bluuebunny/crossref_metadata_2025 huggingface dataset:
Bloch’s law for epitaxial ultrathin dot arrays with uniaxial magnetic anisotropy
Authors: Kipferl W. , Dumm M. , Kotissek P. , Steinbauer F. , Bayreuther G.
Published: May 2004

Dot arrays with dots of well-defined circular shape have been patterned from epitaxial Fe films on GaAs(001). Magnetization reversal and temperature dependence of the spontaneous magnetization were studied by superconducting quantum interference device magnetometry, an alternating gradient magnetometer and the magneto-optical Kerr effect. It was observed that Bloch T3/2 law is valid for all dot diameters. The spin wave parameter B increases with a decrease in dot diameter by a factor of 4, which reduces the magnetization at room temperature by about 25% compared to its value at 10 K for the smallest dots. From this observation it is concluded that additional excitation modes are present in the spin system.
Q-state Potts model with power-law decaying interactions: Along the tricritical line
Authors: Reynal S. , Diep H. T.
Published: May 2004

By relying on a recently proposed multicanonical algorithm adapted to long-ranged models, we shed new light on the critical behavior of the long-ranged q-state Potts model. We refine the controversial phase diagram by an order of magnitude, over a large range of q values, by applying finite-size scaling arguments to spinodal curves. We further offer convincing evidence that the phase transition on the line of inverse-square interactions is not of the first order, by virtue of a very unusual, previously unnoticed, finite-size effect. Finally, we obtain estimates of critical couplings near the mean-field region, which clearly reinforce Tsallis conjecture.
Modeling interlayer exchange coupling in EuS/PbS/EuS trilayers
Authors: Smits C. J. P. , Filip A. T. , Swagten H. J. M. , de Jonge W. J. M. , Chernyshova M. , Kowalczyk L. , Grasza K. , Szczerbakow A. , Story T. , Sipatov A. Yu.
Published: May 2004

All-semiconducting EuS/PbS/EuS trilayers that show antiferromagnetic coupling were studied by superconducting quantum interference device magnetometry. We analyzed our measurements with a modified Stoner–Wohlfarth model from which the interlayer exchange energy and anisotropy were extracted based on the switching field from antiparallel to parallel alignment of the EuS layers and the zero-field susceptibility, respectively. Magnetic moment versus temperature curves were simulated by taking into account Brillouin type temperature dependence of the saturation magnetization of EuS. Despite their simplicity, the simulated curves show good qualitative agreement with the measurements when strong temperature dependence of interlayer coupling is assumed.
Control of pinned layer magnetization direction in spin-valve-type magnetic tunnel junction with an IrMn layer
Authors: Takenaga Takashi , Sadeh Beysen , Kuroiwa Takeharu , Kobayashi Hiroshi , Sato Kazunao
Published: May 2004

We have experimentally investigated a method of controlling the magnetization direction of a CoFe pinned layer in a spin-valve-type magnetic tunnel junction (MTJ) with an IrMn layer. Arbitrary control of the direction of the pinned layer magnetization was performed by a postannealing process in conditions above the blocking temperature of IrMn and in a magnetic field to saturate the magnetization of the pinned layer. The results show that it is possible to control and to uniformly rearrange the direction of the pinned layer magnetization in MTJs with a postannealing process in the magnetic random access memories manufacturing process.
Doping effect in a magnetic TbB50-type B12 cluster compound
Authors: Mori Takao
Published: May 2004

The nonmagnetic doping effect of a TbB50-type compound TbB44Si2 was investigated. HC was interestingly observed to show no variation even for Tb1−xLuxB44Si2 (x=0.5) and a correlation was observed between the number of free Tb spins and x. The results indicate that the transition in the TbB50-type compounds is of a dimeric nature. Furthermore, irreversibilities were not observed in any of the compounds, which is further proof that disorder alone cannot be the driving force for glassiness in these boron cluster compounds of which new spin glasses such as REB22C2N (RE=rare-earth) have recently been discovered. Investigation of the evolution of the conductivity on the doping (which is a simple nonmagnetic substitution versus electronic doping) showed a dependency which directly reflected the introduction of disorder into the system.
Anomalous magnetic properties of the ferrimagnetic semiconductor on Ga-doped sulphur spinel
Authors: Son Bae Soon , Kim Sam Jin , Lee Bo Wha , Kim Chul Sung
Published: May 2004

FeGa x Cr 2−x S 4  (x=0.1 and 0.3) have been studied with Mössbauer spectroscopy, x-ray diffraction, magnetization, and magnetoresistance. Fe ions migrate from the tetrahedral (A) site to the octahedral (B) site with an increase of Ga substitutions. The electric quadrupole splitting of the A and B sites in Mössbauer spectra of the sample x=0.1 at 295 K, are 0.30 and 2.93 mm/s, respectively, whereas, for the sample x=0.3 they are 0.83 and 2.94 mm/s, respectively. It gives a direct evidence that Ga ions stimulate the asymmetric charge distribution of Fe ions in the A site. The temperature dependence of quadrupole interaction leads to the conclusion that orbital angular contribution plays an important role in FeGaxCr2−xS4 (x=0.1 and 0.3).
Intercluster coupling in site-frustrated random magnets
Authors: Beath A. D. , Ryan D. H.
Published: May 2004

The effects of intercluster coupling strength (|JFA|) on the ordering behavior of the site-frustrated Heisenberg model have been investigated. We find that following a weak initial increase, the lower temperature transition is driven to T=0 for |JFA|⋆∼5.0(5), while the upper transition temperature appears to increase without limit.
Synthesis and magnetic properties of monodisperse Fe3O4 nanoparticles
Authors: Parvin K. , Ma J. , Ly J. , Sun X. C. , Nikles D. E. , Sun K. , Wang L. M.
Published: May 2004

We report the high temperature reaction of iron acetylacetonate in phenyl ether in the presence of oleic acid and oleylamine that was used to synthesize monodisperse Fe3O4 nanoparticles. X-ray diffraction profile and high-angle annular dark-field images give evidence of self-assembled arrays with nanoparticle size of 4 nm. Magnetization versus temperature in the temperature range 2.5–160 K was measured in zero-field-cooled and field-cooled experiments and a blocking temperature Tb=20 K was obtained. Above Tb the nanoparticles show superparamagnetic behavior and the magnetization versus field for various temperature follows the Langevin function. M-H curves below Tb indicate the ferromagnetic behavior with Hc=60–400 Oe for temperature T=2.5–18.5 K.
Magnetic entropy in Ni2MnGa single crystals
Authors: Pasquale Massimo , Sasso Carlo Paolo , Lewis L. H.
Published: May 2004

A first-order phase transition in mechanically soft, nonstoichiometric Ni2MnGa oriented single crystals was achieved by the application of a magnetic field lower than 1 T on a sample with a forward martensitic transformation temperature TM of 314 K. The observed change in magnetization corresponds to a temperature decrease of 1 K. The entropy variation, corresponding to this partial phase rearrangement, is of the order of −1.5 J/kg K at 1 T, and reaches a value of −18 J/kg K at 5 T.
Self-interference of charge carriers in ferromagnetic SrRuO3
Authors: Herranz G. , Sánchez F. , Martı́nez B. , Fontcuberta J. , Garcı́a-Cuenca M. V. , Ferrater C. , Varela M.
Published: May 2004

We report a systematic study of the low-temperature electrical conductivity in a series of SrRuO3 epitaxial thin films. At relatively high temperature the films display the conventional metallic behavior. However, a well-defined resistivity minimum appears at low temperature. This temperature dependence can be well described in a weak localization scenario: the resistivity minimum arising from the competition of electronic self-interference effects and the normal metallic character. By appropriate selection of the film growth conditions, we have been able to modify the mean-free path of itinerant carriers and thus to tune the relative strength of the quantum effects. We show that data can be quantitatively described by available theoretical models.
Calorimetric studies of the A1 to L1 transformation in FePt and related ternary alloy thin films
Authors: Barmak K. , Kim J. , Berry D. C. , Wierman K. W. , Svedberg E. B. , Howard J. K.
Published: May 2004

Differential scanning calorimetry, in conjunction with x-ray and electron diffraction, is used to investigate the A1 to L10 ordering transformation in binary FePt films with compositions in the range of 47.5 to 55 at. % Fe, and in ternary alloys of FePt with Cu, Co, Ag, and Au. The lowest kinetic ordering temperatures, in the range of 355–375 °C, are found for Fe-rich binary FePt alloys, namely, Fe53Pt47 and Fe55Pt45, and for ternary FePt-Cu alloys that have the same amount of Pt as these binary alloys, namely, Fe50Cu3Pt47 and Fe50Cu5Pt45. Ternary additions of Co (28 at. %), Ag (11 at. %), and Au (7 and 12 at. %) increase the kinetic ordering temperature when compared to the equiatomic, binary FePt alloy. The activation energies of ordering lie between 1.6 and 1.9 eV, except for the Fe47Pt46Au7 alloy, for which the activation energy is 2.2 eV. The transformation enthalpies are in the range of −6.3 to −13.2 kJ/g atom. The Curie temperatures for the binary FePt alloys increase from 379 to 456 °C in the composition range 47.5 to 55 at. %. Ternary additions have a complex effect on the Curie temperature. However, the Curie temperatures of the ternary Fe-Pt-Cu alloys, with Cu additions of 1–5 at. %, were lower (370–407 °C) than the binary FePt alloys of equal Pt content. Au is seen to phase separate from FePt.
Direct observation of strain fields in epitaxial growth Fe3O4 thin films on MgO substrates
Authors: Chen Y. X. , Chen C. , Zhou W. L. , Wang Z. J. , Tang J. , Wang D. X. , Daughton J. M.
Published: May 2004

Fe 3 O 4 thin films with a thickness of about 140 nm have been deposited on MgO (001) substrates by reactive sputtering. Microstructural studies indicated that monocrystalline Fe3O4 thin films were epitaxially grown on the MgO substrates with a cubic-on-cubic orientation relationship with respect to the substrates. Strain field due to slight lattice mismatch between the films and substrates was observed. The saturation moment and the coercivity for in-plane magnetization hysteresis loop were 235 emu/cc and 500 Oe, respectively. The lower saturation moment value of the Fe3O4 thin film suggested that the strain field may play a role in the reduction of magnetization.
Effects of underlayer on one-directional anisotropy in spin-valve films without any antiferromagnetic layers
Authors: Noma Kenji , Kanai Hitoshi
Published: May 2004

The magnetoresistive (MR) characteristics of spin-valve films with no antiferromagnetic layer were investigated. The films were deposited with various underlayer materials and the one-directional anisotropy in MR curves of the film with Ta underlayer turned out very strong anisotropy compared with that of other materials. It seemed that the strong one-directional anisotropy was caused by increase of coercivity and magnetic anisotropy induced in the pinned layer by external dc magnetic field during deposition. The calculated MR curves by using a torque equation clarified a relation between the magnetic characteristics of the pinned layer and the one-directional anisotropy in measured MR curves.
Intersublattice magneto-optical transitions in diluted ferrimagnetic garnets
Authors: Dionne Gerald F. , Allen Gary A.
Published: May 2004

Investigations of the magneto-optical properties of the magnetically diluted garnet ferrite host compound {Y2.53Bi0.47}[Fe23+](Fe33+)O12 have confirmed that the electric-dipole transitions in the energy range from about 2 to 4 eV result from interaction between Fe3+ ions coupled in the magnetically opposed octahedral [a] and tetrahedral (d) sites. Through covalent coupling within the 3d-electron shells of the Fea3+-O2−-Fed3+ molecule, electric-dipole transitions A6→T4 between spin-opposed ions can satisfy the parity (ΔL=±1) and spin (ΔS=0) selection rules that fail when applied to isolated Fea3+ or Fed3+ ions. Measurements of the off-diagonal permittivity tensor element ε1 were made on separate compositions with the [a] and (d) sublattices diluted by an equal factor of 1/6 from respective substitutions of In3+ and Al3+ ions. An average decrease of 25% in the ε1 intensity was observed almost uniformly over the spectral band of interest for both diluted specimens, with no evidence of separate Fea3+ or Fed3+ transitions. To interpret the effects of dilution quantitatively, a random probability argument is combined with the molecular-field theory. The physical concepts are based on the decrease of Fea3+-O2−-Fed3+ linkages, and the attendant weakening by dilution of intersublattice superexchange. Intersublattice transitions are discussed in the context of molecular bonding and correlation superexchange.
Experimental determination of inter-sublattice exchange constants in amorphous FeGd alloys
Authors: Kita Eiji , Hata Yoshiaki , Yano Kazuo , Suzuki Hiroyuki , Kido Giyu
Published: May 2004

High-field-magnetization measurements were assessed for melt-spun amorphous Fe100−xGdx alloys. Samples with X=22 and 24 clearly revealed ferrimagnetic spin-flip transition around 100–150 kOe at 4.2 K and their magnetizations linearly increased with increasing magnetic field above the transition. This magnetization process with spin flipping is well understood with molecular field approximation assuming a simple two-sublattice ferrimagnet. Inter-sublattice exchange constants JRT were obtained directly and amplitudes were −16.5×10−16 erg for X=22 and −18.1×10−16 erg for X=24 samples. These agree with previously reported values estimated by molecular field analysis.
Magnetic properties and structure of (FeCo)3Pt thin films
Authors: Nahid M. A. I. , Suzuki Takao
Published: May 2004

The (FeCo)3Pt thin films grown on MgO(100) and Al2O3(00⋅1) substrates are found to be fcc with 〈100〉 and 〈111〉 orientations, respectively. Based on these orientations, they show fourfold and sixfold anisotropy in the in-plane. The 〈100〉 oriented film shows in-plane fourfold anisotropy of the order of 105 erg/cc. On the other hand, the film grown on Al2O3(00⋅1) exhibits large basal plane sixfold magnetic anisotropy (∼106 erg/cc) and is strongly dependent on deposition temperature.
Magnetoresistive effects in planar NiFe nanoconstrictions
Authors: Florez S. H. , Dreyer M. , Schwab K. , Sanchez C. , Gomez R. D.
Published: May 2004

This study focuses on domain wall resistance in Ni80Fe20 nanowires containing narrow constrictions down to 15 nm in width. Distinct differences in the magnetoresistance curves were found to depend on the constriction size. Wider constrictions are dominated by the overall anisotropic magnetoresistance of the structure, while constrictions narrower than ∼40 nm exhibit an additional distinct contribution from a domain wall. The effect is negative and typically varies from 1% to 5%.
Critical behavior and irreversibility in La0.5Sr0.5CoO3
Authors: Kunkel H. P. , Roshko R. M. , Viddal C. , Wei Li , Williams Gwyn , Zhou X. Z.
Published: May 2004

We present detailed measurements of the field and temperature dependence of the ac susceptibility, magnetic hysteresis isotherms, and the zero-field-cooled and field-cooled moments of La0.5Sr0.5CoO3. In particular, we present a detailed, quantitative analysis of both the critical behavior in the vicinity of the ferromagnetic ordering temperature TC and the technical/regular magnetic response below TC, with particular emphasis on trying to establish features which are not present in conventional ferromagnets, that is, ferromagnets which do not exhibit spontaneous electronic phase separation. No such features could be identified through the analysis of these macroscopic quantities.
New statistical method for characterization of structured recording media magnetization processes
Authors: Tanasa Radu , Enachescu Cristian , Stancu and Alexandru , Linares Jorge , Varret François
Published: May 2004

In this paper one presents a method for statistical characterization of the magnetization processes in two-dimensional networks of single-domain ferromagnetic particles. These systems are similar with the structured materials that are seen as future high-density recording media. The method allows very interesting developments in the characterization of the stability of the magnetic states which is an important factor for a recording medium.
Spin transfer effect in spin-valve pillars for current-perpendicular-to-plane magnetoresistive heads (invited)
Authors: Lee K. J. , Liu Y. , Deac A. , Li M. , Chang J. W. , Liao S. , Ju K. , Redon O. , Nozières J. P. , Dieny B.
Published: May 2004

Large spin-transfer effects were observed in spin-valve pillars developed for current-perpendicular-to-plane (CPP) magnetoresistive heads. The investigated samples are complex stacks including laminated free, synthetic/laminated pinned, and nano-oxide layers. The magnetoresistive (MR) transfer curves exhibit current-dependent loop shift and in some particular ranges of current and field, very large noise associated either to stochastic jump of the free layer magnetization or to excitations of steady precessional modes. A very unusual phenomenon of inverted coercivity was observed in the low current range. The spin-transfer effects show an asymmetry as a function of current direction. These experimental results indicate that the spin-transfer effects must be considered in the design of CPP MR heads.
Structure and spin dynamics of annealed buried ultra-thin Fe layers on GaAs(001)
Authors: Shaw Justin M. , Park Sungkyun , Falco Charles M.
Published: May 2004

We used Brillouin light scattering (BLS) to study spin dynamics in annealed ultra-thin (0.4–2.0 nm) Fe layers buried by 6.0–8.0 nm of Al. All samples reported here were grown by molecular beam epitaxy on GaAs(001). We correlated our BLS results with film structure obtained from reflection high energy electron diffraction low angle x-ray reflectometry, and in situ scanning tunneling microscopy. Our results find that annealing of room temperature deposited Fe layers to 300 °C has a significant effect on both the magnetic properties and surface structure of the Fe.
Are half-metallic ferromagnets half metals? (invited)
Authors: Dowben P. A. , Skomski R.
Published: May 2004

Several classes of materials are currently under investigation as potential high-spin-polarization materials. Unfortunately, the proposed half-metallic materials, including the semi-Heusler alloys, the manganese perovskites, and the “simpler” oxides such as chromium dioxide and magnetite, suffer from fundamental limitations. First, the postulated half-metallic systems lose their full (T=0) spin polarization at finite temperatures and, second, surfaces, interfaces, and structural inhomogenities destroy the complete spin polarization of half-metallic systems even at zero temperature. In a strict sense, half-metallic ferromagnetism is limited to zero temperature since magnon and phonon effects lead to reductions in polarization at finite temperatures.
A study of magnetic interactions of Ni80Fe20 arrays using ultrasensitive microcantilever torque magnetometry
Authors: Gao L. , Feng D. Q. , Yuan L. , Yokota T. , Sabirianov R. , Liou S. H. , Chabot M. D. , Porpora D. , Moreland J.
Published: May 2004

We have successfully fabricated single and paired 300 nm×1.5 μm×32 nm Ni80Fe20 bars on a microcantilever using focused ion beam milling. Magnetic interactions of the paired bars were studied by using magnetic force microscopy, microcantilever torque magnetometry, and micromagnetic simulation. Our results clearly indicate that the magnetic switching behavior of the paired Ni80Fe20 bars is affected by magnetostatic interactions. The magnetic hysteresis curves for a sample with eight pairs of Ni80Fe20 bars consist of a series of stable switching states that are related to the domain wall motion in the bars.
Magnetic and structural properties of EuS for magnetic tunnel junction barriers
Authors: Smits C. J. P. , Filip A. T. , Kohlhepp J. T. , Swagten H. J. M. , Koopmans B. , de Jonge W. J. M.
Published: May 2004

In view of potential applications as a spin filter in spintronic devices, we systematically studied the growth by sputtering of ferromagnetic EuS barriers. The relationship between growth and magnetic and transport properties, also in combination with magnetic and nonmagnetic materials, was investigated. We demonstrate that growth at lower substrate temperatures (200 °C), followed by an anneal step at elevated temperatures (430 °C), leads to improved magnetic and transport properties of the barrier layer. We tentatively attribute the observed low-temperature magnetoresistance of high-resistive Al/PbS/EuS/PbS/Gd devices to spin filtering.
Dynamic magnetic properties of epitaxial MnAs thin films studied by spin-wave Brillouin scattering
Authors: Murayama A. , Hyomi K. , Sakuma M. , Oka Y. , Okabayashi J. , Mizuguchi M. , Kuramochi H. , Akinaga H.
Published: May 2004

Dynamic magnetic properties of epitaxial MnAs thin films are studied by means of Brillouin light scattering (BLS). The sharp spectral peaks of the inelastic BLS are observed in room temperature, which are attributed to surface spin waves indicating the long-wavelength collective behavior of ferromagnetic spins. The field dependence of the surface spin-wave frequency is strongly affected by an in-plane angle between the crystal axis and the external field direction in a GaAs(100)/MnAs(-1100) film, which originates from uniaxial magnetic anisotropy parallel to the MnAs[11-20] axis and the modified g value. Significant damping of the spin-wave BLS spectrum is observed with increasing excitation laser power, possibly due to thermal effects.
Study of magnetic properties of A2B′NbO6 (A=Ba,Sr,BaSr; and B′=Fe and Mn) double perovskites
Authors: Rama N. , Philipp J. B. , Opel M. , Chandrasekaran K. , Sankaranarayanan V. , Gross R. , Rao M. S. Ramachandra
Published: May 2004

We have studied the magnetic properties of Ba2FeNbO6 and Ba2MnNbO6. It is seen that Ba2FeNbO6 is an antiferromagnet with a weak ferromagnetic behavior at 5 K while Ba2MnNbO6 shows two magnetic transitions, one at 45 K and the other at 12 K. Electron spin resonance measurements at room temperature show that the Mn compound does not show any Jahn-Teller distortion. It is also seen that the Neel temperatures of the A2FeNbO6 (A=Ba,Sr,BaSr) compounds do not vary significantly. However variations in the average A-site ionic radius influence the formation of short range correlations that persist above TN.
Theoretical study on magnetic structures of electron-doped La1−xCexCoO3 compounds
Authors: Zhang Qinfang , Huang Xiaoyun , Zhang Weiyi , Hu An
Published: May 2004

The unrestricted Hartree-Fock approximation on a realistic multiband lattice model has been applied to study the various spin states of electron-doped La1−xCexCoO3 compounds. In the doping range 0.0⩽x⩽1.0, seven spin ordered states are found to be metastable and four of them are the ground states at different doping concentration. The magnetic ground state of the doped system takes a low-spin state for x<0.08, a low-spin–intermediate-spin ferromagnetically ordered state for 0.08⩽x<0.83, an intermediate-spin chain-type antiferromagnetically ordered state for 0.83⩽x<0.86, and followed by an intermediate-spin nearest neighbor antiferromagnetically ordered state for 0.86⩽x⩽1.0. The densities of states of all metastable spin states are computed and their electronic and magnetic properties are discussed.
Exchange bias effects in submicron antiferromagnetic-ferromagnetic dots prepared by nanosphere lithography
Authors: Sort J. , Glaczynska H. , Ebels U. , Dieny B. , Giersig M. , Rybczynski J.
Published: May 2004

Exchange bias effects have been observed in an array of submicron antiferromagnetic-ferromagnetic dots prepared by nanosphere lithography. The angular dependences of the exchange bias field HE, coercivity HC, and squareness ratio MR/MS of the array of dots have been measured and compared with those of a continuous film prepared under the same conditions. An HE enhancement of around 30% is observed along the field-cooling direction in the dots. The possible mechanisms responsible for this enhancement are discussed. Moreover, magnetic imaging reveals that complex magnetization reversal mechanisms occur in the nanostructures, which cause significant differences in the shape of the hysteresis loops, when compared to the exchange biased continuous films.
Magnetic properties of ultrathin Ni/Co/Pt(111) films
Authors: Su C. W. , Shern C. S. , Yao Y. D.
Published: May 2004

Magnetic properties of one monolayer (ML) Ni/1 ML Co/Pt(111) film upon thermal annealing were investigated. Increases in polar Kerr rotation correspond to the topmost Ni layer incorporated with the second Co layer on Pt, and the further alloying of Co-Pt during the annealing. Interestingly, Curie temperature shifted dramatically to 325 K when the film was annealed at 830 K. The alloy formation of Ni-Pt and top-layer enrichment of Pt may be the main reason causing the great shift of Curie temperature.
Magnetic properties of (Ga,Mn)As digital ferromagnetic heterostructures
Authors: Diwekar M. , Borchers J. A. , O’Donovan K. V. , Johnston-Halperin E. , Awschalom D. D. , Shi J.
Published: May 2004

Magnetic properties of (Ga,Mn)As digital ferromagnetic heterostructures have been investigated by polarized neutron reflectometry and magnetometry. Tc of three samples with 20, 50, and 100 ML GaAs spacers ranges from 30 to 40 K. The saturation magnetization of three samples exhibits a pronounced tail extending over 50 K above Tc in addition to a temperature-independent background. For the 50 ML sample, PNR measurements show a similar tail but no background. These behaviors can be explained by a two-step ordering process. In the tail region, two-dimensional islands first individually become ferromagnetic. Long-range order develops as the temperature is decreased below Tc.
Magnetic phase and transport property of Pr1−xCaxMnO3 thin films
Authors: Sakai Joe , Yamamoto Yoshiyuki , Hori Hidenobu , Imai Syozo
Published: May 2004

Pr 1−x Ca x MnO 3  ( PCMO ,x=0.3)/ YBa 2 Cu 3 O 7−z  ( YBCO ) bilayers were fabricated on (100)LaAlO3 single-crystal substrates, and some changes in magnetic properties between high- and low-resistance (HR/LR) states were observed. The samples showing a larger magnetization at 300 K are the ones which could be more easily switched between those two states. According to M-H measurements by superconducting quantum interference device, the HR state showed a slightly larger magnetization. Electron spin resonance measurements exhibited two absorption peaks whose intensity ratio was reversed when the HR/LR transition occurred. Some change was suggested to occur on magnetic properties through HR/LR transition in PCMO (x=0.3)/YBCO bilayered films.
A new approach to modeling the magnetomechanical effect
Authors: Jiles D. C. , Li L.
Published: May 2004

This paper reports on results taken to validate the extension to the theory of the magnetomechanical effect reported recently. This theory is based on a “law of approach” but the underlying equations have been generalized to include linear and nonlinear terms which are analogous to those in the well-known Rayleigh law of magnetization. It is shown that the generalized theory can be applied to materials with negative magnetostriction, such as nickel, and that the stress dependent model parameters can be determined from experimental measurements. It has been found that the results show improved agreement with experimental observation compared with the more restricted previous exposition of the model.
Experimental and simulation of magnetic hysteresis loops of [Co3(pyz)(HPO4)2F2]
Authors: Lee S. F. , Chang C. R. , Yang J. S. , Lii K. H. , Lee M. D. , Yao Y. D.
Published: May 2004

Pure phase of [Co3(pyz)(HPO4)2F2] crystal powder was successfully synthesized. The structure consisted of neutral sheets of [Co3(HPO4)2F2], which were pillared through pyrazine ligand to form three-dimensional frameworks. Below 20 K, the magnetic hysteresis loops showed a ferromagnetic part superimposed with an antiferromagnetic (AF) part. With increasing field magnitude, the AF part showed sharp steps at 5 kOe. Micromagnetic simulation, taking into account the Co ions as AF coupled sublattices and as suggested by the negative Weiss temperature extrapolated by the inverse susceptibility versus temperature behavior, explained the hysteresis loops the temperature dependence qualitatively.
Thermal dependence of magnetic springs location in a DyFe2/YFe2 superlattice
Authors: Dumesnil K. , Dufour C. , Mangin Ph. , Wilhelm F. , Rogalev A.
Published: May 2004

Element selective x-ray magnetic circular dichroism measurements have been performed to unravel the complex magnetization reversal process occurring in antiferromagnetically exchange-coupled Laves phase superlattices. The separate investigation of each magnetic compound in a [DyFe2 (50 Å)/YFe2 (200 Å)] superlattice has enlightened a drastic thermal variation towards an unexpected high-temperature regime, where the magnetization in the hard layers first reverses in positive field, whereas the magnetization in the soft ones remains stuck along the field direction. This transfer of the interface magnetic twists towards the hard layers permits us to explain the thermal evolution of the coercive field.
Intermartensitic transformation in a NiMnGa alloy
Authors: Dai Liyang , Cullen James , Wuttig Manfred
Published: May 2004

The temperature dependencies of the elastic constants of martensitic Ni0.50Mn0.284Ga0.216 were studied in the temperature range from 428 K down to 200 K. Measurements were conducted using the ultrasonic continuous-wave method in a 0.8 T magnetic field. At 220 K abrupt changes were found in the temperature dependences of the velocities of all 11 elastic wave modes, which indicates a structural phase change from the tetragonal (5M) martensite to a second, probably tetragonal, phase (nonlayered) at lower temperature.
7
Li
nuclear magnetic resonance in the hexairon(III) antiferromagnetic molecular ring Fe6:Li
Authors: Lascialfari A. , Borsa F. , Corti M. , Micotti E. , Furukawa Y. , Cornia A. , Gatteschi D.
Published: May 2004

The molecular nanomagnet [LiFe6(OCH3)12(dbm)6]B(C6H5)4⋅5CH2Cl2 (Fe6:Li in short) is formed by six Fe(III) s=5/2 spins arranged in an almost coplanar ring with antiferromagnetic (AFM) nearest-neighbor coupling constant J/kB∼20 K. We report 7Li nuclear magnetic resonance (NMR) spectra and nuclear spin-lattice relaxation rate (NSLR) measurements as a function of temperature from 1.5 to 50 K with applied field H=1.5 T. No evidence of quadrupole effects was found on the 7Li NMR spectrum within the linewidth resolution (∼25 kHz) ruling against a molecular distortion. The 7Li NSLR is compared with the 1H NSLR results in Fe6:Li and in other AFM rings.
Magnetic relaxation of a perturbed equilibrium spin glass state
Authors: Hérisson Didier , Östh Michael , Nordblad Per
Published: May 2004

Magnetic relaxation experiments on a Ag(Mn) spin glass that has been subjected to temperature perturbations are reported. A dynamic quasiequilibrium state is created by allowing the spin glass to equilibrate for an extended time (100 000 s) at constant temperature in the spin glass phase. The “quasiequilibrium” (reached after 100 000 s) state is perturbed by a negative temperature cycle of different duration. The magnetic relaxation rate after the perturbation exhibits an enhanced relaxation rate at short observation times followed by a dip that extends well below the equilibrium relaxation rate at longer observation times.
Half-metallic ferromagnetism in hypothetical semi-Heusler alloys NiVM (M=P, As, Sb, S, Se, and Te)
Authors: Zhang Ming , Liu Zhu-Hong , Hu Hai-Ning , Liu Guo-Dong , Cui Yu-Ting , Wu Guang-Heng , Brück Ekkes , de Boer Frank R. , Li Yang-Xian
Published: May 2004

A theoretical study based on first-principle band-structure calculations is carried out for the hypothetical semi-Heusler alloys NiVM (M=P, As, Sb, S, Se, and Te). For all compounds it is found that the ferromagnetic state is more favorable than the paramagnetic state. NiVAs is predicted to be a half-metallic ferromagnet with a small half-metallic gap of 0.07 eV and an integer magnetic moment of 2 μB, and NiVP and NiVSb are so-called nearly half-metallic ferromagnets. Furthermore, we find a clear indication that the substitution on the sp atoms influences the hybridization between Ni and V atoms, and can even destroy the half metallicity.
Magnetic properties of carbon nanotubes grown on Fe catalyst layer by microwave plasma enhanced chemical vapor deposition
Authors: Fujiwara Yuji , Takegawa Hitoshi , Sato Hideki , Maeda Kohji , Saito Yahachi , Kobayashi Tadashi , Shiomi Shigeru
Published: May 2004

The magnetic properties of carbon nanotube films grown on an Fe catalyst layer were investigated. The easy magnetization direction of the nanotube films was perpendicular to the film plane when the growth time was more than 2 min. In these films, conical Fe catalyst particles could be found at the tips of the nanotubes. The origin of the perpendicular magnetic anisotropy of these films was considered to be due to the anisotropic shape of the conical Fe catalyst particles at the tips. A large perpendicular coercivity of about 1 kOe was obtained in a nanotube film grown for 10 min.
Effect of shape anisotropy on switching behaviors of Pac-man NiFe submicron elements
Authors: Park M. H. , Hong Y. K. , Gee S. H. , Erickson D. W. , Tanaka T. , Choi B. C.
Published: May 2004

We investigated the shape anisotropy effect on switching the behaviors of submicron permalloy Pac-man (PM) elements with a thickness of 40 nm by a magnetic force microscope. The probability to form a vortex configuration at an as-patterned state was lower in an elongated PM type-I (EPM-I) (10%) than a PM-I element (47%). The switching process in PM-I, PM-II, and EPM-I elements was governed by a vortex-driven reversal, while the magnetization of a EPM-II element switches through a single-domain reversal. It was found that a PM element involving a vortex-driven switching process shows a nonreproducible reversal.
Magnetic structure of iron inclusions in copper
Authors: Eisenbach Markus , Stocks G. Malcolm , Újfalussy Balazs
Published: May 2004

We investigate the magnetic ground states of iron inclusions embedded in fcc copper using first principles calculations. We find that even for a single iron atom inclusion the induced magnetic moments on the copper sites order noncollinearly with respect to the prescribed direction of the iron moments. Furthermore, this noncollinear ordering depends on the direction of the iron moment. We study this effect by performing both constrained and fully relaxed moment calculations.
Novel phenomena in dynamic domain configurations in mesoscopic magnetic thin film elements
Authors: Choi B. C. , Arnup G. , Belov M. , Freeman M. R.
Published: May 2004

We have investigated the highly localized magnetic dynamics of mesoscopic Ni80Fe20 thin film elements by time-resolved scanning Kerr microscopy. When a magnetic element is excited by applying a short magnetic field pulse, it is found that the magnetization evolves into a well-developed, labyrinth-shaped domain structure. The emergent domain pattern is little dependent on element shape. We also observed that large amplitude precessional oscillations of closure domain magnetization are actively involved in the switching process far from equilibrium. Pursuant to these oscillations, the magnetization reversal continues by means of the precessional motion of the magnetization vector in other localized regions.
Magnetoresistance in a room temperature ferromagnetic diluted magnetic semiconductor Zn1−xCrxTe
Authors: Saito H. , Yamagata S. , Ando K.
Published: May 2004

We observed negative magnetoresistance (MR) in a ferromagnetic diluted magnetic semiconductor Zn1−xCrxTe (x=0.20). At a temperature of 20 K, the MR ratio was −26% (Δρ=−4100 Ωcm) in a magnetic field of 10 kOe. The MR showed a clear hysteresis loop. Negative MR was observed up to about room temperature, corresponding to a Curie temperature. These behaviors indicate that the electrical properties of Zn1−xCrxTe are strongly affected by its magnetic properties through a strong carrier–spin interaction.
Phase separation and huge enhancement of magnetoresistance in Pr0.65Ca0.35−xSrxMnO3
Authors: Mollah S. , Sun C. P. , Huang H. L. , Ho P. L. , Yang H. D.
Published: May 2004

The electronic, magnetic, and thermal properties of polycrystalline Pr0.65Ca0.35−xSrxMnO3 (x=0–0.35) perovskites have been elaborately investigated. A huge enhancement of magnetoresistance (MR) (10% at H=100 Oe and 99% at H=0.5 T) has been observed in an x=0.1 sample around the metal-insulator (MI) transition temperature (TMI∼80 K) which is induced by the phase separation (PS). This study opens the possibility to search for the polycrystalline colossal magnetoresistive materials with a very high MR at low magnetic fields on the basis of PS phenomena for potential applications.
Disorder effects in (LaTb)0.5(CaSr)0.5MnO3 compounds
Authors: Rana D. S. , Mavani K. R. , Thaker C. M. , Kuberkar D. G. , Kundaliya D. C. , Malik S. K.
Published: May 2004

Electrical, magnetotransport, and magnetization measurements have been carried out on half-doped (La0.5−xTbx)(Ca0.38−ySr0.12+y)MnO3 (0.025⩽x⩽0.125; y=0.8x) compounds. The increase in Tb3+ and Sr2+ contents keeps the average A-site ionic radius constant at ∼1.215 Å but introduces increasing size disorder. The insulator-metal transition temperature (Tp) falls from 191 to 107 K and the Curie temperature (TC) falls from 230 to 106 K as x increases from 0.025 to 0.125. Interestingly, with increasing size disorder, the disparity between TC and Tp disappears and magnetoresistance increases around Tp but decreases at low temperatures. This is discussed in the light of phase segregation.
Spin-valve transistors with high magnetocurrent and 40 μA output current
Authors: Jansen R. , Gokcan H. , van ’t Erve O. M. J. , Postma F. M. , Lodder J. C.
Published: May 2004

The electrical characteristics of silicon-based spin-valve transistors are reported, focusing on how the output current and magnetocurrent depend on the magnitude of the emitter current. Transistors with a different combination of Schottky barriers (Si/Au and Si/Cu) were used. The collector current rapidly increases with emitter current, without significant loss of magnetocurrent. Spin-valve transistors with magnetocurrent around 400% and high output current up to 40 μA are obtained.
The role of erbium magnetization anisotropy during the magnetic reorientation transition in ErFeO3
Authors: Bazaliy Ya. B. , Tsymbal L. T. , Kakazei G. N. , Wigen P. E.
Published: May 2004

Magnetization of ErFeO3 single crystal was measured by a super conducting quantum interference device magnetometer with greatly improved precision. A dramatic (70%) increase of magnetization was observed in the spin-reorientation interval (88–97 K). This and the temperature dependence of the spin-rotation angle are accurately described by the modified mean field theory, which uses the key fact of the magnetic anisotropy of erbium subsystem. Calculated temperature dependence of the rotation angle shows a remarkable correspondence with the experiment with no fitting parameters. Proposed model is general and can be used to analyze orientation transitions in many orthoferrites.
Magnetic domain structure of colossal magnetoresistance thin films and islands
Authors: Olson Trevor W. , Olson Jeanine M. W. , Scholl Andreas , Suzuki Y.
Published: May 2004

We synthesized 10–200 nm thick colossal magnetoresistive La0.7Sr0.3MnO3 (LSMO) thin films under compressive strain, resulting in perpendicular anisotropy. Similar magnetic domain structures in LSMO films thicker than 40 nm were observed by magnetic force microscopy and were also seen with photoemission electron microscopy. Recent transport measurements, in conjunction with this result, suggest a dead layer at the interface, not at the surface. When varying the temperature from below the Curie temperature TC to above, the magnetic domains disappeared. These domains nucleated uniformly across the film when the temperature was subsequently lowered, but their positions were unrelated to the initial domains or to surface defects.
Dependence of anisotropy and damping on shape and aspect ratio in micron sized Ni81Fe19 elements
Authors: Barman A. , Kruglyak V. V. , Hicken R. J. , Scott J. , Kundrotaite A. , Rahman M.
Published: May 2004

We have studied magnetic anisotropy and damping in Ni81Fe19 elements of different shape and aspect ratio by time-resolved scanning Kerr effect microscopy and micromagnetic simulations. Square elements show a fourfold anisotropy that becomes weaker with increasing aspect ratio. Square elements with aspect ratio <230 show an anisotropy of the apparent damping that becomes stronger with decreasing aspect ratio. Variations in the apparent damping may be understood in terms of dephasing of spin wave modes that leads to the appearance of fringes in time-resolved magnetic images.
Paramagnetic properties of covalently linked mixed valence chromium complexes in polymers
Authors: Rakhimov R. R. , Hwang J. S. , Prokof’ev A. I. , Alexandrov I. A. , Zelenetskii A. N. , Aleksandrov A. I.
Published: May 2004

Chromium complexes, where ortho-quinone ligands are covalently linked to polymeric chains of polyethylene, polystyrene, and copolymer of ethylene and vinylacetate are studied. The results of infrared and electron paramagnetic resonance spectroscopic studies of chromium coordination polymers show that covalent linking of quinone ligands is accompanied by the change in the valence states of chromium Cr(III)↔Cr(IV)↔Cr(V). The ligand field of the triplet Cr4+ ion is close to the one in Cr-doped Y2SiO5, a laser material in the visible and infrared regions. Therefore some useful magnetic and/or optical properties in such transition metal coordination polymers can be expected.
An ab initio investigation on the zinc-blende MnAs nanocrystallite
Authors: Qian M. C. , Fong C. Y. , Pickett W. E. , Wang Huai-Yu
Published: May 2004

Among a new class of spintronics materials, nanoscale dots of the zinc-blende (ZB) MnAs have recently been synthesized on the GaAs(001) surface. We apply an ab initio pseudopotential method with the generalized gradient approximation to study magnetic and structural stability for the Mn-centered ZB MnAs4Mn12As24 cluster, which is relaxed both atomically and electronically. The ferromagnetic cluster is shown to have characteristics of a half metal with a large magnetic moment 4μB per Mn atom. The Mn-As bond length is slightly longer than the one in the bulk, in accord with experimental observation. The “semiconducting” gap 1.83 eV is opened up in the minority channel, due to the large bonding-antibonding splitting from the p-d hybridization, similar to the ZB bulk MnAs and Ga1−xMnxAs. We also find an antiferromagnetic coupling in this system such that the moment of the central Mn atom is flipped with respect to those of the second-shell Mn atoms.
Reduction in required magnetic field to induce twin-boundary motion in ferromagnetic shape memory alloys
Authors: Gans Eric , Henry Christopher , Carman Greg P.
Published: May 2004

Tensile and compressive loading experiments were conducted at room temperature on a thin slab (1 mm) of Ni50Mn33Ga17 single crystal ferromagnetic shape memory alloy while subjected to cyclic magnetic field (up to 550 kA/m). Tensile loads ranged from 0.4 MPa to 0.8 MPa while compressive loads ranged from 0.4 MPa to 2.2 MPa, with increasing compressive loads resulting in a reduced overall strain. Results indicate that magnetic field produces significant strains (over 4%) within the material. Experimental data also show that a tensile load reduces the required magnetic field for actuation by almost 80%.
Spin-transfer-induced domain wall motion in a spin valve
Authors: Grollier J. , Boulenc P. , Cros V. , Hamzić A. , Vaurès A. , Fert A. , Faini G.
Published: May 2004

We have studied the current-induced displacement of a domain wall (DW) in the permalloy (Py) layer of a Co/Cu/Py spin-valve structure. At zero and very small applied fields (<10 Oe), the displacement is in opposite direction for opposite dc currents, and the current density required to move DW is of the order of a few 106 A/cm2. At higher applied magnetic fields, the DW motion, even though triggered by the current, has its direction controlled by the field.
Current-driven switching in magnetic multilayer nanopillars (invited)
Authors: Urazhdin S. , Birge Norman O. , Pratt W. P. , Bass J.
Published: May 2004

We summarize our recent findings on how the current-driven magnetization switching in nanofabricated magnetic multilayers is affected by an applied magnetic field, changes of temperature, magnetic coupling between the ferromagnetic layers, variations in the multilayer structure, and the relative rotation of the layers’ magnetizations. We show how these results can be interpreted with a model describing current-driven excitations as an effective current-dependent magnetic temperature.
Investigating magnetization dynamics in permalloy microstructures using time-resolved x-ray photoemission electron microscope
Authors: Kuksov A. , Schneider C. M. , Oelsner A. , Krasyuk A. , Neeb D. , Schönhense G. , De Nadaï C. , Brookes N. B.
Published: May 2004

We present results of a direct imaging approach to visualize the dynamics of magnetic domains on the nanosecond scale. The experiments are carried out by means of an x-ray photoemission electron microscope (X-PEEM) in a stroboscopic mode and exploit the intrinsic time structure of the synchrotron radiation delivered by the storage ring facility ESRF (Grenoble). In this way we combine the high lateral resolution of a PEEM with a subnanosecond time resolution.
Universal charge transport of the Mn oxides in the high temperature limit
Authors: Kobayashi W. , Terasaki I. , Mikami M. , Funahashi R. , Nomura T. , Katsufuji T.
Published: May 2004

We have found that various Mn oxides have the universal resistivity and thermopower in the high temperature limit. The resistivities and thermopowers of all the samples go toward constant values of 7±1 mΩ cm and −79±3 μV/K, which are independent of carrier density and crystal structures. We propose that the electric conduction occurs in a highly localized way in the high temperature limit, where the exchange of entropy and charge occurs in the neighboring Mn3+ and Mn4+ ions.
Current driven resistance changes in low resistance x area magnetic tunnel junctions with ultra-thin Al-Ox barriers
Authors: Deac A. , Redon O. , Sousa R. C. , Dieny B. , Nozières J. P. , Zhang Z. , Liu Y. , Freitas P. P.
Published: May 2004

Current induced resistance changes were investigated in magnetic tunnel junctions with ultrathin Al-Ox barriers. The nonuniformity of the insulator induced a strong coupling between the two magnetic electrodes and no magnetoresistance. However, the current-voltage (I–V) characteristics at low bias voltages were consistent with a tunnellike behavior. At larger bias voltages, they showed an abrupt change of slope that was reversible for an opposite voltage polarity. The resistance versus current (R–I) curves exhibited reversible resistance changes that reached over 100%. We interpret this as controlled electromigration in local nanoconstrictions of the barrier.