the sample against the magnetic force during measurements. Cubic NdFeB magnets of about 50 and 25mm on a side were successfully tested.
Excitation and transport of hot holes in a magnetic tunnel transistor
Authors: Park B. G. , Haq E. , Banerjee T. , Min B. C. , Lodder J. C. , Jansen R.
Published: June 2006

Spin-dependent transport of nonequilibrium holes has been investigated using a magnetic tunnel transistor in which a magnetic tunnel junction is combined with a p-type semiconductor. The device can be used for direct hole injection and collection, or in reverse mode in which holes are created by inelastic decay of injected hot electrons via electron-hole pair generation. In the latter case, the collected hole current is larger, and a magnetocurrent (MC) of 90% is observed at an emitter bias of −0.8V. This positive and large MC indicates that hot holes generated by hot electrons of majority spin contribute mostly to the collector current.
Investigation of Permalloy cross structure using magnetic force microscope and magnetoresistance measurement
Authors: Chang Y. C. , Chang C. C. , Chang Ida , Wu J. C. , Wei Zung-Hang , Lai Mei-Feng , Chang Ching-Ray
Published: June 2006

Magnetic properties of microstructured Permalloy thin film cross have been studied using magnetic force microscopy and magnetoresistance measurement. Three types of magnetization configurations formed within the junction area were observed, including two kinds of magnetic pattern having two inward and two outward magnetizations and one with three outward and one inward magnetizations. The presence of those variant magnetic configurations gives rise to an irreversible magnetoresistance behavior originated from the distinct magnetization history. Asynchronous magnetization reversal of each arm provides a chance to manipulate the magnetic pattern of the cross.
Improvement of pulse diagnostic apparatus with array sensor of magnetic tunneling junctions
Authors: Kim S. W. , Hwang D. G. , Choi Y. K. , Lee H. S. , Park D. H. , Lee S. S. , Kim G. W. , Lee S. G. , Lee S. J.
Published: June 2006

To obtain the spatial feature of arterial pulse, a spatial pulse diagnostic apparatus was designed using a two-dimensional magnetoresistive sensor array. The magnetic-field distribution for the magnet array was simulated using the finite-element method. The field distribution of parallel magnet arrays was observed to be more sensitive and uniform than that of the perpendicular ones. Moreover, the spatial displacements of the magnet array coincided with the output signal of the magnetic tunneling junction sensor array.
Magneto-optical imaging of the magnetization process in colossal magnetoresisitive lanthanum manganite
Authors: Polyanskii A. , Wang X. L. , Yao Q. W. , Dou S. X. , Lin Z. W. , Zhu J. G.
Published: June 2006

To gain insight into the origin of the colossal reduction of resistance in response to magnetic field in colossal magnetoresistance manganite, the magnetic field induced transition in ferromagnetic La0.7Ca0.3MnO3 was studied using a high-resolution magneto-optical imaging (MOI) technique. The MO images were captured in various magnetic fields over a wide temperature range for both highly dense samples with strong-link grain boundaries and porous samples with weak-link boundaries. Formation and evolution of magnetic domains as a function of field or temperature were clearly observed around and far below the Curie temperature TC=240K. Ferromagnetic areas tend to grow to large sizes and finally join together at the expense of paramagnetic areas as the field increases or temperature decreases for strong-link samples. A sharp magnetoresistive transition is observed when the sample changes from a paramagnetic insulator to a metallic ferromagnetic phase in the vicinity of TC. In contrast, the porous samples showed magnetoresistance over a wide temperature range and exhibited a remarkable grain boundary related magnetization process in addition to magnetization within grains. A close correlation is found between the magnetization process observed by MOI and magnetoresistance measurements. Our MOI results indicate that the strong-link or weak-link grain boundaries are responsible, respectively, for magnetoresistance occurring either only in the vicinity of the ferromagnetic transition or over a very wide temperature range.
Fe
3
O
4
+
δ
films prepared by “one-liquid” spin spray ferrite plating for gigahertz-range noise suppressors
Authors: Miyasaka Jin , Tada Masaru , Abe Masanori , Matsushita Nobuhiro
Published: June 2006

We have developed a simple type of ferrite film preparation technique, which we call “one-liquid” spin spraying method. Only one aqueous solution composed of dextran+FeCl2+CH3COOK+NaNO2 is sprayed onto spinning substrates, while, in our previous method, a reaction solution of FeCl2 (source) and an oxidizing solution of CH3COOK(pHbuffer)+NaNO2(oxidizer) were sprayed simultaneously. Dextran [(C6H12O6)n, n=1100–1700] suppresses iron hydroxides from precipitating in the aqueous solution. On optimized conditions, we deposited Fe3O4+δ films to the thickness of 1.6μm for 30min, obtaining film deposition rate of 52nm∕min. The films exhibited good performance of conducted noise suppression; we obtained loss parameter ΔPloss of 33% at 10GHz of Fe3O4+δ films, which was approximately equal to that obtained for the commercialized noise suppression of composite sheet type, and reflection loss parameter S11, less than −10dB. Thus one-liquid method as well will provide a method to prepare the noise suppressors of Fe3O4+δ films workable in the gigahertz range.
Influence of oxide on the structural and magnetic properties of CoPt alloy
Authors: Girt Erol , Wu S. , Lu B. , Ju G. , Nolan T. , Harkness S. , Valcu B. , Dobin A. , Risner J. D. , Munteanu M. , Thangaraj R. , Chang C.-H. , Tran T. , Wu X. , Mryasov O. , Weller D. , Hwang S.
Published: June 2006

Perpendicular recording media consisting of isolated CoPt magnetic grains separated with a nonmagnetic oxide grain boundary can be prepared by sputtering a Ru interlayer and then cosputtering CoPt with an oxide material, with low adatom mobility. The oxide material moves into the grain boundaries and isolates the magnetic grains. An increase in the oxide volume fraction in the magnetic layer does not affect the saturation magnetization but significantly reduces the magnetocrystalline anisotropy of magnetic grains. This may impose a limit on the areal density capability of this media design since media with smaller grains will require a larger oxide volume fraction that will reduce magnetocrystalline anisotropy of the CoPt based magnetic grains.
Experimental study of longitudinal exchange spring media
Authors: Supper N. F. , Margulies D. T. , Moser A. , Berger A. , Do H. , Fullerton Eric E.
Published: June 2006

We have evaluated the magnetic properties and recording potential of longitudinal exchange spring recording media. The media structure consists of a low anisotropy CoCrX spring layer ferromagnetically coupled to a high anisotropy CoPtCrB hard layer via a CoRu interlayer. The interlayer exchange coupling is tuned by varying the CoRu layer thickness. The short-time coercive field (Hc0) as well as the energy barrier (KuV) of the structure are furthermore tuned by varying the thickness of the spring layer. We show that by changing the CoCrX layer thickness from 1to4nm, Hc0 can be decreased by a factor of 2 while the energy barrier can be increased by up to 50% hence improving the stability of the overall structure. More importantly, it is possible to reduce the switching field distribution width leading to an improved overall signal to noise ratio in this CoCrX thickness range.
Thermal robustness in synthetic antiferromagnetic free layer for magnetic random access memory applications
Authors: Takenaga Takashi , Kuroiwa Takeharu , Furukawa Taisuke , Taki Masakazu , Yoshiara Kiichi , Tokuda Yasunori
Published: June 2006

We have investigated the magnetic switching properties of synthetic antiferromagnetic (SyAF) structures consisting of Co90Fe10∕Ru∕Co90Re10 structure with a Ru capping layer annealed at 300°C. After annealing, the coercivity Hc of the structures with a Co90Fe10 thickness below 5nm increased. On the other hand, the Hc was maintained below 70Oe in structures with a Co90Fe10 thickness above 6nm after annealing. Thus, a low switching field for a free layer can be achieved by using the SyAF structures with a Ru capping layer, even after annealing at 300°C, and the SyAF free layer is considered to be effective for downsized memory cells in magnetic random access memories.
Enhancement of ferromagnetic coupling in Mn∕GaAs digital ferromagnetic heterostructure by free-hole injection
Authors: Qian M. C. , Fong C. Y. , Pickett Warren E.
Published: June 2006

We have studied the effect of the free-hole injection on the ferromagnetic coupling in the Mn∕GaAs digital ferromagnetic heterostructure (DFH) using ab initio electronic-structure methods. The DFH is modeled by a supercell periodically consisting of a δ-doped layer of MnAs and 15 layers of GaAs. The injection of free holes is simulated by assigning a range of missing electrons in unit cell. The δ-doped layer of Mn atoms in GaAs introduces three spin-polarized hole bands which are the consequence of hybridization between the d states of the Mn atoms and the p states of the nearest neighboring As atoms. These spin-polarized holes are confined to the vicinity of the MnAs layer. After the injection of free holes, the Fermi energy is lowered, consequently the number of spin-polarized holes in the layer of MnAs increases monotonously. Our results show the enhancement of the ferromagnetic coupling by the free-hole injection, which is in agreement with the experimental observation.
Strong uniaxial anisotropies of iron grown on UHV cleaved InAs(110) investigated by correlated scanning tunneling microscopy and ferromagnetic resonance
Authors: Spoddig Detlef , Urban Christian , You Dai-Hyun , Köhler Ulrich , Meckenstock Ralf
Published: June 2006

The magnetic properties of iron films grown under UHV condition are governed by the deposition condition and the substrate preparation. One way of producing almost perfect surface conditions with large terrace width and exact orientation is cleaving. With this method no additional cleaning process of the surface is needed. Here we present our investigations of iron films (thickness: 0.1–30nm) grown on UHV cleaved InAs substrates using in situ scanning tunnel microscopy (STM) investigations combined with in situ magneto-optical Kerr effect (MOKE) and ex situ angle and frequency dependent conventional ferromagnetic resonance (FMR). The (110) InAs surface allows the investigation of three magnetic axes: in-plane easy (001), hard (111), and intermediate (110) axes of the iron layer. The (110) symmetry of the magnetic cubic crystalline anisotropy should lead to angles of 110° and 70° between the hard axes, respectively. STM images of the clean InAs(110) show 500nm wide terraces with mono atomic steps predominately oriented parallel to the (001) direction. MOKE hysteresis loops were measured during the Fe deposition to prove the ferromagnetic state. The angle dependent in-plane FMR measurement revealed unexpected 90° symmetry. Deducing the anisotropy constants from the FMR resonance position, one finds a slightly increased bulk crystalline anisotropy and a uniaxial anisotropy of the same order of magnitude. This strong uniaxial anisotropy distorts the 110° symmetry to 90° symmetry. The correlation of frequency and angle dependent FMR and STM measurements evidences that the uniaxial anisotropy is due to the dislocations caused by the orientation of the terraces.
Improvement of communication area for implantable signal transmission system with ferrite chip core
Authors: Takura Tetsuya , Somekawa Tatsuo , Sato Fumihiro , Matsuki Hidetoshi , Sato Tadakuni
Published: June 2006

Transcutaneous power and signal transmission system are useful for artificial hearts. The signal transmission system is important to control the implanted device and to monitor the inside condition. They do not have lines penetrating through the skin. The signal transmission coils are set on the power transmission coils. We have proposed integrated power and signal transmission system utilizing eight-figure coils. Using the signal transmission coil pairs we have proposed, we studied through measurements and experiments the communication area for implantable signal transmission system with a ferrite chip core.
The effect of nonmagnetic ion substitution for the FeCr2−xMxS4 (M=Ga,In) by Mössbauer spectroscopy
Authors: Son Bae Soon , Kim Sam Jin , Joo Koan Sik , Kim Chul Sung
Published: June 2006

The Mössbauer spectroscopy has been studied for the sulphur spinel FeCr2−xMxS4 (M=Ga,In) at various temperatures, from 4.2K to room temperature. The spectra consist of two doublets at room temperature, which show that the Ga and In ions are partially occupied to the tetrahedral (A) site. It is found that the Ga and In ions stimulate the asymmetric charge distribution of Fe ions in the A site. The electric quadrupole splittings (ΔEQ) of the A and B sites in the Mössbauer spectra of FeCr2−xGaxS4 (x=0.3) are 0.83 and 2.94mm∕s, respectively, while those for the FeCr2−xInxS4 (x=0.3) are 0.54 and 1.54mm∕s, respectively. The ΔEQ for the Ga doped samples are larger than that for the In doped samples, in spite of the larger ionic radius for In ions. We suggest that stronger covalence associated with the smaller bond length includes a large asymmetric charge distribution.
Influence of magnetoelastic effect and domain structure on pole erasure occurrence in perpendicular recording heads
Authors: Hirata Kei , Yamaguchi Atsushi , Ohtsuki Mitsuo , Roppongi Tetsuya , Noguchi Kiyoshi
Published: June 2006

The influences of the magnetoelastic effect on the occurrence of pole erasure were investigated. It was found that the occurrence of pole erasure was related to the anisotropy energy induced by the magnetoelastic effect in the pole tip. The anisotropy energy by the magnetoelastic effect was dominated by the external stress on the pole tip and the magnetostriction of the pole film. The magnetization state in the yoke also influenced the occurrence of pole erasure. It was found that the yoke with large anisotropy energy in direction to the head height and the complex domain structure in the yoke made pole erasure worse.
Magnetoresistive behavior of current-perpendicular-to-plane trilayer with half-metal insertions
Authors: Bae Seongtae , Tan S. G. , Jalil M. B. A. , Kumar S. Bala , Teo K. L. , Leong Z. Y. , Liew Thomas
Published: June 2006

We investigated the effect of half-metal (HM) conductivity on the magnetoresistance (MR) of the pseudo spin-valve (PSV) structure. We derived a PSV MR model based on the spin transport theory of van Son et al. [Phys. Rev. Lett. 58, 2271 (1987)] and Rashba [Eur. Phys. J. B 29, 513 (2002)] to show that for HM intrinsic polarization (α) below a critical value, the PSV MR shows an anomalous behavior of decreasing with increasing HM resistivity. We attributed this to the competition between the HM and the ferromagnetic (FM) layers in contributing to the overall device MR, and derived the expression for critical α.
Study on the sintering method of Terfenol-D
Authors: Zhao Shuwen , Liu Heyan , Han Xiaoyan , Meng Xiangxi , Qu Jingping , Li Yangxian , Li Songtao
Published: June 2006

A sintering method, which is called low-temperature instantaneous liquid-phase sintering with addition of Sn, is exploited to fabricate Terfenol-D sintered compacts. In this work, the influences of powder size, Sn content, compaction pressure, and sintering technique on the magnetic and mechanical properties have been investigated. A large magnetostriction (λ‖) of 546ppm at 12kOe is obtained for the sintered compact fabricated at the following conditions: a powder size <75μm, a Sn content of 8:100, a compaction pressure of 1.0GPa, and sintering at 250°C for 150s in the rapid thermal processor. In addition, the sintered compact fabricated by this means possesses higher oxidation resistance and its hard brittleness improves.
Nitrogen ion beam synthesis of InN in InP(100) at elevated temperature
Authors: Dhara S. , Magudapathy P. , Kesavamoorthy R. , Kalavathi S. , Sastry V. S. , Nair K. G. M. , Hsu G. M. , Chen L. C. , Chen K. H. , Santhakumar K. , Soga T.
Published: June 2006

The InN phase is grown in crystalline InP(100) substrates by 50keV N+ implantation at an elevated temperature of 400°C followed by annealing at 525°C in N2 ambient. Crystallographic structural and Raman scattering studies are performed for the characterization of grown phases. Temperature- and power-dependent photoluminescence studies show direct band-to-band transition peak ∼1.06eV at temperatures ⩽150K. Implantations at an elevated temperature with a low ion beam current and subsequent low temperature annealing step are found responsible for the growth of high-quality InN phase.
An electron transparent proton detector for neutron decay studies
Authors: Hoedl S. A. , Young A. R. , Ade H. , Lozano A.
Published: June 2006

We have developed an ultrathin (<100nm), very strong polyimide foil which can span more than 6×6cm2 and is ideal for the fabrication of low energy proton detectors. We have produced a proton detector geometry in which protons incident on the foil with kinetic energies greater than about 25keV produce, on average, more than ten secondary electrons in a conversion crystal evaporated on the back face of the foil. These secondary electrons can be “postaccelerated” and counted in a variety of detectors. The polyimide foils are much more durable than carbon foils previously used in similar detection geometries. LiF was chosen as the conversion crystal, which is relatively insensitive to exposure to air, improving their secondary electron yield under typical operating conditions. In addition, we describe the operation of a very simple, small scale proton accelerator and detector testing chamber capable of providing up to 10kHz of beam with energies between 10 and 50keV onto a biased target with a maximum ion contamination of 0.5%.
Femtosecond time-resolved laser-induced breakdown spectroscopy for detection and identification of bacteria: A comparison to the nanosecond regime
Authors: Baudelet Matthieu , Guyon Laurent , Yu Jin , Wolf Jean-Pierre , Amodeo Tanguy , Fréjafon Emeric , Laloi Patrick
Published: June 2006

Bacterial samples (Escherichia coli and Bacillus subtilis) have been analyzed by laser-induced breakdown spectroscopy (LIBS) using femtosecond pulses. We compare the obtained spectra with those resulting from the classical nanosecond LIBS. Specific features of femtosecond LIBS have been demonstrated, very attractive for analyzing biological sample: (i) a lower plasma temperature leading to negligible nitrogen and oxygen emissions from excited ambient air and a better contrast in detection of trace mineral species; and (ii) a specific ablation regime that favors intramolecular bonds emission with respect to atomic emission. A precise kinetic study of molecular band head intensities allows distinguishing the contribution of native CN bonds released by the sample from that due to carbon recombination with atmospheric nitrogen. Furthermore a sensitive detection of trace mineral elements provide specific spectral signature of different bacteria. An example is given for the Gram test provided by different magnesium emissions from Escherichia coli and Bacillus subtilis. An entire spectrum consists of hundred resolved lines belonging to 13 atomic or molecular species, which provides an ensemble of valuable data to identify different bacteria.
Efficiency of silicon micromachining by femtosecond laser pulses in ambient air
Authors: Hwang David J. , Grigoropoulos Costas P. , Choi Tae Y.
Published: June 2006

Femtosecond lasers have proven to be effective tools for precise micromachining. Taking advantage of the reduced heat diffusion and the sharp ablation threshold at comparatively low energy densities, subdiffraction limit sized craters have been machined on silicon wafers by single near infrared Ti:sapphire laser pulses using a high numerical aperture objective lens. Two different ablation regimes have been identified by varying the laser fluence. While two-photon absorption dominates in the low fluence regime, electronic diffusion is a major energy transport mechanism at higher laser fluences. Time-resolved pump-and-probe side-view imaging has been performed to investigate the energy coupling to the target specimen over a wide range of fluences (up to around 1000J∕cm2) at lateral beam dimensions of the order of micrometers. The decrease of the ablation efficiency in the high fluence regime (>10J∕cm2) is attributed to the strong interaction of the laser pulse with the laser-induced plasma.
Thermal budget of superconducting digital circuits at subkelvin temperatures
Authors: Savin A. M. , Pekola J. P. , Averin D. V. , Semenov V. K.
Published: June 2006

Superconducting single-flux-quantum (SFQ) circuits have so far been developed and optimized for operation at or above helium temperatures. The SFQ approach, however, should also provide potentially viable and scalable control and readout circuits for Josephson-junction qubits and other applications with much lower, millikelvin, operating temperatures. This paper analyzes the overheating problem which becomes important in this temperature range. We suggest a thermal model of the SFQ circuits at subkelvin temperatures and present experimental results on overheating of electrons and silicon substrate which support this model. The model establishes quantitative limitations on the dissipated power both for “local” electron overheating in resistors and “global” overheating due to ballistic phonon propagation along the substrate. Possible changes in the thermal design of SFQ circuits in view of the overheating problem are also discussed.
Utilization of magnetoelectric potential in ballistic nanodevices
Authors: Tan S. G. , Jalil M. B. A. , Bala Kumar S. , Teo K. L. , Liew Thomas
Published: June 2006

We propose a ballistic, coherent transmission system that utilizes the magnetic and electric barriers as Boolean input variables to realize functions similar in principle to the conventional logic gates. For practical implementation of these functions, we propose to use a device construct based on the high-electron-mobility transistor (HEMT) with ferromagnetic (FM) and nonmagnetic (NM) metal gates deposited on top of the HEMT heterostructure. This device system can be manipulated to realize multiple logic functions such as OR, AND, and their inverse by applying different magnetic and electric field configurations on the FM and the NM gates. The charge transport simulation is based on the single particle effective mass Hamiltonian and ballistic charge transport. The calculation results demonstrate clear binary outputs corresponding to various logic functions, with “high” (“low”) state having transmission probability of T>90% (T<10%).
Analysis of electron time-of-flight photocurrent data from a-Se
Authors: Emelianova E. V. , Benkhedir M. L. , Brinza M. , Adriaenssens G. J.
Published: June 2006

Electron time-of-flight transient photocurrents from amorphous selenium (a-Se) films were examined over the range of temperatures and applied electric fields in order to deduce a consistent model for the distribution of localized states in the a-Se conduction band tail. Superimposed on an exponential tail with characteristic energy of 20meV, a Gaussian defect band around E−Ec=0.3eV controls the field-independent drift mobility, and a broad distribution of deeper electron traps is responsible for the significant emission currents that are observed for several decades of time after the transit time.
Grain-boundary relaxation and its effect on plasticity in nanocrystalline Fe
Authors: Jang D. , Atzmon M.
Published: June 2006

Grain-boundary relaxation in nanocrystalline Fe was studied by high-resolution transmission electron microscopy (HREM), and its effect on plasticity was characterized by nanoindentation. Samples with grain size of 9.8nm were synthesized by mechanical attrition and subsequently annealed at low temperatures (80 and 100°C) without affecting the grain size. While the hardness is not significantly affected by annealing, the strain-rate sensitivity peaks as a function of annealing time, suggesting two competing processes. HREM images show grain-boundary relaxation during annealing. Initially disconnected lattice planes were observed to evolve into a more continuous and ordered structure with regularly spaced grain-boundary dislocations.
Electrical pulse formation during high temperature reaction between Ni and Al
Authors: Setoodeh Mona , Martirosyan K. S. , Luss Dan
Published: June 2006

An electric voltage pulse (duration of about 2ms) with an amplitude of up to 0.6V was generated during the reaction between nickel and aluminum powders by a high temperature moving reaction front. The electrical signal formed during the initial stages of the combustion was annihilated before the moving front attained its maximum temperature. The voltage amplitude and combustion temperature depended on the particle size of the reactants as well as the Al to Ni ratio in the reactant mixture, and their largest values were attained for a mixture containing 27–31.5wt% Al. The combustion temperature increased when smaller Al particles were used. The electric signals annihilated either due to the growth of the initially formed product layer and∕or as a result of the formation of a molten Al matrix as the reaction propagated. Oscillatory signals formed during unstable combustion in which the reaction front was perturbed. Unipolar and nonoscillating signals formed when the combustion front was planar. We conjecture that the electric field was generated by the different diffusion rates of charge carriers through a reaction generated thin exterior intermediate products shell of Al3Ni∕Al3Ni2.
Finite difference simulations of permittivity and electric field statistics in ceramic-polymer composites for capacitor applications
Authors: Calame J. P.
Published: June 2006

Finite difference quasielectrostatic modeling is used to predict the complex dielectric permittivity of barium titanium oxide (BTO)—polymer composites of interest for capacitor applications. The simulations explore the effects of the microstructural arrangement of spherical ceramic particles, the volume filling fraction of ceramic, and the type of polymer on the composite permittivity. For composites with randomly positioned ceramic particles, a soft percolation regime is found between volume filling fractions of 0.35 and 0.5 that leads to a more gradual growth in permittivity compared to ordered arrangements of particles. For BTO dispersed in a representative relaxor ferroelectric polymer, dielectric constants as high as 300 are predicted at a filling fraction of 0.45. Electric field statistics inside the composites are also computed, and localized intensification factors in the range of three to eight times the applied field are predicted, with an incrementally linear growth in high-field probability with increasing filling fraction in the soft percolation regime. The deleterious effect of air voids on composite permittivity is also explored.
Achieving a photonic band edge near visible wavelengths by metallic coatings
Authors: Lin S. Y. , Ye D.-X. , Lu T.-M. , Bur J. , Kim Y. S. , Ho K. M.
Published: June 2006

A metallic coating method is used to modify the optical properties of a dielectric photonic lattice and to achieve a near visible photonic band edge. It is experimentally shown that the linear scaling rule of a metallic band edge versus lattice constant holds only for perfect conducting metals. When a metal deviates from a perfect conducting behavior near the plasma wavelength, the metallic photonic band edge is pinned and is nearly independent of lattice constant. For our tungsten photonic lattice, the pinning occurs at λ≈1.5–2μm. By using a thin copper coating (∼70nm) to a dielectric photonic lattice, a photonic band edge at λ∼750nm is observed. This achievement is made possible by the fact that copper is a good conductor at visible wavelengths and the linear scaling rule holds. Finally, this coating method allows for tailoring photonic properties through material engineering at the nanometer scale.