bluuebunny/crossref_metadata_2025 huggingface dataset:
High reliability linear drive device for artificial hearts
Authors: Ji Jinghua , Zhao Wenxiang , Liu Guohai , Shen Yue , Wang Fangqun
Published: March 2012

In this paper, a new high reliability linear drive device, termed as stator-permanent-magnet tubular oscillating actuator (SPM-TOA), is proposed for artificial hearts (AHs). The key is to incorporate the concept of two independent phases into this linear AH device, hence achieving high reliability operation. The fault-tolerant teeth are employed to provide the desired decoupling phases in magnetic circuit. Also, as the magnets and the coils are located in the stator, the proposed SPM-TOA takes the definite advantages of robust mover and direct-drive capability. By using the time-stepping finite element method, the electromagnetic characteristics of the proposed SPM-TOA are analyzed, including magnetic field distributions, flux linkages, back- electromotive forces (back-EMFs) self- and mutual inductances, as well as cogging and thrust forces. The results confirm that the proposed SPM-TOA meets the dimension, weight, and force requirements of the AH drive device.
An integrated micro-chip for rapid detection of magnetic particles
Authors: Gooneratne Chinthaka P. , Liang Cai , Giouroudi Ioanna , Kosel Jürgen
Published: March 2012

This paper proposes an integrated micro-chip for the manipulation and detection of magnetic particles (MPs). A conducting ring structure is used to manipulate MPs toward giant magnetoresistance (GMR) sensing elements for rapid detection. The GMR sensor is fabricated in a horseshoe shape in order to detect the majority of MPs that are trapped around the conducting structure. The GMR sensing elements are connected in a Wheatstone bridge circuit topology for optimum noise suppression. Full fabrication details of the micro-chip, characterization of the GMR sensors, and experimental results with MPs are presented in this paper. Experimental results showed that the micro-chip can detect MPs from low concentration samples after they were guided toward the GMR sensors by applying current to the conducting ring structure.
Cobalt driven enhancement of nanomagnetism in iron-oxide nanoparticles encapsulated in a synthetic ferritin shell
Authors: Skoropata E. , Ceci P. , Kasyutich O. , van Lierop J.
Published: March 2012

We have examined the effects of Co doping (0–12% relative to total metal) on the magnetic properties of iron-oxide nanoparticles incorporated in a synthetic ferritin shell. Mössbauer spectroscopy revealed that the nanoparticles consisted of a mixture of Fe3O4 and γ-Fe2O3, and that Co was integrated exclusively into the B-sites of the Fe3O4 phase. Cobalt doping resulted in the formation of CoxFe3-xO4/γ-Fe2O3 nanoparticles with x = 0, 0.25, 0.51, 0.56, and 0.63. Magnetometry and susceptometry experiments showed that substantial enhancements in the coercivities, blocking temperatures and anisotropy constants of the magnetoferritin nanoparticles occurred for all Co doping levels. Our results show that the Co altered significantly the local atomic Fe magnetism and enhanced the magnetic nanoparticle anisotropy considerably.
Influence of ion beam assisted deposition parameters on the growth of MgO and CoFeB
Authors: Ferreira Ricardo , Cardoso Susana , Freitas Paulo P. , Petrova Rumyana , McVitie Stephen
Published: March 2012

The effect of the kinetic parameters of an assistance ion beam on the crystallization of ion beam deposited MgO was investigated. It is shown that the crystallization of MgO in the as-deposited state is strongly dependent on the assistance beam parameters. Furthermore, two deposition regimes corresponding to different ranges of the assistance beam energy are found. XRD and TEM studies of CoFeB/MgO/CoFeB with MgO deposited in the two regimes show that CoFeB crystallization is favored when low energy assist beams are used, despite no differences being found in the MgO.
Modelling and optimization of submicron Hall sensors for the detection of superparamagnetic beads
Authors: Manzin A. , Nabaei V. , Kazakova O.
Published: March 2012

This paper deals with the numerical modeling of the electric potential distribution inside semiconductor Hall effect devices, under the presence of non-uniform magnetic fields. The model is applied to study miniaturized sensors for the detection of superparamagnetic nanobeads. The magnetic moment resolution is evaluated for different Hall probe geometries, by varying the bead size and its distance from the sensor surface.
Magnetically driven spinning nanowires as effective materials for eradicating living cells
Authors: Choi Daniel S. , Hopkins Xiaoping , Kringel Rosemarie , Park Jungrae , Jeon In Tak , Keun Kim Young
Published: March 2012

We present a method to inflame cells, in vitro, by applying an alternating current (ac) magnetic field to ferromagnetic nanowires (NWs) internalized by living cells. Nickel (Ni) NWs were internalized by human embryonic kidney cells (HEK-293). The application of ac magnetic field to the cells induced spinning of the cells via the motion of internalized NWs. This resulted in cell death by physically causing damage. A study of the response of cytokine to cells with spinning NWs shows increased interleukin-6 effects when compared with responses from non-spinning cells. The spinning effect of cells caused by the application of magnetic field can be used to target and inflame the cells. Such experiments suggest the possibility of inflaming cells for the treatment of cancer.
Magnetostriction measurement of a giant magnetoresistance film on a practical substrate covered by a shield layer
Authors: Okita Kazuhiko , Ishiyama Kazushi , Miura Hideo
Published: March 2012

Magnetostriction constant of a magnetic thin film is conventionally measured by detecting the deformation of a coupon sample that consists of the magnetic film deposited on a thin glass substrate (e.g., cover glass of size 10 mm × 25 mm) under an applied field using a laser beam [A. C. Tam and H. Schroeder, J. Appl. Phys. 64, 5422 (1988)]. This method, however, cannot be applied to films deposited on actual large-size substrates (wafers) with diameter from 3 to 6 in. or more. In a previous paper [Okita et al., J. Phys.: Conf. Ser. 200, 112008 (2010)], the authors presented a method for measuring magnetostriction of a magnetic thin film deposited on an actual substrate by detecting the change of magnetic anisotropy field, Hk, under mechanical bending of the substrate. It was validated that the method is very effective for measuring the magnetostriction constant of a free layer on the actual substrate. However, since a Ni-Fe shield layer usually covers a magnetic head used for a hard disk drive, this shield layer disturbs the effective measurement of R-H curve under minor loop. Therefore, a high magnetic field that can saturate the magnetic material in the shield layer should be applied to the head in order to measure the magnetostriction constant of a pinned layer under the shield layer. In this paper, this method was applied to the measurement of the magnetostriction constant of a pinned layer under the shield layer by using a high magnetic field up to 320 kA/m (4 kOe).
X-ray imaging of nonlinear resonant gyrotropic magnetic vortex core motion in circular permalloy disks
Authors: Mesler Brooke L. , Buchanan Kristen S. , Im Mi-Young , Fischer Peter
Published: March 2012

We report experimental evidence of nonlinear gyrotropic vortex core motion. Using soft x-ray transmission microscopy we observed the time-averaged dynamic response of a magnetic vortex core in a 2 μm diameter, 100 nm thick permalloy (Ni80Fe20) disk as a function of the amplitude and frequency of an applied RF magnetic field. At lower amplitude fields a single resonance was observed, but two distinct resonances, above and below the low amplitude resonance frequency, were observed when higher amplitude fields were applied. The results are discussed in the context of a nonlinear vortex energy potential.
Microwave-assisted magnetic recording simulation on exchange-coupled composite medium
Authors: Tanaka T. , Kato A. , Furomoto Y. , Md Nor A. F. , Kanai Y. , Matsuyama K.
Published: March 2012

The potential of microwave-assisted magnetic recording on exchange-coupled composite (ECC) media is investigated by numerically simulating read/write processes with respect to the physical and magnetic properties of the soft section of ECC media. To obtain desirable recording performance, the thickness of the soft section must be comparable to the exchange length. Under such condition, the optimal microwave frequency decreases owing to the non-uniformity of the reversal mode. A relatively high anisotropy field in the soft section produces high signal-to-noise ratios. Moreover, large saturation magnetization of the soft section enhances the magnetization reversal of ECC grains but excessive enhancement is likely to induce wide writing, which decreases the high track density.
Structural expansion and suppression of spiral spin state in Pb-doped BiFeO3 (00l) epitaxial thin films
Authors: Bohra Murtaza , Wu C. P. , Yeh H. J. , Chou H. , Chen W. C. , Lin J. W. , Lin J. G.
Published: March 2012

We demonstrate that Pb-doped BiFeO3 thin films grown on a strain relaxed SrRuO3 bottom layer on SrTiO3 (STO) substrate undergo a structural expansion effect that is highly dependent on growth temperature, TS. Highly symmetric cubic-like or low symmetric tetragonal structures can be grown at lower TS (= 650 °C) and higher TS (= 700 °C), respectively. The structural expansion and changes in symmetry provide the iron ion with a non-vanished orbital quenching effect, which produces the strong spin-orbital coupling that suppresses the spiral spin structure and initiates a canted antiferromagnetic phase with a larger net saturated magnetic moment at room temperature.
Angular dependence and temperature effect on switching field distribution of Co/Pd based bit patterned media
Authors: Li W. M. , Huang X. L. , Shi J. Z. , Chen Y. J. , Huang T. L. , Ding J.
Published: March 2012

The motivation for this work is rooted in the reversal process that occurs in perpendicularly magnetic Co/Pd multilayered based bit-patterned media. In our work, temperature effect and angle dependence of critical fields (Hcr) and switching field distribution (SFD) are studied by both experiment and simulation. From our observation, when temperature increases from 77 to 300 K, the critical field of patterned area decreases from 13 to 11 kOe. Absolute SFD decreases from 2.6 to 2.2 kOe as thermal energy assists islands reversal. The relative SFD (SFD/Hcr) keeps constant with temperature. Although critical fields and absolute SFD vary with angles, relative SFD is independent of the field angle. The interactions between islands broaden relative SFD from 12% to 20% after considering dipolar interactions. The relative SFD by simulation agrees well with our experimental observation.
Structural and magnetic phase transition of mixed olivines LixFe1−yNiyPO4 by lithium deintercalation
Authors: Lee In Kyu , Kim Chin Mo , Kim Sam Jin , Kim Chul Sung
Published: March 2012

The structural and magnetic phase transitions of LixFe1–yNiyPO4 were investigated by x-ray diffraction (XRD), superconducting quantum interference device magnetometry, and Mössbauer spectroscopy. Rietveld refinement of XRD patterns of LiFe1–yNiyPO4 (0.0 ≤ y ≤ 0.6) revealed that the lattice parameters a0 = 10.328, b0 = 6.007, and c0 = 4.692 Å for LiFePO4 changed linearly to a0 = 10.154, b0 = 5.923, and c0 = 4.687 Å for LiFe0.4Ni0.6PO4 with the substitution of Ni ions. Also, the fully lithium-deintercalated Fe1–yNiyPO4 (0.0 ≤ y ≤ 0.6) series had enhanced lattice distortions along the c axis compared to LiFe1-yNiyPO4 because the Jahn–Teller distortion changed as the unit cell volume decreased due to lithium ion deintercalation. LiFe1–yNiyPO4 has an antiferromagnetic order; the magnetic Nèel temperature (TN) decreased from 51 K for LiFePO4 to 36 K for LiFe0.4Ni0.6PO4. Fully deintercalated Fe1–yNiyPO4 has strong antiferromagnetic order; TN decreased from 114 K for FePO4 to 62 K for Fe0.4Ni0.6PO4 due to the charge transition of Fe2+/Fe3+ and Ni2+/Ni3+, mediated by lithium ion vacancies in an olivine structure. The Mössbauer spectra below the TN of LixFe1–yNiyPO4 (x = 0, 1, 0.0 ≤ y ≤ 0.6) were fitted with eight asymmetrical Lorentzian functions. The electric quadrupole splitting value (ΔEQ) of LiFe1–yNiyPO4 is larger than that of Fe1–yNiyPO4 due to more asymmetric charge distributions around Fe2+ (3d6) than Fe3+ (3d5) in FeO6 sites.
Theoretical study of point-contact Andreev reflection spectroscopy for ferromagnetic-metal/multi-band superconductor junctions
Authors: Ohtori Hiroyuki , Imamura Hiroshi
Published: March 2012

This paper theoretically analyzes the Andreev reflection in normal-conductor/multi-band super-conductor junctions. We applied Bogoliubov-de Gennes equations to the case of superconductors with extended s-waves and calculated the respective point-contact Andreev reflection (PCAR) spectra. Our results showed that the PCAR measurement with high-Tc superconductivity can be used as a tool for measuring the spin-polarization of ferromagnetic materials.
Mechanism analysis of ultrafast magnetic switching
Authors: Li J. M. , Xu B. X. , Zhang J. , Ye K. D.
Published: March 2012

The TbFeCo magneto-optical media with the coercivity of bigger than 1 kOe are used for the investigation of ultrafast magnetic switching and thermal demagnetization. The magnetic marks induced by 25 fs laser pulses with circular polarization have been observed. The thermal demagnetization spots are measured based on their digital images for the estimation of laser fluence. Based on the experimental parameters, a theoretical calculation for estimation of the maximum applicable effective magnetic field is conducted, where the 25 fs laser pulses with wavelength of 800 nm, NA of 0.6 and circular polarization is applied. The results show that, with the maximum applicable laser fluence, the effective magnetic field on the outer boundary of the laser spot defined by 1/e electrical field amplitude is about 0.52 kOe. It implies that the spin flips can be implemented by a small effective magnetic field, which can be explained with the analysis of spin temperature.
Rectifying characteristics, magnetic tunability, and photovoltaic response in La0.8Hf0.2MnO3/0.7 wt% Nb-SrTiO3 heteroepitaxial junctions
Authors: Wu Z. P. , Wang L. , Gao J.
Published: March 2012

Heterojunctions composed of tetravalent cation-doped La0.8Hf0.2MnO3 (LHMO) and 0.7 wt% Nb-doped SrTiO3 were fabricated using pulsed laser deposition method and investigated under different fields (electric, magnetic, and optic). The heterojunctions exhibited excellent rectifying behavior in a wide temperature range and significant magnetic field modulated properties. Prominent photovoltaic effect was also observed in the formed junctions. Special attention has been paid to the temperature dependence of the diffusion voltage (Vd) and photovoltage (Voc). When temperature increased from 40 K to 300 K, Vd decreased from 1.13 V to 0.16 V. It is notable that, under illumination of a light with λ = 532 nm, Voc dropped from 650 to 80 mV. No sudden change of Vd and Voc was observed at the metal-insulator transition temperature, which is probably caused by the band structure of the LHMO.
Ordered magnetic microdroplets array on magnetic films
Authors: Lee Chiun Peng , Yang Shu Ting , Wei Zung Hang
Published: March 2012

With the development of magnetic droplet-based biochips, the manipulation of magnetic droplets has become an important issue. In this study, deposited magnetic circular films are used to assist the positioning of magnetic microdroplets, which are separated from a mother droplet caused by the Rosensweig instability under a magnetic field. Magnetic microdroplets are attracted by the concentrated magnetic flux density caused by out-of-plane magnetization of the magnetic films, and magnetic films confine the positions of droplets. Through adjusting the applied field strength, droplet arrays with different number densities can be obtained. One-to-one correspondences between droplets and magnetic films can be achieved within specific magnetic field ranges.
Magnetism of dilute Co(Hf) and Co(Pt) nanoclusters
Authors: Balamurugan B. , Skomski R. , Das B. , Li X. Z. , Shah V. R. , Manchanda P. , Kashyap A. , Sellmyer D. J.
Published: March 2012

An investigation of the magnetic properties of Co-rich nanoparticles alloyed with a small fraction of Pt and Hf is presented. Co(Hf) and Co(Pt) nanoparticles with less than 15 at% of dopants were produced using a cluster-deposition method. The nanoparticles have sizes of less than 10 nm and show improved magnetic properties upon doping. Maximum coercivities of 900 Oe (at 300 K) and 2000 Oe (at 10 K) were observed for Co nanoparticles alloyed with 14.1 at% of Hf. Doped nanoparticles also exhibit high anisotropies, such as K1 = 9.98 Mergs/cm3 (14.1 at% of Hf) and K1 = 8.24 Mergs/cm3 (9.5 at% of Pt), as compared to Co nanoparticles (K1 = 6.21 Mergs/cm3).
Tunnel magnetoresistance effect in magnetic tunnel junctions with epitaxial Co2FeAl0.5Si0.5 Heusler electrodes on MgO (110) single substrates
Authors: Tezuka N. , Mitsuhashi F. , Sugimoto S.
Published: March 2012

Tunnel magnetoresistance effect has been investigated for magnetic tunnel junctions with Co2FeAl0.5Si0.5 Heusler electrodes on a Cr-bufferd MgO (110) substrate. The grown Co2FeAl0.5Si0.5 has L21 structure for annealing above 500 °C. The TMR ratio of 73% at room temperature and 103% at 5 K were obtained for a junction consists of MgO(110) substrate/Cr/Co2FeAl0.5Si0.5/Al-oxide/Co75Fe25/IrMn/Ta. The tunnel magnetoresistance ratio obtained in this study is almost the same as that estimated by using magnetic tunnel junction with the same kind of Co2FeAl0.5Si0.5 electrode on a Cr-bufferd MgO (001) substrate. Smaller temperature dependence of magnetoresistance ratio was also found for the junctions on Cr-bufferd MgO(110) substrates.
Sputter-prepared BiFeO3(001) films on L1 FePt(001)/glass substrates
Authors: Chang H. W. , Yuan F. T. , Shih C. W. , Wang C. R. , Chang W. C. , Jen S. U.
Published: March 2012

The preparation of BFO films by sputtering at a temperature as low as 450 °C on glass and commercial Pt/Ti/SiO2/Si(001) substrates have been studied. The underlayers with different orientations were prepared on the glass substrates including strongly textured Pt(111) and L10-FePt(001) induced by rapid thermal annealing process. Isotropic perovskite BFO grains with size of about 200 nm formed on the commercial substrates, showing larger surface roughness. Pt(111) suppresses BiFeO3 phase. Single phase perovskite BFO with strong (001) texture, reduced surface roughness and fine grain size was formed on the L10-FePt(001) buffer layer. Considerable enhancement of ferroelectric properties was achieved as compared to the films grown on commercial substrate.
Magnetic specific heat studies of two Ising spin 1/2 chain systems M(N3)2(bpy)
Authors: Hamida Youcef , Danilovic Dusan , Yuen Tan , Li Kunhao , Li Jing
Published: March 2012

M(N3)2(bpy) [where M = Cu(II), Co(II), N3 = azide, and bpy = 4,4′-bipyridine] are two newly synthesized metal-organic framework (MOF) systems, in which the divalent M ions are connected though the azide ligands forming almost ideal magnetic 1 D chains. Specific heat measurements were performed on these compounds and the magnetic specific heats were deduced using appropriate methods for estimating the lattice specific heat. The magnetic specific heat data were analyzed and fit to the Ising model. The exchange interaction J/kB values of 13.1 K for Cu(N3)2(bpy) and 8.2 K for Co(N3)2(bpy) were obtained and compared to the J values from fitting the measured magnetic susceptibility data.
Thermally induced synchronization and stochastic resonance between magnetization regimes in spin-transfer nano-oscillators
Authors: d’Aquino M. , Serpico C. , Bonin R. , Bertotti G. , Mayergoyz I. D.
Published: March 2012

The thermally induced synchronization of transitions between different magnetization regimes with weak ac-injected spin-polarized current is considered for a spin-valve-like magnetic nano-system, where magnetization dynamics is described by the Landau-Lifshitz-Slonczewski equation. We apply suitable averaging techniques and derive a non-autonomous stochastic differential equation for the free energy. By using this equation, we demonstrate that synchronization of thermal transitions with weak ac excitation is ascribed to a general form of stochastic resonance. Numerical computations confirm the accuracy of the theory.
Microfabrication of magnetostrictive beams based on NiFe film doped with B and Mo for integrated sensor systems
Authors: Alfadhel A. , Gianchandani Y. , Kosel J.
Published: March 2012

This paper reports the development of integrated micro-sensors consisting of 1 -µm-thick magnetostrictive cantilevers or bridges with 500 µm in length and conducting interrogation elements. The thin films are fabricated by sputter deposition of NiFe doped with B and Mo, and the magnetic properties are enhanced by field annealing, resulting in a coercivity of 2.4 Oe. In operation, an alternating current applied to the interrogation elements magnetizes the magnetostrictive structures. The longitudinal resonant frequency is detected as an impedance change of the interrogation elements. The magnetostrictive micro-beams provide high resonant frequencies—2.95 MHz for the cantilever and 5.46 MHz for the bridge—which can be exploited to develop sensors of high sensitivity.
Modeling for write synchronization in bit patterned media recording
Authors: Lin Maria Yu , Chan Kheong Sann , Chua Melissa , Zhang Songhua , Kui Cai , Elidrissi Moulay Rachid
Published: March 2012

Bit patterned media recording (BPMR) is a contender for next generation technology after conventional granular magnetic recording (CGMR) can no longer sustain the continued areal density growth. BPMR has several technological hurdles that need to be overcome, among them is solving the problem of write synchronization. With CGMR, grains are randomly distributed and occur almost all over the media. In contrast, BPMR has grains patterned into a regular lattice on the media with an approximate 50% duty cycle. Hence only about a quarter of the area is filled with magnetic material. During writing, the clock must be synchronized to the islands or the written in error rate becomes unacceptably large and the system fails. Maintaining synchronization during writing is a challenge as the system is not able to read and write simultaneously. Hence reading must occur periodically between the writing frequently enough to re-synchronize the writing clock to the islands. In this work, we study the requirements on the lengths of the synchronization and data sectors in a BPMR system using an advanced model for BPMR, and taking into consideration different spindle motor speed variations, which is the main cause of the mis-synchronization.
Synthesis of Fe–Co nanoparticles with high saturation magnetization by low-temperature post-annealing
Authors: Ogawa Tomoyuki , Takano Hideaki , Kura Hiroaki , Takahashi Migaku
Published: March 2012

Fe–Co nanoparticles were synthesized by the thermal decomposition of a mixed precursor of Fe(CO)5 and Co2(CO)8. As-synthesized Fe–Co nanoparticles formed clusters 20 nm in diameter consisting of many primary 5-nm nanoparticles. The saturation magnetization of as-synthesized Fe–Co nanoparticles was about 140 emu/gnet. This was only 60% of the saturation magnetization of bulk Fe70Co30, due to the presence of a surfactant and the small grain size within the primary nanoparticles of less than 20 nm. During post-annealing at 250 °C, the primary NPs sintered, and the nanoparticle clusters grew into a single crystal by atomic diffusion. As a result, the saturation magnetization reached a maximum of 212 emu/gnet for Fe : Co = 68 : 32, and varied with chemical composition in a relationship similar to the Slater-Pauling curve.
Structural and magnetic properties of planar nanowire arrays of Co grown on oxidized vicinal silicon (111) templates
Authors: Arora S. K. , O’Dowd B. J. , Nistor C. , Balashov T. , Ballesteros B. , Lodi Rizzini A. , Kavich J. J. , Dhesi S. S. , Gambardella P. , Shvets I. V.
Published: March 2012

We fabricated planar arrays of Co nanowires (NWs) on oxidized step-bunched Si (111) templates using shallow angle deposition. These planar NW arrays exhibit ferromagnetic behavior at room temperature for NW widths down to 25 nm. The NWs possess polycrystalline character with hcp-crystal structure, and present a lightly oxidized interface when capped with MgO. The magnetic anisotropy of the NW array is dominated by the shape anisotropy, which keeps the magnetization in-plane with easy axis parallel to the wires. By reducing the inter-wire separation, we obtain NW arrays with reduced coercivity demonstrating the importance of magneto-static interactions in determining the magnetic properties of the NWs.
Dynamic magnetoelastic properties of epoxy-bonded Sm0.88Nd0.12Fe1.93 pseudo-1-3 negative magnetostrictive particulate composite
Authors: Yang Fang , Leung Chung Ming , Or Siu Wing , Liu Wei , Zhang Zhidong , Duan Yuan-Feng
Published: March 2012

Pseudo-1-3 negative magnetostrictive particulate composite is prepared by embedding and aligning light rare earth (Sm and Nd)-based negative magnetostrictive Sm0.88Nd0.12Fe1.93 particles with randomly distributed sizes of 10–180 μm in a passive epoxy matrix using a particle volume fraction of 0.5. The dynamic magnetoelastic properties of the composite are investigated as a function of both magnetic bias field and frequency under a constant magnetic drive field. The dynamic relative permeability (μr33) exhibits a flat frequency response with no observable dispersion at all bias field levels, except for the fundamental shape resonance range of 40–50 kHz. The free (μr33T) and clamped (μr33S) relative permeabilities attain their maximum values at low bias field levels of ≤10 kA/m because of the relatively easy 180° domain-wall motion. The elastic modulus at constant magnetic field strength (E3H) and that at constant magnetic flux density (E3B) show a maximum negative-ΔE effect, accompanying a maximum dynamic strain coefficient (d33) of −2 nm/A, at about 100 kA/m due to the maximum motion of non-180° domain walls.
Tuning exchange anisotropy in nanocomposite AgMn alloys
Authors: Jiménez-Villacorta F. , Marion J. L. , Sepehrifar T. , Lewis L. H.
Published: March 2012

Silver manganese alloys of composition Ag100−xMnx (25 ≤ x ≤ 40) were prepared by rapid solidification to investigate their reported antiferromagnetic character. Thorough characterization of their structural, compositional, and magnetic features indicates the formation of a phase-separated fcc-type structure in all studied alloys with lattice parameters and coherently diffracting region sizes on the order of 40–100 nm that are strongly correlated with the Mn content. Magnetic measurement reveals a blocking temperature TB ∼ 105 K that is accompanied by unprecedented exchange bias values up to 1.7 T (17 kOe) at low temperatures. The magnitudes of the exchange bias field and the blocking temperature increase with increasing Mn concentration, suggesting a very sensitive balance between Mn content and magnetic character in these alloys that fosters tuning of the resultant exchange bias.
Time-dependent dynamic behavior of light diffraction in ferrofluid
Authors: Chung Min-Feng , Chou S. E. , Fu Chao-Ming
Published: March 2012

The time-dependent dynamic behavior of diffraction patterns induced by external magnetic field in a suspension of nano-sized magnetic particles (Fe3O4) in a water-based magnetic fluid was investigated. It was observed that the diffraction pattern changed with time as the magnetic field was applied. In the absence of applied magnetic field, there was no diffraction pattern in the screen. When the magnetic field was applied, the transmitted light was perpendicular to the magnetic field, and the diffraction pattern was unstable. There were many small lines and points moving with time. After one minute, the diffraction pattern turned stable, and the small lines became longer. This time-dependent behavior helps us to understand the evolution of the forming chains of magnetic nanoparticles. Moreover, we have measured the other diffraction pattern, the transmitted light propagating parallel to the applied field. These time-dependent diffraction patterns give a new point to understand the dynamic three-dimensional structure of magnetic fluid under a dc magnetic field.
Excitation of magnetic normal modes by spin-torque: a Lagrangian approach
Authors: Consolo G. , Giovannini L. , Zivieri R.
Published: March 2012

In this paper the spin-wave normal modes in a nanopillar with circular cross-section, excited by the simultaneous action of an external magnetic field and a spin-polarized current, are investigated. The study is performed by using a micromagnetic approach based upon a linearized Lagrangian formalism which requires to solve a complex generalized nonHermitian eigenvalue problem. In all the studied configurations it is shown that, in the linear regime and independently of the orientation of the external bias field, a spatially uniform spin-polarized current excites the lowest-frequency mode, which is not necessarily the quasi-uniform mode of the spectrum. The obtained numerical results are also confirmed by finite-difference time-domain numerical simulations.
Numerical simulation of a W-band four-cavity gyroklystron amplifier
Authors: Xu Shou-Xi , Liu Pu-Kun , Geng Zhi-Hui
Published: March 2012

Using a self-consistent nonlinear code and particle-in-cell simulation, the beam-wave interaction of a W-band four-cavity gyroklystron amplifier has been analyzed. The gyroklystron amplifier operates in the fundamental harmonic TE01 circular electric mode. The dependence of the efficiency and gain on the input power and the electron velocity ratio are studied. The effect of the electron velocity spread on the bandwidth and the electronic efficiency is analyzed. The simulated results show that the designed stable gyroklystron amplifier can produce an output power of over 142 kW, 33.8% electronic efficiency, 37 dB gain, and a 3 dB bandwidth of 1 GHz for a 70 kV, 6 A electron beam.
Solitary waves and double layers in an ultra-relativistic degenerate dusty electron-positron-ion plasma
Authors: Roy N. , Tasnim S. , Mamun A. A.
Published: March 2012

A rigorous theoretical investigation has been made on the formation of the nonlinear structures (viz., solitary waves, double layers) in a dusty electron-positron-ion plasma (containing inertialess degenerate electrons and positrons, cold, mobile, inertial ions, and negatively charged stationary dust). The pseudo potential method has been employed in this theoretical investigation. The basic features of the solitary waves and double layers, which are associated with positive ion dynamics and pressures of degenerate electrons and positrons, are identified. The co-existence of positive and negative solitary waves, and existence of either positive or negative double layers have been theoretically observed for certain range of different plasma parameters. The implications of our results in astrophysical compact objects have been briefly discussed.
Diffusion, sedimentation, and rheology of concentrated suspensions of core-shell particles
Authors: Abade Gustavo C. , Cichocki Bogdan , Ekiel-Jeżewska Maria L. , Nägele Gerhard , Wajnryb Eligiusz
Published: March 2012

Short-time dynamic properties of concentrated suspensions of colloidal core-shell particles are studied using a precise force multipole method which accounts for many-particle hydrodynamic interactions. A core-shell particle is composed of a rigid, spherical dry core of radius a surrounded by a uniformly permeable shell of outer radius b and hydrodynamic penetration depth κ−1. The solvent flow inside the permeable shell is described by the Brinkman-Debye-Bueche equation, and outside the particles by the Stokes equation. The particles are assumed to interact non-hydrodynamically by a hard-sphere no-overlap potential of radius b. Numerical results are presented for the high-frequency shear viscosity, η∞, sedimentation coefficient, K, and the short-time translational and rotational self-diffusion coefficients, Dt and Dr. The simulation results cover the full three-parametric fluid-phase space of the composite particle model, with the volume fraction extending up to 0.45, and the whole range of values for κb, and a/b. Many-particle hydrodynamic interaction effects on the transport properties are explored, and the hydrodynamic influence of the core in concentrated systems is discussed. Our simulation results show that for thin or hardly permeable shells, the core-shell systems can be approximated neither by no-shell nor by no-core models. However, one of our findings is that for κ(b − a) ≳ 5, the core is practically not sensed any more by the weakly penetrating fluid. This result is explained using an asymptotic analysis of the scattering coefficients entering into the multipole method of solving the Stokes equations. We show that in most cases, the influence of the core grows only weakly with increasing concentration.
Field-induced degeneracy regimes in quantum plasmas
Authors: Akbari-Moghanjoughi M.
Published: March 2012

It is shown that in degenerate magnetized Fermi-Dirac plasma where the electron-orbitals are quantized distinct quantum hydrodynamic regimes emerge in which the nonlinear density waves behave differently. The Coulomb interaction among degenerate electrons affects the electrostatic nonlinear wave dynamics more significant in the ground-state Landau quantization or the so-called quantum-limit (l = 0) rather than in the classical-limit (l=∞). It is also remarked that the effective electron quantum potential like the number-density and degeneracy pressure is independent of the applied magnetic field in the classical-limit plasma, while it depends strongly on the field strength in the quantum-limit. Current findings are equally important in the study of wave dynamics in arbitrarily high magnetized astrophysical and laboratory dense plasmas.
Charged-particle oscillation in direct current voltage biased plane-parallel conductors
Authors: Nae Cho Sung
Published: March 2012

The phenomenon of charged-particle oscillation in DC voltage biased plane-parallel conductors is discussed. Traditionally accepted mechanism for explaining the oscillatory behavior of charged particles in such system attributes the phenomenon to a process of charge exchange, which takes place when charged-particle is in close proximity to one of the electrodes. A novel finding here reveals that for microscopic or smaller particles under special circumstances, charged-particle oscillation does not involve charge exchanges. Such system radiates and the frequency of emitted radiation is controlled by a DC voltage biased across the two plane-parallel electrodes.
Three-dimensional quantitative chemical roughness of buried ZrO2/In2O3 interfaces via energy-filtered electron tomography
Authors: Zhong X. Y. , Kabius B. , Schreiber D. K. , Eastman J. A. , Fong D. D. , Petford-Long A. K.
Published: March 2012

The protocol to calculate the chemical roughness from three-dimensional (3-D) data cube acquired by energy-filtered electron tomography has been developed and applied to analyze the 3-D Zr distribution at the arbitrarily shaped interfaces in the ZrO2/In2O3 multilayer films. The calculated root-mean-square roughness quantitatively revealed the chemical roughness at the buried ZrO2/In2O3 interfaces, which is the deviation of Zr distribution from the ideal flat interface. Knowledge of the chemistry and structure of oxide interfaces in 3-D provides information useful for understanding changes in the behavior of a model ZrO2/In2O3 heterostructure that has potential to exhibit mixed conduction behavior.
Size-dependent ferromagnetic phase transition in Sm.5Sr.5MnO3 nanoparticles
Authors: Zhou S. M. , Guo Y. Q. , Zhao J. Y. , Wang C. L. , He L. F. , Shi L.
Published: March 2012

Magnetic properties of Sm0.5Sr0.5MnO3 nanoparticles with different particle sizes are investigated. It is found that all the nanoparticles show a first-order ferromagnetic transition under low magnetic fields, but a second-order one above a critical field HCR. As the particle size decreases, the ferromagnetic transition temperature, the thermal hysteresis width in the magnetizations, and HCR exhibit a significant decrease, which indicates that the ferromagnetism is weakened and the first-order transition is softened. A detailed analysis on the magnetic susceptibilities of these nanoparticles reveals that this weakening and softening are attributed to the weakened double-exchange interactions and the strongly suppressed charge-ordered antiferromagnetic state by the size reduction, respectively.
The effect of safety factor profile on transport in steady-state, high-performance scenarios
Authors: Holcomb C. T. , Ferron J. R. , Luce T. C. , DeBoo J. C. , Park J. M. , White A. E. , Turco F. , Rhodes T. L. , Doyle E. J. , Schmitz L. , Van Zeeland M. A. , McKee G. R.
Published: March 2012

An analysis of the dependence of transport on the safety factor profile in high-performance, steady-state scenario discharges is presented. This is based on experimental scans of q95 and qmin taken with fixed βN, toroidal field, double-null plasma shape, divertor pumping, and electron cyclotron current drive input. The temperature and thermal diffusivity profiles were found to vary considerably with the q-profile, and these variations were significantly different for electrons and ions. With fixed q95, both temperature profiles increase and broaden as qmin is increased and the magnetic shear becomes low or negative in the inner half radius, but these temperature profile changes are stronger for the electrons. Power balance calculations show the peak in the ion thermal diffusivity (χi) at ρ=0.6-0.8 increases with q95 or qmin. In contrast, the peak in the electron diffusivity (χe) decreases as qmin is raised from ∼1 to 1.5, and it is insensitive to q95. This is important for fully non-inductive scenario development because it demonstrates that elevated qmin and weak or reversed shear allow larger electron temperature gradients and, therefore, increased bootstrap current density to exist at ρ=0.6-0.8. Chord-averaged measurements of long wavelength density fluctuation amplitudes (ñ) are shown, and these have roughly the same dependence on q-profile as χi. This data set provides an opportunity for testing whether theory based transport models can provide insight into the underlying transport physics of high performance scenarios and if they can reproduce observed experimental trends. To this end, we applied the trapped gyro-Landau fluid (TGLF) code to calculate the linear stability of drift waves and found that the resulting variation of growth rates with q-profile are mostly inconsistent with the observed trends of χi, χe, and ñ with q-profile. TGLF simulations of the temperature profiles consistent with heating sources also have mixed agreement with the measured profiles, such that the simulated electron and ion heat flux in low qmin discharges are too low and heat fluxes in high qmin discharges are too high.
A magnetic nozzle calculation of the force on a plasma
Authors: Fruchtman A. , Takahashi K. , Charles C. , Boswell R. W.
Published: March 2012

The measured axial force imparted from a magnetically expanding current-free plasma has been shown recently [Takahashi, Phys. Rev. Lett. 107, 235001 (2011)] to equal the axial force on that plasma calculated by a two-dimensional fluid model. Here, we calculate the same axial force on the plasma by a quasi one-dimensional model of a magnetic nozzle. The quasi one-dimensional magnetic nozzle model provides us with an estimate of the force on the plasma that is similar to that found by the more accurate two-dimensional model.
Monotonically convergent optimization in quantum control using Krotov's method
Authors: Reich Daniel M. , Ndong Mamadou , Koch Christiane P.
Published: March 2012

The non-linear optimization method developed by A. Konnov and V. Krotov [Autom. Remote Cont. (Engl. Transl.) 60, 1427 (1999)] has been used previously to extend the capabilities of optimal control theory from the linear to the non-linear Schrödinger equation [S. E. Sklarz and D. J. Tannor, Phys. Rev. A 66, 053619 (2002)]10.1103/PhysRevA.66.053619. Here we show that based on the Konnov-Krotov method, monotonically convergent algorithms are obtained for a large class of quantum control problems. It includes, in addition to nonlinear equations of motion, control problems that are characterized by non-unitary time evolution, nonlinear dependencies of the Hamiltonian on the control, time-dependent targets, and optimization functionals that depend to higher than second order on the time-evolving states. We furthermore show that the nonlinear (second order) contribution can be estimated either analytically or numerically, yielding readily applicable optimization algorithms. We demonstrate monotonic convergence for an optimization functional that is an eighth-degree polynomial in the states. For the “standard” quantum control problem of a convex final-time functional, linear equations of motion and linear dependency of the Hamiltonian on the field, the second-order contribution is not required for monotonic convergence but can be used to speed up convergence. We demonstrate this by comparing the performance of first- and second-order algorithms for two examples.
Nanoscale stacking faults induced low thermal conductivity in thermoelectric layered metal sulfides
Authors: Wan Chunlei , Wang Yifeng , Norimatsu Wataru , Kusunoki Michiko , Koumoto Kunihito
Published: March 2012

Layered metal sulfides (MS)1+x(TiS2)2 (M = Pb, Sn, Bi) with alternative stacking of MS layers and TiS2 layers (a natural superlattice) have been proposed as thermoelectric materials. In this paper, various nanoscale stacking faults have been found in these materials, including the translational disorder in (SnS)1.2(TiS2)2 and the staging disorder in (BiS)1.2(TiS2)2. The lattice thermal conductivities along the layers are systematically and significantly reduced by these stacking faults which are only a few unit cells apart, without deteriorating the electron mobility, demonstrating a “phonon-blocking, electron-transmitting” scenario.
Transverse dynamics of а surface wave excited by а wide electron beam
Authors: Fedotov A. E. , Makhalov P. B.
Published: March 2012

A non-stationary two-dimensional theory of interaction of a surface wave and a wide sheet electron beam is developed. This theory is used for studying the problem of mode competition and non-coherent transverse distribution of the microwave field in the surface-wave generation process. According to numerical simulations based on a quasi-optical equation, transverse diffraction of surface wave provides stable stationary generation in a wide range of beam widths and currents. The developed theory can be applied both to surface-wave oscillator and to a Smith-Purcell free-electron laser, where surface pi-type eigenmode excitation provides the beam bunching and enhances the power of the Smith-Purcell radiation at the frequency harmonics of the surface wave.
Influence of the ion wake-field on the collisional entanglement fidelity in complex dusty plasmas
Authors: Jung Young-Dae , Hong Woo-Pyo
Published: March 2012

The ion wake-field effects on the entanglement fidelity for the elastic electron-dust grain collisions are investigated in complex dusty plasmas. The screened effective potential and partial wave analysis are employed to obtain the entanglement fidelity in dusty plasmas as a function of the Mach number, Debye length, and collision energy. It is shown that the ion wake-field effect suppresses the entanglement fidelity in dusty plasmas. It is also found that the ion wake-field effect on the entanglement fidelity decreases with an increase of the collision energy.
Lone conduction band in Cu2ZnSnSe4
Authors: Gütay Levent , Redinger Alex , Djemour Rabie , Siebentritt Susanne
Published: March 2012

We present experimental proof for a narrow first conduction band in Cu2ZnSnSe4 semiconductor films as it has been predicted by theoretical calculations. The optical absorption characteristics of Cu2ZnSnSe4 thin films are analyzed by optical transmission spectroscopy. The experimental data show strong evidence for three absorption edges, as expected from theory, involving the valence band and two conduction bands, which are separated by a second band gap.
Ion-acoustic solitary waves in ion-beam plasma with Boltzmann electrons
Authors: Choi C.-R. , Ryu C.-M. , Rha K.-C. , Min K.-W. , Lee D.-Y.
Published: March 2012

Particle simulations and a pseudopotential method were used to study ion-acoustic solitary waves in a plasma composed of Boltzmann electrons and kinetic beam ions. Pseudopotential theory was first applied to determine how ion-acoustic solitary waves can exist in a two-component plasma. Then, particle simulations were carried out, wherein ion-acoustic solitary waves were excited by modulating the bias grid voltage in a double plasma model. For the modulation, the potential of the grid bias was rapidly decreased, such that hump-type ion-acoustic solitary waves with good Gaussian shape were excited one after another, forming a train of waves. The simulation also showed that the phase velocities of ions decrease sharply when the solitary wave occurs, which indicates that the solitary ion-acoustic wave is excited via the inverse Landau damping process.
Different exciton behaviors in blue and green wells of dual-wavelength InGaN/GaN MQWs structures
Authors: Long H. , Yu T. J. , Liu L. , Yang Z. J. , Fang H. , Zhang G. Y.
Published: March 2012

Staggered structures with blue and green quantum wells (QWs) were grown by metal organic vapor phase epitaxy (MOVPE) and characterized by photoluminescence (PL) and time resolved photoluminescence (TRPL) at various temperatures from 10 K to 300 K. High efficiency green light was observed, accompanying with decreased intensity of blue light. Efficiency of the green band was lower than that of the blue band below 100 K, but became two times greater than the efficiency of blue when temperature increased to room temperature. Three-dimensional and two-dimensional exciton behaviors were observed by TRPL measurements corresponding to blue and green bands, respectively. It is considered that carrier tunneling from blue wells is a key process for high efficiency luminescence in green QWs.
Stabilizing effects of edge current density on pedestal instabilities
Authors: Zhu P. , Hegna C. C. , Sovinec C. R.
Published: March 2012

Resistive MHD computations using the NIMROD code have found strong dependence of the low-n edge localized instabilities on edge current density distribution. The computations confirm that the low-n edge localized modes can be driven unstable by increasing the edge current density. When the edge peaked current density is sufficiently large, the q profile develops a region where the magnetic shear becomes negative. In these cases, the low-n edge instabilities are partially or fully stabilized. The stabilizing effects of edge current density in regions with reversed magnetic shear appear to be consistent with analytical predictions on a necessary condition for the stability of peeling modes. Nonlinear simulations indicate that the stabilizing effects of edge current density on the low-n edge instabilities through reverse shear can persist throughout the nonlinear exponential growth phase. Near the end of this nonlinear phase, the filament size in radial direction can exceed the pedestal width, and disconnected blob-like substructures start to develop within the filaments. Relative pedestal energy loss from these radially extending filaments can reach above the average experimental level of 10%.