bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and magnetic properties of magnetically isotropic and anisotropic Nd–Fe–B permanent magnets prepared by spark plasma sintering technology
Authors: Liu W. Q. , Cui Z. Z. , Yi X. F. , Yue M. , Jiang Y. B. , Zhang D. T. , Zhang J. X. , Liu X. B.
Published: April 2010

Spark plasma sintering technique had been applied to prepare bulk isotropic and anisotropic nanostructured Nd–Fe–B permanent magnets via hot pressing and subsequent hot deformation process. Influences of processing conditions and deformation height reduction on the structure and magnetic properties of the magnets were investigated. For the hot deformed magnet with 80% height reduction, XRD patterns of the anisotropic magnets show dominant (00l) diffraction peaks indicating evident c-axis crystallographic alignment in the magnet. Under the optimal processing conditions, the anisotropic magnet with 80% height reduction exhibits excellent magnetic properties as remanence (Br) of 1.492 T, coercive force (Hci) of 1004 kA/m, and the maximum energy product [(BH)max] of 400 kJ/m3, which are among the highest reported magnetic properties of nanostructured Nd–Fe–B permanent magnets.
Sweep rate dependence of the coercivity and fluctuation field in some RE-Fe(Co)–Al, RE=Nd or Pr, bulk amorphous ferromagnets
Authors: Collocott S. J.
Published: April 2010

Bulk amorphous alloys of composition Nd60Fe30Al10, Nd60Fe20Co10Al10, and Pr58Fe24Al18 have been prepared, and all alloys exhibit hard magnetic properties at room temperature. Magnetic field sweep rate measurements show the intrinsic coercivity to be proportional to the logarithm of the field sweep rate. The fluctuation field, Hf, for each alloy, is determined from both sweep rate and magnetic viscosity measurements. In the case of the latter it is determined by using both the waiting time method and S/χirr, where S is the magnetic viscosity parameter and χirr the irreversible susceptibility. Differences in the value of Hf determined from the sweep rate and magnetic viscosity experiments are discussed, and the value of the activation volume for each alloy determined.
Magnetic properties of Er1−xDyxAl2 (≤x≤1) compounds in low applied fields
Authors: Nirmala R. , Paudyal Durga , Pecharsky V. K. , Gschneidner K. A.
Published: April 2010

Low field magnetic properties of the Laves phase RAl2 compounds (where R is a mixture of Er and Dy, i.e., Er1−xDyx and x=0, 0.1, 0.14, 0.18, 0.25, 0.33, 0.5, and 1) have been studied. These compounds order ferromagnetically, and the middle members show both metastability in a narrow temperature window within the ferromagnetically ordered state and signatures of first order transitions in low applied fields. Results of first principles electronic structure calculations on Er0.75Dy0.25Al2 indicate a significant difference in the spin polarization in the 5d states of Er3+ and Dy3+ moments. In addition, anisotropic exchange and crystalline electric field effects arise from the random distribution of rare earth ions in the lattice. These and quadrupolar effects triggered by aspherical charge distributions of Er3+ and Dy3+ ions may compete and lead to the low temperature anomalies observed in low field magnetization data.
Magnetic domain observation of hydrogenation disproportionation desorption recombination processed Nd–Fe–B powder with a high-resolution Kerr microscope using ultraviolet light
Authors: Takezawa M. , Maruko K. , Tani N. , Morimoto Y. , Yamasaki J. , Nishiuchi T. , Hirosawa S.
Published: April 2010

A Kerr microscope that uses ultraviolet (UV) light for high-resolution domain observation was built, and the domain structure and magnetization process of hydrogenation disproportionation desorption recombination (HDDR) powder were examined. The UV Kerr microscope could observe nanometer-sized domain patterns. Applying a dc field of 1.0 kOe to HDDR powder at a desorption recombination (DR) time of 12 min produced abrupt wall motion. The pinning force exerted by the grain boundaries is inadequate for producing high coercivity because the Nd-rich phase layers along these boundaries are absent at a DR time of 12 min. For HDDR powder at a DR time greater than 14 min, changing the magnetic field by up to 1.0 kOe produced no observable wall motion. It follows that the high coercivity of HDDR powder is due to domain wall pinning at the grain boundaries.
Investigation on microstructure, texture, and magnetic properties of hot deformed Nd–Fe–B ring magnets
Authors: Li A. H. , Li W. , Lai B. , Wang H. J. , Zhu M. G. , Pan W.
Published: April 2010

Radially oriented Nd–Fe–B ring magnets have been prepared by backward extrusion of melt-spun powder. The position dependent of the microstructure, the magnetic properties, and the crystal alignment of the extruded rings have been investigated. The magnetic properties in radial direction increase slightly along the axis from the bottom to the middle then steeply decrease at the upper end of the ring. The magnetic properties and x-ray diffraction patterns of the upper end are very close to that of the isotropic pressed precursor. It suggests that the extruded ring approximately retains the initial structure at its upper end which is because the formation of texture is difficult at the initial stage of hot extrusion. Characteristic microstructure morphologies were found at different spatial positions: flake-shaped grains for the inner, elongated grains for the middle, and particle-shaped grains for the outer region in the cross section. Only particle-shaped grains were observed at the upper end of the ring. But the circumferential homogeneity of the surface magnetic flux densities is better in an extruded ring magnet than in a radially oriented ring prepared by sintering method. The deformation and texture formation processes were discussed. The deformation and texture formation in backward extruded magnets from melt-spun Nd–Fe–B precursors may possibly involve grain boundary sliding and grain rotation, solution-precipitation process, and preferred growth of Nd2Fe14B nanograins along the easy growth a-axis.
Tuning the exchange bias in large area Co/CoO nanowire arrays
Authors: Tripathy D. , Adeyeye A. O. , Chakrabarti K. , Singh N.
Published: April 2010

The exchange bias effect in Co (25 nm)/Co (5 nm)/Cu (2 nm) nanowire arrays has been systematically investigated. The exchange bias field HE is strongly dependent on the orientation of field cooling relative to the easy axis of the nanowires. We have exploited the competition between field cooling induced unidirectional anisotropy and shape anisotropy of the nanowires to tune both the direction and magnitude of exchange bias. A strong interplay between thermal activation effects and CoO domain size confinement in the nanowires also results in HE for the nanowire arrays being either smaller or larger than the continuous film.
Direct observation of magnetization reversal behaviors in exchange-coupled NiO/Fe films
Authors: Lee Hun-Sung , Ryu Kwang-Su , Jeon Kun-Rok , Shin Sung-Chul
Published: April 2010

We have investigated the magnetization reversal behavior in exchange-coupled NiO/Fe films with varying the NiO thicknesses using a magneto-optical microscope magnetometer capable of direct domain observation in real time. Interestingly enough, the magnetization reversal mechanism is gradually changed from a domain wall-motion process to a nucleation process as the NiO thickness increases. This result clearly demonstrates that the exchange coupling effect between the NiO and Fe layers increases the domain wall pinning effect of the Fe layer, resulting in the nucleation reversal mode.
Measurement of the antiferromagnet activity in exchange bias systems
Authors: Vallejo-Fernandez G. , Deakin T. , O’Grady K. , Oh S. , Leng Q. , Pakala M.
Published: April 2010

In this work, we describe the results of a recent set of experimental measurements on samples of CoFe/IrMn ferromagnet/antiferromagnet (AF) bilayer exchange bias materials. Careful magnetic measurement protocols and detailed particle size measurements have enabled us to confirm the link between the exchange field (Hex) and the distribution of grain volumes in the IrMn AF layer. This can be achieved by fitting the blocking temperature curve to obtain an effective value for the Néel temperature (TN). The value of (TN) is then used to determine the stable and set fraction of the grain volume distribution. Through a comparison of samples with different seed layer structures, we demonstrate control of the exchange bias where almost all the AF grains contribute to Hex. These samples have an AF with a mean grain diameter of 8.7 nm and an anisotropy constant of 7.8×106 ergs/cc. Our results indicate a reduction in the value of the Néel temperature (TN) of up to 100 K.
Exchange coupling and magnetoresistance in CoFe/NiCu/CoFe spin valves near the Curie point of the spacer
Authors: Andersson S. , Korenivski V.
Published: April 2010

Thermal control of exchange coupling between two strongly ferromagnetic layers through a weakly ferromagnetic Ni–Cu spacer and the associated magnetoresistance is investigated. The spacer, having a Curie point slightly above room temperature, can be cycled between its paramagnetic and ferromagnetic states by varying the temperature externally or using joule heating. It is shown that the giant magnetoresistance vanishes due to a strong reduction in the mean free path in the spacer at above ∼30% Ni concentration—before the onset of ferromagnetism. Finally, a device is proposed which combines thermally controlled exchange coupling and large magnetoresistance by separating the switching and the readout elements.
Magnetostriction and effective magnetic anisotropy of Co-contained Finemet nanocrystalline alloys
Authors: Wang Zhi , Yang Jing , Han Ye-mei , Zhang Dong-xu , Fu Bin , Ye Rong-chang
Published: April 2010

The microstructure and magnetic properties of Co-contained Finemet nanocrystalline alloys were investigated. By contrasting with Finemet, the Co-contained Finemet nanocrystalline alloys have a broad temperature range for precipitating a single α-FeCo crystalline phrase and a relatively higher Curie temperature of amorphous phase. After full nanocrystallization they exhibit improved high-temperature soft magnetic properties. However the room-temperature permeability of Co-contained Finemet was obviously lower than that of Finemet. For clarifying the reason, the effective magnetic anisotropy ⟨K⟩ and the saturation magnetostriction λs were measured, respectively, and the ⟨K⟩ of Co-contained Finemet is about 100–137 J/m3, which is the same order of magnitude as Finemet, but the λs of Co-contained Finemet-type alloy is much higher than that of Finemet which results in a relatively lower permeability.
Immunomagnetic reduction assay using high-Tc superconducting-quantum-interference-device-based magnetosusceptometry
Authors: Chieh J. J. , Yang Shieh-Yueh , Horng Herng-Er , Yu C. Y. , Lee C. L. , Wu H. L. , Hong Chin-Yih , Yang Hong-Chang
Published: April 2010

Via immunomagnetic reduction assay, biomolecules can be quantitatively detected with aid of biofunctionalized magnetic nanoparticles, which are used as labeling markers for specific biomolecules. To achieve ultra-high sensitivity in detecting biomolecules, superconducting quantum interference device (SQUID) is a promising candidate to act as a sensor to the magnetic signal related to the concentration of detected biomolecules. In the past, we developed a single channel SQUID-based magnetosusceptometry. In order to increase the detection through-put, multichannel SQUID-based magnetosusceptometry is developed. In this work, the design and working principle of four-channel SQUID-based magnetosusceptometry are introduced. Using utilizing scanning technology, four samples can be simultaneously logged into the SQUID-based magnetosusceptometry. Notably, only single SQUID magnetometer is used in the magnetosusceptometry. The precision and sensitivity in detecting biomolecules using the four-channel SQUID-based magnetosusceptometry are investigated.
Coercivity enhancement of sintered Nd14.4Fe78.4Co1.3B5.9 magnets by dysprosium diffusion in grain boundaries of rapidly solidified strips
Authors: Ding Y. , Chen R. J. , Liu Z. , Lee D. , Yan A. R.
Published: April 2010

A new coercivity enhancement process using dysprosium diffusion in grain boundaries of rapidly solidified strips was developed. The effects of the dysprosium diffusion on microstructure and magnetic properties of sintered Nd14.4Fe78.4Co1.3B5.9 magnets have been investigated. The transmission electron microscope observation showed that the intergranular phases of rapidly solidified strips were optimized through the grain boundary diffusion process of strips. From the mapping distribution of dysprosium atoms in sintered magnets and the fact that remanence almost kept constant, one could suppose that dysprosium element preferred the interface of the matrix grains, which was probably a reason of coercivity enhancement. The coercivity of the magnets made from diffusion heat treatment strips was increased by 1100 Oe, while the remanence was almost kept constant. Reduction in remanence is from 14.1 to 13.92 kG. The energy product of the magnets was slightly increased from 46.4 to 47.4 MGOe.
Rodlike disproportionation microstructure in the Pr13Fe80B7 alloys treated by conventional HDDR process
Authors: Han Jingzhi , Kong Xiangpeng , Liu Shunquan , Lin Zhong , Wang Changsheng , Du Honglin , Yang Jinbo , Yang Yingchang
Published: April 2010

Anisotropic Pr13Fe80B7 magnetic powders are obtained by shortening the disproportionation time of the hydrogenation disproportionation desorption recombination (HDDR) process. The magnetic powders with a disproportionation time of 30 min have the magnetic properties of Br=0.93 T and Mr/Ms=0.75, and show a high degree of crystal texture along the c axis, whereas the magnetic powders obtained with a prolonged disproportionation time are isotropic. A rodlike structure is observed in the 30 min-disproportionation products and is transformed into spherical morphology with a prolonged disproportionation time. It suggests that the rodlike disproportionated microstructure is very important for the formation of crystal texture in the conventional HDDR powders.
Improved energy product in grained aligned and sintered MRE2Fe14B magnets (MRE=Y+Dy+Nd)
Authors: Tang W. , Wu Y. Q. , Oster N. T. , Dennis K. W. , Kramer M. J. , Anderson I. E. , McCallum R. W.
Published: April 2010

Sintered [Nd0.45(Y3Dy1)0.25∗0.55]2.8Fe14B magnets were prepared for the first time. Magnetic properties and microstructures of the magnets were investigated by magnetic measurements and electron microprobe analysis. The microstructure consists of a MRE2Fe14B (2-14-1) phase matrix having a grain size of ∼10 μm and a RE-rich grain boundary phase. However, sintering resulted in segregation of Y to the inner and Nd to the outside of the 2-14-1 grains. The magnet has a room temperature (BH)max of 25.4 MGOe, which is two times higher than that of the isotropic melt spun ribbons with similar compositions. The temperature coefficients of Br (α) and Hcj (β) for the magnet are −0.150 and −0.632%/°C from 27 to 127 °C, respectively. These temperature coefficients, especially for β, are also much higher than those of melt spun ribbons. The composition segregation in the 2-14-1 grains is believed to be responsible for the higher temperature coefficients.
Micromagnetic study of magnetic domains in platelets with perpendicular uniaxial anisotropy
Authors: Van de Wiele Ben , Dupré Luc , De Zutter Daniël
Published: April 2010

This paper studies the domain configurations in platelets with perpendicular uniaxial anisotropy. Due to the large sample dimensions, one typically relies on the domain theory to describe the domain patterns. The growing computer resources make it however possible to perform full micromagnetic simulations on the domain scale. We compare the domain configurations obtained from micromagnetic simulations with those predicted by different domain theory models for a varying anisotropy strength Ku. It is found that the Landau structure is valid for small Ku, while the open Landau–Kittel structure only poorly describes the closure domains for higher Ku. The model proposed by Hubert, enabling closure domains with a tilted magnetization angle is the most accurate.
High performance nanostructured Nd–Fe–B fine powder prepared by melt spinning and jet milling
Authors: Chen Zhongmin , Miller David , Herchenroeder Jim
Published: April 2010

Isotropic Nd–Fe–B nanocrystalline fine powders with particle size in the range of 1–10 μm have been developed using melt spinning and jet milling. The processing steps primarily consist of melt spinning Nd–Fe–B alloy to obtain ribbons with 25–50 μm thickness, crushing the ribbon to obtain coarse powder with average particle size of about 200 μm, and jet milling the coarse powder to obtain fine powder with average particle size of about 5–6 μm. The effects of jet milling conditions on powder particle size, microstructure, and magnetic properties were systematically studied. For a magnet alloy nominally composed of Nd11.9(Fe0.93Co0.07)82.6B5.5, a particulate yield of D10=2 μm, D50=6 μm, and D90=11 μm and magnetic properties of Br=8.82 kG, Hci=9.5 kOe, and (BH)max=15.3 MGOe have been achieved in melt-spun and jet milled fine powders. The combined advantage of small particle size and high magnetic performance will make the Nd–Fe–B fine powder an attractive candidate for applications such as magnetic fluids, inks, micromachines, and flexible sheets.
Fe–Co–Cr nanocomposites for application in self-regulated rf heating
Authors: Miller K. J. , Colletti A. , Papi P. J. , McHenry M. E.
Published: April 2010

Fe–Co–Cr alloys have been developed with a Curie temperature, Tc, appropriate for ferrofluid cooling and self-regulated heating applications. These alloys have low Curie temperatures, moderate magnetic moments and provide increased heat capacity in a liquid used in a thermal cycle. Amorphous powders have been synthesized by cryo-SPEX milling melt-spun ribbons at 77 K. Transmission electron microscopy reveals cryomilled magnetic nanoparticles (MNPs) with a mean diameter of 4.2 nm to form agglomerates ∼30 nm in size. Vibrating sample magnetometer and superconducting quantum interference device magnetometry of amorphous powders reveal a specific magnetization, σs, of 104 emu/g at 4 K in a 300 mT field and a Tc of 335 K. Nanoparticles were suspended in ferrofluids by ultrasonication with a Pluronic F127 surfactant to stabilize them in aqueous solution. Ferrofluids of varying MNP concentration were rf heated in a 27.2 mT field at 267 kHz. For 1.24 vol % of MNPs in the ferrofluid, a solution reached temperatures>50 °C in ∼70 s, and showed Curie-limiting temperature behavior at ∼75 °C. These results demonstrate self-limited heating of FeCoCr MNPs at 75 °C which may have application in polymer curing.
Reduction in hysteresis losses and large magnetic entropy change in the B-doped La(Fe,Si)13 compounds
Authors: Shen Jun , Wang Fang , Zhao Jin-Liang , Wu Jian-Feng , Gong Mao-Qiong , Hu Feng-Xia , Li Yang-Xian , Sun Ji-Rong , Shen Bao-Gen
Published: April 2010

The effect of the B-addition on magnetic entropy change ΔSM and hysteresis loss in La(Fe,Si)13 is studied. The maximal values of ΔSM for LaFe11.9Si1.1, LaFe11.5B0.4Si1.1, LaFe11.5Si1.5, and LaFe11.0B0.5Si1.5 are found to be 27.0, 26.1, 23.7, and 21.2 J/kg K at Curie temperature TC for a field change in 0–5 T, respectively. The maximal hysteresis losses around TC are 43 and 21 J/kg for LaFe11.9Si1.1 and LaFe11.5Si1.5, respectively, while almost no magnetic hysteresis is observed for the B-doped compounds. Our result reveals that a large ΔSM and a small hysteresis loss can be simultaneously achieved in NaZn13-type La(Fe,Si)13 compounds by the addition of B.
Magnetocaloric effect and refrigerant capacity in Sr-doped Eu8Ga16Ge30 type-I clathrates
Authors: Phan M. H. , Franco V. , Chaturvedi A. , Stefanoski S. , Kirby H. , Nolas G. S. , Srikanth H.
Published: April 2010

Magnetic properties, the magnetocaloric effect (MCE) and refrigerant capacity (RC) were investigated in Eu8Sr8−xGa16Ge30 (x=0,4) type-I clathrates. The substitution of Sr for Eu decreases the Curie temperature (TC) and saturation magnetization (MS) from 35 K and 65 emu/g for the x=0 composition to 15 K and 35 emu/g for the x=4 composition. This is attributed to the increase in the Eu–Eu distance with Sr substitution. The large MCE and RC are achieved in both specimens. For a field change of 3 T, the MCE and RC reach the largest values of 5.8 J/kg K and 127.6 J/kg for x=0 composition and 4.3 J/kg K and 72.1 J/kg for x=4 composition. The broadening of the MCE curves is likely associated with the ordering of the magnetic moments of Eu that occurs below 10 K. The large values of MCE and RC, in addition to the absence of thermal and field hysteresis indicate that these clathrate materials are very interesting for cryogenic magnetic refrigeration applications.
Enhanced glass-forming ability of FeCoBSiNb bulk glassy alloys prepared using commercial raw materials through the optimization of Nb content
Authors: Fu Ying , Shen Baolong , Kimura Hisamichi , Makino Akihiro , Inoue Akihisa
Published: April 2010

We optimized the alloy compositions by modifying the Nb content in [(Fe0.5Co0.5)0.75B0.20Si0.05]100−xNbx(x=3.6–4.4) alloy system. As a result, it was found that the Nb content of 4.3 at. % was effective for approaching alloy to a eutectic point. By copper mold casting, [(Fe0.5Co0.5)0.75B0.20Si0.05]95.7Nb4.3 bulk glassy alloy rods with diameters up to 4 mm were successfully synthesized even using commercial raw materials. These glassy alloys exhibit a rather high saturation magnetization of 0.77 T and low coercive force of 2.5 A/m.
Increased induction in FeCo-based nanocomposite materials with reduced early transition metal growth inhibitors
Authors: Miller K. J. , Leary A. , Kernion S. J. , Wise A. , Laughlin D. E. , McHenry M. E. , Keylin Vladimir , Huth Joe
Published: April 2010

We report on new high-saturation induction, high-temperature nanocomposite alloys with reduced glass formers. The amounts of the magnetic transition metals and early transition metal growth inhibitors were systematically varied to determine trade-offs between higher inductions and fine microstructures with consequently lower magnetic losses. Alloys of nominal composition (Fe65Co35)79.5+xNb4−xB13Si2Cu1.5 (x=0–4) were cast into a 28 mm wide, 20 μm thick ribbon from which toroidal cores were wound. Inductions and magnetic losses were measured after nanocrystallization and stress relief. We report technical magnetic properties: permeability, maximum induction, remanence ratio, coercive field, and high frequency magnetic losses as a function of composition and annealing temperature for these alloys. Of note is the development of maximum inductions in excess of 1.76 T in cores made of alloys with the x=4 composition and maximum inductions in excess of 1.67 T in alloys with the x=3 composition, which also exhibit power losses smaller than 10 W/kg at 0.2 T induction levels in 20 kHz fields. We discuss optimization of induction with chemistry and correlate the microstructures with losses.
Coupling of blocking and melting in cobalt ferrofluids
Authors: Wen Tianlong , Liang Wenkel , Krishnan Kannan M.
Published: April 2010

Zero-field-cooling and field-cooling (FC) measurements were performed on ferrofluids of cobalt magnetic nanoparticles (MNPs) in various organic solvent. Two peaks, one broad peak corresponding to the blocking transition (TB), and one sharp peak corresponding to the melting of the solvent (TM), were observed. Furthermore, for a given MNP size, when the blocking and melting transitions were superposed by choosing an appropriate solvent, the strongest intensity of the sharp peak at the melting point of the organic solvent was obtained. This observation is explained by applying the M spectrum theory. Additionally, a first order, melting-induced magnetic phase transformation was observed at the melting point of the solvent. Associated with the first order phase transition and the supercooling effect, a thermal hysteresis loop in the FC curve was observed.
Magnetic and magnetotransport properties of arrays of nanostructured antidots obtained by self-assembling polystyrene nanosphere lithography
Authors: Tiberto Paola , Boarino Luca , Celegato Federica , Coïsson Marco , De Leo Natascia , Vinai Franco , Allia Paolo
Published: April 2010

A well-ordered nanopatterned structure has been obtained in sputtered magnetic thin films by self-assembling of polystyrene nanospheres. Arrays of holes in Co, Ni, and Ni80Fe20 films having a mean size ranging in the interval of 200–400 nm depending on the experimental condition have been prepared. Sample microstructure has been studied by scanning electron microscopy and atomic force microscopy. Room-temperature hysteresis loops have been measured in the parallel and perpendicular configuration (Hmax=20 kOe). Magnetoresistance (MR) measurements have been performed by means of a standard four-contact technique at several angles between the current and the magnetic field (Hmax=70 kOe) in the temperature interval of 4–200 K. An anisotropic MR effect has been observed in all compositions independent on the hole mean dimension. The role on magnetic and magnetotransport properties of either sample microstructure or composition has been studied in such patterned structures.
Magnetic properties of arrays of nanowires: Anisotropy, interactions, and reversal modes
Authors: Lavin R. , Denardin J. C. , Espejo A. P. , Cortés A. , Gómez H.
Published: April 2010

Arrays of Co and Ni nanowires of different lengths have been prepared by electrodeposition into nanopores of alumina membranes. The dependence of the coercivity of the arrays as a function of temperature and measurement angle of the nanowires has been measured. A simple model is presented in order to explain the behavior of the magnetic properties as a function of the angle of measurement. The analytical calculations show that while for Ni nanowires demagnetization reversal in the array is driven by means of the nucleation and propagation of a transverse wall, in Co arrays the reversal mode changes from curling to coherent when the angle of measurements changes.
Experimental characterization of thermal conductance switching in magnetorheological fluids
Authors: Cha Gilhwan , Ju Y. Sungtaek , Ahuré Louise A. , Wereley Norman M.
Published: April 2010

We experimentally investigate thermal conductance switching in Fe-based magnetorheological fluids (MRFs). The transient hot-square technique is employed to directly measure enhancement in the thermal conductivity of bulk samples with volume concentrations up to 33% along the field direction. The ratio of the thermal conductivities of bulk MRFs under no and strong (∼290 kA/m) field is approximately 1.3, nearly independent of particle concentration. Significantly higher on-off conductance ratios can be achieved at a device level by exploiting the normal field instability to form columns of MRFs across an air gap. We experimentally demonstrate reversible switching in one implementation of this device concept.
Using the infrared magnetorefractive effect to compare the magnetoresistance in (100) and (111) oriented Fe3O4 films
Authors: Thompson S. M. , Lazarov V. K. , Bradley R. C. , Deakin T. , Kaeswurm B. , Sterbinsky G. E. , Cheng J. , Wessels B. W.
Published: April 2010

The infrared magnetorefractive effect (MRE) is used to compare the magnetoresistance (MR) in epitaxial thin films of Fe3O4 grown on MgO with (100) and (111) crystal orientations. The smaller MRE detected in the (111) film is shown to correlate with the smaller electrically measured MR, its behavior consistent with a lower density of antiphase boundaries in the (111) film
Large negative magnetoresistance in nickel-rich Ni–Mn–Ga Heusler alloys
Authors: Pal D. , Mandal K. , Gutfleisch O.
Published: April 2010

Electrical resistivity ρ and magnetoresistance of ferromagnetic Heusler alloys Ni2+xMn1−xGa have been measured up to a magnetic field of 8 T and within a temperature range from 4.2 to 300 K. A substantial jump in resistivity has been observed while the martensitic transformation takes place. A large negative magnetoresistance (∼8%) was obtained at room temperature due to a change of 8 T magnetic field for the sample Ni2.208Mn0.737Ga, where martensite-austenite structural and ferro-para magnetic transition temperatures almost coincide with each other.
Formation of Co2FeSi/SiOxNy/Si tunnel junctions for Si-based spin transistors
Authors: Hayashi Kengo , Takamura Yota , Nakane Ryosho , Sugahara Satoshi
Published: April 2010

The authors developed a fabrication technique of Co2FeSi/SiOxNy/Si tunnel junctions, employing rapid thermal annealing (RTA). The full-Heusler Co2FeSi (CFS) alloy thin film was directly formed on the ultrathin SiOxNy barrier layer without a buffer layer by RTA-induced silicidation reaction of a Co/Fe/amorphous-Si multilayer deposited on the barrier layer. The ultrathin SiOxNy layer formed on a Si substrate effectively blocked the diffusion of Co and Fe atoms into the Si substrate, leading to the formation of a high quality tunnel junction. It was found from crystallographic analyses that the CFS film on SiOxNy has a highly (110)-oriented texture structure with the L21 ordering and the CFS/SiOxNy interface was atomically flat without intermixing and crystallinity degradation.
Highly ordered Co2FeSi Heusler alloys grown on Ge(111) by low-temperature molecular beam epitaxy
Authors: Kasahara K. , Yamamoto K. , Yamada S. , Murakami T. , Hamaya K. , Mibu K. , Miyao M.
Published: April 2010

We demonstrate high-quality epitaxial growth of Heusler alloy Co2FeSi on Ge(111) by molecular beam epitaxy (MBE) at 200 °C. Even for growth at such a low temperature, L21-ordered crystal structure is formed and highly uniform magnetic environments around the Fe sites are realized, by transmission electron diffraction and conversion electron Mössbauer spectroscopy, respectively. We also find that the magnetic moment reaches 5.37 μB/f.u., which is the highest value in thin-film Co2FeSi samples reported.
Hyperfine magnetic field on iron atoms and Co–Fe disordering in Co2FeSi
Authors: Ksenofontov Vadim , Wójcik Marek , Wurmehl Sabine , Schneider Horst , Balke Benjamin , Jakob Gerhard , Felser Claudia
Published: April 2010

The Heusler compound Co2FeSi is a prospective half-metallic material for spintronic applications. Defects and antisite disordering play a crucial role among the factors reducing spin polarization in such materials. To clarify effects of possible off-stoichiometry, a continuous series of model solid solutions Co3−xFexSi (0.6≤x≤1.4) was investigated by F57e Mössbauer spectroscopy and C59o nuclear magnetic resonance. It has been shown that the hyperfine magnetic fields on Fe can be used to monitor Co–Fe disordering in Co2FeSi-based bulk samples and thin films.
Magnetic link design for a robotic laparoscopic camera
Authors: Simi Massimiliano , Ciuti Gastone , Tognarelli Selene , Valdastri Pietro , Menciassi Arianna , Dario Paolo
Published: April 2010

The use of magnetic fields to control and steer assistive and operative devices is increasing in minimally invasive surgical applications. The design of the magnetic link between an external permanent magnet, maneuvered by an industrial robot, and a robotic laparoscopic camera was investigated in this paper, with the objective to obtain accurate positioning and steering in visualization.
Magnetic anisotropy of Ga1−xMnxAs films with additional nonmagnetic donor doping
Authors: Kim Hyung-chan , Khym S. , Lee Sanghoon , Liu X. , Furdyna J. K.
Published: April 2010

We have investigated the magnetic anisotropy properties of a series of ferromagnetic Ga1−xMnxAs:Si films by transport measurements. The angular dependences of the planar Hall resistance (PHR) were analyzed in terms of the magnetic free energy to obtain the anisotropy fields. The cubic component of the magnetic anisotropy is much stronger than the uniaxial component at low temperature, although its dominance rapidly decreases with increasing temperature. The direction of the uniaxial anisotropy at 16 K lies along either the [1¯11] or the [110] direction depending on the Mn composition in the series. The uniaxial anisotropy direction, however, changed along the [110] direction regardless of the Mn concentration in the samples as the temperature increases.
Effect of atomically controlled interfaces on Fermi-level pinning at metal/Ge interfaces
Authors: Yamane K. , Hamaya K. , Ando Y. , Enomoto Y. , Yamamoto K. , Sadoh T. , Miyao M.
Published: April 2010

We study electrical properties of metal/Ge contacts with an atomically controlled interface, and compare them with those with a disordered one, where atomically controlled interfaces can be demonstrated by using Fe3Si/Ge(111) contacts. We find that the Schottky barrier height of Fe3Si/n-Ge(111) contacts is unexpectedly lower than those induced by the strong Fermi-level pinning at other metal/n-Ge contacts. For Fe3Si/p-Ge(111) contacts, we identify clear rectifying behavior in I-V characteristics at low temperatures, which is also different from I-V features due to the strong Fermi-level pinning at other metal/p-Ge contacts. These results indicate that there is an extrinsic contribution such as dangling bonds to the Fermi-level pinning effect at the directly connected metal/Ge contacts.
Free energy source for flow shear driven instabilities in electron-magnetohydrodynamics
Authors: Sundar Sita , Das Amita
Published: April 2010

The paper discusses the free energy source for the flow shear driven instability in the context of electron-magnetohydrodynamic (EMHD) system. In EMHD as the electron flow velocity also corresponds to the current in the system, the flow shear driven instability has often been identified both as the fluid Kelvin–Helmholtz (KH)-like mode and as the current gradient driven sausage and kinklike modes. It has been shown here that the free energy source for the flow shear driven instability is the kinetic energy of the electron flow and the instability is essentially a fluid KH mode. The manuscript also provides interpretations for certain characteristic features, such as existence of a threshold wavenumber along the flow direction, the order of magnitude estimation of the growth rate, etc., from physical considerations.
Multireference Mukherjee’s coupled cluster method with triexcitations in the linked formulation: Efficient implementation and applications
Authors: Bhaskaran-Nair Kiran , Demel Ondřej , Pittner Jiří
Published: April 2010

We have formulated the multireference Mukherjee’s coupled clusters method with triexcitations (MR MkCCSDT) in the linked version and implemented it in the ACES II program package. The assessment of the new method has been performed on the first three electronic states of the oxygen molecule, on studies of singlet-triplet gap in methylene and twisted ethylene, where a comparison with other multireference CC treatments and with experimental data is available. The MR MkCCSDT results show accuracy comparable to which can be achieved with CCSDT in single reference cases. Comparison of the previously developed MkCCSD(T) method with MkCCSDT as a reference suggests, that MkCCSD(T) might be a promising candidate for an accurate treatment of systems where the static correlation plays an important role, at least for situations where small model spaces are sufficient.
X-ray radiography and scattering diagnosis of dense shock-compressed matter
Authors: Le Pape Sebastien , Neumayer Paul , Fortmann Carsten , Döppner Tilo , Davis Paul , Kritcher Andrea , Landen Otto , Glenzer Siegfried
Published: April 2010

Highly coupled Boron plasma has been probed by spectrally resolving an x-ray source scattered by the plasma. Electron density was inferred from the inelastic feature in the collective scattering regime. In addition, the mass density inferred from the noncollective x-ray Thomson scattering has been tested with independent characterization using x-ray radiography in the same drive condition. High-intensity laser produced K-alpha radiation was used as a backlighter for these dynamically compressed plasma experiments providing a high temporal resolution of the measurements. Mass density measurements from both methods are in good agreement. The measurements yield a compression of 1.3 in agreement with detailed radiation-hydrodynamic modeling. From the charge state measured in the noncollective regime and the electron density measured in the collective regime mass density can then be constrained to 3.15±0.7.
An electrostatic deceleration lens for highly charged ions
Authors: Rajput J. , Roy A. , Kanjilal D. , Ahuja R. , Safvan C. P.
Published: April 2010

The design and implementation of a purely electrostatic deceleration lens used to obtain beams of highly charged ions at very low energies is presented. The design of the lens is such that it can be used with parallel as well as diverging incoming beams and delivers a well focused low energy beam at the target. In addition, tuning of the final energy of the beam over a wide range (1 eV/q to several hundred eV/q, where q is the beam charge state) is possible without any change in hardware configuration. The deceleration lens was tested with Ar8+, extracted from an electron cyclotron resonance ion source, having an initial energy of 30 keV/q and final energies as low as 70 eV/q have been achieved.
Violet and blue upconversion luminescence in Tm3+/Yb3+ codoped Y2O3 transparent ceramic
Authors: Hou Xiaorui , Zhou Shengming , Lin Hui , Teng Hao , Li Yukun , Li Wenjie , Jia Tingting
Published: April 2010

Tm 3 + / Yb 3 + codoped Y2O3 transparent ceramics were fabricated and characterized from the point of upconversion luminescence. All the samples exhibited high transparency not only in near-infrared band but also in visible region. Under 980 nm excitation, the ceramics gave upconversion luminescence with very intense blue (485 nm) and considerably intense violet (360 nm) emissions. It was worthy to point out that the upconversion luminescence contained six emission bands, which dispersed in the region from 294 to 809 nm. The strongest blue emission (485 nm) was obtained with (Tm0.002Yb0.03Y0.958Zr0.01)2O3 ceramic (Yb/Tm=15). The mechanism of all upconversion emission bands were investigated in detail. The absorption, emission, and gain cross-section of blue emission (485 nm) were calculated, which indicated that Tm3+/Yb3+ codoped Y2O3 transparent ceramic has tremendous potential in short wavelength laser.
Interference effects on bound-to-continuum quantum dot absorption
Authors: Houel J. , Sauvage S. , Lemaître A. , Boucaud P.
Published: April 2010

We have investigated the bound-to-continuum absorption of InGaAs quantum dots as a function of n-doping. We show that the combination of multipass waveguide geometry, large number of quantum dot layers, and spectrally broad absorption leads to significant spectral oscillations on the absorption spectra. The oscillations result from the standing wave pattern caused by the interference of optical beams incident and totally reflected at the sample/air interface. The spectral modulations on the absorption spectra should not be attributed to resonant intersublevel transitions.
Hysteretic giant magnetoresistance curves induced by interlayer magnetostatic coupling in [Pd/Co]/Cu/Co/Cu/[Co/Pd] dual spin valves
Authors: Yang P. Y. , Zhu X. Y. , Chen G. , Zeng F. , Pan F.
Published: April 2010

The giant magnetoresistance (GMR) characteristics of hybrid perpendicular/Cu/in-plane magnetic anisotropy [Pd/Co]/Cu/Co single spin valves and [Pd/Co]/Cu/Co/Cu/[Co/Pd] dual spin valves with applied field perpendicular and parallel to the film plane are studied. Linear and nonhysteretic GMR behaviors are observed for the two spin valves in perpendicular-to-plane applied fields due to the coherent rotation of the Co layer driven by the in-plane shape anisotropy. The GMR value of the dual spin valve is 1.8 times as large as that of the single spin valve. The correlations between the magnetic configuration of the devices and the resistance evolvement are analyzed. In-plane GMR curves with maximum applied field of 30 kOe deviate from the linear behavior and can be well described by the Stoner–Wohlfarth model including high order anisotropy terms. Moreover, obvious hysteresis behavior is observed in the in-plane GMR curve of the dual spin valve. This phenomenon results from the hindered rotation of the Co/Pd moments due to the magnetostatic coupling between the top and bottom Co/Pd multilayers in the dual spin valve.
Pressure effects on superconductivity of Fe1+yTe1−xSx single crystals
Authors: Zhang Z. T. , Yang Z. R. , Li L. , Pi L. , Tan S. , Zhang Y. H.
Published: April 2010

We have investigated the pressure effect on superconductivity of Fe1+yTe1−xSx single crystals. We show that the applied pressure leads to opposite variation in the superconductivity between homogeneous and inhomogeneous samples. With increasing pressure to 10 kbar, the superconductivity of homogenous sample S1 is suppressed gradually, however Tcmag of inhomogeneous S4 can be raised up to 21 K. The increase in Tcmag in S4 is believed as stabilizing the structure by strain effect in inhomogeneous sample, thereby avoiding structural transition under pressure. Our results imply that higher Tc could be expected in iron chalcogenides if this structural instability could be suppressed.
Semiconductor-to-insulator transition of undoped-BaTiO3 in quenched state
Authors: Kwon Hyung-Soon , Yoo Han-Ill , Kim Chang-Hoon , Hur Kang-Heon
Published: April 2010

It has been believed that the defect structure of “undoped” BaTi1−ηO3−δ be governed by background acceptor impurities, most likely AlTi′, in its near stoichiometry regime (δ≈0). Its electrical conductivity versus oxygen activity should, thus, be expected to be similar to that of Al-doped BaTiO3 not only in equilibrium state at elevated temperatures, but also in quenched state at low temperatures. In quenched state, however, the “undoped” BaTiO3 from various sources totally betray this expectation: A landmark of the quenched-state defect structure, semiconductor-to-insulator transition falls at an oxygen activity >10 orders lower than that of the Al-doped and it is rather similar to that of variable-valent Mn-doped BaTiO3. The transition is found to systematically depend on the nonmolecularity (η), suggesting the defect structure being governed by the multiply-charged cation vacancies. The hole-trapping energies of VBa″ and VTi⁗ are estimated and compared with those for the fixed-valent AlTi′ and variable-valent MnTi″.
Distributed feedback laser biosensor incorporating a titanium dioxide nanorod surface
Authors: Ge Chun , Lu Meng , Zhang Wei , Cunningham Brian T.
Published: April 2010

A dielectric nanorod structure is used to enhance the label-free detection sensitivity of a vertically-emitting distributed feedback laser biosensor (DFBLB). The device is comprised of a replica molded plastic grating that is subsequently coated with a dye-doped polymer layer and a TiO2 nanorod layer produced by the glancing angle deposition technique. The DFBLB emission wavelength is modulated by the adsorption of biomolecules, whose greater dielectric permittivity with respect to the surrounding liquid media will increase the laser wavelength in proportion to the density of surface-adsorbed biomaterial. The nanorod layer provides greater surface area than a solid dielectric thin film, resulting in the ability to incorporate a greater number of molecules. The detection of a monolayer of protein polymer poly (Lys, Phe) is used to demonstrate that a 90 nm TiO2 nanorod structure improves the detection sensitivity by a factor of 6.6 compared to an identical sensor with a nonporous TiO2 surface.
Geminate electron-hole recombination in organic solids in the presence of a donor-acceptor heterojunction
Authors: Wojcik Mariusz , Michalak Przemyslaw , Tachiya M.
Published: April 2010

Geminate electron-hole recombination is one of the main factors limiting the efficiency of organic solar cells. We present a systematic study of this process based on both analytical and simulation models. We determine how the charge-pair separation probability is affected by the hopping length of charge carriers, the presence of a donor-acceptor heterojunction, electron and hole mobilities, and other factors. We show that the charge-pair separation probability of an electron and a hole which are initially at the contact distance is maximized when the electron and hole mobilities are equal to each other.
Localized Joule heating produced by ion current focusing through micron-size holes
Authors: Viasnoff V. , Bockelmann U. , Meller A. , Isambert H. , Laufer L. , Tsori Y.
Published: April 2010

We provide an experimental demonstration that the focusing of ionic currents in a micron size hole connecting two chambers can produce local temperature increases of up to 100 °C with gradients as large as 1°K μm−1. We find a good agreement between the measured temperature profiles and a finite elements-based numerical calculation. We show how the thermal gradients can be used to measure the full melting profile of DNA duplexes within a region of 40 μm. The possibility to produce even larger gradients using submicron pores is discussed.
Long range resonant tunneling in quantum cascade structures
Authors: Buffaz A. , Carras M. , Doyennette L. , Trinité V. , Marcadet X. , Berger V.
Published: April 2010

Tunneling transport in a quantum cascade detector is investigated. With regard to coherent transport in quantum cascade lasers, a Kazarinov–Suris approach R. F. Kazarinov and R. A. Suris, [Sov. Phys. Semicond. 6, 120 (1972)] needs to be modified through the introduction of an additional Fermi–Dirac factor in order to properly model the experimental data at low temperature. Electronic current is completely dominated by tunneling transport; the model here presented should help to suppress it in the future design of efficient quantum cascade detectors.
“Rainbow” trapped in a self-similar coaxial optical waveguide
Authors: Hu Qing , Zhao Jin-Zhu , Peng Ru-Wen , Gao Feng , Zhang Rui-Li , Wang Mu
Published: April 2010

We report in this paper that the light waves with different frequencies can be selectively guided and spatially separated in a self-similar dielectric waveguide, where a hollow core is surrounded by a coaxial Thue–Morse multilayer. Due to the self-similar furcation feature in the photonic band structure, the transmission multibands are achieved. More interestingly, this dielectric waveguide supports “cladding modes,” which are spatially separated and confined along the waveguide. Consequently, a “rainbow” can be trapped (spatial confined but not stopped) in the Thue–Morse waveguide. The finding can be applied to designing miniaturized compact photonic devices, such as spectroscopy on a chip.
Low frequency and large amplitude oscillations of cantilevers in viscous fluids
Authors: Aureli Matteo , Porfiri Maurizio
Published: April 2010

We study nonlinear vibrations of cantilever beams oscillating in viscous fluids. A handleable expression for the inertial and damping loads due to the encompassing fluid is proposed. We expand on the canonical viscous diffusion theory by incorporating vortex shedding effects at large oscillation amplitudes. Comparison with experimental results on underwater low frequency and large amplitude oscillations of cantilevers is reported. The approach is applicable to the analysis of ionic polymer metal composites vibrating underwater.
One-dimensional alignment of nanoparticles via magnetic sorting
Authors: Bouskila R. , McAloney R. , Mack S. , Awschalom D. D. , Goh M. C. , Burch K. S.
Published: April 2010

Near room temperature, MnAs films align into two phases, one ferromagnetic and the other paramagnetic. These phases take the intriguing form of nanoscale wires. We have exploited this phase coexistence to form linear arrays of magnetite nanoparticles without the need for photolithography. This is confirmed via extensive scanning probe microscopy.