bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical properties of spark plasma sintering Nd–Fe–B permanent magnets
Authors: Yue Ming , Cao Aili , Wang Gongping , Liu Weiqiang , Zhang Jiuxing
Published: December 2007

Nd–Fe–B based permanent magnets were prepared by both spark Plasma Sintering (SPS) and conventional sintering technique. Mechanical properties and microstructure of the magnets were investigated. Compared with conventional sintered magnet, SPS Nd–Fe–B magnet possesses better mechanical strength in terms of both impact toughness and bending strength, which have an increase of 31.0% and 44.3% from conventional magnet to SPS one, respectively. Microstructure and fracture morphology observation shows that the fracture model of the magntets changes from inter‐granular fracture of conventional sintered magnet to intra‐granular fracture of SPS magnet. The fine and uniform Nd–Fe–B main phase crystal grains and even distributed Nd‐rich phase are responsible for the improvement of mechanical properties of the SPS Nd–Fe–B magnet. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Remote temperature sensor composed of an amorphous magnetic ribbon and a low Curie temperature ferrite tube
Authors: Nakamura M. , Yoshizawa S. , Kutsuzawa N. , Kambe S. , Ishii O.
Published: December 2007

This paper describes the application of remote temperature sensors made of an amorphous magnetic ribbon and a low Curie temperature ferrite tube to the measurement of temperature in an arbitrary range. By combining an amorphous magnetic ribbon and a ferrite tube with a Curie temperature of 40 °C, a resonant frequency change rate of 6.3%/°C was realized in the 35 to 40 °C temperature range. Similarly, by combining an amorphous magnetic ribbon and a ferrite tube with a Curie temperature of 47 °C, a resonant frequency change rate of 4.9%/°C was achieved in the 41 to 47 °C temperature range. These values are ∼100 times larger than that of the previously reported remote temperature sensor made only of an amorphous ribbon. Therefore, this confirms that a highly sensitive remote temperature sensor can be realized in an arbitrary temperature range. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of Nb concentration on the microstructure of Al and the magnetoresistive properties of the magnetic tunnel junction with a Nb‐doped Al‐oxide barrier
Authors: Park Sung‐Min , Chung Ha‐Chang , Lee Seong‐Rae
Published: December 2007

We have investigated the composition dependence of magnetic tunnel junctions (MTJs) with Nb‐alloyed Al‐oxide (NbAlOx) and analyzed the microstructure changes and electrical property of Nb alloyed Al‐oxide layer. After annealing, tunnel magnetoresistance (TMR) ratio of MTJ with Nb‐alloyed Al‐oxide barrier increased up to 38.5% at 9.26 at.% Nb. As the Nb concentration increases, the grain size decreases and the microstructure becomes a dense, fine equiaxed‐type structure with fine, continuous selected area diffraction (SAD) patterns, until Nb concentration reaches 9 at.%. The microstructural changes of Nb‐alloyed Al layer results in smooth interface roughness, so that we could achieve a high TMR ratio. Resistance decreased from 900 Ω to 220 Ω and barrier height decreased from 1.62 eV to 0.847 eV at 9.26 at.% Nb. We speculated that the reduction of junction resistance of the MTJ with Nb‐doped Al‐oxide barrier was due to Nb d states formation in the band gap. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of magnetic field annealing on magnetic properties and microstructure of Nd‐Fe‐B‐Ti‐C based nanocomposite permanent magnet
Authors: Ishii Rintaro , Yasuda Hideyuki , Miyoshi Toshio , Kanekiyo Hirokazu , Hirosawa Satoshi
Published: December 2007

Rapidly solidified ribbons of Nd9Fe73B12.6C1.4Ti3Nb1 were annealed with or without a static magnetic field of 10 T. The remanence (Br) of the ribbon annealed with the magnetic field was higher than that of the ribbon annealed without the magnetic field. Improved magnetic properties of the ribbon annealed with the magnetic field may be attributed to a uniformly fine grain size. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GISAXS study of the alignment of oriented carbon nanotubes grown on plain SiO2/Si(100) substrates by a catalytically enhanced CVD process
Authors: Mane Mane J. , Cojocaru C. S. , Barbier A. , Deville J. P. , Thiodjio Sendja B. , Le Normand F.
Published: December 2007

Among the contributions in this issue of pss (a) two articles were selected as Editor's Choice [1, 2]. Rudziński et al. [1] study the influence of substrate orientation on GaN film growth on 4H‐SiC, suggesting a model for the formation of rows of threading edge dislocations and directional cracking in these films.

The cover picture is extracted from the article by Mane Mane et al. [2]. The picture illustrates the successful combined use of the GISAXS technique within the Effective Layer Born Approximation (ELBA) and the Distorted Wave Born Approximation (DWBA), in conjunction with the description of diffusing entities as C tubes, Co cylinders and intermixed Co–C clusters, in order to calculate the full experimental GISAXS images of uncorrelated carbon nanotubes grown on cobalt catalyst. The strong contribution of the surface reflectivity to the collected GISAXS signal is emphasized in the paper. Compare the experimental GISAXS pattern of carbon nanotubes in the upper left panel to the ELBA images considering Co cylinders and C tubes with (upper right) and without (lower left) intermixed C–Co tubes. The lower right panel shows the resulting DWBA pattern.

The first author, Dr. Jeannot Mane Mane, graduated with a Ph.D. from the University Henri Poincaré in Nancy in 1993. He currently holds a Senior Lecturer position at the University of Yaounde I (Cameroon) as well as a research position at the CNRS Institut de Physique et Chimie des Matériaux de Strasbourg (France). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Processes involved in the high‐temperature thermoluminescence of a Mn2+‐doped MgF2 phosphor
Authors: Secu M. , Jipa S. , Secu C. E. , Zaharescu T. , Georgescu R. , Cutrubinis M.
Published: December 2007

The thermoluminescence (TL) glow curve recorded after gamma‐irradiation at room temperature of Mn2+‐doped MgF2 phosphor shows two intense TL peaks at 364 K and 420 K accompanied by several weaker peaks up to 600 K. The TL spectra have shown Mn2+ luminescence at about 560 nm. The 364 K TL peak disappears after one day of storage, and so is probably related to the recombination of carriers from some shallow traps. Based on thermal bleaching and optical bleaching (in the 260 nm F‐centre absorption band) experiments, the 420 K TL peak was ascribed to the thermally activated recombination between an F‐centre and a hole centre trapped in the neighbourhood of the Mn2+ impurity which results in Mn2+ luminescence. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Luttinger–Ward method applied to the 2D Coulomb gas
Authors: Agnihotri M. P. , Apel W. , Weller W.
Published: December 2007

We review the Luttinger–Ward method and show how one can combine it with the theory of Baym and Kadanoff in order to get conserving approximations in many‐body perturbation theory. We solve the variation procedure numerically using an ansatz for the selfenergy in the case of the two‐ dimensional Coulomb problem. Comparison with results of the traditional iteration of the selfconsistency equation yields satisfactory agreement for parameters where the iteration converges. The extremalization of the Luttinger–Ward functional works beyond that point. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low‐frequency 1/f noise in relaxor ferroelectric PMN–PZT
Authors: Gridnev S. A. , Tsotsorin A. N. , Kalgin A. V.
Published: December 2007

The dielectric properties of relaxor ferroelectric ceramics (1 – x)PbMg1/3Nb2/3O3–(x)PbZr0.53Ti0.47O3(PMN–PZT) have been studied at various frequencies in the temperature range of the diffuse phase transition. Dispersion of the complex dielectric permittivity ε * characteristic for relaxors was revealed in the vicinity of the ε * maximum temperature Tm. It has been determined that low‐frequency 1/f noise in the studied system is mainly caused by the polarization relaxation in local polar regions and the spectral density of the noise depends on the relaxor composition and temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diffusion mechanism of implanted Be in GaAs
Authors: Koumetz S. D. , Pesant J.‐C. , Dubois C.
Published: December 2007

The transient enhanced diffusion of low and high dose implanted beryllium in undoped gallium arsenide during post‐implant rapid thermal annealing in the temperature range of 700–900 °C for 60–240 s has been studied and successfully simulated by the kick‐out diffusion model, involving singly positively charged Be interstitials and doubly positively charged Ga self‐interstitials. Using the “plus one” approach for Ga interstitial generation after implantation with the local Ga interstitial sink concept as well as the appropriate initial and boundary conditions for involved mobile species, and taking into account Fermi‐level and built‐in electric field effects, the obtained partial differential equations have been solved numerically by means of an explicit finite difference method. The thermal equilibrium concentrations and the diffusivities of Be and Ga interstitials, all as a function of temperature, have been deduced from the fits of the experimental profiles obtained by the secondary ion mass spectrometry technique. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control synthesis of iron oxide nanospheres using solution chemistry
Authors: Wu M. Z. , Lee H. , Hwang S. Y.
Published: December 2007

A facile solution chemistry approach to the batch synthesis of magnetite nanocrystals is developed. By using different starting materials, the control of particle size and size distribution can be achieved. Detailed investigations into the morphology and size distribution of the final products were carried out with the aid of field emission scanning electronic microscopy (FESEM). The crystal structure was studied by powder X ray diffraction (XRD). Vibrating sample magnetometer (VSM) was used to study the magnetic properties of these sphere‐like products. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
In vivo and in vitro antitumor activity of doxorubicin‐loaded magnetic fluids
Authors: Park S. I. , Lim J. H. , Hwang Y. H. , Kim K. H. , Kim S. M. , Kim J. H. , Kim C. G. , Kim C. O.
Published: December 2007

Doxorubicin‐loaded magnetic particles with lecithin and polyethylene glycol as an interlayer were synthesized by multi‐step process of high temperature thermal decomposition and ultrasonic, respectively. The change of particle size and the magnetic property were investigated for the estimation of the carrier characteristic with doxorubicin addition. And, the loading efficiency of drug and the loaded drug released fraction were discussed for the estimation of drug effect. Also, the remedial efficiency of adsorbed drug on the magnetic nanoparticle was investigated by comparing the cytotoxicity of tumor cell between bare‐ and doxorubicin‐loaded magnetic nanoparticles. And, in‐vivo test was performed to estimate the effect of anticancer therapy by using C57BL/6 mice as an animal sample. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Etch characteristics of magnetic tunnel junction stack using a high density plasma in a HBr/Ar gas
Authors: Min Su Ryun , Cho Han Na , Noh Su Jin , Kim Kee Won , Seo Sun Ae , Chung Chee Won
Published: December 2007

Etch characteristics of magnetic tunnel junction (MTJ) stack masked with TiN thin films were investigated using an inductively coupled plasma reactive ion etching in HBr/Ar gas for the application of magnetic random access memory. The effect of HBr gas concentration on the etch profile of MTJ stacks was examined. As HBr gas concentration increased, the sidewall angles of etched patterns of MTJ stacks were slightly improved. The effect of etch parameters including coil rf power, dc‐bias voltage, and gas pressure on the etch profile of MTJ stack was explored. At low coil rf power, low dc‐bias voltage, and high gas pressure, the etching of MTJ stack displayed better etch profile. A high degree of anisotropic etching of MTJ stacks without redeposition was achieved using HBr/Ar gas at the optimized etch conditions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Property of nitrogenated tetrahedral carbon on magnetic head prepared by filtered cathodic arc deposition
Authors: Mingchu Yang , Gonzaga Leonard , Bo Liu
Published: December 2007

Nitrogenated tetrahedral carbon films were prepared by filtered cathodic arc deposition. Raman spectroscopy analysis shows N incorporation increases the clustering of the sp2 phase, Nanoindentaion shows the hardness reduction caused by N incorporation can be compensated by optimization of C ion energy in the deposition. Ta‐C:N films shows higher extinction coefficient and less transparency. The good morphology of films implies ta‐C:N overcoat has good coverage on magnetic head. Corrosion experiment reveals ta‐C:N overcoat has better anti‐corrosion performance. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Texture in die‐upset Nd‐Fe‐B magnet produced using HDDR‐treated particles
Authors: Lee J. I. , Kwon H. W. , Choi G. S.
Published: December 2007

The die‐upset Nd15Fe77B8 material consisting of near single domain Nd2Fe14B grains was prepared using the HDDR‐treated material. Texture (c‐axis alignment) of the Nd2Fe14B grains in the die‐upset HDDR material was investigated, and compared with that in the die‐upset melt‐spun Nd‐Fe‐B material. The die‐upset HDDR material showed a texture, in which the easy magnetisation c‐axis of the Nd2Fe14B grains was aligned parallel to the compression direction. The texture obtained from the die‐upset HDDR material was much poorer with respect to that from the die‐upset melt‐spun material (Nd13.5Fe80Ga0.5B6). The poor texture in the HDDR material was due to the greater grain size of the material. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
LC filter‐type magnetoimpedance sensors with multilayer film structure
Authors: Tanaka K. , Shin K. H. , Uchida H. , Inoue M
Published: December 2007

We have investigated the basic characteristics and applicability of the LC high pass filter configuration for signal conditioning of the magnetoimpedance (MI) sensor. The MI sensor elements were fabricated through photolithography and lift‐off process of CoZrNb/Au/CoZrNb multilayer, and the LC high pass filters were configured using the fabricated sensor elements and surface mount capacitors. To confirm the high frequency performance of the sensor elements, frequency dependence of the impedance was measured as function of external magnetic field using a network analyzer. The output increased to reach the peak value with increase of magnetic field to around 20 Oe, which was almost the same with the anisotropic field of the multilayer film pattern, and the measured maximum change ratio is 49%. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A magnetic heat pump with porous magneto caloric material
Authors: Vuarnoz D. , Kitanovski A. , Diebold M. , Gendre F. , Egolf P. W.
Published: December 2007

At present magnetic refrigeration shows a realistic potential to penetrate into some niche markets in the field of cold and hot “production”. It is well known that a refrigerator for cooling and a heat pump for heating are machines based on the same principle. A small review on magnetic heat pump studies is outlined and a simple engineering calculation scheme to determine the coefficient of performance for a magnetic heat pump with a rotary porous structure heat exchanger is presented. Magnetic heat flux line distributions are calculated by a 2‐d finite element method numerical simulation program with the objective to obtain high field's μ0H with not too heavy permanent magnets assemblies. The porous structures are geometrically optimised to obtain maximal magnetic field inductions. It is shown that for a water/ethylene‐glycol magnetic heat pump the coefficient of performance is higher than that of a conventional heat pump. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of nanostructure (In15Sb85)100–xZnx thin films
Authors: Ou Sin‐Liang , Kuo Po‐Cheng , Sheu Shu‐Chi , Wu Ting‐Hau , Chiang Don‐Yau , Tang Wei‐Tai
Published: December 2007

The (In15Sb85)100–xZnx films (x = 0∼13.7) were deposited on nature oxidized Si wafer at room temperature by dc co‐sputtering of Sb target and InZn composite target. Effects of Zn content on the optical properties of (In15Sb85)100–xZnx film were examined by X‐ray diffraction and reflectivity thermal analyzer. It is found that the crystallization activity energy of the film is increased with Zn content, this indicates that the thermal stability of amorphous state is improved by doping Zn. The structure of as‐deposited (In15Sb85)100–xZnx film was amorphous and it would transform to Sb, InSb, and ZnSb coexisting phases after annealing at 250 °C. The reflectivity of annealed film was higher than that of as‐deposited film. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large area magnetic domain imaging of magnetite films with Spin‐SEM
Authors: Kaji Eisaku , Subagyo Agus , Sueoka Kazuhisa
Published: December 2007

The surface crystallographic structure and magnetic structure of magnetite thin films epitaxially grown on a MgO(001) substrate were investigated by means of a scanning tunnelling microscope (STM), magnetic force microscope (MFM) and Spin‐polarized scanning electron microscopy (Spin‐SEM). The STM investigation and MFM measurement were performed in‐situ and in an ambient condition, respectively. After exposing the sample to air, a Spin‐SEM image was acquired. Spin‐dependent contrasted SEM images could be obtained after cleaning the sample surfaces. The cleaning procedure is annealing the sample at 250 °C in an ultra high vacuum (UHV) below 3 x 10–8 Pa for 3 hours. The STM observation indicates the thin films have antiphase domains and the observed MFM images reflect a cease in micromagnetic domain structures. Spin‐SEM images indicate that large‐scale magnetic inhomogeneity of a few μm is the inhomogeneity of the perpendicular magnetic moments of the films. Due to the spatial resolution limitation of our Spin‐SEM system, the correlation between the fine and coarse magnetic structures of the thin films induced by the antiphase domain boundaries is not clear, however, we have suggested the annealing process alone in a UHV makes the spin configuration of the thin films visible using a conventional Spin‐SEM system. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anomalous magnetoimpedance in Co–Fe–Al–O thin films
Authors: Tuan L. A. , Phan M. H. , Ha N. D. , Kim C. G. , Kim C. O. , Yu S. C.
Published: December 2007

The high‐frequency giant magnetoimpedance (GMI) effect in a Co47.5Fe21.9Al17.2O15.2 thin film was systematically investigated. In the frequency range of 100–500 MHz, GMI profiles showed a double‐peak characteristic, reflecting an evident existence of the transverse magnetic anisotropy in the film, which coincided with the magnetization data. Interestingly, there was an anomalous transformation in the GMI profile from “positive” to “negative” and this was associated with the complex phase transformation of permeability. The GMI ratio decreased with decreasing film‐thickness, due to an increase of the electrical resistivity and a decrease of the magnetic softness. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of film thickness on the electrical and magnetic properties of Co–Fe–Al–O films
Authors: Phan M. H. , Tuan L. A. , Ha N. D. , Phan T. L. , Kim C. G. , Kim C. O. , Yu S. C.
Published: December 2007

Influence of film thickness (t) on the electrical and magnetic properties of Co–Fe–Al–O films has been systematically investigated via means of vibrating sample magnetometry (VSM), permeability spectra and magneto‐optical Kerr effect (MOKE). It is found that the electrical resistivity (ρ) decreases as the film thickness increases; ρ = 412.5 µΩcm for the t = 600 nm sample decreases to ρ = 368.2 µΩcm for the t = 1200 nm sample. The coercive force, measured along the easy‐axis direction, decreases as the film thickness increases. Interestingly, along the hard‐axis magnetization direction, the magnetic hysteresis loop is reversed and the coercive force is negative for the t = 600 and 800 nm samples. However, this peculiar feature disappears as t reaches 1200 nm, which is probably attributed to the microstructural change with respect to changes of film thickness. At a frequency of 1GHz, the hard‐axis effective permeability decreases from 1252 to 1000 as the film thickness increases from 600 to 1200 nm, respectively. The VSM and MOKE results reveal an increase in magnetic anisotropy in the near‐surface region of the film. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructure of single stage hot deformed anisotropic Nd–Fe–B magnets
Authors: Tian Hao , Li Ying , Zhu Mingyuan , Jin Hongming , Jin Dongzhe
Published: December 2007

Single stage hot deformation (SSHD) process is an effective method to fabricate anisotropic magnet. In this study, the influences of particle size and hot press temperature on microstructure were discussed, respectively. Anisotropic magnetic properties are affected by SSHD process conditions through the changing the microstructure of the magnets. SEM investigation shows that, good magnetic properties related with suitable geometric shapes of the grains and their better alignment. Good alignment could be obtained when the particle size of raw material MQPA powders is between 45∼100 μm and the SSHD magnet is made at 700 °C. When the deformation temperature is below the melting temperature of Nd rich phase, the platelet‐shaped Nd2Fe14B grains could not be formed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Current status and future of magnetic heads for HDD
Authors: Terunuma K.
Published: December 2007

The rapid growth in consumer electronics application requires higher capacity data storage. For hard disk drive (HDD), many new technologies, such as media, heads, head‐disk interface (HDI), pre‐amp. and so on, have been introduced in order to increase the recording density. This paper focus on magnetic head technologies, such as materials, structures, fabrication process and head performance for HDD. For read heads, tunneling magnetoresistive (TMR) heads have come successively to replace giant magnetoresistive (GMR) heads. Barrier materials have been studied to obtain higher magnetoresisance (MR) ratio with lower resistance area product (RA). AlOx have been used as barrier for 100–120 Gb/in2 TMR heads. MgO barrier shows significantly large MR ratio and is also workable to TMR heads as AlOx one. For longitudinal magnetic recording (LMR) writer, recording performance has been improved with reducing yoke length and coil turns and changing to pole materials with higher saturation magnetization (Bs). Perpendicular magnetic recording (PMR) is introduced for over 120 Gb/in2. Combination between head and medium is much more important in PMR than LMR. The magnetic head is still one of the key component of HDD and is expected to be going to further promote the redording density and performance of HDD in the future. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Observation of multiple transitions on permalloy ring by magnetic force microscopy
Authors: Lin L. K. , Kuo C. Y. , Ou J. Y. , Chang C. C. , Chang C. R. , Horng Lance , Wu J. C.
Published: December 2007

We present a study of magnetization reversal on microstructured permalloy thin film rings using a magnetic force microscopy in the presence of external magnetic fields up to 540 Oe. Permalloy rings with fixed thickness/outside diameter of 23 nm/5 μm and inside diameter of 2.2 and 2.6μm, respectively, were fabricated by using standard electron beam lithography through a lift‐off process. Four transitions during magnetization reversal were observed on the one with 2.2 μm inside diameter, in which the magnetization was evolved from onion to vortex‐pair, vortex‐pair to vortex, vortex to vortex‐core, vortex‐core to reverse onion state. The remanent state was flux closure vortex state. A similar magnetization evolution occurred on the one with 2.6 μm inside diameter except that the remanent state was vortex pair. The numerical simulation results using OOMMF showed good agreement with the experimental results. These multiple stable states during the magnetization reversal may provide an excellent opportunity for developing multi‐bit storage cells. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic properties of spin valves having extremely thin underlayers
Authors: Kim Jiwon , Jo Soonchul , Kim Sang Yoon , Ko Hoon , Lee Chang‐Woo
Published: December 2007

Magnetic properties of spin valve elements having Mo(N) and Ta(N) underlayers were studied by varying their thickness. Spin valve structure was Si/SiO2/Underlayer(tÅ)/NiFe(21 or 42Å)/CoFe(28Å)/Cu(22Å)/CoFe(18Å)/IrMn(65Å)/Ta(25Å). Spin valve elements having exteremely thin Mo(N) and Ta(N) underlayers showed high MR ratio of about 7 ‐ 8%. Annealing of such spin valve elements having underlayer thickness of 7 to 8 Å showed comparable behavior with the spin valve elements with thicker (35Å) underlayer, which can be utilized to reduce overall device thickness. Also, it was found that Mo(N) underlayers for spin valve elements may be used as diffusion barriers between Si substrate and ensuing active spin valve layers, simultaneously. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of the magnetization behavior in Nd and Sm substituted La0.7Pb0.3MnO3 systems
Authors: Shen C. Y. , Kao M. C. , Chen H. Z. , Young S. L. , Shi J. B. , Lin C. C. , Lin C. H. , Ou C. R. , Jhang M. C.
Published: December 2007

In this work, the magnetization behavior of two maganite oxide systems, La0.7–xNdxPb0.3MnO3 and La0.7–xSmxPb0.3MnO3, has been synthesized. The partial replacement of La ions by Nd or Sm results in a considerable decrease in the ferromagnetic ordering temperature TC. Moreover, clearly irreversible behavior in the field‐cooling and zero‐field‐cooling curves at a low applied field shows the short‐range spin order phase. These facts are in agreement with the smaller ionic radii of Nd (0.127 nm) and Sm (0.124 nm) ions in contrast to La ion (0.136 nm) with the corresponding larger distortion of perovskite structure. The saturation magnetization MS is increased as Nd content is increased which provides a relative contrast with the decrease of MS by the increase of Sm content. This can be interpreted in terms of the competition between the suppression of ferromagnetism due to structure tuning induced by the small ionic radius of the interpolated cation into the La‐site and the increase of ferromagnetic spins due to the introduction of magnetic Nd or Sm ions with f ‐shell electrons. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic and recording performance of perpendicular magnetic media with new soft underlayer structure
Authors: Yoon S. Y. , Kong S. H. , Lee H. S. , Lim C. K. , Kim H. J. , Oh H. S. , Park J. B. , Choa S. H.
Published: December 2007

In this study, we introduced the new concept SUL (Soft Underlayer) of PMR (Perpendicular Magnetic Recording) media for the superior recording performance. The recording performance of PMR media with various SUL types were investigated by Guzik spin stand. Our new concept SUL, which was denoted by the modified SAF (Synthetic Antiferromagnetic Coupling) structure, showed more excellent recording properties than those of others. These improved recording performances may be generated by decreased SUL noise and increased filed gradient with new SUL structure. The obtained results indicated that the modified SAF SUL structure can be helpful to high recording density. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New method for detecting the early stage of structural changes by using HTSC squid‐based magnetometer
Authors: Park D. G. , Chandrasekhar A. , Kim D. W. , Timofeev V. P. , Cheong Y. M.
Published: December 2007

The new method of detection the early stage of structural changes in stainless steel samples is proposed and used. It includes the registration of initial magnetization line shift, the zero region of magnetic hysteretic loop (B‐H). This method is based on the use of high sensitive SQUID magnetic sensor. As a result, the spontaneous magnetic moment that treated sample manifests in zero external magnetic fields is recoded. The magnetic moments of cold worked 316 stainless steel have been measured as an application of this type of HTSC (High Tempe rapture SuperConducting) SQUID‐based magnetometer. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Design optimization of the bit and word lines in magnetic random access memory in the Stoner‐Wohlfarth model
Authors: Lee T. H. , Lim S. H.
Published: December 2007

The optimization in the design of the bit and word lines in magnetic random access memory is performed in the Stoner‐Wohlfarth model. This is done by calculating the asteroid curves as a function of the angle between the bit and word lines. The calculation essentially involves finding the energy minima of the system. The switching field is reduced greatly when the angle between the bit and word lines is deviated from the right angles. Thermal stability of half‐selected cells, which is estimated by calculating the energy barrier, is also improved significantly. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carrier doping dependence of the Tc in double perovskite Sr2FeMoO6
Authors: Kim J. , Kim C. S. , Lee B. W.
Published: December 2007

Carrier doping effects on the Curie temperature Tc of double perovskite Sr2FeMoO6 have been studied along the series polycrystalline Sr2–xAxFeMoO6 (A = Ba and K) samples. The partial substitution of K+ for Sr2+ considerably reduces the Tc from 399 K for x = 0 to 352 K for x = 0.2 with cell volume increasing. This decrease of Tc with K+ doping originates from carrier doping effects in addition to ionic size ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The changes of the magnetic properties in ion irradiated Fe–Cr alloys
Authors: Park D. G. , Heo K. C. , Kim W. W. , Choong Y. M.
Published: December 2007

Fe–Cr alloys are one of the important structural materials for fusion reactor applications, and often used as a model alloys for studying the basic mechanisms governing their behavior under an irradiation. In this study, Fe ions are irradiated on to Fe–Cr alloys with 9% of Cr contents. The magnetic Barkhausen Noise (BN) and Ferro Magnetic Resonance (FMR) experiments are conducted to investigate the changes of their magnetic properties under an ion irradiation. The BN and FMR resonance fields are increased with an increasing ion dosage. The directional ordering by irradiation induced defects seems to be responsible for the changes in the magnetic properties. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Permanent magnets circuit for collagen orientation
Authors: Shinohara Tadashi , Saito Tomoyuki , Saito Daisuke , Kotani Makoto , Aoki Masaaki
Published: December 2007

To synthesize artificial bones, the collagen orientation is one of the key issues. It is reported that high magnetic field could be generated by superconducting magnets, are effective in controlling collagen orientation. In this paper, magnetic circuit using permanent magnets for collagen orientation is studied. As the results, a compact magnetic circuit with magnetic field strength around 3 T has been developed. By using the magnetic circuit, collagen was highly oriented, and orientation order was 0.9. Mouse osteoblast cells were seeded on the orientated collagen solution and cultured. The collagen‐gel shrinkages by cells were observed. The shrinkage rates of oriented collagen are higher than that of not oriented one. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of ion‐beam bombardment and post‐annealing on the structural and magnetic properties of Fe/Pt multilayers
Authors: Guo J.‐Y. , Liu C.‐Y. , Ouyang H. , Lin K.‐W. , Tsai C.‐J. , Lierop J. van , Phuoc N. N. , Suzuki T.
Published: December 2007

We have investigated the structures and magnetic properties of as‐deposited and annealed [Pt(20 Å)/Fe(15 Å)]10/Pt(30 nm) multilayers under different End‐Hall voltages (VEH = 0 ∼ 150 V). The films deposited with no End‐Hall voltage consisted of Fe (a = 2.91 Å), Pt (3.96 Å), and disordered FePt (a = 3.82 Å) phases. Increasing VEH helps compact the individual Fe and Pt layers, while preventing FePt intermixing. However, increasing the annealing temperature to 550 °C resulted in an ordered f.c.t. FePt (a = 3.85 Å, c = 3.73 Å) phase for films deposited with VEH = 0V, and a mixture of Fe and Pt phases with grain coarsening was found for films prepared with VEH = 150 V. A drastic increase in coercivity (Hc ∼ 4600 Oe) in the annealed sample (VEH = 0 V) is attributed to the formation of FePt phases. A decrease in Hc with increasing VEH indicates that FePt formation may be suppressed via more energetic ion beam bombardment that resulted in the activation barrier of diffusion increasing dramatically. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and magnetic properties of ion‐beam bombarded Co/Pt multilayers
Authors: Lin K.‐W. , Guo J.‐Y. , Lin S.‐R. , Ouyang H. , Tsai C.‐J. , van Lierop J. , Phuoc N. N. , Suzuki T.
Published: December 2007

A series of [Pt(2 nm)/Co(2 nm)]10/Pt(30 nm) multilayers were deposited by using an ion‐beam technique. X‐ray diffraction and transmission electron microscopy results have shown that as‐deposited samples consist of h.c.p. Co and f.c.c. Pt phases. Disordered CoPt3 phases were developed with increasing End‐Hall voltage (VEH) that induces greater ion‐beam bombardment energy during deposition. This indicates that intermixing of Co and Pt increases with ion‐beam bombardment. The coercivities (ranging from 100 Oe to 300 Oe) of Co/Pt multilayers decreased with increasing VEH. After annealing, the formation of CoPt3 was observed in these ion‐beam bombarded samples, resulting in lower coercivities (Hc ∼ 50 Oe). The depressed transition temperature of CoPt3 for films deposited with the largest VEH was attributed to distorted CoPt3 structures that appeared with annealing. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magneto‐transport properties of ZnO/La0.7Sr0.3MnO3 bilayer on p‐Si(100)
Authors: Park S. Y. , Lee Hyung Woo , Lee Young Soo , Wang D. F. , Lee Y. P. , Rhee J. Y.
Published: December 2007

Polycrystalline ZnO/La0.7Sr0.3MnO3 (LSMO) heterostructures were fabricated onto Si(100) substrates by magnetron sputtering. A rectifying behavior, as well as an enhanced magnetoresistance (MR) ratio (∼ 12%), was obtained in the heterostructure with respect to the LSMO single layer (a MR ratio ∼ 6%). The degradation of the rectifying behavior for the LSMO layer thinner than 20 nm is mainly due to the change in hole concentration. We suggest a possibility that the magneto‐transport and the magneto‐optical properties of manganites can be modified by the formation of this kind of heterostructure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Percolated perpendicular medium of FePt‐MgO/MgO bilayer films for ultra‐high magnetic recording
Authors: Sun An‐Cheng , Tsai Y. C. , Hsu Jen‐Hwa , Kuo P. C. , Huang H. L. , Sharma Puneet
Published: December 2007

Percolated perpendicular (FePt)100–x‐(MgO)x thin films with x = 0–10.07 vol.% were fabricated on glass substrate with MgO(200)underlayer. When the substrate temperature was 580 oC, a significant enhancement in coercivity was observed at 1.23 vol.% of MgO, which was due to the precipitation of MgO in FePt film causing the hindrance in domain wall motion. As the amount of MgO was increased above 1.23 vol.%, the percolated perpendicular structure began to transform into granular perpendicular structure. Meanwhile, the MgO was found to segregate along grain boundaries of FePt grains, leading to the reduction of FePt grain size. As a result the coercivity and ordering parameter became smaller. In this study the percolated perpendicular medium using FePt film with doping adequate amount of MgO has shown possibility to be an efficient method to increase recording density if the film processing conditions are optimized further. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of film thickness on the soft magnetic properties of sputtered Co‐Fe‐Hf‐O films
Authors: Le Anh‐Tuan , Ha Nguyen Duy , Phan Manh‐Huong , Lee Kwang‐Eun , Kim Chong‐Oh , Lee Heebok , Yu Seong‐Cho
Published: December 2007

Influence of film thickness on the soft magnetic properties of Co19.35Fe53.28Hf7.92O19.35 films, which were deposited on Si(100) substrates using the oxygen reactive RF‐sputtering method, has been thoroughly investigated. It is found that as the film thickness (t) increases from 50 to 430 nm, the easy‐axis coercivity (HCE) strongly decreases from 26.2 to 1.5 Oe, while the hard‐axis anisotropy field (HKH) significantly increases from 68.7 to 84.8 Oe and the saturation magnetization (4πMs) tends to increase from 16.8 to 19.7 kG. As t exceeds 430 nm, HKH gradually decreases, while both HCE and 4πMs remain almost unchanged. It reveals that a strong phase separation appears to occur in films with t > 430 nm, resulting in the decrease of HKH. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Giant parallel and perpendicular exchange biases in MnPd/Co bilayers
Authors: Nam Nguyen Thanh , Thuy Nguyen Phu , Tuan Nguyen Anh , Phuoc Nguyen Nguyen , Suzuki Takao
Published: December 2007

A systematic study of exchange bias in MnPd/Co bilayers has been carried out in both parallel and perpendicular directions, where the dependences of blocking temperature, exchange bias and unidirectional anisotropy constant on the thicknesses of MnPd and Co layers were investigated. One of the particular interests is that the blocking temperature of parallel exchange bias is higher than that of perpendicular exchange bias which can be interpreted as the difference of the ordering in parallel and perpendicular direction. The other is that a huge unidirectional anisotropy constant, JK = 5.5 erg/cm2 was observed, which is in reasonable agreement with the theoretical prediction based on the model by Meiklejohn and Bean. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical breakdown of Co/AlOx/Co tunneling junction
Authors: Horikiri K. , Shiiki K.
Published: December 2007

To clarify a mechanism of electrical breakdown of magnetic tunneling junctions (MTJs), the change of characteristics by constant voltage stress was investigated. There were two breakdown processes. In the case of low applied voltage stress, tunnel resistance increased. On the other hand, if the applied voltage stress was higher, tunnel resistance decreased monotonously. The lifetime of MTJs with an inhomogeneous barrier was shorter than that of MTJs with a homogeneous barrier. In the breakdown process, the homogeneous barrier gradually became inhomogeneous, just before the breakdown. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Mössbauer study of a Ge–Fe thin film
Authors: Ahn G. Y. , Kim C. S. , Lim S. H.
Published: December 2007

Magnetic phases of a Ge48.2Fe51.8 (in atomic%) thin film, fabricated by thermal co‐evaporation onto an oxidized Si substrate, are analyzed by Mössbauer spectroscopy as well as magnetometry. Magnetic measurements indicate a superparamagnetic behavior due to the formation of Fe precipitates in an amorphous matrix with an average blocking temperature of 160 K and a spin glass behavior with a spin freezing temperature of 30 K. The superparamagnetic behavior is confirmed from the Mössbauer spectra taken at room temperature. The isomer‐shift values indicate that the Fe atom in the amorphous phase is in the high‐spin Fe3+ charge state. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Can undoped semiconducting oxides be ferromagnetic?
Authors: Hong Nguyen Hoa , Barla Alessandro , Sakai Joe , Huong Nguyen Que
Published: December 2007

Experimental results on TiO2, HfO2, In2O3, and ZnO have confirmed that ferromagnetism (FM) is certainly possible in undoped oxide thin films. As for the TiO2, In2O3, and HfO2 films, FM is most probably due to oxygen vacancies. Additionally, our X‐ray magnetic circular dichroism (XMCD) measurements on TiO2 films doped with transition ‐ metal elements (Cr, Mn, Co) show that these contribute only with a paramagnetic component to the total magnetization, thus implying that FM in these films must originate from the TiO2 host matrix. As for ZnO, our data have revealed that the FM in this compound does not originate from oxygen vacancies but more likely from defects on Zn sites. We propose a model that is based on an electronic structure calculation using the tight binding method in the confinement configuration: vacancy site in TiO2, HfO2, In2O3 films could create spin splitting and high spin state, so that the exchange interaction between the electrons surrounding the oxygen vacancy with the local field of symmetry could lead to a FM ground state of the systems. The theoretical calculations give the results of 3.18 μB per vacancy for TiO2, 3.05 μB /vac for HfO2 and 0.16 μB /vac for In2O3. It also proves that the mechanism for ZnO system must be different, that FM cannot stem from oxygen vacancies but from other sources. The model strongly suggests that confinement effects should play a key role in shaping up magnetic properties of low dimension systems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interdiffusion effect on exchange coupling in annealing NiFe/FeMn and FeMn/NiFe systems
Authors: Chen Kuang‐Ching , Yang Cheng‐Ta , Wu Y. H. , Huang Chao‐Hsien , Wu Kuo‐Ming , Wu J. C. , Young S. L. , Horng Lance
Published: December 2007

The effect of interdiffusion on the exchange coupling field (Hex) and coercivity (Hc) in annealing NiFe/FeMn and FeMn/NiFe systems was investigated in the study. Type I samples: Silicon substrate/Ta/NiFe/FeMn/Ta and Type II samples: Silicon substrate/Ta/FeMn/NiFe/Ta were prepared. Annealing was carried out at 200 to 450 °C for two hours under 720 Oe, respectively. The results show that the Hex and Hc in two types samples were dependent on the annealing temperature. For both types the magnetization loss ratio (ΔM/MS) is negative, which reflects a loss of magnetization associated with interfacial mixing caused by annealing. The magnetization loss ratio becomes larger when the annealing temperature increases. The exchange coupling of these two types samples is associated with interfacial diffusion between the NiFe and FeMn interface. The annealing treatment also affected the Hc. In these two types samples, the exchange coupling was improved from modification of the interface between layers by annealing. The extended annealing (above 375 °C) changes the exchange coupling in these two types samples due to serious interdiffusion of the interface between NiFe and FeMn layers. It results in unwanted interdiffusion effects at the interface and a concomitant reduction in the exchange bias field. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication of monodisperse FePt@Au core‐shell nanoparticles
Authors: Wei D. H. , Hung D. S. , Ho C. S. , Wang J. W. , Yao Y. D.
Published: December 2007

Hydrophobic FePt@Au core‐shell nanoparticles were chemically synthesized and with controllable surface‐function properties. The enhanced optical property is due to the contribution of Au shell. The surface modification of FePt@Au nanoiparticles by using 11‐mercaptoundecanoic acid (MUA) was hydrophilic through ligand exchange and with good biocompatibility for future multi‐functional applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Annealing effect on magnetostatic properties of nanocomposite Fe‐Zr‐N films
Authors: Shalyguina E. , Sheftel E. , Usmanova G. , Mukasheva M. , Utitskich S. , Inoue M. , Fujikawa R.
Published: December 2007

Results on the investigation of the magnetic properties and microstructure of the as‐deposited and annealed at T = 200‐700 °C Fe‐Zr‐N films are presented. The Fe‐Zr‐N films with the 0.7‐µm thickness were deposited by RF sputtering onto glass square substrates. Structural properties of the films were studied by means of the X‐ray diffraction technique. The bulk magnetic characteristics of the films have been measured by a vibrating sample magnetometer (VSM). The study of the near‐surface magnetic properties of the Fe‐Zr‐N samples was carried out employing magneto‐optical micromagnetometer with a surface sensitivity of about 20 nm of the thickness depth. The strong annealing effect on the values of the coercivity HC and the saturation field HS of the films was revealed. The values of HC and HS of the films, annealed at T = 450 and 500 °C, were found to be minimal. The temperature dependences of HC and HS were explained by microstructure changes of the studied films after their post‐deposition heat treatment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructure of nanopores in AAO templates favoring the growth of nickel nanowires by electrodeposition
Authors: Jeong Jong‐Hyun , Kim Sun‐Hong , Choi Y. , Kim Sung‐Soo
Published: December 2007

Morphology of periodical nanoscale pores in AAO templates has been studied in relation with anodizing process, focusing on the growth of nickel nanowires by electrochemical deposition. The AAO templates were prepared by a two‐step anodization process. The high purity aluminum plates were anodized in oxalic acid aqueous solution with variation of cell voltage. The pore size and interpore distance both increase with the applied potential. During the post treatment of barrier thinning, small‐size pores with split‐up structure at the tips are observed due to current‐limited anodizing process (decreasing cell potential). The rectifying properties of the barrier layer allow the pores to be filled by nickel by AC electrodeposition. The nickel nanowires array shows the ferromagnetic properties with a preferred magnetic orientation along the wire axis. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Composition‐dependent magnetic properties of FePt nanoparticles synthesized by the SiO2‐nanoreactor method
Authors: Tamada Y. , Yamamoto S. , Takano M. , Nasu S. , Ono T.
Published: December 2007

We investigated effects of compostion on magnetic properties of FePt nanoparticles synthesized by the “SiO2‐nanoreactor” method in the composition range from Fe41Pt59 to Fe60Pt40. The magnetization studies implied that, in all samples, FePt nanoparticles can form the L10 structure although only a minor amount of unconverted precursor fcc‐FePt nanoparticles which behave superparamagnetic at room temperature still remained. It was revealed that composition of Fe54Pt46 has the smallest amount of the unconverted fcc‐FePt nanoparticles. Together with the results of composition‐dependence of coercivity, it can be concluded that slightly iron‐rich compositions is optimum to produce high quality L10‐FePt nanoparticles. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Depinning field from notches on Co/Pd multilayer nanowires with perpendicular magnetic anisotropy
Authors: Choe Sug‐Bong
Published: December 2007

Domain‐wall pinning and depinning mechanisms of ferromagnetc nanowires with perpendicular magnetic anisotropy were investigated. Micromagnetic simulation results revealed that the depinning field from notches were determined solely by the gap distance between the notches, irrespective to the wire width and the notch size. The double‐notch wires exhibited two‐fold décalcomanie domain patterns and one half patterns were identical to those of single‐notch wires. Therefore, the double‐notch wires showed the same depinning field compared to single‐notch wires with half width. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron‐spin‐resonance study on the size effects of La0.7Sr0.3MnO3 nanoparticles
Authors: Shih Yu‐Chou , Lin J. G.
Published: December 2007

In this work, a detailed analysis on the electron spin resonance (ESR) spectra within a broad temperature range (80‐400 K) is performed for studying the size effects of La0.7Sr0.3MnO3 nanoparticles synthesized by a sol‐gel route. Our ESR results reveal that La0.7Sr0.3MnO3 nanoparticles with grain sizes of 28 and 48 nm have two magnetic states below the Curie temperatures Tc, which is attributed to the different surface states. One is with the alligned surace spins, the other is with the disordered surface spins. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)