bluuebunny/crossref_metadata_2025 huggingface dataset:
Antiferromagnetic thickness dependence of the CrTe–MnTe exchange-bias system
Authors: Lu H. , Bi J. F. , Teo K. L. , Liew T. , Chong T. C.
Published: May 2010

We report the antiferromagnetic (AFM) thickness dependence study of zinc-blende CrTe/ZnTe/MnTe layered structure grown on GaAs (100) by low temperature molecular beam epitaxy. The coercivity (HC) and exchange bias field (HE) show a nonmonotonic dependence on the AFM thickness. Both (HC) and HE exhibit a maximum value at the AFM thickness of ∼15 nm. With decreasing AFM thickness, we found that the blocking temperature drops from 70 (Néel temperature of bulk MnTe) to 22 K, while the Curie temperature is found to increase from 100 to 190 K. Additionally, a vertical magnetization shift is observed in the M-H loop, which can be attributed to the presence of frozen ferromagnetic spins at the interface.
Radio frequency detection of structural anomaly and magnetoimpedance in La0.67Ba0.23Ca0.1MnO3
Authors: Naik V. B. , Lam M. C. , Mahendiran R.
Published: May 2010

We report the ac electrical response of polycrystalline La0.67Ba0.23Ca0.1MnO3 while passing the rf current directly through the sample in the frequency range f=1–20 MHz. The simultaneous measurement of the ac resistance (R) and reactance (X) reveals that X in zero field for f≤5 MHz shows an abrupt increase followed by a peak close to TC=300 K and a steplike decrease at low temperature (T=165 K) while cooling. The low temperature anomaly exhibits hysteresis while warming. It is suggested that the high temperature peak in X is due to the onset of ferromagnetism and the low temperature anomaly is due to rhombohedral-orthorhombic structural transition. We report a huge ac magnetoresistance −19% at f=20 MHz and magnetoreactance (−37% at f=5 MHz) at TC under H=1 kG. Our study suggests that rf electrical transport is a valuable tool to investigate the structural transitions occurring below TC in manganites.
High-quality ZrO2/Si(001) thin films by a sol-gel process: Preparation and characterization
Authors: Döscher H. , Lilienkamp G. , Iskra P. , Daum W. , Helsch G. , Becker S. , Wrobel R. J. , Weiss H. , Suchorski Y.
Published: May 2010

ZrO 2 films with a sub-10-nm thickness and a roughness of about 0.2 nm have been prepared on Si(001) by a sol-gel process based on zirconium-(IV)-n-propoxide. The topography of the obtained samples has been controlled by atomic force microscopy. Chemical composition and interface reactions of the deposited films have been studied by x-ray photoemission spectroscopy and Auger electron spectroscopy. The ZrO2 films are stable against heating (up to 700 °C) in a moderate oxygen atmosphere (2×10−5 mbar oxygen partial pressure). Minor changes in the surface composition occur after rapid annealing up to 1000 °C.
A molecular dynamics study of the role of pressure on the response of reactive materials to thermal initiation
Authors: Weingarten N. Scott , Mattson William D. , Yau Anthony D. , Weihs Timothy P. , Rice Betsy M.
Published: May 2010

To elucidate the mechanisms of energy release in a reacting nickel/aluminum bilayer, we simulate the exothermic alloying reactions using both microcanonical and isoenthalpic-isobaric molecular dynamics simulations and an embedded-atom method type potential. The mechanism of the mixing consists of a sequence of steps in which mixing and reaction first occurs at the interface; the resulting heat generated from the mixing then melts the Al layer; subsequent mixing leads to further heat generation after which the Ni layer melts. The mixing continues until the alloying reactions are completed. The results indicate that pressure has a significant influence on the rates of atomic mixing and alloying reactions. Local pressures and temperatures within the individual layers at the time of melting are calculated, and these results are compared with the pressure-dependent melting curves determined for pure Al and pure Ni using this interaction potential.
Impurity-related photoluminescence line shape asymmetry in GaAs/AlAs multiple quantum wells: Fractional-dimensional space approach
Authors: Kundrotas Jurgis , Čerškus Aurimas , Valušis Gintaras , Johannessen Agne , Johannessen Erik , Harrison Paul , Linfield Edmund H.
Published: May 2010

The optical transitions in 20 nm wide silicon and beryllium δ-doped GaAs/AlAs multiple quantum wells with various doping levels were investigated at different excitation intensities. A fractional dimensionality model was used to describe the free hole-donor and free electron-acceptor transitions in the quantum wells. The measured photoluminescence spectra from samples of different doping level related to donor-impurity or acceptor-impurity induced effects in the photoluminescence lineshape, were compared within the framework of these model calculations. Both experimentally and theoretically it was shown that acceptor and donor related optical transitions and photoluminescence line shapes were related to the difference in the effective masses of holes and electrons. This effect also leads to a difference in the photoluminescence spectra in which the luminescence band for the donor related spectrum is narrower in comparison to the acceptor related spectrum.
Effect of annealing on microstructural changes of Nd-rich phases and magnetic properties of Nd–Fe–B sintered magnet
Authors: Park D. W. , Kim Tae-Hoon , Lee Seong-Rae , Kim D. H. , Jang T. S.
Published: May 2010

The microstructural changes of Nd-rich interface phases during postsintering annealing were investigated. A mixture of very fine (about 2–3 nm) crystallites of hexagonal h-Nd2O3, cubic Ia3¯-Nd2O3 (C-Nd2O3), and amorphous phases were observed at the interface phase in the as-sintered magnet and after the first postsintering annealing process. The transformation from h-Nd2O3 to C-Nd2O3 occurred during the second postsintering annealing process, and the resulting C-Nd2O3 has the proper crystallographic relation with the main phase. The reduced lattice mismatch between the (110) plane of C-Nd2O3 interface phase and the (001) or (100) plane of Nd–Fe–B main phase after the second postsintering annealing process is the primary reason for the enhancement in the magnetic properties.
Effects of Fe doping and the dielectric constant on the room temperature ferromagnetism of polycrystalline CeO2 oxides
Authors: Wen Qi-Ye , Zhang Huai-Wu , Yang Qing-Hui , Song Yuan-Qiang , Xiao John Q.
Published: May 2010

Ce 1 − x Fe x O 2 − δ polycrystalline samples with x=0%–8% were synthesized by the solid phase reaction method at a low sintering temperature of 1250 °C, and the effect of Fe content on the magnetic behaviors has been systemically investigated. It is found that the pure CeO2 samples are diamagnetic, while doped samples unambiguously show the existence of room temperature (RT) ferromagnetism (FM). With the increase in x, the saturation magnetization (Ms) exhibits a steep increase to a maximum Ms of 1 emu/g at x=2.7% and then drop exponentially. A small amount of Fe doping (0.9%) promotes the densification and induces a large dielectric constant (ε). Our result shows that a relatively large ε and a proper Fe concentration are critical to establish the magnetic polaron and provide strong RT FM in CeO2.
Self-aligned nanostructures created by swift heavy ion irradiation
Authors: Gehrke Hans-Gregor , Nix Anne-Katrin , Hofsäss Hans , Krauser Johann , Trautmann Christina , Weidinger Alois
Published: May 2010

In tetrahedral amorphous carbon (ta-C) swift heavy ions create conducting tracks of about 8 nm in diameter. To apply these nanowires and implement them into nanodevices, they have to be contacted and gated. In the present work, we demonstrate the fabrication of conducting vertical nanostructures in ta-C together with self-aligned gate electrodes. A multilayer assembly is irradiated with GeV heavy ions and subsequently exposed to several selective etching processes. The samples consist of a Si wafer as substrate covered by a thin ta-C layer. On top is deposited a SiNx film for insulation, a Cr layer as electrode, and finally a polycarbonate film as ion track template. Chemical track etching opens nanochannels in the polymer which are self-aligned with the conducting tracks in ta-C because they are produced by the same ions. Through the pores in the polymer template, the Cr and SiNx layers are opened by ion beam sputtering and plasma etching, respectively. The resulting structure consists of nanowires embedded in the insulating carbon matrix with a built in gate electrode and has potential application as gated field emission cathode.
Phonon emission in germanium and silicon by electrons and holes in applied electric field at low temperature
Authors: Wang G.
Published: May 2010

The cryogenic dark matter search employs Ge and Si detectors to search for weakly interacting massive particle dark matter via its elastic-scattering interactions with nuclei while discriminating against interactions of background particles. These detectors distinguish nuclear recoils from electron recoils by simultaneously measuring phonon and ionization production in semiconducting substrates at sub-kelvin temperatures. They also reconstruct event position by quadrant-segmented measurement of the phonon signal. The ionization drift field does work on the electrons and holes. The charge carriers radiate this energy as acoustic phonons. At the typical applied field of 300 V/m in Ge (400 V/m in Si), we self-consistently model the behavior of the electrons and holes using independent drifted Maxwellian distributions, each characterized by an average drift velocity and an effective temperature, and including acoustic phonon emission. We calculate the phonon power angular and frequency distributions. We find that the bias polarity affects these distributions and, therefore, the phonon collection efficiency in Ge.
Influence of miscut direction on magnetic anisotropy of magnetite films grown on vicinal MgO (100)
Authors: Golub V. O. , Dzyublyuk V. V. , Tovstolytkin A. I. , Arora S. K. , Ramos R. , Sofin R. G. S. , Shvets I. V.
Published: May 2010

Ferromagnetic resonance (FMR) was used to study the influence of miscut direction on the in-plane fourfold and uniaxial magnetic anisotropies of epitaxial Fe3O4 films grown on vicinal MgO (100) surfaces. In-plane angular dependent measurements at room temperature on Fe3O4 films on two different miscut directions (miscut along ⟨011⟩ and ⟨010⟩ directions) of MgO showed the presence of both in-plane fourfold (cubic) and in-plane uniaxial anisotropies. Temperature dependent FMR investigations show that the in-plane fourfold anisotropy constant (K4) is approximately the same for both samples at room temperature. The magnitude of K4 increases gradually with decreasing temperature and changes sign from negative to positive values at 130 K. This behavior is consistent with that of bulk magnetite. In addition to K4, we find an additional uniaxial component (K2), whose strength is quite different for the different miscut directions. The magnitude of K2 shows very little or no temperature dependence. The observed differences in the magnitude of K2 with miscut directions are related to the changes in the antiphase boundary structure and altered magnetic configurations at the boundaries.
Spectrally tunable magnetic nanoparticles designed for distribution/recollection applications
Authors: McDowall Nicholas B. , Wilkins James R. , Carroll Kyler J. , Edwards Jarrod D. , Nelson Jean D. , Carpenter Everett E. , Glaspell Garry P.
Published: May 2010

The comprehensive goal of this research is the synthesis and characterization of nanomaterials that are spectrally tunable in terms of their electromagnetic signal, are robust, magnetic (allowing their piloted movement), and have the potential to be functionalized for the detection of CBRNE threats. Various chemical methods were utilized for synthesis of magnetic (iron) and luminescent rare earth (RE) components, and their mixtures. Effects of integrating an iron core into RE luminescent lattices (excited by UV, emit in the VIS) were investigated. The determination of the optimum balances between magnetic and luminescent components such that the magnetism was maximized while maintaining acceptable fluorescence integrity will be discussed. The emphasis of this work is focused on developing a distributed sensor suitable for use in the terrestrial environment. The robust properties of using a RE luminescent shell would allow the particles to be resistant to photobleaching. Additionally the chemical stability of the RE shell would allow operation in a variety of pH conditions. The magnetic core will ultimately allow the distributed particles to be recollected.
Optimization of magnetic anisotropy and applied fields for hyperthermia applications
Authors: Sohn Hweerin , Victora R. H.
Published: May 2010

Magnetic anisotropy and applied fields for hyperthermia applications have been optimized for iron cobalt nanocrystalline particles using numerical micromagnetics. The optimized anisotropy energy is 7.6 kBT at 500 KHz and the hysteresis loss at this optimized energy is approximately 120×106 ergs/(s∗g) for a very small oscillating field of magnitude 10 Oe. We have also investigated the effects of varying the applied field and find that the addition of a 20 Oe static field applied perpendicular to the oscillating field approximately doubles the energy loss without subjecting the patient to additional radiation. This is an important benefit for magnetic hyperthermia.
Crystalline analysis of permalloy narrow wires subject to current pulses
Authors: Togawa Yoshihiko , Takayanagi Kazuya , Kimura Takashi , Harada Ken , Akashi Tetsuya , Tonomura Akira , Mori Shigeo , Otani Yoshichika
Published: May 2010

We investigate crystalline structures of a permalloy nanowire subject to current pulses by using standard transmission and scanning electron microscope techniques, together with the analysis of magnetic states by means of Lorenz microscopy. We find that crystalline grains grow slightly larger in a current region around the Curie temperature, which does not affect significantly the uniformly-magnetized state in the wire because of strong uniaxial shape anisotropy given by the wire geometry. When crystalline grains grow large enough to additionally provide in-plane anisotropy comparable to the shape anisotropy by averaging crystalline anisotropy over the grains, the magnetic ripple will be induced in the wire. Such situations can be found in the case when very large current pulses are applied to the wire.
Lithium-ion conduction in complex hydrides LiAlH4 and Li3AlH6
Authors: Oguchi H. , Matsuo M. , Sato T. , Takamura H. , Maekawa H. , Kuwano H. , Orimo S.
Published: May 2010

Lithium-ion conduction in complex hydrides LiAlH4 and Li3AlH6 was investigated using ac complex impedance measurements. The conductivities at room temperature were 8.7×10−9 S/cm in the case of LiAlH4 and 1.4×10−7 S/cm in the case of Li3AlH6. To enhance the conductivity of Li3AlH6 having good thermal stability in heating/cooling cycles, mechanical milling, and addition of lithium halides (LiCl, LiI) were implemented. The maximum value of 2.5×10−4 S/cm at 393 K was observed when 0.33 M ratio of LiI was added to Li3AlH6. This study demonstrated two research directions to enhance the lithium-ion conductivity in a variety of complex hydrides.
New four-dimensional integrals by Mellin–Barnes transform
Authors: Allendes Pedro , Guerrero Natanael , Kondrashuk Igor , Notte Cuello Eduardo A.
Published: May 2010

This paper is devoted to the calculation of a special class of integrals by Mellin–Barnes transform. It contains double integrals in the position space in d=4−2ϵ dimensions, where ϵ is parameter of dimensional regularization. These integrals contribute to the effective action of the N=4 supersymmetric Yang–Mills theory. The integrand is a fraction in which the numerator is the logarithm of the ratio of space-time intervals, and the denominator is the product of powers of space-time intervals. According to the method developed in the previous papers, in order to make use of the uniqueness technique for one of two integrations, we shift exponents in powers in the denominator of integrands by some multiples of ϵ. As the next step, the second integration in the position space is done by Mellin–Barnes transform. For normalizing procedure, we reproduce first the known result obtained earlier by Gegenbauer polynomial technique. Then, we make another shift of exponents in powers in the denominator to create the logarithm in the numerator as the derivative with respect to the shift parameter δ. We show that the technique of work with the contour of the integral modified in this way by using Mellin–Barnes transform repeats the technique of work with the contour of the integral without such a modification. In particular, all the operations with a shift of contour of integration over complex variables of twofold Mellin–Barnes transform are the same as before the δ modification of indices, and even the poles of residues coincide. This confirms the observation made in the previous papers that in the position space all the Green’s function of N=4 supersymmetric Yang–Mills theory can be expressed in terms of Usyukina–Davydychev functions.
Tunable slow light in semiconductor metamaterial in a broad terahertz regime
Authors: Bai Qiang , Liu Cong , Chen Jing , Cheng Chen , Kang Ming , Wang Hui-Tian
Published: May 2010

We demonstrate theoretically and numerically that tunable slow light can be realized in planar semiconductor metamaterials with the unit cell composed of two different elements in a broad terahertz regime. In the unit cell, one element is a semiconductor split ring resonator and another one is a semiconductor cut wire. The interaction between the two elements of the unit cell, induced directly or indirectly by the incident electromagnetic wave, leads to a transparent window, resembling the classical analog of electromagnetically induced transparency. This transparent window, caused by the coupling of bright-bright modes or dark-bright modes, can be continuously tuned in a broad frequency regime. The strong normal phase dispersion in the vicinity of this transparent window results in the slow light effect. This scheme provides an alternative way to achieve tunable slow light in a broad frequency band and can find important applications in active and reversibly tunable slow light devices.
Growth of crystalline cobalt ferrite thin films at lower temperatures using pulsed-laser deposition technique
Authors: Raghunathan A. , Nlebedim I. C. , Jiles D. C. , Snyder J. E.
Published: May 2010

Cobalt ferrite thin films were grown on SiO2/Si(100) substrates using pulsed-laser deposition technique at substrate temperatures ranging from 250 to 600 °C. Thermal expansion mismatch between the film and substrate appears to have a substantial effect on the magnetic properties of the cobalt ferrite films, due to the large magnetoelastic coupling of cobalt ferrite. It was shown in this study, that polycrystalline films with (111)-preferred orientation could be prepared at substrate temperatures as low as 250 °C. The growth of crystalline cobalt ferrite films at such low temperatures indicates the potential to use cobalt ferrite for microelectromechanical systems devices and sensor applications including integration with a wider range of multilayer device structures.
Theoretical modeling of spin quantum cross structure devices with noncollinear ferromagnetic electrodes
Authors: Kondo Kenji
Published: May 2010

Recently, we have proposed a spin quantum cross structure (SQCS) device toward the realization of novel switching devices. The SQCS device consists of two ferromagnetic metal thin films with their edges facing each other at an angle of θ, and sandwiches a few molecules and atoms. In this paper, the calculation of electronic transport has been performed for SQCS devices with the Ni noncollinear magnetic films as both electrodes within the framework of the Anderson Hamiltonian, taking into consideration both polar angle θ, and azimuthal angle ϕ. We have obtained the general noncollinear spin transport formula, and the polar angle dependence of current-voltage characteristics of SQCS devices. The noncollinear spin transport is determined only by the angle θ defined by the inner product of two spins. Also, it is implied that SQCS devices can serve as multivalued memory devices by varying the angle θ.
Tunable tunneling magnetoresistance in a ferromagnet-metal-insulator-ferromagnet tunneling junction
Authors: Chen Sui-Pin
Published: May 2010

The tunneling magnetoresistance (TMR) ratio is investigated in a ferromagnet-metal-insulator-ferromagnet planar tunneling junction by use of the spin-polarized free-electron model. In this paper, the bias voltage is exploited to alter the tunneling direction and to tune the barrier height of the insulator, and then to shift oscillatory peaks of the attenuated TMR ratio. We find that the phase change between the forward and backward bias voltages is larger than the phase change due the strength of the bias voltages, and that the direction of the bias voltages can be used to control the sign of the TMR ratio if the wave vector within the M2 layer is close to the imaginary wave vector within the I3 insulator.
Magnetic field dependence of low frequency noise in tunnel magnetoresistance heads
Authors: Han G. C. , Zong B. Y. , Luo P. , Wang C. C.
Published: May 2010

Field dependence of low frequency noise in tunnel magnetoresistance (TMR) heads with different barrier materials of TiO2, Al2O3, and MgO has been studied. It is found that for MgO-TMR heads, the noise amplitude increases as the sensor is driven from parallel to antiparallel magnetization configurations. However, this field dependence of the noise is not magnetic in origin and can be accounted for by the coherent tunneling mechanism in MgO-TMR heads. For TiO2- and Al2O3-TMR heads, low frequency noise is generally independent of magnetic field when the heads are biased properly by hard bias. A noise spike related to a resistance jump in the transfer curve is measured in a head without proper hard bias. Field-dependent low frequency noise is observed for TMR heads without hard bias. The noise amplitude follows the sensitivity function of the sensor and can be attributed to the thermally activated magnetization fluctuations. Spin transfer (ST) effect on low frequency noise was examined by noise measurements of field dependence at different current directions. Extra noise appears when the TMR head is in antiparallel magnetization configurations. The results suggest that the ST-induced extra noise can be either pure 1/f noise or the combination of both 1/f and random telegraph noises.
Magnetic force microscopy study of magnetically annealed Tb0.36Dy0.64(Fe0.85Co0.15)2 polycrystals
Authors: Ma Tianyu , Zhang Changsheng , Zhang Jingjing , Tao Shan , Yan Mi
Published: May 2010

Magnetic force microscopy (MFM) is used to study the domain structures on both transverse and longitudinal sections of Tb0.36Dy0.64(Fe0.85Co0.15)2 ⟨110⟩ oriented polycrystals, which were annealed in a magnetic field of 0.3 T. Different MFM patterns were observed after either perpendicular or parallel field annealing, suggesting that the magnetization of each domain rotates when cooling through their Curie temperature. The long axes of most domains tend to align parallel to the annealing field direction. It gives direct evidence to show the change in the initial magnetic states induced by field annealing, which should be responsible for the variation in the magnetoelastic properties.
Effect of temperature variation on the magnetostrictive properties of CoAlxFe2−xO4
Authors: Nlebedim I. C. , Ranvah N. , Melikhov Y. , Williams P. I. , Snyder J. E. , Moses A. J. , Jiles D. C.
Published: May 2010

The effect of temperature variation on the magnetoelastic properties of the CoAlxFe2−xO4 system (for x=0.0, 0.2, 05, and 0.7) has been studied. Substitution of Al3+ for Fe3+ was found to lower the Curie temperature of the samples and to change the lattice parameter. The magnitude of peak to peak magnetostriction, strain sensitivity, magnetomechanical hysteresis, and relative contributions of λ111 and λ100 to the resultant magnetostriction were found to vary with temperature. The results show the possibility of tailoring the magnetoelastic properties of highly magnetostrictive cobalt ferrite at temperatures of interest by cation substitution.
dc- and ac-magnetic field-induced strain effects in ferromagnetic shape memory composites of Ni–Mn–Ga single crystal and polyurethane polymer
Authors: Zeng Min , Or Siu Wing , Chan Helen Lai Wa
Published: May 2010

Ferromagnetic shape memory composites of multilayer and sandwich types were fabricated by laminating Ni–Mn–Ga single-crystal plates with polyurethane (PU) polymer plates. The dc- and ac-magnetic field-induced strains (MFISs) in the composites were measured as functions of both magnetic field and mechanical load, and the results were compared with those of the single crystal. It was found that the load-free dc-MFISs were 5.6%, 1.5%, and 0.8%, while the load-free ac-MFISs were 0.3%, 0.8%, and 0.5% in the single crystal, multilayer composite, and sandwich composite, respectively. The relatively smaller load-free dc-MFISs and larger load-free ac-MFISs in the composites than the single crystal originated from the stress bias of the Ni–Mn–Ga plates by the PU plates in the composites. The dc-MFISs of all samples and the ac-MFISs of the composites decreased with the increase in mechanical load amplitude, while the ac-MFIS of the single crystal peaked at 1.6 MPa load.
First-principles investigation of huge magnetostriction in cubic L12 Fe3Pt
Authors: Odkhuu Dorj , Hong Soon Cheol
Published: May 2010

Using the highly precise full-potential linearized augmented plane-wave method, magnetostriction of ferromagnetic shape memory alloy Fe3Pt in the cubic L12 structure is investigated. Being consistent with experiments, the giant magnetostrictive coefficient (λ001) of −1050 ppm was calculated from strain-induced magnetocrystalline anisotropy energy. Microscopic origin of the giant magnetostriction of Fe3Pt is explained by spin-orbit coupling interactions in terms of single particle energy spectra.
Effect of the stimulus frequency and pulse number of repetitive transcranial magnetic stimulation on the inter-reversal time of perceptual reversal on the right superior parietal lobule
Authors: Nojima Kazuhisa , Ge Sheng , Katayama Yoshinori , Ueno Shoogo , Iramina Keiji
Published: May 2010

The aim of this study is to investigate the effect of the stimulus frequency and pulses number of repetitive transcranial magnetic stimulation (rTMS) on the inter-reversal time (IRT) of perceptual reversal on the right superior parietal lobule (SPL). The spinning wheel illusion was used as the ambiguous figures stimulation in this study. To investigate the rTMS effect over the right SPL during perceptual reversal, 0.25 Hz 60 pulse, 1 Hz 60 pulse, 0.5 Hz 120 pulse, 1 Hz 120 pulse, and 1 Hz 240 pulse biphasic rTMS at 90% of resting motor threshold was applied over the right SPL and the right posterior temporal lobe (PTL), respectively. As a control, a no TMS was also conducted. It was found that rTMS on 0.25 Hz 60 pulse and 1 Hz 60 pulse applied over the right SPL caused shorter IRT. In contrast, it was found that rTMS on 1 Hz 240-pulse applied over the right SPL caused longer IRT. On the other hand, there is no significant difference between IRTs when the rTMS on 0.5 Hz 120 pulse and 1 Hz 120 pulse were applied over the right SPL. Therefore, the applying of rTMS over the right SPL suggests that the IRT of perceptual reversal is effected by the rTMS conditions such as the stimulus frequency and the number of pulses.
Comparison of the nature of magnetism in α-Ni(OH)2 and β-Ni(OH)2
Authors: Rall James D. , Seehra M. S. , Shah N. , Huffman G. P.
Published: May 2010

For the two stable phases of Ni(OH)2, viz. α-Ni(OH)2 and β-Ni(OH)2, structural and magnetic properties are compared employing x-ray diffraction (XRD), scanning electron microscopy/transmission electron microscopy (TEM/SEM), and variation of the magnetization (M) with temperatures (2–350 K) and magnetic fields (up to ≈65 kOe). Both phases crystallize in the layered hexagonal structure with a=3.04 Å (3.12 Å) and c=23.6 Å (4.67 Å) for the α(β) phase with clear evidence for turbostraticity in the α-phase. From TEM/SEM, the β-phase consists of nanoplates of dimensions 30(10)×3(1) nm, whereas the α-phase has flowerlike morphology with petal thickness ≈5(1) nm. The low-field M versus T data for the zero-field-cooled/field cooled cases bifurcates at Tp=25 K (13 K) for the β(α) phase. For T>Tp, Curie–Weiss variation of M versus T is observed yielding positive θ=20.6 K (32 K) with μ=2.95 μB (3.13 μB) for the Ni2+ ions in the β(α) phase. The M versus H data at 2 K shows antiferromagnetic (ferromagnetic) like variation for the β(α) phase with dM/dH showing peaks at Hc1=28 kOe and Hc2=55 kOe for the β-phase. It is concluded that β-Ni(OH)2 is a metamagnet for T<TN=25 K, whereas α-Ni(OH)2 is a hard ferromagnet with Tc=13 K and domain structure for H<5 kOe.
Exchange-coupling modified spin wave spectra in the perpendicularly magnetized Permalloy nanodot chain arrays
Authors: Dou Jian , Hernandez Sarah C. , Yu Chengtao , Pechan Michael J. , Folks Liesl , Katine Jordan A. , Carey Matthew J.
Published: May 2010

Spin wave spectra in exchange-coupled nanoscale dot chain arrays were studied using ferromagnetic resonance. The dot chain arrays, with dot diameters of 300 nm and thicknesses of 40 nm, coupled via Permalloy bridges of width ranging from 0 (no bridge) to 60 nm, were fabricated using e-beam lithography. In the perpendicularly magnetized isolated dots, multiple sharp ferromagnetic resonant peaks were observed, which are associated with the quantized in-plane wave vector due to the finite dot radius. These spectrum lines shift to higher fields for samples with wider bridges due to the increasing effective demagnetizing factor. For coupled dots, additional satellite peaks were observed at both sides of higher order spin wave modes and at the lower field side of the uniform mode. We show that these satellite peaks can be attributed to the excitation in each bridged dot and the interdot exchange coupling, respectively.
Dual mode nanoparticles: CdS coated iron nanoparticles
Authors: Radwan F. N. , Carroll K. J. , Carpenter E. E.
Published: May 2010

Reverse micelles can be used in a sequential fashion to make core-shell nanoparticles. Using this technique it is possible to make a magnetic quantum dot, by coating an iron core with a cadmium sulfide shell. Transmission electron microscopy indicated core-shell morphology and narrow size distribution of the obtained particles. Collectively, x-ray powder diffraction and x-ray photoelectron spectroscopy verified the presence of cadmium sulfide on the surface of the nanoparticles. Optical properties of the coated particles were demonstrated using fluorescence spectroscopy. A vibrating sample magnetometer was used to determine magnetic properties. Dual mode cadmium sulfide coated iron core-shell nanoparticles make unique candidates for the use in biomedical applications.
Lorentz transmission electron microscopy observation of magnetic domains in La0.825Sr0.175(Mn,Al)O3
Authors: Mori S. , Yoshidome K. , Nagamine Y. , Togawa Y. , Yoshii K. , Takenaka K.
Published: May 2010

Nonmagnetic Al substitution effect on the stability of a ferromagnetic (FM) metallic state in double-exchange manganite, La0.825Sr0.175MnO3, was investigated by Lorentz transmission electron microscopy (TEM), in combination with magnetic measurements. Both FM transition temperature (Tc) and the rhombohedral-to-orthorhombic (R-to-O) transition temperature (Ts) decreased by a few percent of Al substitution. An in situ Lorentz TEM observation revealed that drastic change of the FM domain structure took place through the R-to-O structural transition. The magnetization decreased slightly at Ts and characteristic spin-glass state is realized in the low-temperature region below Ts.
Interstitial-nitrogen effect on phase transition and magnetocaloric effect in Mn(As,Si) (invited)
Authors: Cui W. B. , Lv X. K. , Yang F. , Yu Y. , Skomski R. , Zhao X. G. , Liu W. , Zhang Z. D.
Published: May 2010

The effect of interstitial nitrogen on the phase transition and magnetocaloric behavior of MnAs1−xSixNδ (x=0.03, 0.06, and 0.09) is investigated. The interstitial nitrogen atoms cause the step-scanned x-ray diffraction peaks to shift toward lower angles and lower the Curie temperature, whereas silicon addition increases the Curie temperature to near room temperature. The thermal hysteresis is reduced to nearly 0 in MnAs1−xSixNδ, which is beneficial to practical applications. For a field change of 5 T, the largest magnetic entropy change and refrigerant capacity are 14.6 J kg−1 K−1 at 247 K and 360 J kg−1, which is slightly higher than the entropy change in the parent alloy. Finally, we briefly discuss the occurrence and origin of the “virgin effect” in MnAs.
Effect of annealing on the structure and magnetic properties of Mn1.1Fe0.9P0.8Ge0.2 compound
Authors: Yue M. , Li Z. Q. , Xu H. , Huang Q. Z. , Liu X. B. , Liu D. M. , Zhang J. X.
Published: May 2010

Effect of homogenization of the chemical composition and crystal structure on the magnetocaloric effects have been studied for bulk Mn1.1Fe0.9P0.8Ge0.2 alloy prepared by mechanical alloying and subsequent spark plasma sintering method. After optimal homogenization treatment, the ferromagnetic impurity, Ge6Fe3Mn4 phase was completely eliminated from the alloy; furthermore, the crystal lattice constant of the MnFePGe main phase, which possesses a hexagonal Fe2P-type structure, varies obviously compared with that of the sintered sample. As a result, the Curie temperature, TC, of the alloy increases from 253 to 267.5 K and the maximum magnetic entropy change, |ΔSm|, also increases from 36.36 to 44.35 J/kg K under 3 T magnetic field. Furthermore, the thermal hysteresis of M-T curves around TC upon heating and cooling, a signature of a first-order magnetic phase transition, reduces from 15 K for as-sintered sample to 9 K for annealed sample.
Magnetization reversal dynamics in clusters of single domain Ni nanoparticles
Authors: Rana Bivas , Agrawal Milan , Pal Semanti , Barman Anjan
Published: May 2010

We present the magnetization reversal dynamics of clusters of single domain nickel nanoparticles. Experimental results of magnetization reversal of nickel nanoparticles are completely different from that of bulk nickel and single nickel nanoparticles in terms of the overall shape, coercive field, and the saturation magnetization. Simulations show that a cluster consists of minimum 5×5×3 nanoparticles with no physical overlap between the particles reproduces the loop shape and the coercive field but not the saturation magnetization. However, the same cluster with partially overlapped nanoparticles reasonably reproduces all features of the magnetization reversal due to the presence of both magnetostatic and exchange interactions between the particles. Simulated magnetization images show that the reversal of the cluster occurs through the formation of a C-like state, followed by the creation and annihilation of a vortex like structure, an inverse C-state, and finally, a fully saturated reversed magnetic state. Additional simulations on random clusters show lower coercive field and nearly bulklike saturation magnetization, which are much different than the experimental results. This suggests that the experimental clusters are not totally random or periodically arranged but have a certain amount of ordering.
Synthesis of SiO2 coated NiFe2O4 nanoparticles and the effect of SiO2 shell thickness on the magnetic properties
Authors: Coşkun M. , Korkmaz M. , Fırat T. , Jaffari G. H. , Shah S. I.
Published: May 2010

In this work, the results of synthesis of core-shell NiFe2O4 nanoparticles and influence of silica coating on the magnetic properties of nanoparticles are presented. Spherical NiFe2O4 nanoparticles were prepared via a normal micelles process. NiFe2O4 nanoparticles homogeneously coated with SiO2 of various shell thickness were synthesized by reverse microemulsion. The interparticle spacing was varied by changing the amount of added tetraethylorthosilicate. The microstructures and morphologies of these nanoparticles were studied by x-ray diffraction and transmission electron microscopy techniques. The magnetic parameters such as saturation magnetizations, blocking temperatures, and magnetic anisotropies have been calculated from dc magnetization and ac susceptibility measurements.
Site determination and magnetism of Mn doping in protein encapsulated iron oxide nanoparticles
Authors: Pool V. , Klem M. , Jolley C. , Arenholz E. A. , Douglas T. , Young M. , Idzerda Y. U.
Published: May 2010

Soft x-ray absorption spectroscopy, soft x-ray magnetic circular dichroism, and alternating current magnetic susceptibility were performed on 6.7 nm iron oxide nanoparticles doped with (5%–33%) Mn grown inside the horse-spleen ferritin protein cages and compared to similarly protein encapsulated pure Fe-oxide and Mn-oxide nanoparticles to determine the site of the Mn dopant and to quantify the magnetic behavior with varying Mn concentration. The Mn dopant is shown to substitute preferentially as Mn+2 and prefers the octahedral site in the defected spinel structure. The Mn multiplet structure for the nanoparticles is simpler than for the bulk standards, suggesting that the nanoparticle lattices are relaxed from the distortions present in the bulk. Addition of Mn is found to alter the host Fe-oxide lattice from a defected ferrimagnetic spinel structure similar to γ-Fe2O3 to a nonferromagnetic spinel structure with a local Fe environment similar to Fe3O4.
Magnetodielectric effect in trilayered Co65Fe35B20/PVDF/Co65Fe35B20 composite materials. Prediction and measurement for tunable microwave applications
Authors: Rasoanoavy F. , Laur V. , De Blasi S. , Lezaca J. , Quéffélec P. , Garello K. , Viala B.
Published: May 2010

The variation in the permeability of a multilayered polyvinylidene fluoride/CoFeB (piezoelectric/magnetostrictive) composite material under the action of a dc voltage is demonstrated. The driven-voltage permeability is first predicted using a finite element method-based multiphysics calculation. The simulation allows us to determine a magnetic anisotropy field of 45 Oe induced in the ferromagnetic layers by the mechanical coupling between magnetostrictive and piezoelectric layers due to the applied dc voltage. A variation of 30% for the permeability of the ferromagnetic layers is then measured using a radiofrequency permeameter and under the application of a dc voltage of 15 V applied on the ferromagnetic layers, which also act as electrodes for the bias of the polyvinylidene fluoride (PVDF). An additional measurement of the trilayered structure under the application of a dc magnetic field is finally performed to evaluate the magnetic field needed to get a 30% variation in the magnetic layers permeability in order to compare this value to the one predicted by multiphysics calculation. These experimental results are in good agreement with calculations and are very encouraging for the application of the CoFeB/PVDF/CoFeB composite material to ensure the tunability of microwave devices (filters, phase shifters, antennas, etc.)
Phonon transport in atomic chains coupled by thermal contacts: The role of buffer layer
Authors: Zhao Xuean , Li Jing , Au Yeung T. C. , Kam C. H. , Chen Qing-Hu , Sun Chang Q.
Published: May 2010

In this work, ballistic phonon transport in atomic chain nanostructures is investigated by atomic nonequilibrium Green’s functions and embedded atom method. Bond length and strength modification in atomic chain (low-dimensional structure) was taken into consideration by using bond-order-length-strength correlation premise. We especially focus on the contact interface effects on phonon transmission and thermal conductance. It is found that the contact interfaces between an atomic chain and contact reservoir, i.e., neck region or buffer layers, play an important role in phonon transport. The more buffer layers the less thermal conductance.
Magnetically tunable double-negative material composed of ferrite-dielectric and metallic mesh
Authors: He Guanghua , Wu Rui-xin , Poo Yin , Chen Ping
Published: May 2010

We designed and studied a magnetic tunable metamaterial composed of ferrite-dielectric and metallic mesh. The retrieved electromagnetic parameters and the transmission characteristic showed the composite has a double-negative regime in magnetized state. Moreover, this regime is tunable in external magnetic fields. The composite has a lower loss with minimum about −0.3 dB/mm. The simulations of the wave propagation on the interface of the composite clearly display a negative refraction. The negative indexes calculated from Snell’s law are in good agreement with the indexes retrieved from S parameters, quantitatively confirms the negative index of the composite.
Band alignment and excitonic localization of ZnO/Cd0.08Zn0.92O quantum wells
Authors: Matsui Hiroaki , Osone Takamasa , Tabata Hitoshi
Published: May 2010

The band structure and excitonic recombination of a Cd0.08Zn0.92O/ZnO single quantum well (SQW) were shown to vary according to well width (LW). The excitonic localization of a Cd0.08Zn0.92O single layer used as a well layer of the SQW was based on alloy disorder by spatial inhomogeneity of the Cd atoms. It was shown that photoexcited excitons localized into potential fluctuations of 18 meV from a measurement of temperature-dependent photoluminescence (PL), which became an important guide to estimate the degree of excitonic localization for the SQW. The LW of SQW remarkably influenced excitonic localization, which gradually increased with a narrowing of LW. When LW was less than the excitonic Bohr diameter (Rex: 3.6 nm) of ZnO, the excitonic localization was determined by both alloy disorder and interface fluctuations of the barrier/well interfaces. On the other hand, the excitonic localization became remarkably weak for LW greater than Rex mainly because of the quantum-confined Stark effect (QCSE). The formation of the QCSE was clarified by an excitation-power-dependent PL of SQW and an identification of band alignment of a Cd0.08Zn0.92O/ZnO heterostructure. Finally, the excitonic localization of SQW for LW comparable to Rex was determined by the alloy disorder generated in the well.
Correlation between saturation magnetization, bandgap, and lattice volume of transition metal (M=Cr, Mn, Fe, Co, or Ni) doped Zn1−xMxO nanoparticles
Authors: Anghel J. , Thurber A. , Tenne D. A. , Hanna C. B. , Punnoose A.
Published: May 2010

This work reports on transition metal doped ZnO nanoparticles and compares the effects doping with different transition metal ions has on the structural, optical, and magnetic properties. Zn1−xMxO (M=Cr, Mn, Fe, Co, or Ni) nanoparticles were prepared by a chemical process for x=0.02 and 0.05 in powder form. The powders where characterized by x-ray diffraction (XRD), spectrophotometry, and magnetometry. The Zn1−xMxO samples showed a strong correlation between changes in the lattice parameters, bandgap energy, and the ferromagnetic saturation magnetization. Unit cell volume and bandgap, determined from XRD and spectrophotometry respectively, were maximized with Fe doping and decreased as the atomic number of the dopant moved away from Fe. Bandgap was generally lower at x=0.05 than x=0.02 for all dopants. The saturation magnetization reached a maximum of 6.38 memu/g for Zn0.95Fe0.05O.
Intrachain antiferromagnetic interaction and Mott state induced by spin-orbit coupling in Sr3NiIrO6
Authors: Zhang G. R. , Zhang X. L. , Jia T. , Zeng Z. , Lin H. Q.
Published: May 2010

The intrachain magnetic interaction and the electronic structure of Sr3NiIrO6 are investigated by performing the first-principles density functional calculations. The results show that the interaction between Ir and Ni is antiferromagnetic in each quasi-one-dimensional chain. More importantly, the GGA+U calculations hardly reproduce the insulating characteristics of Sr3NiIrO6 in the region of reasonable correlation parameter. Interestingly, the spin-orbit coupling (SOC) together with the electron-electron correlation (GGA+SOC+U) can lead to the insulating characteristics of Sr3NiIrO6. This provides apparent evidence that Sr3NiIrO6 belongs to a new category of insulator: SOC induced Mott insulator.
X-ray absorption and magnetic circular dichroism of graphene/Ni(111)
Authors: Dedkov Yu. S. , Sicot M. , Fonin M.
Published: May 2010

We present systematic investigations of the electronic and magnetic properties of the graphene/Ni(111) system by means of x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) at the Ni L2,3 and C K absorption edges. The XAS C 1s→π∗,σ∗ spectra show dramatic changes as the angle, α, between the electrical vector of light and normal of the sample is varied reflecting the symmetry of the final state (σ or π). XMCD spectra reveal an induced magnetic moment of the carbon atoms in the graphene layer. Our experimental results are discussed in the light of previous results on the observation of induced magnetism in nonmagnetic materials.
Magnetic properties of Y0.7Er0.3Fe2(H,D)4.2 compounds under continuous magnetic field up to 35 tesla
Authors: Guillot M. , Paul-Boncour V. , Leblond T.
Published: May 2010

The study of the Y0.7Er0.3Fe2(H,D)4.2 shows that the Y for Er substitution modifies both structural and magnetic properties of the hydrides and deuterides. Their cell volume is smaller than for the nonsubstituted compounds. Under high magnetic field two field-induced transitions are observed, the first one that takes place between 4.2 and 26 K (hydride) and 53 K (deuteride) originates from the erbium magnetic behavior, the second one found above 101 K (hydride) and 60 K (deuteride) is mainly attributed to an antiferro-ferromagnetic transition in the Fe sublattice. This important isotopic effect is attributed to the change of the cell volume induced by the deuterium and hydrogen insertion. Comparison with YFe2H4.2 and YFe2D4.2 compounds shows that the temperature at which appears the second transition is shifted to lower values. The transition field increases linearly versus temperature but with a much larger ΔHTR/ΔT slope for the deuteride compared to the hydride whereas there were similar in the nonsubstituted compounds. The roles of both cell volume change and erbium magnetic contribution are briefly discussed.
Effect of B2O3–Bi2O3–SiO2–ZnO glass on the dielectric and magnetic properties of ferroelectric/ferromagnetic composite for low temperature cofired ceramic technology
Authors: Ling Weiwei , Zhang Huaiwu , Li Yuanxun , Chen Daming , Wen Qiye , Shen Jian
Published: May 2010

Ni–Cu–Zn ferrite/BaTiO3 composites with different additive amounts of B2O3–Bi2O3–SiO2–ZnO (BBSZ) glass have been prepared by a conventional solid-reaction method and sintered at 900 °C to adapt to low temperature cofired ceramic (LTCC) technology. The dielectric and magnetic properties of the composites can be effectively improved with increasing BBSZ content. Here, the BBSZ glass mainly plays two roles, one is as a sintering aid promoting grain growth and the other is as a low permittivity phase or nonmagnetic phase leading to dilution effect on the dielectric or magnetic properties of the composites. The effect degree of above two roles is related to the variation in BBSZ content and has been discussed combining with the effective medium theory. The lower and upper bounds for the effective permittivity and permeability have been given by the Maxwell–Garnett rules.