bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal structure and microwave permeability of very thin Fe–Si–Al flakes produced by microforging
Authors: Yoshida Shigeyoshi , Ando Shinsuke , Shimada Yutaka , Suzuki Kei , Nomura Kiyoshi , Fukamichi Kazuaki
Published: May 2003

Fine flakes of Fe–Si–Al produced by long-duration microforging exhibit a peculiar dual-peak dispersion in their frequency characteristics of the imaginary part of the permeability. This dual dispersion has a high potential to be a electromagnetic noise suppressor, works effectively in the microwave band. In a previous report we clarified that one of the dispersions (D II), which appears in the lower frequency range, is correlated to a shape anisotropy of the flakes. In this article, the origin of another dispersion (D III) is studied by analyses of crystalline structure changes during forging (100–180 h) and annealing processes. X-ray diffraction and Mössbauer spectra strongly suggest that the annealed flakes have a composition gradient structure consisting of an Fe-rich mother phase and a Si/Al-rich surface layer. The fact that dispersion D III is enhanced with development of this phase separation leads to the conclusion that dispersion D III is caused by a magnetoelastic anisotropy near the flake surface.
Influence of pressure on itinerant electron metamagnetic transition in La(FexSi1−x)13 compounds
Authors: Fujita A. , Fukamichi K. , Yamada M. , Goto T.
Published: May 2003

The influence of pressure on the itinerant electron metamagnetic (IEM) transition has been investigated for a La(FexSi1−x)13 compound. The critical temperature T0 defined as the disappearance point of the IEM transition decreases with increasing hydrostatic pressure. Since the pressure dependence of T0 is smaller than that of TC, the temperature range for appearance of the IEM transition becomes wider with increasing hydrostatic pressure. These results are consistent with the theoretical model based on the Landau expansion of free energy including the influence of spin fluctuations and the magnetovolume effect. On applying pressure, the critical field Bc for the IEM transition increases proportionally with temperature in low pressures, whereas it exhibits a quadratic temperature dependence with lowering the Curie temperature in high pressures. The change in the temperature dependence of Bc is explained by a change in the thermal growth rate of spin fluctuations.
Transmission electron microscopy study on ferromagnetic (Ga,Mn)N epitaxial films
Authors: Chang J. Y. , Kim G. H. , Lee J. M. , Han S. H. , Kim H. J. , Lee W. Y. , Ham M. H. , Huh K. S. , Myoung J. M.
Published: May 2003

We report on the crystal structure of epitaxial (Ga,Mn)N films with Mn=0.2% grown by plasma-enhanced molecular beam epitaxy, exhibiting n-type conductivity and room temperature ferromagnetism (Ms=0.76 emu/cm3, Hc=90 Oe). The additional diffraction spots are found in the zone axis of B=[11̄00] for the (Ga,Mn)N epilayer due to a single twin orientation in the closed packed hexagonal matrix. High-order Laue zone measurements reveal the expansion of lattice parameter a (3.1851–3.1865 Å) by doping Mn, demonstrating that Mn ions substitute for Ga ions in the (Ga,Mn)N.
Room-temperature preparation and magnetic behavior of Co2MnSi thin films
Authors: Kämmerer S. , Heitmann S. , Meyners D. , Sudfeld D. , Thomas A. , Hütten A. , Reiss G.
Published: May 2003

Our study presents experimental results on Co2MnSi thin-film preparation and resulting magnetic properties of the Co2MnSi Heusler alloy. The focus of our work is on the important role of the microstructure and the magnetic properties relationships of Co2MnSi thin films prepared using dc magnetron sputtering. We examined the microstructure evolution determined with x-ray diffraction for various substrates, e.g., MgO, SrTiO3, Si and SiO2, at different substrate temperatures. Polycrystalline growth observed at high substrate temperatures is independent of the nature and orientation of the substrate. These films show soft magnetic behavior at a net magnetization of 4.12μB. In contrast, textured growth is obtained at room temperature by introducing a vanadium seed layer. These samples are magnetically harder but possess a magnetization of 0.25μB only. This behavior indicates a two phase film consisting of an amorphous and textured volume. Consequently, sputtering at low argon pressure at high temperature result in very smooth Co2MnSi Heusler films, enabling the Co2MnSi Heusler alloys to serve as electrodes in tunnel magnetoresistance structures.
Electron beam stimulated spin reorientation
Authors: Monchesky T. L. , Unguris J. , Celotta R. J.
Published: May 2003

Using scanning electron microscopy with polarization analysis, we observed the electron beam induced switching of the magnetic state of epitaxial single-crystal Fe(110) films grown on atomically flat cleaved GaAs(110). For low film thickness the magnetization lies along the [−110] in-plane direction, while above a thickness of 19 monolayers, the ground state magnetization configuration switches to the [001] in-plane direction. If Fe films are grown to a thickness greater than the critical thickness of the reorientation, the magnetization is caught in a metastable state, oriented along [−110]. We discovered that we can locally switch the metastable state to the stable [001] direction by irradiating the metastable magnetic state with a suitable electron current density. The reversal proceeds by the nucleation and growth of lancet-shaped domains that move in discrete jumps between pinning sites. Our results show that there is a permanent reduction of the strength of defect sites without a permanent change in the overall anisotropy. We demonstrate how an electron beam can be used to locally control domain structure.
Magnetic moment in an ultrathin magnetite film
Authors: Morrall P. , Schedin F. , Langridge S. , Bland J. , Thomas M. F. , Thornton G.
Published: May 2003

We have investigated the magnetic properties of a Cu capped thin film of magnetite (Fe3O4) grown epitaxially on Pt(111). Conversion electron Mössbauer spectroscopy data show good agreement with those from bulk Fe3O4, evidencing a good degree of structural order. The data point to in-plane ferrimagnetic alignment of the magnetic moment in the Fe3O4 layer. Polarized neutron reflectivity (PNR) data determines the layer thinknesses to be 53±6 Å for the magnetite film and 106±5 Å for the Cu capping layer. The average magnetic moment determined by PNR for the Fe3O4 layer is 2.8±0.3 μB, smaller than the value of 4.1 μB for bulk Fe3O4. It is suggested that the reduced moment is in part a result of a reduced ordering temperature in the ultrathin film.
Enhancement of Curie temperature in double perovskites Ba2−xLaxFeMoO6
Authors: Yang H. M. , Lee W. Y. , Han H. , Lee B. W. , Kim C. S.
Published: May 2003

We have investigated effects of the partial substitution of trivalent La for divalent Ba on the magnetic properties of the double perovskite Ba2FeMoO6. Polycrystalline Ba2−xLaxFeMoO6 samples have been prepared by the conventional solid-state reaction in a stream of 5% H2/Ar gas. Magnetization (15 K, 5 kOe) is 2.6μB/f.u. for x=0.5 which is smaller than the value of 3.8μB/f.u. for x=0. The partial substitution of La3+ for Ba2+ considerably enhances the Curie temperature TC. The TC increases from 316 K for x=0 to 336 K for x=0.5.
Tunable magnetization reversal in epitaxial bcc Fe1−xCox films on vicinal surfaces
Authors: Wolf J. A. , Anderson K. K. , Dahlberg E. D. , Crowell P. A. , Chen L. C. , Palmstrøm C. J.
Published: May 2003

The magnetic reversal of bcc Fe1−xCox thin films on vicinal Sc1−yEryAs/GaAs(100) is modified by changing the relative strength of the uniaxial and cubic magnetocrystalline anisotropies using substrates with different miscut angles. The surface miscut and applied field geometry are used to induce several changes in the reversal process, which includes up to three first-order jumps. Increasing the miscut angle of the substrate converts one of the easy axes of the cubic anisotropy into a hard axis. When the anisotropy has a local maximum, the first jump in the reversal process occurs at positive magnetic fields. As the angle between the in-plane magnetic field and the hard axis increases, this jump crosses over to continuous rotation. Two-component magneto-optical Kerr effect measurements are used to map out the hysteresis loops, and both components of the magnetization agree qualitatively with the results of a simple coherent rotation model.
Magnetic field induced phase transitions in Gd5(Si1.95Ge2.05) single crystal and the anisotropic magnetocaloric effect
Authors: Tang H. , Pecharsky A. O. , Schlagel D. L. , Lograsso T. A. , Pecharsky V. K. , Gschneidner K. A.
Published: May 2003

Magnetization measurements using a Gd5(Si1.95Ge2.05) single crystal with the magnetic field applied along three crystallographic directions, [001], [010] and [100], were carried out as a function of the applied field (0–56 kOe) at various temperatures (∼5–320 K). The magnetic field (H)–temperature (T) phase diagrams were constructed for the Gd5(Si1.95Ge2.05) single crystal with field along the three directions. A small anisotropy was observed. The magnetocaloric effect was calculated from isothermal magnetization data, and the observed anisotropy correlates with the H–T phase diagrams. The results are discussed in connection with the magnetic field induced martensitic-like structural transition observed in Gd5(Si2Ge2)-type compounds.
Effect of Be doping on the properties of GaMnAs ferromagnetic semiconductors
Authors: Lee S. , Chung S. J. , Choi I. S. , Yuldeshev Sh. U. , Im Hyunsik , Kang T. W. , Lim W.-L. , Sasaki Y. , Liu X. , Wojtowicz T. , Furdyna J. K.
Published: May 2003

We have studied two series of molecular beam epitaxy grown Ga1−xMnxAs epilayers with several different Be doping levels. Two Mn concentrations x were chosen for this study: 0.03 and 0.05, and these values were maintained constant in each series. These samples were characterized by using SQUID and magnetotransport measurements. A systematic increase of the Curie temperature TC was observed in SQUID measurements on the series of Ga1−xMnxAs with x=0.03. The resistivity measured at zero magnetic field shows a local maximum near the Curie temperature, reflecting the effects of critical scattering near TC. The observed increase of TC in Ga1−xMnxAs for this low range of x can be explained by the increase of the free carrier concentrations in the system arising from Be doping. However, in the series of Ga1−xMnxAs with the higher concentration of Mn (x=0.05), the measurements reveal that the TC systematically decreases with increasing Be doping level. We discuss this effect in terms of a fundamental limitation of the carrier concentration that can be thermodynamically accommodated by Ga1−xMnxAs epilayers.
Microstructure and magnetic properties of CoZr thin film
Authors: Yao Xiao-Feng , Wang Jian-Ping , Zhou Tie-Jun , Chong Tow Chong
Published: May 2003

Annealing effects on the microstructure and magnetic properties of CoZr thin films are investigated in this article. It was found that a change in magnetic phase occurs by annealing the as-deposited films at temperatures of above 550 °C for 2 h. A much lower annealing temperature and shorter annealing time are needed to obtain a hard magnetic phase in thin films than in rapidly quenched CoZr bulk samples. Hard magnetic phase Co11Zr2 and ferromagnetic phase Co23Zr6 formed after annealing. All the annealed films show perpendicular magnetic anisotropy.
Change in entropy at a first-order magnetoelastic phase transition: Case study of Gd5(SixGe1−x)4 giant magnetocaloric alloys
Authors: Casanova Fèlix , Batlle Xavier , Labarta Amı́lcar , Marcos Jordi , Mañosa Lluı́s , Planes Antoni
Published: May 2003

The change in entropy, ΔS, at the first-order magnetoelastic phase transition in Gd5(SixGe1−x)4 alloys for x⩽0.5 has been measured with a high-sensitivity differential scanning calorimeter with built-in magnetic field, H. Scaling of ΔS is achieved by changing the transition temperature, Tt, with x and H from 70 to 310 K. Tt is thus the relevant parameter in determining the giant magnetocaloric effect in these alloys. The calorimetric determination of the change in entropy is also in agreement with the indirect calculation obtained from the magnetization curves measured up to 23 T using both the Clausius–Clapeyron equation and the Maxwell relation. A simple phenomenological model based on the magnetization curves accounts for these results.
X-ray magnetic circular dichroism study of SmAl2 using the M4,5 x-ray absorption edges
Authors: Dhesi S. S. , Bencok P. , Brookes N. B. , van der Laan G. , Galéra R. M.
Published: May 2003

The application of x-ray magnetic circular dichroism sum rules to the M4,5 edges of rare-earth metals has been developed for Sm3+. The jj mixing of intensities between the spin–orbit split M4,5 edges and the influence of the magnetic dipole term, T, on the sum rules have been evaluated by comparison with results from neutron scattering and magnetometry. This analysis leads to the unusual result that 〈Tz〉 is parallel to the orbital magnetic moment, 〈Lz〉, but antiparallel to the spin magnetic moment, 〈Sz〉.
Thermodynamics of a magnetic impurity in a small metallic grain
Authors: Schlottmann P.
Published: May 2003

We consider a small metallic sphere with a spin-1/2 impurity at its center. For a contact Kondo exchange and equally spaced s states, the problem is reduced to the Bethe Ansatz solution of the Kondo model in a finite box. The energy spacing is an additional energy scale competing with the Kondo temperature. We obtain the energy levels as a function of TK for four s states. The entropy and the susceptibility are exponentially activated at low T. The low-T results depend on the purity of the number of s-states.
Magnetic properties and superconductivity of mechanically alloyed (Mg1−xFex)B2 samples with x=0.0–0.4
Authors: Gao Y. D. , Ding J. , Rao G. V. S. , Chowdari B. V. R.
Published: May 2003

In the current work, we have prepared and studied (Mg1−xFex)B2 samples with x=0.0–0.4 prepared by mechanical alloying and subsequent vacuum annealing. All the as-milled powders were found to be amorphous in x-ray diffraction examination and no superconductivity was evident until 4.2 K. The MgB2 phase was formed after a vacuum annealing at 450 °C or higher. For the pure MgB2 sample without Fe substitution, critical temperatures of 38–39 K was measured for the samples after heat treatment at 450 °C or higher. For Fe-containing samples (Mg1−xFex)B2 with x=0.05–0.2, the solubility of Fe in the MgB2 phase decreased with increasing annealing temperature as confirmed by x-ray diffraction and Mössbauer studies. Besides MgB2, other phases (α-Fe, Fe2B, and MgB4) were observed. The critical temperature Tc increased with increasing annealing temperatures, indicating that Tc decreased with increasing Fe concentration in the MgB2 phase. For (Mg0.6Fe0.4)B2, the MgB2 phase could not be formed after heat treatment and MgB4 and Fe2B were the major phases after crystallization. Superconductivity was not observed in the as-milled and subsequently annealed (Mg0.6Fe0.4)B2 specimens.
Time evolution of the second magnetization peak in Bi2Sr2CaCu2O8+δ
Authors: Kalisky B. , Shaulov A. , Tamegai T. , Yeshurun Y.
Published: May 2003

Local magnetization curves at different times, extracted from high-temporal resolution magneto-optical measurements in Bi2Sr2CaCu2O8+δ, demonstrate the absence of the second magnetization peak at short times, its appearance at longer times, and the movement of its onset toward higher-induction fields approaching the thermodynamic vortex order–disorder transition field. We relate this phenomena to metastable disordered states induced by edge contamination for inductions in the vicinity of the order–disorder vortex phase transition. We show that the time evolution of the second magnetization peak is governed by the relaxation times of the metastable disordered vortex states.
Aspherical magnetically modulated optical nanoprobes (MagMOONs)
Authors: Anker Jeffrey N. , Behrend Caleb , Kopelman Raoul
Published: May 2003

Aspherical magnetic particles orient in a magnetic field due to magnetic shape anisotropy. They also emit different fluxes of light from their different geometric faces due to self-absorption and total internal reflection within the particles. The particles rotate in response to rotating magnetic fields and appear to blink as they rotate. We have made pancake and chain shaped particles and magnetically modulated their fluorescent intensities. Demodulating the signal extracts the probe fluorescence from electronic and optical backgrounds dramatically increasing signal to noise ratios. The probes have applications in sensitive and rapid immunoassays, improved intracellular sensors, and inexpensive single molecule analysis.
Effects of intense magnetic fields on sedimentation pattern and gene expression profile in budding yeast
Authors: Ikehata Masateru , Iwasaka Masakazu , Miyakoshi Junji , Ueno Shoogo , Koana Takao
Published: May 2003

Effects of magnetic fields (MFs) on biological systems are usually investigated using biological indices such as gene expression profiles. However, to precisely evaluate the biological effects of MF, the effects of intense MFs on systematic material transport processes including experimental environment must be seriously taken into consideration. In this study, a culture of the budding yeast, Saccharomyces cerevisiae, was used as a model for an in vitro biological test system. After exposure to 5 T static vertical MF, we found a difference in the sedimentation pattern of cells depending on the location of the dish in the magnet bore. Sedimented cells were localized in the center of the dish when they were placed in the lower part of the magnet bore while the sedimentation of the cells was uniform in dishes placed in the upper part of the bore because of the diamagnetic force. Genome wide gene expression profile of the yeast cells after exposure to 5 T static MF for 2 h suggested that the MF did not affect the expression level of any gene in yeast cells although the sedimentation pattern was altered. In addition, exposure to 10 T for 1 h and 5 T for 24 h also did not affect the gene expression. On the other hand, a slight change in expressions of several genes which are related to respiration was observed by exposure to a 14 T static MF for 24 h. The necessity of estimating the indirect effects of MFs on a study of its biological effect of MF in vitro will be discussed.
Nerve excitation and recovery processes under strong static magnetic fields
Authors: Eguchi Yawara , Ueno Shoogo , Tatsuoka Hozumi
Published: May 2003

The membrane excitation and refractory processes of nerve fibers exposed to strong static magnetic fields of 8 T were studied. Sciatic nerve bundles of frogs were electrically excited by a pair of pulses with varying interpulse intervals, and the compound action potentials were measured under magnetic field exposures. Our experimental results show that the conduction velocity was not affected by 8 T magnetic fields; however, the membrane excitation during the recovery process in the relative refractory period was enhanced by 10% of maximal peak of nerve excitation by magnetic field exposure for 3 h. In this study, the optimal time interval for increased membrane excitation during the recovery process was between 1.0 and 1.1 ms. In other words, membrane excitation during the recovery process in the relative refractory period was affected by the magnetic fields just after Na+ channels were inactivated.
High interfacial exchange energy in TbFeCo exchange-bias films
Authors: Lin Chao-Cheng , Lai Chih-Huang , Jiang Ruo-Fan , Shieh Han-Ping D.
Published: May 2003

The exchange-bias films of ferrimagnetic/ferrimagnetic, ferromagnetic/ferromagnetic, and ferromagnetic/antiferromagnetic bilayers were fabricated to investigate their interfacial exchange energy Δσ. Δσ of TbFeCo bilayers is larger than 5 erg/cm2 at room temperature. By varying the composition of TbFeCo layers, both positive and negative exchange bias have been observed. A highly uncompensated-spin interface model was proposed to explain the strong exchange interaction in TbFeCo bilayers. Due to the characteristics of highly uncompensated-spin interface at TbFeCo bilayers, the exchange coupling field in TbFeCo bilayers exhibited less dependence on interfacial roughness than that in IrMn/NiFe bilayers. In addition, by adjusting the composition of TbFeCo, the anisotropy of pinning layer can be manipulated and exhibits strong effects on exchange bias of TbFeCo bilayers.
Resonant suppression of exciton spin relaxation in Zn0.96Mn0.04Se/CdSe superlattices
Authors: Buyanova I. A. , Rudko G. Yu , Chen W. M. , Toropov A. A. , Sorokin S. V. , Ivanov S. V. , Kop'ev P. S.
Published: May 2003

Spin relaxation processes in strained Zn0.96Mn0.04Se/CdSe superlattices are studied in detail by using hot photoluminescence combined with tunable excitation spectroscopy. A drastic enhancement in occupation of the upper-lying |+1/2,−3/2〉 state of the heavy-hole excitons is observed when excitation photon energy is resonantly tuned near an integer number of the LO phonon energy above the |+1/2,−3/2〉 state. Assuming the Boltzmann distribution between the excitonic states, the spin temperature of the excitons is deduced to be as high as 85 K, well above the lattice temperature of 2 K. The observed behavior provides experimental evidence for a surprisingly strong suppression of spin relaxation from the upper spin-split excitonic branch for small values of wave vector.
Digitally doped magnetic resonant tunneling devices: High tunneling magnetoresistance systems
Authors: Stewart D. A. , van Schilfgaarde M.
Published: May 2003

Magnetic resonant tunneling devices (RTDs) have been recognized as one possible route to developing a near ideal spin valve. With the advent of dilute magnetic semiconductors, the ability to grow these devices using traditional semiconductor techniques provides a distinct advantage over present metal-based giant magnetoresistance devices. We examine the effect of replacing dilute magnetic semiconductor leads (GaMnAs) with Ga0.5Mn0.5As monolayers adjacent to the RTD structure. We examine transmission through a series of GaAs/AlAs RTDs using principal layer Green function technique in the linear muffin-tin orbital framework. Self-consistent calculations using a linear response technique are done for both nonmagnetic RTDs and ones with Mn doped layers outside the AlAs barriers. The Mn dopant layers lead to splitting of the transmission peaks in both the conduction and the valence bands. The transmission peaks shift as the quantum well width increases in accordance with quantum well states. In addition, transmission in the minority spin channel is suppressed as valence quantum well states move closer to the Fermi energy. Preliminary zero bias conductance calculations give tunneling magnetoresistance values in excess of 1000%. While this estimate does not include spin scattering sources such as spin-orbit coupling, the actual tunneling magnetoresistance should still be very high.
Thickness dependence of the magnetic anisotropy in La2/3Ca1/3MnO3 thin films grown on LaAlO3 substrates
Authors: Valencia S. , Balcells Ll. , Martı́nez B. , Fontcuberta J.
Published: May 2003

Magnetic anisotropy of sputtered epitaxial La2/3Ca1/3MnO3 (LCMO) thin films grown on top of LaAlO3 (LAO) substrates has been studied as a function of thickness. A series of films with thickness ranging from 20 to 150 nm have been prepared. LCMO films grown on LAO substrates are subjected to an in-plane biaxial compressive strain that progressively relaxes as film thickness increases as deduced from the variation of the c cell parameter. Nevertheless, some strain is observed even in 150-nm-thick films. The relaxation process is accompanied by an improvement of the magnetic and transport properties approaching that of the bulk material. The observed magnetic easy axis evolves from perpendicular to plane for thin films towards in plane as film thickness increases. Values of the effective anisotropy constant of K1eff≈2.2×107 erg/cm3, at T=10 K, and magnetostriction constant of λ≈2×10−4 are found.
Low-frequency noise in patterned La0.7Sr0.3MnO3 thin films
Authors: Méchin L. , Yang F. , Routoure J.-M. , Robbes D.
Published: May 2003

The low frequency noise in patterned La0.7Sr0.3MnO3 thin film bridges with different geometries was measured at 300 K in ambient magnetic field. Films were deposited by pulsed laser ablation on (100) SrTiO3 substrates. The measured 1/f noise was well described by the semiempirical Hooge relation, which indicates that the low frequency noise could be originated by resistance fluctuations. The measured noise magnitude was compared with bibliographic data for epitaxial La1−xSrxMnO3 (LSMO) and La1−xCaxMnO3 thin films. The normalized Hooge parameter α/n for our films was in the range of 2–4×10−28 m3, which is the order of magnitude of the best results reported in literature for oxygen annealed films. Finally the noise equivalent temperature of a thermometer fabricated with such LSMO films was estimated to be 3.4×10−6 K/Hz at 300 K, 10 Hz, and I=100 μA. These results demonstrate that the intrinsic low frequency noise of LSMO is not a limitation and that LSMO thin films can advantageously be used as performant thermometers for the fabrication of room temperature microbolometers.
Magnetoresistive behavior of Cr-doped manganites Pr0.44Sr0.56MnO3
Authors: Jirák Z. , Hejtmánek J. , Knı́žek K. , Maryško M. , Martin C. , Maignan A. , Hervieu M.
Published: May 2003

A complex structural, magnetic, and electric transport investigation shows that the Cr doping on Mn sites in the A-type antiferromagnet Pr0.44Sr0.56MnO3 provokes a nonuniform magnetic state with coexisting ferromagnetic and antiferromagnetic regions. Irrespective of the ratio of magnetic phases, the samples exhibit a nonmetallic behavior of resistivity and thermopower, pointing to the nanoscopic nature of the phase separation. A particularly large magnetoresistance encountered in a broad range of temperatures for samples with Cr doping of 4%–6% supports such an idea.
Magnetic transition and large low-field magnetoresistance near Curie temperature in polycrystalline La2/3A1/3MnO3 (A=Ca,Sr)
Authors: Li Run-Wei , Sun Ji-Rong , Li Qing-An , Zhu Tao , Zhang Shao-Ying , Shen Bao-Gen
Published: May 2003

By means of electron spin resonance, magnetization, and resistivity measurements, phase separation and a large low-field magnetoresistance (MR) accompanied by a first-order metamagnetic transition in the vicinity of Curie temperature (TC) were observed in polycrystalline La2/3Ca1/3MnO3, but were not observed in polycrystalline La2/3Sr1/3MnO3. It is obvious that the phase separation and large low-field MR near the TC are not universal features of the colossal MR materials. By combining the magnetic field dependence of magnetization and resistance, it was suggested that the first-order metamagnetic transition from the paramagnetic to ferromagnetic state induced by a magnetic field should be responsible for the large low-field MR observed in polycrystalline La2/3Ca1/3MnO3. Undoubtedly, this observation is very important for exploring large low-field MR in high temperature, which is necessary for practical application of the colossal magnetoresistance effect.
Phase diagram and Hall effect of the electron doped manganite La1−xCexMnO3
Authors: Raychaudhuri P. , Mitra C. , Mann P. D. A. , Wirth S.
Published: May 2003

We report on the electronic, transport, and magnetic properties of the Ce-doped manganite, La1−xCexMnO3. This material is remarkably similar to the heavily investigated hole doped manganite La1−xCaxMnO3; e.g., both materials show Curie temperatures of TC∼250 K for x=0.3. The main difference which makes the Ce-doped material highly interesting for basic research as well as for possible applications (e.g., in spintronics) is the fact that Ce doping drives the manganese in a mixture of Mn2+ and Mn3+ induced by electron doping. We present conclusive evidence for electron doping by x-ray absorption spectroscopy and Hall measurements on single phase epitaxial thin films. From transport measurements on a series of La1−xCexMnO3, the magnetic phase diagram of La1−xCexMnO3 is established.
Enhancement of ferromagnetism and metallicity in Ru-doped layered manganite system La1.2Ca1.8Mn2−xRuxO7 (x=0,0.1,0.5,1.0)
Authors: Sudhakar Nori , Rajeev K. P. , Nigam A. K.
Published: May 2003

We report here the interesting magnetic and electrical transport properties of Ru-doped two-dimensional manganite system La1.2Ca1.8Mn2−xRuxO7 (x=0,0.1,0.5,1.0). This work aims to investigate the nature of the magnetic phase especially at low temperatures and electrical transport in the light of metal insulator transition exhibited by similar systems. The Ru doping is found to affect the magnetic and electrical properties considerably. The ferromagnetic ordering temperature (Tc) increases from 264 K for x=0 to 285 K for x=0.5 sample.
Study of internal permanent magnet rotor made of 0.6C–13Cr–Fe dual state magnetic material
Authors: Mita Masahiro , Masuzawa Masahiro , Hirao Noriyoshi , Kimura Fumio
Published: May 2003

We have successfully developed an internal permanent magnet (IPM) rotor using dual state bulk magnetic material to increase usable magnetic flux dramatically. The most significant benefit of the IPM rotor is its mechanical reliability, because permanent magnets are inserted in slots of soft magnetic material. On the other hand, there is significant leakage flux between adjoining permanent magnets in the soft magnetic rotor core, reducing the usable magnetic flux flowing into the stator core. To solve this problem, we used a dual state magnetic material, 0.6C–13Cr–Fe alloy. This soft magnetic material could locally be changed into nonmagnetic material by localized heat treatment. By changing the material at leakage flux path into nonmagnetic, we can reduce the leakage flux, while keeping the rotor mechanically sound. By applying the dual state magnetic material to an experimental eight pole IPM rotor, the useful flux flowing in the stator core differs by 8% when compared to an all soft magnetic rotor core.
Reversing exchange fields in CoFe/PtMn and CoFe/IrMn bilayers by carbon field irradiation
Authors: Yang C. H. , Lai Chih-Huang , Mao S.
Published: May 2003

C-ion irradiation was performed in CoFe/PtMn and CoFe/IrMn systems with an applied field during irradiation to investigate the effects of the energy transfer between C ions and antiferromagnetic atoms (AF) on the exchange field Hex. The irradiated CoFe/PtMn samples showed reduced exchange fields and coercivity, which was attributed to the lattice distortion of PtMn. When samples were irradiated with an applied field antiparallel to the original exchange-bias direction, a partially reversed Hex was found in CoFe/PtMn, while a fully reversed Hex in CoFe/IrMn was observed at the dose of 2×1014 ions/cm2. Rapid energy transfer and temperature increase, originating from the interaction between C ions and AF atoms, resulted in spin reversal and formation of reversed AF domains when samples were irradiated in antiparallel fields. In addition, the thermal relaxation of Hex in CoFe/IrMn was suppressed by ion irradiation.
Mn diffusion effect in the exchange biased NiFe/FeMn/NiFe trilayers
Authors: Kim S. W. , Kim J. K. , Kim J. H. , Kim B. K. , Lee J. Y. , Lee S. S. , Hwang D. G. , Rhee J. R.
Published: May 2003

We have fabricated NiFe/Mn/FeMn/Mn/NiFe multilayers using ultrahigh vacuum ion-beam deposition system to study the diffusion effect of the inserted Mn on exchange biasing. As the thickness of the Mn layer was changed from 0 to 1.5 nm, the exchange biasing field Hex(top) at the top interface of FeMn/Mn/NiFe was decreased from 258 Oe to 24 Oe. On the other hand, the Hex(bottom) was slightly decreased 103 Oe to 78 Oe without a change in the coercive field Hc. Above 1.2 nm, a reverse phenomena of Hex was observed. After annealing at 200 °C, the Hex(top) was increased by almost a factor of 2; however, the Hex(bottom) did not change. The analyses of x-ray patterns and Auger spectroscopy showed that the abnormal tendency of Hex(bottom) originated from the diffusion of Mn atoms at bottom interface into the FeMn layer during film growth, and that the Mn was concentrated at the interface by annealing.
Increased efficiency and accuracy in micromagnetic calculations of switching astroids
Authors: Scheinfein M. R. , Arrott A. S.
Published: May 2003

The “path method” is introduced to use results of one or a few full Landau–Lifshitz–Gilbert dynamical micromagnetic calculations to predict switching diagrams for magnetic elements in random access memories. The utility of the method is demonstrated for an element in the form of a trapezoidally distorted generalized ellipse, where the symmetry produces the C state in the absence of applied fields. The element switches by almost uniform rotation of the S-state configuration in the presence of an adequate bias field. The path method relies on the empirically observed insensitivity of the magnetization patterns in a switching process to the amount by which the field exceeds that necessary for switching.
Comparison of analytical solutions of Landau–Lifshitz equation for “damping” and “precessional” switchings
Authors: Bertotti G. , Mayergoyz I. , Serpico C. , Dimian M.
Published: May 2003

The analytical solutions to the Landau–Lifshitz equation for “damping” and “precessional” switchings of materials with uniaxial anisotropy are found. These solutions lead to the expressions for the switching times and critical fields. Comparison of these two distinct modes of switching is presented.
Equivalence of sweep-rate and magnetic-viscosity dynamics
Authors: Skomski R. , Kirby R. D. , Sellmyer D. J.
Published: May 2003

The irreversible response of magnetic materials to magnetic fields of arbitrary time dependence is investigated by a master-equation approach. The magnetization reversal is expressed in terms of renormalized magnetization modes, and the resulting set of two-level master equations is solved by direct integration. The theory applies not only to linear energy-barrier laws but also to the physically more reasonable case where the activation energy is a nonlinear function of the applied field. Particular emphasis is on the relation between sweep-rate and magnetic-viscosity dynamics. Other regimes, such as oscillating magnetic fields, can be mapped onto sweep-rate dynamics. Magnetic-viscosity and sweep-rate experiments reflect the same fundamental magnetization processes, but energy barriers probed by dynamic experiments are smaller by about 20%.
Analytical solutions of Landau–Lifshitz equation for precessional switching
Authors: Serpico C. , Mayergoyz I. D. , Bertotti G.
Published: May 2003

A rigorous analysis of the precessional switching dynamics in uniformly magnetized particles and films is presented. Magnetization dynamics are described by the Landau–Lifshitz equation and the precessional switching is realized by applying a field pulse orthogonal to the easy axis of the particle or the film. The analysis of the switching process is based on the explicit knowledge of two integrals of motion for the magnetization dynamics and leads to closed form analytical expressions for the magnetization in terms of Jacobi elliptic functions. It is shown that switching can occur only beyond a critical field threshold. The analytical solutions are used to predict the magnetization trajectory and the switching time under external field pulses of different amplitudes and durations.
Residual stresses in punched laminations: Phenomenological analysis and influence on the magnetic behavior of electrical steels
Authors: Maurel Vincent , Ossart Florence , Billardon René
Published: May 2003

The magnetic properties of laminated electrical steels are degraded by punching because of plasticity localized along the cutting edge, but also because of residual stresses, which may spread over the whole lamination. In this article, long-range residual stresses are analyzed via a simplified mechanical analysis. Then, their effect on the global magnetic behavior of the lamination is calculated by a magnetoelastic coupled model. It is found that the relative influence of residual stress is as important as the one of plasticity alone.
Magnetic properties of Fe100−x−ySixPy (0⩽x⩽4, 0⩽y⩽0,6) soft magnetic composites prepared by diffusion sintering
Authors: De Wulf Marc , Anestiev Ljubomir , Dupré Luc , Froyen Ludo , Melkebeek Jan
Published: May 2003

In the presented work, iron-based soft magnetic composite materials are produced and studied. The proposed production method combines sintering and diffusion processes. The applications that are aimed at for these materials are electrical machines and other low-frequency electromechanical applications. The material characteristics are studied in the frequency range from dc to 100 Hz. The material specimens are shaped as rectangular rods and magnetic characterization is done on a miniature single sheet tester, which is calibrated with respect to the Epstein test. The experimental procedure for determining the magnetic properties is outlined. The production method was tested on Fe100−x−ySixPy (0⩽x⩽4, 0⩽y⩽0.6). Because of the poor plasticity, such compositions cannot be produced directly from powder. This article discusses the results of the diffusion sintering and the combined influence of Si and P on the magnetic properties of the obtained materials. It is found that an increase of the Si and P content improves both the dc and ac behavior of the materials.
Magnetic core loss of ultrahigh strength FeCo alloys
Authors: Cheng X. M. , Zhang X. K. , Zhang D. Z. , Lee S. H. , Duckham A. , Weihs T. P. , Cammarata R. C. , Xiao John Q. , Chien C. L.
Published: May 2003

Hiperco® 50 alloy heat treated between 450 and 650 °C exhibits superior mechanical properties. We report the measurements of the ac core loss at various frequencies up to 4500 Hz of the Hiperco® 50 alloy samples annealed at 450 and 650 °C. The 650 °C annealed specimens have lower ac core loss than that of the 450 °C annealed ones. The total core loss, consisting of contributions from hysteresis core loss and eddy-current core loss, depends on frequency f as af+bf2. The eddy-current loss of a single laminate is minor compared to the hysteresis loss.
Ion irradiation of Co/Pt multilayer films
Authors: Bonder M. J. , Telling N. D. , Grundy P. J. , Faunce C. A. , Shen T. , Vishnyakov V. M.
Published: May 2003

This article describes a microstructural and magnetic investigation of the modification of Co/Pt multilayer films by Ar ion irradiation which results in a change of the orientation of the magnetization from perpendicular to the film plane to the in-plane direction. Transmission electron microscopy observation confirms the general structure of the as-deposited samples and correlates with the x-ray reflectivity measurements in showing the eventual mixing of the layers and a large increase in grain size caused by the irradiation. TRIM (transport of ions in matter) calculations show that large numbers of recoils are placed outside the individual layers and in the adjacent layers on irradiation. This signifies considerable roughening of the interfaces and mixing in the multilayer structure. Magnetic measurements and magnetic force microscopy observations confirm the decrease of perpendicular anisotropy and the changes of the magnetization direction from the perpendicular direction to an in-plane direction after irradiation.
Interlayer exchange coupling of epitaxial Fe/Al/Fe trilayer films: Dynamic and static measurements
Authors: Kuanr Bijoy K.
Published: May 2003

This report deals with the interlayer exchange coupling of epitaxial Fe(3 nm)/Al(tAl=0.4–0.9 nm)/Fe(2 nm) trilayers studied by using ferromagnetic resonance (FMR), Brillouin light scattering (BLS) and magneto-optic Kerr effect (MOKE) measurement techniques. A very strong antiferromagnetic (AFM) interlayer exchange coupling (>3 erg/cm2) was observed at a spacer Al thickness of 0.7 nm. The bilinear (J1) and the biquadratic (J2) coupling constants were determined from (i) the fitting of angular variation (θH) of resonance field (Hres) from FMR, (ii) field variation of acoustic and optic surface mode frequencies from BLS and (iii) by fitting of longitudinal MOKE hysteresis loops. The samples with strong antiferromagnetic (AFM) coupling have a higher Hres along the easy axis than that along hard axis and their magnetizations are canted. The eightfold-like symmetry, of the acoustic Hres as a function of in-plane field angle at room temperature, is due to the strong competition between the fourfold anisotropy energy (HK) and the AFM interfacial coupling energy. This behavior vanished at low temperatures due to a strong increase of AFM coupling in comparison to HK. We distinguish the existence of canted magnetization states at resonance by fitting the experimental Hres(θH) data to the model calculation.
Dependence of the perpendicular anisotropy in Co/Au multilayers on the number of repetitions
Authors: Gubbiotti G. , Carlotti G. , Albertini F. , Casoli F. , Bontempi E. , Depero L. E. , Mengucci P. , Di Cristoforo A. , Koo H. , Gomez R. D.
Published: May 2003

The correlations between structure and magnetism in [Co(0.9 nm)/Au(5 nm)]×N multilayer films with different number of repetitions N=10, 30, and 50, have been studied by the combined use of complementary structural and magnetic techniques, such as x-ray reflectivity, x-ray diffraction, and transmission electron microscopy, alternating gradient force magnetometry, magnetic force microscopy and Brillouin light scattering. On increasing the value of N, an overall improvement of the multilayer quality is observed which corresponds to a change in the micromagnetic structure and to an enhancement of the perpendicular anisotropy. These effects have been attributed to a reduction of the magnetostatic energy associated with the formation of perpendicular magnetic domains in multilayers with increasing number of layers repetitions.
Fabrication and magnetoresistance of tunnel junctions using half-metallic Fe3O4
Authors: Kim Woochul , Kawaguchi Kenji , Koshizaki Naoto , Sohma Mitsugu , Matsumoto Tetsuro
Published: May 2003

Magnetite (Fe3O4) is believed to be half metal, providing 100% spin-polarized conduction electrons. The half-metallic nature of magnetic electrodes for tunneling junction devices is expected to induce a large magnetoresistance. We investigated the structural and chemical properties of interfaces in ferromagnet–insulator–ferromagnet (Fe3O4/MgO/Fe) tunnel junctions. Al/Ag/Fe3O4/MgO multilayers for magnetic tunnel junction have been fabricated on α-Al2O3 (001) and MgO (100) substrates by a molecular beam epitaxy system. The Fe3O4 quality was examined by reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD), superconducting quantum interference device magnetometry, atomic force microscopy (AFM), and in situ x-ray photoelectron spectroscopy. RHEED and XRD results showed that the epitaxial Fe3O4 layer with a smooth surface was successfully grown on substrates. The stoichiometric Fe3O4 was confirmed by Verway transition in temperature dependence of magnetization. AFM data showed relatively smooth surface for Fe3O4 prepared at Ts=250 °C and P(O2)=3×10−3 Pa. The Fe 2p3/2 and Fe 2p1/2 peak profiles for Fe3O4 layer are little changed by overlaying MgO in the XPS measurements. These results suggest the Al/Ag/Fe3O4/MgO multilayers available for spin-dependent tunnel junction.
Fe/MgO/FeCo(100) epitaxial magnetic tunnel junctions prepared by using in situ plasma oxidation
Authors: Mitani S. , Moriyama T. , Takanashi K.
Published: May 2003

Fe/MgO/FeCo epitaxial magnetic tunnel junctions (MTJs) were prepared on MgO(100) single crystal substrates by using in situ plasma oxidation for the formation of MgO barriers. The epitaxial relationship of Fe(001)/MgO(001)/FeCo(001) and Fe[100]//MgO[110]//FeCo[100] in the junctions was observed by reflection high-energy electron diffraction. Tunneling transport was clearly observed at low temperatures below about 150 K, and the barrier height of MgO is estimated to be 0.9 eV, which is smaller than the value expected from half of the band gap of bulk MgO. Tunnel magnetoresistance of 23% and 20% was observed at 4.2 and 77 K, respectively. The results suggest that plasma oxidation is useful for fabricating epitaxial magnetic tunnel junctions.
High bias voltage dependence in tunneling magnetoresistance of a ramp-type junction
Authors: Lee Sang-Suk , Kim Young-Il , Hwang Do-Guwn , Rhie Kungwon , Kim Sun-Wook , Rhee Jang-Roh
Published: May 2003

A ramp-type tunneling magnetoresistance (TMR) junction having structure NiO(60 nm)/pinned Co(10 nm)/NiO(60 nm)/barrier Si3N4(2–6 nm)/free NiFe(10 nm) with the 15° slope was investigated. We obtained nonlinear I–V characteristics for ramp-type tunneling junctions that are distinctively different with and without an applied magnetic field. In the barrier with a Si3N4 thickness of 4 nm, the bias voltage dependence of TMR was stable up to 10 V with a negative TMR ratio of about −10%. The negative TMR is very peculiar for an asymmetric tunneling process between a wedge Co pinned layer and a free NiFe layer.
High data rate recording: Moving to 2 Gbit/s
Authors: Taratorin A. , Yuan S. , Nikitin V.
Published: May 2003

High data rate recording can be achieved using fast write drivers and fast heads. Advanced short-yoke write heads and write drivers with 450 ps rise time and programmable current overshoot were used to study recording at data rates up to 2 Gbit/s. The head flux rise time causes shifts of recorded transitions. It is well known that current overshoot helps to overcome bandwidth limitations in the write driver, interconnects, and write head. However, excessive overshoot may cause pattern-dependent transition shifts and significant distortions of recorded transitions. We present the data rate performance of short-yoke recording heads, analysis of nonlinear pattern-dependent distortions, and optimization of the write current wave form in the 1–2 Gbit/s range. Simple dibit and tribit patterns were recorded at 2 Gbit/s. Low-distortion recording for arbitrary data patterns was demonstrated at 1.6 Gbit/s after optimization of write current overshoot.
Write-to-read coupling study of various interconnect types
Authors: Jang Eunkyu , Zhang Xiaofeng
Published: May 2003

The use of suspension interconnects has brought about a great concern for the coupling of the write signal into read lines during write operations. The cross-talk coupling can result in amplitude degradation of giant magnetoresistive (GMR) element at high data rates. In this study, write-to-read couplings of GMR heads during writing operations are studied as a function of write frequency for various interconnects. The coupling current of interconnects with a ground plane is 2–3 times smaller than interconnect without the ground plane. It was found that the ground plane is more important in write-to-read coupling than separation between write and read traces.
Transverse field anneal studies of high moment FeCoB and FeCoZr films
Authors: Minor M. Kevin , Klemmer Timothy J.
Published: May 2003

Ever increasing areal densities have driven the need for high moment materials with large saturation magnetizations greater than 2 T. In addition, for applications such as write poles and soft underlayers, the high moment materials must exhibit soft and uniaxial magnetic properties which are thermally stable during high temperature processing. In this work, we examine 2.1 T FeCoB and 1.8 T FeCoZr films which are amorphous in the as-deposited state. The films are given longitudinal field anneals (LFAs) at 220 and 250 °C for 4 h. FeCoZr films remain amorphous after the 220 and 250 °C LFAs. FeCoB films remain amorphous after the 220 °C LFA, however, the 250 °C LFA results in crystallization in the FeCoB film. This crystallization is accompanied by a degradation in soft magnetic properties. As-deposited and 220 and 250 °C LFA FeCoB and FeCoZr films are then given transverse field anneals (TFAs) at 150 °C. As-deposited FeCoB and FeCoZr experience a 90° rotation of Hk or switching after less than 2 h of TFA. LFAs result in improved thermal stability in all FeCoB and FeCoZr films. The crystalline FeCoB film given a 250 °C LFA exhibited the best thermal stability, however, the magnetic properties were not optimal due to crystallization.