bluuebunny/crossref_metadata_2025 huggingface dataset:
Thin CNx overcoats deposited using various sputtering gases
Authors: Wei G. , Gong J. , Zangari G. , Weaver M. L. , Barnard J. A.
Published: May 2003

This work presents systematic studies of the effect of various sputtering gases (Ar, Kr, and Xe) on the roughness, density, coverage, stress, and nanomechanical properties of CNx thin films. CNx (1–11 nm) was deposited on Si (100) substrates using dc magnetron sputtering. A three-parameter roughness analysis was carried out using atomic force microscopy. Film thickness and density were measured by x-ray reflectivity. Nanoindentation hardness and modulus were measured using a Hysitron TriboScope® nanomechanical system, while stress measurements were performed using a Flexus thin film stress measurement system. The coverage of CNx is assessed using a pinhole-decoration technique. As the mass of the sputtering gases increases, the density and hardness of CNx increases, while the deposition rate, surface roughness, and compressive stress decrease. Using Kr or Xe, a 3-nm-thick dc-sputtered CNx overcoat displaying good coverage is obtained.
Ex situ annealing method for c-axis oriented barium ferrite thick films
Authors: Gee S. H. , Hong Y. K. , Erickson D. W. , Tanaka T. , Park M. H.
Published: May 2003

A barium hexaferrite (BaFe12O19, magnetoplumbite structure, BaM) multilayered film, with a total thickness of 0.63 μm, was deposited on a Si substrate by stacking several 0.09 μm layers using a rf sputtering technique. Each 0.09 μm layer was ex situ annealed at 800 °C for 10 min prior to deposition of the succeeding layer. A vibrating sample/torque magnetometer was employed to characterize the magnetic properties of both the BaM multilayered and a single layered film of the same thickness. The 0.63 μm thick BaM multilayered and single layered films show a squareness (SQ=Mr/Ms at 7 kOe) of 0.81 and 0.62, respectively. An anisotropy field (HA) was found to be 17 kOe for the BaM multilayered film and 14.5 kOe for the single layered film. A stacking of BaM layers, with ex situ annealing between each layer, improves the c-axis orientation and anisotropy field as compared to a single layered film with the same thickness. This is attributed to limiting the number of nucleation sites for randomly oriented BaM crystallites existing in films thicker than 0.1 μm.
Determination of rotatable anisotropy in exchange-biased bilayers using anisotropic magnetoresistance technique
Authors: Kim J. K. , Kim S. W. , Lee K. A. , Kim B. K. , Kim J. H. , Lee S. S. , Hwang D. G. , Kim C. G. , Kim C. O.
Published: May 2003

We improved the anisotropic magnetoresistance model to determine the quantity and direction of rotatable anisotropy in FeMn/NiFe structures independent of the thickness of the antiferromagnet layer. In our model, there are two important parameters, the magnitude α=Hrot/Hex and direction β=θrot/θa of rotatable anisotropy, where Hrot and θrot are an effective magnetic field and angle of a rotatable anisotropy, and Hex and θa are the exchange bias field and angle of applied field. As FeMn thickness decreased from 20 nm to 3.5 nm, α value increased from about 0.15 to 0.55. This proves that weak exchange coupling regions increase as the antiferromagnet thickness decreases. The α and β almost did not change as the NiFe thickness increases from 7 nm to 15 nm, even if the Hex was reduced from 170 Oe to 70 Oe.
Writing induced nanodeformation and its effects on head-disk clearance
Authors: Liu B. , Han Y. F.
Published: May 2003

Further reducing the head-disk spacing down to 3–4 nm will be needed for future extremely high-density magnetic recording systems of areal densities of 800–1000 Gbits/sq2. On the other hand, it is important to not only reduce the head-disk spacing but also retain the stability of the head-disk interface. This article reports an observation of the spacing change caused by thermal induced nanodeformation of the slider body even when writing current and the writing frequency are just within their value range in normal writing operations. Results indicate that the combination of the internal heating generated by writing operation with the cooling effect of the airflow over the air-bearing surface leads to not only local protrusion of the area around the transducer but also the variation of the crown value of the slider and, therefore, the change of the head-disk spacing. A crown deformation model is proposed and the validity of the proposed model is confirmed by both computer modeling and experimental observations.
Exchange anisotropy of (001) oriented Mn1−xPtx/NiFe epitaxial films
Authors: Kume T. , Sugiyama Y. , Kato T. , Iwata S. , Tsunashima S.
Published: May 2003

Exchange anisotropy was investigated for Mn1−xPtx (x=0.06–0.40)/NiFe bilayers prepared by molecular-beam epitaxy on MgO (001) substrates. The bilayers exhibited a large exchange bias field without postannealing, which showed a maximum value of 140–160 Oe around x=0.11. This result is almost the same as those for the (111) oriented bilayers. The exchange anisotropy is induced with the easy direction parallel to the 〈110〉 axes in spite of the fact that the magnetic field is applied along the 〈100〉 direction during the deposition. Diffraction peaks from an ordered phase of Mn3Pt alloy were not observed in the reciprocal space map measured by x-ray diffraction. The origin of the exchange anisotropy is attributed to the antiferromagnetic spin arrangements of the MnPt layer with a disordered face-centered-cubic structure.
Magnetic properties of high Si steel with variable ordering obtained through thermomechanical processing
Authors: Ruiz D. , Ros-Yañez T. , Vandenberghe R. E. , De Grave E. , De Wulf M. , Houbaert Y.
Published: May 2003

Alloys with a Si content of 4.2 and 5.4 wt % Si were produced to investigate the effect of increasing the Si on the materials processing and properties and to understand the effect of the order–disorder phenomenon on its magnetic properties. Different cooling rates after hot rolling were applied: Slow cooling from 780 °C to room temperature in 26 h, air cooling and water quench, followed by cold rolling until 0.5 to 0.7 mm thickness. Magnetic properties were measured after pickling and annealing at 950 °C for 2 h. Fe57 Mössbauer spectroscopy was used to study the effect of thermomechanical cycles on the ordering phenomena. It was noticed that the quenched samples have the highest values for the magnetic polarization, while slowly cooled samples have the lowest, for the power losses higher values are obtained for the quenched materials. The highest values for the polarization in the quenched samples were explained as a result of a higher B2 ordering.
One-dimensional magnetophotonic crystals with granular magnetic films
Authors: Yoshida Takashi , Nishimura Kazuhiro , Uchida Hironaga , Inoue Mitsuteru
Published: May 2003

A one-dimensional magnetophotonic crystal (1D-MPC) with a granular magnetic film has a large Faraday rotation angle at a localized photonic state inside a photonic forbidden band gap. The great advantage of using the granular magnetic film is that a thermal annealing process is unnecessary, which is in contrast to a 1D-MPC with a Bi:YIG film. We describe that the improved performance of the 1D-MPC with the granular film is obtained without thermal annealing.
ac-response of magnetic moments of diluted Ho3+ ions
Authors: Giraud R. , Tkachuk A. M. , Barbara B.
Published: May 2003

Low-temperature dynamics of mesoscopic magnetic moments of a 0.1% at Ho3+-doped LiYF4 single crystal is probed by ac-susceptibility measurements above T=1.75 K. In the temperature and frequency range studied (1.75 K⩽T⩽5 K,10 Hz⩽f⩽1500 Hz), the results clearly show that both thermally activated quantum tunneling of a nearly isolated magnetic moment and spin–spin cross relaxations occur. This interpretation is strongly supported by the calculated electro-nuclear Zeeman diagram either of a single ion or of a pair of diluted ions.
Heisenberg model of a {Cr8}-cubane magnetic molecule
Authors: Luban Marshall , Kögerler Paul , Miller Lance L. , Winpenny Richard E. P.
Published: May 2003

A Heisenberg model of eight CrIII paramagnetic centers (spins s=3/2) at the vertices of a cube with four distinct exchange interactions is found to provide a reasonably accurate description of the magnetic susceptibility of the cubane-type magnetic molecule [Cr8O4(O2CC6H5)16]={Cr8} from 2–290 K for an external field of 0.5 T. We find that two exchange bonds are antiferromagnetic (13, 24 K) and two are ferromagnetic (5, 13.5 K), with an accuracy of approximately 1 K. The determination of the four exchange constants is greatly facilitated using the exact high-temperature expansion of the weak-field susceptibility, effectively reducing the number of unknown parameters to two. We have calculated the thermodynamic properties of the system and these can be compared with the results of future experiments. At temperatures below 0.5 K sharp increases are expected in the magnetization versus external magnetic field at approximately 6 and 12 T and higher fields due to level crossings. Inelastic neutron scattering could check our predictions for the low-lying magnetic energy levels.
Thermal stability of self-assembled FePt nanoparticles
Authors: Vedantam T. S. , Liu J. P. , Zeng H. , Sun S.
Published: May 2003

We have produced self-assembled FePt nanoparticles by chemical synthesis and subsequent thermal annealing. The self-assembled samples were annealed in nitrogen or forming gas (95%Ar+5%H2) atmosphere for varying annealing time and temperatures. Thermal annealing above 500 °C resulted in phase transformation of the as-synthesized FePt from the chemically disordered fcc to chemically ordered fct structure which has a high uniaxial magneto-crystalline anisotropy. With increasing annealing temperature, the coercivity and the thermal stability factor KV/kT were found to increase due to improved chemical ordering, irrespective of the annealing atmosphere. For samples annealed at 580 °C for 30 min in forming gas, the maximum coercivity obtained was 6.95 kOe. The samples annealed in forming gas showed higher coercivity and KV/kT values than those annealed in nitrogen for the same annealing time and temperature. We have also measured the Curie temperatures of the FePt nanoparticle assemblies. The Curie temperatures were found to increase with increased annealing time for the samples annealed in nitrogen at 580 °C.
Origin of the orientation ratio in sputtered longitudinal media
Authors: Demczyk B. G. , Zhou J. N. , Choe G. , Stach E. , Nelson E. C. , Dahmen U.
Published: May 2003

The surface morphology, thin film microstructure, and crystallography of sputtered longitudinal media were examined by atomic force and transmission electron microscopy. It was found that surface features along the texture lines in addition to the line density affect the measured orientation ratio. In addition, c-axis alignment along the texture line direction was established. These results point to magnetocrystalline anisotropy associated with the c axis as a major contributor to a high orientation ratio in these materials.
Transport anisotropy in hetero-amorphous (CoFeB)–SiO2 thin films
Authors: Johnsson P. , Aoqui S.-I. , Grishin A. M. , Munakata M.
Published: May 2003

We here present resisitivity and magnetoresistance measurements of two granular (CoFeB)–SiO2 amorphous thin films, with a different amount of metallic content. The films were deposited onto substrates sitting on a rotating cylinder. This induces anisotropy in the film plane, which is higher for the sample with less metallic content. This film exhibits typical isotropic giant magnetoresistance (GMR), while the film with higher-metallic content has less anisotropic resistivity, and shows a mixture of GMR and anisotropic magnetoresistance (AMR). The AMR appears at fields below 500 Oe. We believe that this has not been observed before in amorphous samples.
Domain model for the magnetoimpedance of metallic ferromagnetic wires
Authors: Betancourt I. , Valenzuela R. , Vazquez M.
Published: May 2003

Complex inductance formalism (L) is used to calculate the complex circular permeability (μcirc) in a domain model for the magnetoimpedance (MI) of soft ferromagnetic wires. An excellent agreement between calculated and experimental values of μcirc as a function of frequency is observed. In addition, a very good agreement is also exhibited between experimental and calculated plots of μcirc as a function of an applied dc magnetic field before and above the relaxation frequency (also known as single- and double-peak MI effect). These results confirm the validity of L as an alternative approach to MI phenomena in soft ferromagnetic wires.
Characteristics of magnetic tunnel junctions consisting of amorphous CoNbZr layers
Authors: Chun Byong Sun , Lee Seong-Rae , Kim Young Keun
Published: May 2003

Magnetic tunnel junctions comprising amorphous CoNbZr layers have been investigated. Co85.5Nb8Zr6.5 (in at. %) layers were employed to substitute traditionally used Ta layers with an emphasis given on understanding underlayer effect. The typical junction structure was SiO2/CoNbZr or Ta 2/CoFe 8/IrMn 7.5/CoFe 3/Al 1.6+oxidation/CoFe 3/CoNbZr or Ta 2 (nm). For both as-deposited state and after annealing, the CoNbZr-underlayered structure showed superior surface smoothness up to the tunnel barrier than Ta-underlayered one (0.16 vs 0.34 nm). Ultrasmooth layer structure was proven beneficial for reducing temperature-dependent magnetoresistance properties. A longer annealing degraded the properties most likely due to Mn interdiffusion toward the bottom ferromagnetic electrode as confirmed by Auger electron spectroscopy. By a slight change in the bottom electrode thickness (CoNbZr 4/CoFe 10), the tunneling magnetoresistance ratio can be increased up to 32% after 10 min annealing at 300 °C.
Thickness dependence of the magnetic hysteresis of NiFe-31% films as a function of an applied isotropic in-plane stress
Authors: Garrett Claude , Holland Patrick , Geerts Wilhelmus J. , Ragan Dustin , Dubey Archana , Rios Steve , Bandyopadhyay Anup K.
Published: May 2003

The magnetic hysteresis of dc magnetron-sputtered Ni69Fe31 films that were sandwiched between titanium layers was investigated as a function of an externally applied isotropic in-plane strain. The hysteresis curves were measured with a Kerr magnetometer that monitored the longitudinal Kerr ellipticity as a function of the in-plane magnetic field. The strain was created by bending the samples in two dimensions using a pressure cell. Measurements were performed on films with different thicknesses. The magnetoelastic properties appeared to be much smaller for films with a thickness of 100 nm than for films with a thickness of 288 or 500 nm. This might be due to a change of the domain wall pinning, or a change of the domain wall density as a function of the film thickness. Measurements under compressive isotropic in-plane stress were shown to be possible by flipping the sample in the pressure holder and measuring through the glass substrate. The Faraday effect and stress-induced birefringence in the glass substrate did not hinder the accumulation of noiseless hysteresis data. The magnetoelastic effects appeared to be different for positive and negative values of the applied stress.
Ferromagnetic resonance in exchange spring thin films
Authors: Crew D. C. , Stamps R. L.
Published: May 2003

The ferromagnetic resonance frequencies have been calculated for a soft/hard Co/CoPt exchange spring thin film system. In this geometry the magnetostatics are crucial to understanding the variation of resonant frequency with field due to the out-of-plane component of magnetization of the CoPt hard layer. When exchange coupling between films exists, significant changes in the resonant frequency occur. For in-plane reverse applied fields, a spiral is formed in the soft Co layer. This appears as a double minimum in the resonant frequency as a function of the in-plane applied field. The positions of the frequency minima correspond to the beginning and end of the spiral formation in the Co layer. The frequency of the maximum provides a sensitive measure of the perpendicular anisotropy in the cobalt film.
High speed signal transmission with magneto-couplers
Authors: Ganzer S. , Bayreuther G. , Hauch J. , Rieger G.
Published: May 2003

Couplers in general serve for galvanically isolated signal transmission between sensitive equipment. Standard opto-couplers are generally limited to a bandwidth of 25 MHz. However, with ever-increasing data transfer rates the need for couplers with much higher bandwidth is steadily growing. For this purpose magneto-couplers are very promising because their bandwidth is expected to be limited only by the Larmor precession of the magnetic moments with frequencies in the range of 1–10 GHz. In magneto-couplers the signal to be transmitted is converted into a current through a micro-coil. The resulting magnetic field is detected by a giant magnetoresistance (GMR) sensor element separated by an isolation layer. In the present case this element is a Wheatstone bridge consisting of four spin valves. The voltage across the bridge resulting from the magnetization change of the soft layers due to the field pulses is detected with a 1 GHz storage oscilloscope. Present experiments indicate a bandwidth larger than 500 MHz. After proper termination of the signal paths and applying a dc-bias field the rise time of the input signal of less than 1 ns is not increased by the coupler. Furthermore we show that the driving pulse may be completely reproduced in shape by applying external dc-bias fields. It will also be discussed how capacitive and inductive crosstalk between the coil and the spin valves and nonideal termination of the signal paths affect the achievable bandwidth.
Low temperature magnetocaloric properties of HoNi2
Authors: Gomes A. M. , Oliveira I. S. , Guimarães A. P. , Lima A. L. , von Ranke P. J.
Published: May 2003

The magnetocaloric properties of the HoNi2 intermetallic compound are presented. Theoretical results predicted that the crystalline electric field is responsible for the second peak in the magnetic entropy change curve at low temperatures in HoNi2 single crystal oriented in the [100] direction. We present the isothermal magnetization and adiabatic heat capacity data obtained on HoNi2 polycrystalline samples. The experimental data were used to calculate the magnetic entropy change after a field variation of 40 kOe. Independently, we extended the theoretical analysis for a polycrystalline sample in order to compare with the experimental results.
Atomic clusters of magnetic oxides: Structure and phonons
Authors: Kirilyuk A. , Demyk K. , von Helden G. , Meijer G. , Poteryaev A. I. , Lichtenstein A. I.
Published: May 2003

This work represents a combined experimental and theoretical study of structural and magnetic properties of clusters made of cobalt, chromium, and manganese oxides. The clusters were prepared in a molecular cluster source by oxidation of laser-vaporized metal and studied in a time-of-flight spectrometer. Infrared laser-induced cluster dissociation experiments revealed the spectrum of cluster vibrational states. We also performed ab initio local spin density approximation calculations of the equilibrium geometry, electronic structure, and magnetic properties of these clusters.
Vortex pinning at individual defects in magnetic nanodisks
Authors: Rahm M. , Biberger J. , Umansky V. , Weiss D.
Published: May 2003

We studied the interaction between magnetic vortices and artificial point defects by using micro-Hall magnetometry. Disk-shaped Permalloy particles with diameters between 300 and 800 nm and thicknesses from 20 to 60 nm, which contain a single lithographically defined defect, were examined. Magnetization reversal curves were measured for different in-plane directions of the applied field. The data indicate that the magnetic vortex structure can be pinned at the point defect.
Towards direct synthesis of fct-FePt nanoparticles by chemical route
Authors: Jeyadevan B. , Hobo A. , Urakawa K. , Chinnasamy C. N. , Shinoda K. , Tohji K.
Published: May 2003

The possibility for direct synthesis of fct-FePt nanoparticles of the order of 3–4 nm in diameter through the coreduction of iron and platinum ions in a polyol has been explored. We have succeeded in the synthesis of face-centered cubic structured 3–4 nm diameter FePt particles whose composition was very close to Fe50Pt50. The Fe:Pt ratio was influenced little by the molar ratios of Fe and Pt acetylacetonate dissolved in ethylene glycol. However, depending on the polyol/Pt ratio, the as-prepared samples were either superparamagnetic or ferromagnetic. The transition temperature (Tt) and magnetic properties of the as-prepared FePt were very sensitive to the reaction conditions, and the Tt varied between 593 and 893 K and the particles were ferromagnetic. The as-prepared FePt under the optimum condition had a Tt as low as 593 K and Hc as high as 1.11 kOe at an applied field of 1 T at room temperature. Furthermore, when the as-prepared FePt nanoparticles with Tt around 593 K were annealed at 673 K in H2/N2 atmosphere for an hour they transformed to the ordered fct (L10) structure with coercivity as high as 4.2 kOe at 300 K. This confirmed the lowering of Tt by the manipulation of the reaction condition alone.
Tricritical points in La-based ferromagnetic manganites
Authors: Amaral V. S. , Araújo J. P. , Pogorelov Yu. G. , Sousa J. B. , Tavares P. B. , Vieira J. M. , Algarabel P. A. , Ibarra M. R.
Published: May 2003

A detailed study of the magnetization M(H,T) of manganites near TC is presented. Analysis, in the framework of Landau theory of phase transitions (G=G0+1/2AM2+1/4BM4+1/6CM6−MH) reveals that for La0.67Ca0.33MnO3 (TC=267 K), La0.8MnO3 (TC=250 K), and La0.60Y0.07Ca0.33MnO3 (TC=150 K) the phase transition is first-order and the B coefficient is temperature dependent, negative near TC. In field (H<HC*) and temperature (TC<T<TC*) ranges, below the critical point of the first-order phase transition, clear features are found, with hysteresis. For La0.60Y0.07Ca0.33MnO3, HC*∼20 kOe, ΔT=TC*−TC∼20 K. For La0.67Ca0.33MnO3, on the other hand, HC* is only 250 Oe and ΔT<1 K. These effects are related with electronic and elastic energy contributions coupled to the magnetic order parameter. The analysis of the vanishing of B above TC suggests that a tricritical point should occur at T∼310 K, in agreement with the temperature at which the magnetic and structural transitions in La0.7(Ca1−ySry)0.3MnO3 coincide.
Effect of Co substitution on the crystallization behavior and magnetic properties of melt-spun (Pr,Tb)2(Fe,Nb,Zr)14B/α-Fe nanocomposites
Authors: Wang H. , Zhang Y. , Jin Z. Q. , Hadjipanayis G. C.
Published: May 2003

The influence of Co substitution on the crystallization behavior and magnetic properties of (Pr,Tb)2(Fe,Nb,Zr)14B/α-Fe nanocomposites was investigated in melt-spun Pr7Tb1Fe87Nb0.5Zr0.5B4 and Pr7Tb1Fe57Co30Nb0.5Zr0.5B4 samples. Crystallographic textures were observed for all constituent phases in both sample S spun at wheel speeds less than 15 m/s. Both alloys show a fully amorphous structure when spun at a speed faster than 40 m/s which crystallizes into the TbCu7 structure before it finally transforms into the 2:14:1 phase. The Curie temperature of α-Fe and Pr2Fe14B phase increases greatly with the substitution of 30% Co for Fe. However, both the coercivity and energy product decrease. Optimum magnetic properties are found in the Pr7Tb1Fe87Nb0.5Zr0.5B4 sample with coercivity Hc=6.84 kOe and (BH)max=11.8 MG Oe.
Magnetic-field dependence of conductance quantization in ferromagnetic point contacts
Authors: Shimizu M. , Saitoh E. , Miyajima H.
Published: May 2003

The conductance in ferromagnetic Ni point contacts has been investigated by using break junction techniques. We successfully kept each conductance plateau for about a minute. Reversible switching of the quantized conductance by the application of the magnetic field was observed. These results suggest that the mechanical aspect of quantum point contacts (QPC) formation and the local magnetic property around Ni QPC can affect the conductance quantization in Ni QPC.
The improved magnetic properties in phosphorus substituted Pr–Fe–P–B nanocomposites
Authors: Jin Z. Q. , Zhang Y. , Wang H. L. , Klaessig A. , Bonder M. , Hadjipanayis G. C.
Published: May 2003

Phosphorus substituted (Pr,Tb)8(Fe,Nb,Zr,P)88B4 nanocomposites have been produced by melt-spinning. The effects of phosphorus substitution as well as wheel speed on the crystallization behavior and magnetic properties of the melt-spun samples have been investigated. With the substitution of phosphorus, the crystallization temperature of amorphous phase increases. The optimum wheel speed was found to be around 25 m/s for as-spun ribbons and 40 m/s for the annealed samples, both of which present excellent second quadrant hysteresis loop shapes due to the fine grain size of α-Fe which is around 20 nm. The addition of phosphorus also greatly improves the coercivity of Pr–Fe–B nanocomposites without a significant loss of saturation magnetization. A higher coercivity of 9.2 kOe in P-substituted samples was obtained as compared to 8.1 kOe in P-free samples. This is attributed to a narrower temperature span between the crystallization into TbCu7 structure and the transformation into the 2:14:1 phase caused by the phosphorus substitution.
Magnetic frustration effects in LaCaMnO3 single crystals
Authors: Phan Manh-Huong , Srinivas V. , Yu Seong-Cho , Hur Nam Hwi
Published: May 2003

We investigated dc and ac susceptibilities of La1−xCaxMnO3 (x=0.2,0.3) single crystals. Obtained results show that La0.8Ca0.2MnO3 is clearly magnetically more frustrated than La0.7Ca0.3MnO3, indicating that charge/orbital fluctuation is enhanced in La0.8Ca0.2MnO3. A remarkable magnetic anomaly in the imaginary component of the ac susceptibility appears around 100 K for La0.8Ca0.2MnO3 to be attributed to the magnetic frustration arising from the strong competition between antiferromagnetic and ferromagnetic interactions that favor the existence of short-range charge/orbital ordering in this sample. In connection with the resistivity data, we propose that the order parameter of magnetic origin should be coupled to the other degrees of freedom in the case of La0.8Ca0.2MnO3 rather than La0.7Ca0.3MnO3.
Plasma sprayed Nd–Fe–B permanent magnets
Authors: Willson M. , Bauser S. , Liu S. , Huang M.
Published: May 2003

This study demonstrated that the plasma spray deposition method is an alternative process for producing Nd–Fe–B magnets in addition to the two existing principal processes: the powder metallurgy process for producing sintered Nd–Fe–B magnets and the melt spinning process for bonded Nd–Fe–B magnets. Plasma spray is a potentially better process for producing magnetic parts with complicated shape, large area, thin thickness, small dimension, or unusual geometry. High intrinsic coercivity greater than 15 kOe was readily obtained for Nd16Dy1Fe76B7 even in the as-deposited condition when the substrate was preheated. The plasma spray process contains only three steps: melting, crushing, and plasma spray, which is much simpler than the powder metallurgy and melt spinning processes. Without preheating the substrate, the coercivity was usually very low (∼0.1 kOe) in the as-deposited condition and it increased to 10 to >15 kOe after anneal. Evidence of magnetocrystalline anisotropy was observed in plasma sprayed Nd15Dy1Fe77B7 magnets when the substrate was not preheated. It is believed that a crystal texture was developed during the plasma spray as a result of the existence of a temperature gradient in the solidifying melt.
Effect of ZrB2 addition on SmCo-1:7 high temperature magnets
Authors: Rhen Fernando M. F. , Venkatesan M. , Harris I. R. , Coey J. M. D.
Published: May 2003

This work focuses on a search for magnets that can be used at elevated temperature. We have studied the effect of ZrB2 addition on the magnetic properties and stability of nanocrystalline 1:7 type Sm(Co,Ti,Zr) magnets up to 500 °C. Amorphous ball milled powder was annealed to develop the TbCu7 type structure. The room temperature coercivity of SmCo6.5(ZrB2)0.033Ti0.4 is 2.1 T. The microstructure is stable at 400 °C, where the coercivity is 0.5 T.
Computer aided design of an axial-field permanent magnet brushless dc motor for an electric vehicle
Authors: Upadhyay P. R. , Rajagopal K. R. , Singh B. P.
Published: May 2003

This article presents the computer-aided design and analysis of a pancake-type three-phase axial-field permanent magnet brushless dc motor meant for the direct drive of an electric two-wheeler. The motor has been designed for accommodating inside the rim of the wheel. Initially, the motor design was carried out using the conventional procedure. Then three-dimensional finite element analysis was carried out to arrive at the optimum design by tuning the geometry to achieve the best utilization of all materials used. The effects of all machine parameters on performance of the motor have been studied in detail and the results of this parametric study are provided. The entire design procedure is explained with the help of a flow chart. All steps involved in the design of the motor such as selection of the configuration, design of the magnetic circuit, selection of materials, calculation of machine parameters, and calculation of performance are discussed.
Synthesis, thermal expansion, and magnetic properties of Gd3(Fe,Co,Cr)29 compounds
Authors: Wang J. L. , Marquina C. , Ibarra M. R. , Wang W. Q. , Yang F. M. , Wu G. H. , Tegus O. , Klaasse J. C. P. , Brück E. , de Boer F. R.
Published: May 2003

We have obtained single-phase compounds Gd3Fe29−x−yCoxCry with the Nd3 (Fe,Ti)29-type. Cr is a stabilizing element and also increases the solid-solution limit of Co in the Gd3Fe29−x−yCoxCry compounds. Substitution of Co by Fe results in a significant change of the magnetocrystalline anisotropy and changes the easy magnetization direction from basal-plane to easy-axis when x>10 and y=4. The intensity of the magnetic interactions in Co-rich Gd3Fe29−x−yCoxCry compounds has been calculated from the high-field magnetization measurements. The Co substitution suppresses the Invar anomaly found in the Gd3(FeCr)29 compounds.
Formation of envelope solitons from parametrically amplified and conjugated spin wave pulses
Authors: Serga A. A. , Demokritov S. O. , Hillebrands B. , Slavin A. N.
Published: May 2003

Formation of dipolar spin wave envelope solitons from input pulses parametrically amplified by microwave pumping has been investigated experimentally in an axially magnetized yttrium–iron–garnet (YIG) film waveguide by means of the space- and time-resolved Brillouin light scattering technique. The interaction of a linear input spin wave packet with double-frequency microwave pumping leads to the formation of two parametrically amplified contrapropagating wave packets: forward and phase-conjugated reversed. It was found that both forward and reversed packets immediately after the interaction with pumping increase their lengths almost two times compared to the length of the input packet. In the course of further propagation both wave packets demonstrate a significant compression in length (up to 2.5 times) which depends on the power of the input signal and is a clear signature of envelope soliton formation.
Possible half-metallic ferromagnetism in zinc blende CrSb and CrAs (invited)
Authors: Shirai M.
Published: May 2003

Theoretical study based on a first-principles band structure calculation is carried out for new room-temperature ferromagnets, zinc blende CrSb and CrAs. It is found from the total-energy calculation that the ferromagnetic state is energetically favorable for both materials. By using the value of the difference in total energy between ferromagnetic and the antiferromagnetic states, the Curie temperatures of these ferromagnets are estimated as 1600–1800 K within mean-field approximation of the Heisenberg model. The magnetic moment is evaluated to be 3 Bohr magnetons per formula unit for both materials, which agrees well with the saturation moments estimated experimentally. Furthermore, these ferromagnets are half metallic, and the spin polarization at the Fermi level is almost unaffected even if spin–orbit interaction is taken into account.
Study of domain wall magnetoresistance by submicron patterned magnetic structure
Authors: Yu C. , Lee S. F. , Tsai J. L. , Huang E. W. , Chen T. Y. , Yao Y. D. , Liou Y. , Chang C. R.
Published: May 2003

Through the proper design of submicron permalloy (Ni80Fe20) wires, domain wall magnetoresistance is investigated. A positive contribution to magnetoresistance (MR) was found for domain walls in these wires after extracting the anisotropic MR effect. Some theoretical models are used to discuss our results.
Unusual magnetic effects in an itinerant electron antiferromagnetic Cr–Pt alloy single crystal
Authors: Venter A. M. , Alberts H. L. , Prinsloo A. R. E. , Dawe A. M.
Published: May 2003

Thermal expansion and neutron diffraction measurements are reported on a Cr+0.16 at. % Pt alloy single crystal. Anomalous hysteresis behavior is observed in the temperature dependence of the magnetovolume (Δω) and of the magnitude of the spin-density-wave (SDW) wave vector (Q) below the incommensurate-commensurate SDW phase transition temperature. The hysteresis effects in Δω and Q seem to be related, but are not linked in theoretical models.
Measurement of evoked electroencephalography induced by transcranial magnetic stimulation
Authors: Iramina Keiji , Maeno Takashi , Nonaka Yukio , Ueno Shoogo
Published: May 2003

This study focused on the measurement of evoked potentials induced by transcranial magnetic stimulation (TMS) for observing the neuronal connectivity in the brain. We developed an electroencephalography (EEG) measurement system to eliminate the electromagnetic interaction emitted from TMS. EEG activities 5 ms after TMS stimulation were measured. Using this artifact free amplifier, we investigated the intensity dependence of brain activation induced by TMS. When the stimulus intensity was changed at three levels, TMS-evoked EEG responses were measured. Several components of the evoked potential appeared at 9 ms, 20 ms, and 50 ms after stimulation. A large response appeared at about 9 ms after cerebellar TMS. There was a significant dependence of these responses on the stimulus intensity. During right-hand side motor area stimulation, there was no clear peak of the wave forms within 10 ms latency. Occipital stimulation caused more evoked responses to spread to the center of the brain than at other areas of stimulation. The evoked signal by TMS was possibly conducted posteriorly to anteriorly along the pathways of the neuronal fiber exiting the cerebellum into the cerebral cortex.
Fluctuating spin density waves revealed by perturbed angular correlation spectroscopy
Authors: L’abbé C. , Meersschaut J. , Rots M. , Bader S. D.
Published: May 2003

We present a theory to analyze pertubed angular correlation spectra in the framework of dynamical processes. It can be applied to study superparamagnetic properties of magnetic nanostructures, and was used recently to identify dynamical fluctuations in spin-density-wave ordered Cr. We showed that the spin fluctuations give rise to the biquadratic coupling in Fe/Cr(100) multilayers [J. Meersschaut, C. L’abbé, M. Rots, and S. D. Bader, Phys. Rev. Lett. 87 107201 (2001)].
Noise properties of magnetic and nonmagnetic tunnel junctions
Authors: Park Wan Kyu , Moodera Jagadeesh S. , Taylor John , Tondra Mark , Daughton James M. , Thomas Andy , Brückl Hubert
Published: May 2003

Low-frequency voltage fluctuations in magnetic and nonmagnetic tunnel junctions have been investigated. Tunneling magnetoresistance ratio of junctions ranged from 8.6% to 50% at room temperature. The origin of voltage noise was observed to be nonmagnetic. It was found that the resistance fluctuations lead to 1/f noise at room temperature, whereas the white noise was dominant at 77 K. A phenomenological noise parameter, defined for the comparison of noise levels in different junctions, was shown to scale with the junction resistance–area product. This observation suggests that low values of resistance×area are required for a low noise operation as well as for the integration of magnetic tunnel junctions.
Magnetic and Mössbauer study of Fe/Si multilayers
Authors: Luciński T. , Kopcewicz M. , Hütten A. , Brückl H. , Heitmann S. , Hempel T. , Reiss G.
Published: May 2003

The magnetic and structural properties of Fe/Si multilayers (Mls) have been studied by x-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS) methods. Strong antiferromagnetic (AF) coupling J=−1.93 mJ/m2 accompanied by saturation field of 1.5 T has been found for Si layer thickness dSi=1.4 nm. Magnetic moment measurements of Fe/Si Mls vs Fe thickness revealed that 0.25 nm of Fe per single interface is magnetically inactive. The CEMS spectra recorded at room temperature consist of the Zeeman sextet characteristic of the pure Fe phase (hyperfine field of about 32.8 T) accompanied by two spectral components related to FeSi system: magnetic broad sextet and a quadrupole doublet. The broad sextet could originate from various Fe sites at the interface. The nonmagnetic quadrupole split (QS) doublet is most probably associated with the nonstoichiometric c-Fe1−xSix phase. For larger Si layer thickness (dSi>2 nm) the spectral contribution of the QS doublet increases from 5.7% to about 16%.
Effects of swift heavy ion bombardment on magnetic tunnel junction functional properties
Authors: Conraux Y. , Nozières J. P. , Da Costa V. , Toulemonde M. , Ounadjela K.
Published: May 2003

In this article, we report on recent irradiation experiments on magnetic tunnel junctions (MTJ) using either light (C, O) or heavy (Ni) ion beams with energies in the range of 10 MeV/A. For all ions, albeit with different fluence thresholds, the tunnel magnetoresistance decreases irreversibly with increasing ion fluence, with conversely little or no impact on overall resistance. This can only be explained by a modification of the alumina barrier stoechiometry, rather than by interdiffusion. Measurements on irradiated so-called “spin-mirrors” sheet films show that AlOx/metal interface is altered by radiations. Finally, it is shown that MTJs are not a fortiori insensible to swift heavy ion bombardment.
Interface spin–flip scattering model for point contact Andreev reflection
Authors: Kant C. H. , Kurnosikov O. , Filip A. T. , Swagten H. J. M. , de Jonge W. J. M.
Published: May 2003

Point contact Andreev reflection measurements show a correlation between measured spin polarization and the interface scattering parameter Z extracted from fits of the modified Blonder–Tinkham–Klapwijk model to the conductance–voltage curves of superconductor/ferromagnet point contacts. We present a simple spin–flip scattering model which identifies Z2 as the effective scattering parameter and explains the observed exponential decay of the spin polarization.
Biological investigation of a citrate-coated cobalt–ferrite-based magnetic fluid
Authors: Kückelhaus S. , Garcia V. A. P. , Lacava L. M. , Azevedo R. B. , Lacava Z. G. M. , Lima E. C. D. , Figueiredo F. , Tedesco A. C. , Morais P. C.
Published: May 2003

The present study reports on several in vivo biological tests carried out with a cobalt–ferrite, citrate-coated, magnetic fluid sample developed for biomedical purposes. Systematic biological investigation was performed after endovenous injection in mice. Morphological analysis showed magnetic nanoparticle (MNP) infiltration in the parenchyma or vessels of all investigated organs. Nevertheless, at the investigated dose and period of treatment, no cell damage or inflammatory processes were observed. Cytometry alterations and genotoxic effects were not observed. Although precipitation of MNPs in tissues may be taken as undesirable, the absence of morphological alterations is very promising. The data show that the investigated sample is biocompatible and useful for biomedical applications.
Investigation of lipid peroxidation and catalase activity in magnetic fluid treated mice
Authors: Freitas M. L. L. , Silva L. P. , Freitas J. L. , Azevedo R. B. , Lacava Z. G. M. , Homem de Bittencourt P. I. , Curi R. , Buske N. , Morais P. C.
Published: May 2003

The increasing interest in magnetic fluids (MFs) for biomedical applications demands a deeper knowledge of their effects in biological systems. To evaluate the in vivo response of a MF sample based on magnetite nanoparticles stabilized by a precoating double layer of dodecanoic acid plus ethoxylated polyalcohol (MFDE), the inflammation-related oxidative stress and antioxidant tissue response were both addressed in this study. MFDE sample was intraperitoneally administrated to mice at three different doses. The lipid peroxidation and the antioxidant defense induced in the liver and spleen were evaluated, respectively, by thiobarbituric acid-reactive substances (TBARS) and catalase activity, 1, 14, and 28 days after MFDE treatment. The liver and spleen responded with a huge increase in TBARS after MFDE treatment. We observed that oxidative changes as well as the variations in the liver catalase activity were time and MFDE-dose dependent.
Biological applications of multifunctional magnetic nanowires (invited)
Authors: Reich D. H. , Tanase M. , Hultgren A. , Bauer L. A. , Chen C. S. , Meyer G. J.
Published: May 2003

Magnetic particles that can be bound to cells and biomolecules have become an important tool for the application of force in biology and biotechnology. Multifunctional magnetic nanowires fabricated by electrochemical deposition in nanoporous templates are a type of magnetic carrier that offers significant potential advantages over commercially available magnetic particles. Recent experimental work aimed at developing these wires for this purpose is reviewed. Results on chemical functionalization of Au and Au/Ni wires and magnetic manipulation of wires in suspension are described. Fluorescence microscopy was used to demonstrate the covalent binding of thiol-terminated porphyrins to Au nanowires, and to optimize functionalization of two-segment gold–nickel nanowires for selectivity and stability of the nanowire–molecule linkages. Magnetic trapping is a technique where single nanowires are captured from fluid suspension using lithographically patterned micromagnets. The influence of an external magnetic field on this process is described. The dynamics of magnetic trapping is shown to be well described by a model based on the interplay of dipolar forces and viscous drag.
Method for synthesizing ferrite nanoparticles ∼30 nm in diameter on neutral pH condition for biomedical applications
Authors: Tada M. , Hatanaka S. , Sanbonsugi H. , Matsushita N. , Abe M.
Published: May 2003

Nanosized ferrite spherical particles, ∼30 nm in diameter as revealed by scanning electron microscopy, were synthesized from an aqueous Fe(OH)2 suspension (pH=7.6–8.0) at 25 °C by oxidizing it with H2O2. The nanoparticles were of a spinel structure of an intermediate between Fe3O4 and γ-Fe2O3, as revealed by x-ray diffraction. Compared to the nanoparticles synthesized by our previous method in which an aqueous solution of Fe2++Fe3+ was oxidized by air (oxygen), the nanoparticles increased in size, from ∼10 nm (previous method) to 30 nm. Also saturation magnetization increased, though slightly, from 76 emu/g (previous method) to 80 emu/g (present method). Therefore, the ferrite nanoparticles synthesized by this method will improve the efficiency of magnetic separation. Because synthesis is performed at room temperature and neutral conditions (pH=7.1–7.8), which are compatible with most bioactive molecules (e.g., antibodies and proteins), these molecules will be immobilized onto the surface of the nanoparticles during their syntheses.
Direct immobilization of fluorescent dyes onto ferrite nanoparticles during their synthesis from aqueous solution
Authors: Hatanaka S. , Matsushita N. , Abe M. , Nishimura K. , Hasegawa M. , Handa H.
Published: May 2003

FITC-avidin, a fluorescent substance, was successfully immobilized onto the surfaces of nanoparticles of ferrite of a mixture between Fe3O4 and γ-Fe2O3, during the synthesis of the nanoparticles an aqueous solution from containing Fe2+, Fe3+, and FITC-avidin. The particles were spherical in shape and ∼10 nm in size. The process was performed in open air, on near neutral conditions of pH 7–9, and at ∼4 °C. Utilizing the fluorescent magnetic particles, we successfully observed magnetic patterns (track pitch 187.5 μm) written on a floppy disk.
Spin-wave modes in magnetic nanowires
Authors: Skomski R. , Chipara M. , Sellmyer D. J.
Published: May 2003

Spin-wave modes in magnetic transition-metal nanowires having diameters of about 10 nm and lengths on the order of 1 μm are investigated by model calculations. There are quasicontinuous modes with k vectors parallel to the wires axis and discrete modes with k vectors perpendicular to the wire axis. Due to the small cross section of the wires, the perpendicular modes can be ignored in many cases and the low-temperature behavior of the wires is quasi one-dimensional. Using an analytic approach and exploiting the analogy between micromagnetism and quantum mechanics it is shown that all spin-wave modes with k vectors parallel to the wire axis are localized. The spin-wave localization is a micromagnetic analog to the Anderson localization of conduction electrons due to randomness in less than two dimensions, and, as in the electron analogy, arbitrarily small disorder is sufficient to cause the localization of all modes.
Electronic line-up in light-emitting diodes with alkali-halide/metal cathodes
Authors: Brown T. M. , Friend R. H. , Millard I. S. , Lacey D. J. , Butler T. , Burroughes J. H. , Cacialli F.
Published: May 2003

The electronic nature of metal-semiconductor contacts is a fundamental issue in the understanding of semiconductor device physics, because such contacts control charge injection, and therefore play a major role in determining the electron/hole population in the semiconductor itself. This role is particularly important for organic semiconductors as they are generally used in their pristine, undoped form. Here, we review our progress in the understanding of the energy level line-up in finished, blue-emitting, polyfluorene-based light-emitting diodes, which exploit LiF and CsF thin films in combination with Ca and Al to obtain cathodes with low injection barriers. We have used electroabsorption measurements, as they allow the noninvasive determination of the built-in potential when changing the cathode. This provides precious experimental information on the alteration of the polymer/cathode interfacial energy level line-up. The latter is found to depend strongly on the electrode work function. Thus, the Schottky–Mott model for the energy level alignment is found to be a better first-order approximation than those models where strong pinning or large interface dipoles determine the alignment (e.g., Bardeen model), except for electrodes that extensively react with the polymer, and introduce deep gap states. In addition, we show results that validate the approximation of rigid tilting of polymer energy levels with bias (for biases for which no significant injection of carriers occurs). To investigate further the consequences of the electronic line-up on device operation, we complemented the electroabsorption measurements with characterization of the emissive and transport properties of the light-emitting diodes, and confirmed that the cathodic barrier lowering in CsF/Ca/Al and LiF/Ca/Al electrodes leads to the best improvements in electron injection. We found that luminance and overall current are greatly affected by the barrier-reducing cathodes, indicating a truly bipolar transport, with comparable electron and hole currents. We also found significant indications of CsF/Ca/Al cathodes strongly reacting with the polymer, which is suggestive of CsF dissociation and diffusion in the bulk of the polymer.