bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual pumping of magnetostatic and spin-wave modes in yttrium–iron–garnet spheres
Authors: Araújo W. , de Aguiar F. M. , Azevedo A. , Rezende S. M.
Published: May 2003

In ferrimagnetic materials subjected to a static magnetic field H, a parallel rf magnetic field h gives rise to nonlinear absorption due to the unstable growth of certain spin waves when exceeding a parametric instability threshold (PIT), h=hc. The excited spin waves have half the pumping frequency and a wave number k that depends on H, such that the curve hc vs H resembles the Greek symbol ν and is thus called a “butterfly curve.” Recent experiments in a yttrium–iron–garnet sphere have shown that the PIT is resonantly reduced in the presence of a simultaneous perpendicular rf field at half the parallel-pumping frequency only on the right wing of the butterfly curve, where “volume” magnetostatic modes (k∼0) are primarily excited. Here, dual pumping experiments are reported at lower frequencies (8.882 and 4.441 GHz), allowing the presence of “surface” magnetostatic modes on the left wing and corresponding resonant PIT reduction in that region, where spin waves with k∼105 cm−1 are primarily excited by the parallel-pumping field. The results qualitatively agree with a model that put no restriction on the pumping frequency, thus extending earlier calculations by White and Schlömann [R. M. White and Schlömann, J. Appl. Phys. 33, 2437 (1962)].
Magnetic dynamics of single-domain Ni nanoparticles
Authors: Goya G. F. , Fonseca F. C. , Jardim R. F. , Muccillo R. , Carreño N. L. V. , Longo E. , Leite E. R.
Published: May 2003

The dynamic magnetic properties of Ni nanoparticles diluted in an amorphous SiO2 matrix prepared from a modified sol–gel method have been studied by the frequency f dependence of the ac magnetic susceptibility χ(T). For samples with similar average radii ∼3–4 nm, an increase of the blocking temperature from TB∼20 to ∼40 K was observed for Ni concentrations of ∼1.5 and 5 wt %, respectively, assigned to the effects of dipolar interactions. Both the in-phase χ′(T) and the out-of-phase χ″(T) maxima follow the predictions of the thermally activated Néel–Arrhenius model. The effective magnetic anisotropy constant Keff inferred from χ″(T) vs f data for the 1.5 wt % Ni sample is close to the value of the magnetocrystalline anisotropy of bulk Ni, suggesting that surface effects are negligible in the present samples. In addition, the contribution from dipolar interactions to the total anisotropy energy Ea in specimens with 5 wt % Ni was found to be comparable to the intrinsic magnetocrystalline anisotropy barrier.
Magneto-optical properties of iron oxide films
Authors: Tepper T. , Ilievski F. , Ross C. A. , Zaman T. R. , Ram R. J. , Sung S. Y. , Stadler B. J. H.
Published: May 2003

Iron oxide films have been grown onto MgO and oxidized silicon substrates using pulsed laser deposition with a 248 nm excimer laser. The films were deposited in a vacuum from an α-Fe2O3 target. Films grown epitaxially on MgO consisted of the ferrimagnetic γ-Fe2O3 phase, with an average saturation magnetization of 353±26 kA/m. The Faraday rotation of the γ-Fe2O3 films was measured at 645 nm and 1550 nm wavelengths, and was found to be 4 and 2.5 degrees/μm, respectively. It is assumed that the high Faraday rotation, accompanied by a relatively high absorption, is associated with a transition of Fe2+ ions in octahedral sites.
Magnetic studies of crystal-engineered molecular nanostructures (invited)
Authors: Srikanth H. , Hajndl R. , Moulton B. , Zaworotko and M. J.
Published: May 2003

Magnetic studies of dimeric copper complexes reveal interesting and predictable cooperative responses governed by the underlying topological lattice configurations. Temperature dependent susceptibility in several compounds measured with a physical property measurement system indicates predominantly antiferromagnetic exchange coupling. Both intra- and interdimer interactions are found to be important and the data could be fit well with a modified Bleaney–Bowers model from which these interaction parameters are extracted. Crystal engineering methods have been used to generate open and closed framework molecular nanostructures. A Kagome lattice configuration with the Cu(II) dimers arranged using triangular symmetry yields distinct hysteresis loops that are consistent with the occurrence of weak ferromagnetism.
Dynamical Ising-like model for the two-step spin-crossover systems
Authors: Boukheddaden K. , Linares J. , Codjovi E. , Varret F. , Niel V. , Real J. A.
Published: May 2003

In order to reproduce the two-step relaxation observed experimentally in spin-crossover systems, we investigate analytically the static and the dynamic properties of a two-sublattice Ising-like Hamiltonian. The formalism is based on a stochastic master equation approach. It is solved in the mean-field approximation, and yields two coupled differential equations that correspond to the HS fractions of the sublattices A and B.
Fabrication and characterization of ordered FePt nanoparticles
Authors: Huang Y. H. , Zhang Y. , Hadjipanayis G. C. , Weller D.
Published: May 2003

Ordered FePt nanoparticles with unique magnetic properties were obtained by direct deposition of FePt and C onto heated substrates at temperature above 450 °C. The FePt particle sizes were controlled in the range from a few nanometers to 20 nm by adjusting the sputtering time from both the FePt and C targets. The tiny FePt nanoparticles (less than 3 nm) showed superparamagnetic behavior at room temperature. However, larger particles showed huge coercivities at room temperature (23 and 34 kOe for particles with average sizes of around 8 and 15 nm, respectively). For a certain FePt to C ratio, the films can show strong perpendicular anisotropy which is favorable for high density recording media.
Studies of switching field and thermal energy barrier distributions in a FePt nanoparticle system
Authors: Wu X. W. , Zhou H. , van de Veerdonk R. J. M. , Klemmer T. J. , Liu C. , Shukla N. , Weller D. , Tanase M. , Laughlin D. E.
Published: May 2003

Dynamic remanent hysteresis loops were measured at several time scales for a L10 ordered Fe45Pt55 nanoparticle array sample. At a fixed percentage of magnetization switched, Sharrock’s formula was applied to obtain both the thermal stability factor and the intrinsic switching field. From the magnetization dependence of the thermal stability factor, the width of the thermal energy barrier distribution was determined to be about 0.30. In comparison with the particle volume distribution width obtained from transmission electron microscopy, the energy barrier width is reduced significantly due to strong interparticle exchange interaction. The magnetization dependence of the intrinsic switching field was used to obtain the intrinsic, i.e., short time, remanent magnetization curves. The intrinsic switching field distribution width was found to be 0.34.
Magnetoelastic hysteresis of amorphous ribbons
Authors: Kraus L. , Švec P.
Published: May 2003

The influence of tensile stress on hysteresis loops and the magnetomechanical effect in high-magnetostrictive Fe-rich and low-magnetostrictive Co-rich amorphous ribbons were investigated. In the as-quenched Fe-rich alloy a very complex behavior is observed, which indicates the interplay of different types of magnetization processes. Uniaxial magnetic anisotropies, induced by stress annealing, eliminate the rotational processes in Fe-rich materials and the domain-wall motion in Co-rich materials. Thus, the role of the two different mechanisms in the magnetoelastic hysteresis can be studied separately. It is shown that irreversible domain-wall movements are responsible for the large hysteresis in the Fe-rich alloy, while the purely rotational magnetization process can account for the essentially anhysteretic behavior of the Co-rich alloy. The theoretical model by Livingston [J. D. Livingston, Phys. Status Solidi 70, 591 (1982)] can well explain the anhysteretic behavior.
Magnetic antidot arrays from self-assembly template methods
Authors: Zhukov A. A. , Goncharov A. V. , de Groot P. A. J. , Bartlett P. N. , Ghanem M. A.
Published: May 2003

Using self assembly from lyotropic liquid crystalline phases and from colloidal suspensions of polystyrene spheres templates, we have prepared well-ordered, nanostructured magnetic materials. We present the results of electrochemical deposition of magnetic metals and alloys in the interstitial space between these templates. This technique has enabled us to create magnetic nanostructures with three-dimensional achitectures on length scales of 4 nm–1 μm. We find changes in coercive field, by more than 1 order of magnitude, dominated by the effects of the nanoscale shapes. Varying the parameters in the preparation allows us to produce materials with predetermined magnetic parameters. The templated electrodeposition technique offers the potential of a low-cost preparation method for submicron patterned magnetic media.
Self-assembly of FePt nanoparticles into nanorings
Authors: Zhou Weilie L. , He Jibao , Fang Jiye , Huynh Tuyet-Anh , Kennedy Trevor J. , Stokes Kevin L. , O’Connor Charles J.
Published: May 2003

The application of nanoparticles as quantum dots in nanoelectronics demands their arrangement in ordered arrays. Shape controlled self-assembly is a challenge due to the difficulties of obtaining proper self-assembling parameters, such as solvent concentration, organic ligands, and nanoparticle size. In this article, hard magnetic FePt nanoparticles were synthesized using a combination approach of reduction and thermal decomposition. The nanoparticles are about 4.5 nm and appeared as truncated octahedral enclosed by the {100} and {111} crystal facets of fcc structure. The nanoparticles are of hexagonal close packing and orient randomly in the self-assembly nanoarrays. By diluting the solution for large-area self-assembly, monolayer, submonolayer, and multilayer nanorings of FePt nanoparticles were formed. The nanoring formation is determined by hydrodynamics, surface effects, and interaction between the FePt nanoparticles and substrates.
Anomalously large damping in magnetization reversal
Authors: Wang Xiaobin , Bertram H. Neal
Published: May 2003

Anomalously large damping has been obtained for magnetic reversal based upon a model that adds damping and thermal fluctuations to normal modes around equilibrium. This accelerated reversal behavior is due to a large damping rate associated with damped nonlinear oscillation motion away from equilibrium. We suggest that this result may shed light on understanding the large damping rates observed in some magnetic reversal experiments.
Magnetoresistance and magnetization reversal process of Co nanowires covered with Pt
Authors: Hausmanns B. , Krome T. P. , Dumpich G.
Published: May 2003

The magnetoresistance (MR) of single Co nanowires of various width is investigated at low temperatures in magnetic fields up to 5 T. The in-plane longitudinal MR shows pronounced features at coercive fields indicating the magnetization reversal process. The nanowires are prepared by electron beam lithography. Some of the wires are covered with a 2 nm thick Pt layer, the others are uncovered. The MR behavior of the Pt covered Co nanowires shows significantly different behavior from that of the uncovered nanowires. This is interpreted mainly as arising from an oxidation of the Co surface leading to a formation of an antiferromagnetic CoO layer on top of the uncovered Co nanowires. The CoO layer hinders the magnetization reversal process by domain wall pinning, which is reflected by the MR behavior of these samples. In contrast, the MR behavior of the Pt covered Co nanowires shows no pinning effects. Thus, we conclude that covering the Co nanowires in situ with a 2 nm thick Pt layer prevents oxidation effects.
Simultaneous detection of perpendicular and in-plane magnetization component in a [Co/Pd]n perpendicular magnetic recording media
Authors: Das Sarbanoo , Yoshikawa Hironori , Nakagawa Shigeki
Published: May 2003

Hall effect measurement has been used to detect the perpendicular and in-plane magnetization components simultaneously in a [Co/Pd]n multilayer thin film with strong magnetic anisotropy along the direction perpendicular to the film plane. The angle between the driving current direction and the in-plane projection of the applied magnetic field was varied to investigate the contribution of in-plane magnetization component to the measured Hall voltage. Hall voltage under the canted magnetic field revealed that the output is the superposition of the anomalous Hall effect (AHE) due to the perpendicular component of magnetization and the planar Hall effect (PHE) due to the in-plane magnetization component. Odd symmetry characteristics of AHE and even symmetry characteristics of PHE with respect to applied field have been applied to extract the Hall voltage contributed by the two different magnetization components from their combined characteristic. Anomalous Hall voltage from the perpendicular magnetization component exhibited an irreversible hysteresis loop while that from the in-plane magnetization component was found almost reversible with respect to applied magnetic field. The method was effective to evaluate the in-plane component of magnetization in an ultrathin film under the canted magnetic field.
Hard mask fabrication for magnetic random access memory elements using focused ion beam assisted selective chemical vapor deposition
Authors: Kubota H. , Hamada M. , Ando Y. , Miyazaki T.
Published: May 2003

The fabrication of carbon masks for very small magnetic tunnel junctions (MTJs) was investigated using focused ion beam assisted selective chemical vapor deposition. Gaseous phenanthrene, absorbed on the sample surface, was decomposed into solid carbon by irradiation with a Ga ion beam. The carbon layer deposited showed a lower (higher) etching rate for Ar (O2) ion etching. The width of the carbon mask patterns varied from about 30 to 500 nm. Arrays of MTJs with size on the 100 nm scale were fabricated successfully using the carbon mask patterns.
Magnetization processes and magnetostriction of Tb0.27Dy0.73Fe2 single crystal along 〈110〉 direction
Authors: Wang B. W. , Busbridge S. C. , Guo Z. J. , Zhang Z. D.
Published: May 2003

The magnetostriction and magnetization process of a twin-free Tb0.27Dy0.73Fe2 single crystal along the 〈110〉 direction has been studied by strain gauge, vibrating sample magnetometer, and domain observation techniques. It was observed that the magnetostriction of the sample remained unchanged with increasing magnetic fields when H<1 kOe and quickly increased in the range 1<H<7.5 kOe. No “jump” effect was observed during the magnetization process and the magnetostrictive hysteresis was large when H<2.5 kOe. Observations by the Bitter colloid technique at room temperature revealed curved domain walls which became straight at higher and lower temperatures in {100} and {111}, respectively, indicating the transition to different 180° walls for H<1 kOe. The domain patterns were clearest on a {100} surface. Above the spin reorientation temperature, 109° and 71° wall motions dominated the magnetization process in the range 1.5 kOe<H<4 kOe, but below it, clear 90° wall motions were observed. Little change in the magnetized domain pattern was observed at different temperatures suggesting that many domain walls occupy the same planes. Similar room temperature patterns were observed at remanence with an applied stress along 〈111〉 in excess of 5 MPa. These results are consistent with theoretical magnetomechanical behavior based on a 〈1uu〉, 0<u<1, transition in easy direction.
Texture and grain morphology dependencies of saturation magnetostriction in rolled polycrystalline Fe83Ga17
Authors: Kellogg R. A. , Flatau A. B. , Clark A. E. , Wun-Fogle M. , Lograsso T. A.
Published: May 2003

Textured polycrystalline Fe-Ga alloys exhibit magnetostrictive strains of 100 ppm or greater and may function as a mechanically robust actuator/sensing material. Current efforts seek to combine the 300+ ppm magnetostrictive strain performance of [100] oriented single crystals with the mechanical properties of polycrystalline forms. One approach to combining these properties is to control the crystallographic texture through deformation processing such as rolling. To determine the relationship between saturation magnetostriction, degree of texturing, and grain morphology we compare the results of three-dimensional finite element simulations with the analytical solution for a random polycrystal and the experimental responses of rolled polycrystalline Fe83Ga17. Textured specimens were produced through rolling reductions up to 99% of an as-cast ingot and a subsequent 1100 or 590 °C anneal. The high temperature anneal produced a recrystallized grain structure having a wide variation in crystal orientation as determined by orientation imaging microscopy. This recrystallized specimen exhibited a net magnetostriction of ∼170 ppm in the rolling direction and was well correlated with the finite element model result. The low temperature annealed specimen possessed fine elongated grains having dispersed {001}〈110〉 and {111}〈211〉 textures. Net magnetostrictions of 30 and 37 ppm were measured in the rolling direction and 45° off the rolling direction, respectively. The low magnetostriction value in the 45° direction disagrees substantially with the finite element solution of 157 ppm and suggests that unknown factors are dominating the response.
Magnetic force microscopy study on amorphous TbFe thin films
Authors: Sun Zhi-gang , Zhu Tao , Zhang Zhen-rong , Shen Bao-gen , Han Bao-shan , Shih Jhy-Chau , Chin Tsung-Shune
Published: May 2003

By using magnetic force microscope (MFM), honeycomb domain structures were found in the as-deposited amorphous TbFe thin films with perpendicular magnetic anisotropy. The domain structures were composed of many small white round dots embedded in the black matrix, which formed an irregular hexagonal pattern with some deformation. MFM measurements were performed with various scanning heights and opposite tip magnetization directions. The z component of both the magnetization and the stray field of the dots were determined quantitatively within the point probe approximation. Charge contrast and susceptibility contrast were separated by forming the difference and sum of two images with opposite tip magnetization.
In situ applied field imaging of a magnetic tunnel junction using magnetic force microscopy
Authors: Leib J. , Lo C. C. H. , Snyder J. E. , Jiles D. C.
Published: May 2003

Knowledge of domain behavior in magnetic tunnel junctions is an essential component, together with knowledge of the electron band structure, for understanding their magnetoelectronic properties. To this purpose, the magnetization reversal processes of a multilayer tunnel junction of structure substrate/NiFe/AlOx/FeCo/CrPtMn/Al of tapered half-ellipsoid shape have been imaged using a magnetic force microscope (MFM) with in situ applied magnetic fields. Stripe domains through both the stack and free layers observed at zero applied field were erased by a ∼100 Oe field applied to the left followed by applying a small field to the right. Magnetic domain structure did not reappear in the MFM images until a field of ∼400 Oe was applied to the right. This domain pattern then persisted when the magnetic field was reduced to zero. A drastic difference in domain patterns throughout the rotational processes to saturation in each direction was also observed. When the field was applied to the left, domain walls rotated toward the direction perpendicular to the applied field before disappearing. However, in near-saturation fields to the right, domain walls formed nearly parallel to the applied field and rotated away from parallel as the applied field strength was decreased. From these images, therefore, significant insight has been gained into the magnetization processes and physical phenomena behind the magnetoresistive behavior of these junctions.
Extraordinary magnetoelasticity and lattice softening in bcc Fe-Ga alloys
Authors: Clark A. E. , Hathaway K. B. , Wun-Fogle M. , Restorff J. B. , Lograsso T. A. , Keppens V. M. , Petculescu G. , Taylor R. A.
Published: May 2003

Extraordinary magnetostrictive behavior has been observed in Fe-Ga alloys with concentrations of Ga between 4% and 27%. λ100 exhibits two peaks as a function of Ga content. At room temperature, λ100 reaches a maximum of 265 ppm near 19% Ga and 235 ppm near 27% Ga. For compositions between 19% and 27%, λ100 drops sharply to a minimum near 24% Ga and exhibits an anomalous temperature dependence, decreasing by as much as a factor of 2 at low temperatures. This unusual magnetostrictive behavior is interpreted on the basis of a single maximum in the magnetoelastic coupling |b1| of Fe with increasing amounts of nonmagnetic Ga, combined with a strongly temperature dependent elastic shear modulus (c11−c12) which approaches zero near 27% Ga. λ111 is significantly smaller in magnitude than λ100 over this composition range, and has an abrupt change in sign from negative for low Ga concentrations to positive for a concentration of Ga near 21%.
Analysis of mechanical and magnetic instabilities in Ni-Mn-Ga single crystals
Authors: Pasquale Massimo , Sasso Carlo Paolo , Bertotti Giorgio , L’vov Victor , Chernenko Volodymyr , De Simone Antonio
Published: May 2003

In this paper experimental stress-strain and magnetization versus field curves measured for Ni2MnGa alloys are compared with modeling results obtained using a statistical model. The model is based on the assumption of equivalence between the magnetic field and mechanical stress through magnetoelastic interactions. The approach is extended to describe the complex irreversible behavior of strain and magnetization using a statistical distribution of the energy barriers that separate the metastable states of the martensite twins. A theoretical value of the energy conversion coefficient cme=1.57×10−4 MPa (kA/m)−2 is found, which is in good agreement with the experimentally determined value of 1.25×10−4 MPa (kA/m)−2.
Magnetic field-induced strain in iron-based ferromagnetic shape memory alloys
Authors: Sakamoto Tatsuaki , Fukuda Takashi , Kakeshita Tomoyuki , Takeuchi Tetsuya , Kishio Kohji
Published: May 2003

Magnetic field-induced strain (MFIS) along the [001]P (the symbol “P” represents parent phase) direction due to the conversion of martensite variants has been investigated for a disordered Fe–31.2Pd(at. %) single crystal and an ordered Fe3Pt single crystal exhibiting martensitic transformations from cubic phases to tetragonal phases at 85 and 230 K, respectively. The tetragonality c/a of Fe–31.2Pd at 77 K is 0.940 and that of Fe3Pt at 14 K is 0.945. When magnetic field is applied to the martensite phase along the [001]P direction, the specimen expands along the field direction for Fe–31.2Pd and contracts for Fe3Pt, suggesting that the c axis is the hard axis of magnetizaion for Fe–31.2Pd and is the easy axis for Fe3Pt. The conversion of variants by magnetic field is almost perfect for Fe–31.2Pd and is not perfect for Fe3Pt. The recoverable strain in the field removing process is small for Fe–31.2Pd and is about 0.6% for Fe3Pt. In the cooling process under magnetic field of 3.2 MA/m, the fraction of preferable variants reaches 100% in a narrow temperature range for Fe–31.2Pd, but it does not reach 100% for Fe3Pt (the maximum fraction is about 80%), although the fraction increases with decreasing temperature.
Investigation of the crystallographic texture and interface roughness on CoCrPt /Ti magnetic thin films
Authors: Sun C. J. , Chow G. M. , Wang J. P. , Soo E. W. , Je J. H.
Published: May 2003

The structure and interface of Co74Cr16Pt10 (40 nm thick)/Ti (10 nm thick) films for perpendicular magnetic recording were studied using x-ray scattering and transmission electron microscopy. Improved out-of-plane coercivity and squareness resulted from the combined effects of higher crystallinity and better texture of the CoCrPt (002) film, and increased interface roughness. The relationship of sputtering pressure to the structural effects is discussed.
Growth and magnetic properties of epitaxial ultrathin Ni films on Cu(111) using Sb as a surfactant
Authors: Matthes F. , Rzhevskii A. , Tong L.-N. , Venus D. , Schneider C. M.
Published: May 2003

We studied the growth and magnetism of ultrathin Ni films on the (111) surface of Cu using Sb as a surfactant. For this purpose we deposited Sb under UHV conditions at room temperature onto the Cu surface prior to the Ni film growth. When the Sb precoverage exceeded a certain threshold [0.7 monolayers (ML)], pronounced intensity oscillations of the medium energy electron diffraction signal indicated a layer-by-layer growth of the deposited Ni films. Low energy electron diffraction patterns of the Ni films revealed a hexagonal structure with a threefold symmetry. Using this approach we prepared high quality epitaxial Ni(111) films up to a thickness of 20 ML and performed in situ magneto-optical Kerr measurements. At a thickness of 7–8 ML an inverse spin reorientation transition occurs from an in-plane magnetization at lower thicknesses to an out-of-plane orientation for higher thicknesses.
Antidot density-dependent reversal dynamics in ultrathin epitaxial Fe/GaAs(001)
Authors: Moore T. A. , Wastlbauer G. , Bland J. A. C. , Cambril E. , Natali M. , Decanini D. , Chen Y.
Published: May 2003

Easy axis dynamic magneto-optic Kerr effect loops have been obtained from ultrathin (20 Å) epitaxial Fe/GaAs(001) patterned with antidot arrays of different densities (antidot spacings s=10 and 50 μm). The external field was driven sinusoidally in time with frequency in the range 0.01 Hz–2.3 kHz. In the low-frequency regime (f<20 Hz) coercivity Hc increases with 1/s, in agreement with existing phenomenological laws of geometric coercivity scaling in quasistatic fields, e.g., Hc=ζt/x, where t is the film thickness, x is a length parameter of the magnetic structure, and ζ is a constant of proportionality. However, in the transitional region between the low- and high-frequency regimes (20 Hz<f<1000 Hz), we find that scaling parameter ζ is no longer constant and increases with frequency: at low antidot density (s=50 μm) the coercivity in the transitional region falls to a minimum, while at high antidot density (s=10μm) it remains almost a constant. The dip in coercivity for s=50 μm is attributed to a resonance of the sweeping applied field with the domain-wall propagation in the film. Meanwhile, the suppression of the dip for s=10 μm is ascribed to a change in the relative importance of wall propagation and domain nucleation mechanisms in dynamic magnetization reversal.
Demonstration and characterization of 130 Gb/in2 magnetic recording systems
Authors: Stoev K. , Liu F. , Chen Y. , Dang X. , Luo P. , Chen J. , Wang J. , Kung K. , Lederman M. , Re M. , Choe G. , Zhou J. N. , Yu M.
Published: May 2003

We have successfully demonstrated longitudinal recording at areal density of 130 Gb/in2 at a data rate as high as 170 Mbps (21 MB/s) and at a bit-aspect-ratio (BAR) of 2.9, using merged inductive-write/spin-valve-read heads on low noise thin film disks. The heads were fabricated with the standard photolithography and wafer pole trimming used in our currently available commercial products. The reader is a bottom synthetic spin valve (BSSV) with a 0.09 μm gap, and the writer has a conventionally trimmed pole with 0.09 μm gap. The reader magnetic read width (MRW) was measured at 0.10 μm. At read bias of ∼4 mA we measured reader sensitivity as high as 20 mV/μm. The write head was also optimized for tracks as narrow as 0.14 μm operating at overwrite (OW) of 36 dB and nonlinear transition shift (NLTS) better than −25 dB at 610 kBPI, without precomp. Using conventional media we measured total spectral SNR∼18 dB. The media to electronics noise ratio was 4.8, showing that we are still operating in a media noise limited system. Low-flying air bearing surface (ABS) design and advanced pole tip recession (PTR) control were required to achieve magnetic spacing of about 15 nm.
Influence of master medium structure on magnetic contact duplication performance
Authors: Sugita R. , Muranoi T. , Nishikawa M. , Nagao M.
Published: May 2003

In the magnetic contact duplication technique using lithographically patterned master media, when the master media have magnetic films not only in the protrusion parts but in the dent parts, the depth of the dent parts affects the duplication performance. For the master media with a pattern width L of 2.5 μm, both experimental and simulation results show that even though there are magnetic films at the dent parts, if the depth of the dent d is 0.5 μm, the degree of magnetization reversal at transitions of duplicated slave media is much the same as that for the master media without magnetic films at the dent parts. It is inferred from simulations that for the master media with L of 0.1 and 0.4 μm, if d is 0.1 and 0.2 μm, respectively, magnetic films at the dent parts have no influence on the duplication performance.
Magnetic tunnel junctions with Hf oxide and modified Hf oxide tunnel barriers
Authors: Park B. G. , Lee T. D. , Lee T. H. , Kim C. G. , Kim C. O.
Published: May 2003

Magnetic tunnel junctions (MTJ’s) with Hf oxide and modified Hf oxide barriers were fabricated by ozone oxidation. The tunnel magnetoresistance (TMR) ratio in Hf oxide junction was 13% at room temperature and 21% at 77 K. In order to understand the low TMR ratio in MTJ’s with Hf oxides compared to those with Al oxides, tunnel barriers were modified by inserting a thin Al oxide layer of 0.3 nm at the interfaces between ferromagnetic electrodes and Hf oxide insulating layers. As the Al layer of 0.3 nm was inserted at top and bottom interfaces, the TMR ratio was restored to the value of the junctions with Al oxides. This implies that the polarization of CoFe contacted with Al oxide is larger than that of CoFe contacted with Hf oxide and the low TMR ratio in MTJ’s with Hf oxides may be attributed to the reduction of spin polarization of the CoFe electrodes due to CoFe/Hf oxide interface interaction.
Prediction of the magnetic field beyond a rectangular array of sensors
Authors: Kildishev Alexander V. , Kamondetdacha R. , Nyenhuis John A
Published: May 2003

A mathematical method is developed for the reconstruction of the magnetic field of a source with sensors arranged in a rectangular array on a plane. A prolate spheroidal shell encloses the source. The magnetic field of the source is expressed in prolate spheroidal coordinates and the prolate spheroidal expansion coefficients are determined by the application of the derived selective functions to the x component of the measured magnetic field. In a simulation with 192 sensors, the magnetic field is accurately reconstructed for sample sources in the presence of sensor noise, sensor position, and orientation error. The reconstruction error is the least for sources with significant dipolar component.
Magnetic properties of ultrafine cobalt ferrite particles
Authors: Tung L. D. , Kolesnichenko V. , Caruntu D. , Chou N. H. , O’Connor C. J. , Spinu L.
Published: May 2003

We have studied magnetic properties of a diluted system of ultrafine cobalt ferrite nanoparticles (d∼3.3 nm). From the peak of the zero-field-cooled measurements, we obtained the blocking temperature TB of about 90.5 K and it is virtually independent of the applied magnetic field up to 5 kOe. At the superparamagnetic region T>TB, the system follows the modified Curie-law variation of the magnetic susceptibility χ=χo+C/T. We observed that the saturation magnetization follows a spin-wavelike temperature dependence at temperature above 10 K. In spite of the cubic structure for cobalt ferrite, at 2 K, the reduced remanence Mr/Ms is equal to 0.46 which is close to the theoretical value of 0.5 expected for noninteracting uniaxial single-domain particles with the easy axis randomly oriented. From the ac susceptibility measurements at different frequencies, we obtained a linear dependence of the logarithm of the experimental time window τex as function of inverse blocking temperature (1/TB). The fitting results in the anisotropy constant value K of 3.15×107 erg/cm3 that is one order of magnitude higher than 1.8–3.0×106 erg/cm3 in bulk CoFe2O4 materials.
Mössbauer spectroscopic and x-ray diffraction studies of structural and magnetic properties of heat-treated (Ni0.5Zn0.5)Fe2O4 nanoparticles
Authors: Yang De-Ping , Lavoie Lindsey K. , Zhang Yide , Zhang Zongtao , Ge Shihui
Published: May 2003

Because of their high electrical resistivity and high magnetic permeability, nickel–zinc ferrites are among the best soft magnetic materials for high-frequency applications. In this work, a precursor of nanostructured (Ni0.5Zn0.5)Fe2O4 was obtained by a sol–gel method modified for large quantity production. Six heat-treated samples were produced by calcining the precursor for 3 h at 450, 500, 600, 650, 700, and 1100 °C, respectively. X-ray diffraction peak width data have been used to estimate the particle sizes of the calcined samples. Room-temperature and low-temperature Fe57 Mössbauer effect experiments allowed us to determine whether the heat-treated nanoparticles are crystalline or amorphous, whether there is a superparamagnetic phase, and which calcining temperature is optimum for obtaining a large magnetic hyperfine field and a homogeneous magnetic phase. Room-temperature Mössbauer spectra revealed that the precursor is paramagnetic, while the heat-treated samples have the ferrimagnetic phase. The samples heat treated at a calcining temperature of 650 °C or higher showed no residual paramagnetic phase, indicating that 650 °C is the threshold calcining temperature for homogeneous (Ni0.5Zn0.5)Fe2O4 nanoparticles. A comparison between low-temperature and room-temperature Mössbauer spectra demonstrated that the precursor is paramagnetic, whereas the heat-treated (500 °C) sample has a component that shows superparamagnet relaxation.
Transmission electron microscopy estimation of Bi–YIG nanoparticle hybridized with plastic material
Authors: Kim Tae-Youb , Hirano Teruyoshi , Yamazaki Yohtaro , Hong Yeong-Dae
Published: May 2003

We have developed a magneto-optical Bi1.8Y1.2Fe5O12 nanoparticle hybrid material and milling system. The Bi1.8Y1.2Fe5O12 nanoparticles were prepared with a coprecipitation and annealing processes. The 100 h milling nanoparticle system has θF about 1×103 degrees/cm but it has very small Ms (∼2.5 emu/cm3). In this material system, the particle size and crystalline size of the nanoparticles were estimated with a transmission electron microscope and transmission electron diffraction methods. The crystal phase sizes of the Bi1.8Y1.2Fe5O12 nanoparticles are the same as the nanoparticle sizes. The high-powered transmission electron microscope images show moiré fringes of the nanoparticles. The 5–8 nm particles are primary nanoparticles. We show a possibility of the synthesis for the crystalline nanoparticles dispersed in hybrid materials by mechanical milling process.
Multiple magnetic transitions and large magnetoresistance of Y0.8Dy0.2Mn6Sn6 compound
Authors: Zhang Shao-ying , Yao Jin-lei , Zhang Li-gang , Li Lu , Shen Bao-gen , Zhu Tao
Published: May 2003

Magnetic transitions and magnetoresistance of HfFe6Ge6-type Y0.8Dy0.2Mn6Sn6 compound have been investigated in the temperature range of 5–375 K. It was found that the compound displays paramagnetism, ferrimagnetism, antiferromagnetism, and reentrant ferrimagnetism with decreasing temperature. At low temperatures, the strong exchange interaction between the Dy and Mn sublattices results in ferrimagnetism. The metamagnetic transition from the antiferro- to ferrimagnetic state can be induced by a fairly small threshold field (⩽7 kOe). The magnetic transition is accompanied by a large magnetoresistance effect of about −29% and −7% at 5 and 293 K, respectively.
Magnetization-orientation dependence of the superconducting transition temperature and magnetoresistance in the ferromagnet-superconductor-ferromagnet trilayer system
Authors: Gu J. Y. , You Chun-Yeol , Jiang J. S. , Bader S. D.
Published: May 2003

The superconducting transition temperature (Tc) of a ferromagnet-superconductor-ferromagnet film system is predicted to exhibit a dependence of the magnetization orientation of the ferromagnetic layers. We have grown CuNi/Nb/CuNi films via magnetron sputtering and verified experimentally that the Tc is slightly higher in the case that the mutual magnetization direction of the two CuNi layers is antiparallel (AP) compared to the parallel (P). We also find that an ∼25% resistance change occurs near Tc in CuNi(5 nm)/Nb(18 nm)/CuNi(5 nm) when the two CuNi layers change their magnetization directions from P to AP.
Domain formation in exchange biased Co/CoO bilayers
Authors: Welp U. , te Velthuis S. G. E. , Felcher G. P. , Gredig T. , Dahlberg E. D.
Published: May 2003

The magnetic behavior of exchange biased Co/CoO polycrystalline thin films has been investigated using magnetometry and magneto-optical (MO) imaging. For CoO layer thicknesses of about 30 Å, these films exhibit a strong training effect below the blocking temperature of 130 K. A sharp initial reversal of the magnetization of the FM Co layer after field-cooling is followed by S-shaped magnetization loops with reduced coercive fields. The MO images show that during the initial magnetization reversal the remagnetization front moves from the edge of the sample into the homogenously magnetized film, leaving behind an irregular pattern of domains of the order of 10 μm. These domains, once generated during the first reversal, do not expand or move on subsequent magnetization loops and can be erased only by heating above the blocking temperature. This suggests that the domains are related to domains in the antiferromagnetic CoO layer.
Effects of intermediate layers on magnetic properties and read/write performance in CoCrPt perpendicular recording media with an FeHfN soft magnetic underlayer
Authors: Hong D. H. , Shin J. N. , Lee T. D. , Hong S. Y. , Lee H. J.
Published: May 2003

In this study, the effects of CoCrPtTa and CoCrPtB magnetic intermediate layers (ILs) on the magnetic properties and read/write performance of CoCrPt/soft magnetic layer perpendicular recording media were investigated. Even though the perpendicular coercivity of the media with these ILs was reduced by 500 Oe, these media still showed a low exchange slope of 1.4 and a large negative nucleation field of about −1000 Oe. Additionally, the reduced grain size of the media with these IL was observed by transmission electron microscopy. From the read/write test, these media with ILs showed improved performance of 3–5 dB higher signal-to-noise ratio and overwrite ratio (OW) compared to the media without ILs. These enhancements could be attributed to the reduction of grain size of the magnetic layer and weakening of the intergranular interaction between grains by insertion of the IL.
Interface and microstructure evolutions in synthetic ferrimagnet-based spin valves upon exposure to postdeposition annealing
Authors: Kim Young Keun , Park Gun-Hyung , Lee Seong-Rae , Min Seok-Hong , Won Jeong Yun , Song Se Ahn
Published: May 2003

Synthetic ferrimagnet-based spin-valve (SV) films comprising Ta 5/NiFe 2/IrMn 9/CoFe (P1) 1.5/Ru 0.7/CoFe (P2) 3/Cu 2.8/CoFe 1.6/NiFe 3.2/Ta 5 (in nanometers) were examined with an emphasis given on understanding the interface evolution of IrMn/CoFe (P1) upon postdeposition annealing. A 300 °C, 5 h annealing resulted in 12% and 42% decreases in effective pinning field and 29% and 53% decreases in MR ratio for the bottom (B) and top (T) SV, respectively. Because both structures exhibit different thermal degradation behaviors, we were curious to uncover the underlying causes by employing various analytical methods. The column sizes of the B–SV and T–SV were about 30 and 15 nm, respectively. No major difference in the (111) crystal texture was observed. We found that the main cause was due to the interlayer diffusion of atomic constituents such as Mn, most likely through grain boundaries and IrMn/CoFe interface, where the degree of the diffusion was considerably higher for the T–SV. Due to the surface free energy differences depending on the deposition sequence, two types of SV structures behaved differently upon exposure to annealing. The B–SV featuring less grain boundaries and nonabrupt IrMn/CoFe (P1) interface could effectively impede interlayer diffusion and, as a result, exhibited less thermal degradation in MR properties.
Mn doping effect on structure and magnetism of epitaxial (FePt)1−xMnx films
Authors: Huang J. C. A. , Chang Y. C. , Yu C. C. , Yao Y. D. , Hu Y. M. , Fu C. M.
Published: May 2003

We study the structure and perpendicular magnetism of molecular beam epitaxy grown (FePt)1−xMnx films with doping concentration x=0, 1%, 2%, 3%, 4%, and 5%. The (FePt)1−xMnx films were made by multilayers growth of [Fe/Pt/Mn]×N at 100 °C and annealed at 600 °C. X-ray diffraction scans indicate that relatively better L10 ordered structure for low Mn doping (x<2%). The (001) and (003) superstructure peaks decrease with the increase of the Mn doping for x⩾2%, and a significant (111) peak appears for x>3%. The perpendicular magnetic anisotropy effect of the (FePt)1−xMnx films tends to decrease with the increase of Mn doping for x>1%. However, the x=1% doped films possess slightly better perpendicular magnetic anisotropy effect than the zero doped film. The perpendicular magnetic anisotropy constant are of about 1.3×107 and 1.6×107 erg/cm3 for x=0% and x=1%, respectively.
Bottom IrMn-based spin valves by using oxygen surfactant
Authors: Hwang J. Y. , Kim M. Y. , Rhee J. R. , Lee S. S. , Hwang D. G. , Kim J. K. , Lee S. H. , Yu S. C.
Published: May 2003

Bottom IrMn-based spin valves through exposure of part of the CoFe pinned layer to O2 with the structure Ta30/NiFe20/IrMn70/CoFet/oxidation/CoFe(30−t)/Cu20/CoFe30/Ta35 (all thickness in angstroms) (oxidation indicates exposure to different O2 flows) were deposited by dc magnetron sputtering on thermally oxidized Si (111) substrates. Within the range of O2 flows (0.4–2.8 sccm) studied, the value of the magnetoresistance (MR) ratio is seen to be quite low at a relatively large t of >16 Å and a exchange coupling field (Hex) decreases when the O2 exposed CoFe surface is too close to IrMn. Under optimal conditions, a MR ratio of 8.6% with Hex∼275 Oe for the bottom single spin valve and a MR ratio 12.2% with Hex∼268/220 Oe for the dual spin valve are obtained. X-ray reflectivity data show smoother interfaces for the spin valves subjected to O2 exposure. The enhanced MR ratio coupled with the lower interlayer coupling field (Hint), sheet resistance, and magnetic moment of the specular spin valve can be attributed to an enhanced specularity as a result of smoother interfaces after O2 exposure.
Cadmium ferrite ionic magnetic fluid: Magnetic resonance investigation
Authors: Silva O. , Lima E. C. D. , Morais P. C.
Published: May 2003

In contrast to all magnetic resonance investigations previously performed using magnetic fluids (MFs) based on spinel ferrite nanoparticles, cadmium–ferrite-based MFs present an intense, relatively sharp resonance line near g=4, in addition to the typical, broad structure near g=2. The broad resonance structure is associated with larger cadmium–ferrite nanoparticles, whereas the sharp resonance line is associated with ultrasmall cadmium–ferrite nanoparticles. Transmission electron microscopy (TEM) data confirm the bimodal particle size distribution in the sample investigated. The temperature T dependence of the resonance field HR is almost linear, for both high-field (HF) and low-field (LF) resonance lines, in the range of 100–300 K. In support of the identification of the HF line (around g=2) and LF line (around g=4) with larger and smaller Cd–ferrite nanoparticles, respectively, the slope of the HR versus T curve is lower for the HF line (1.3 G/K) compared to the LF line (1.69 G/K), whereas the intercept constant of the HF line (3050 G) is higher than the intercept constant of the LF line (1130 G).
Magnetoelastic coupling constants in epitaxial Co80Pt20 films
Authors: Xu Bin , Doyle William D.
Published: May 2003

Magnetoelastic coupling constants in epitaxial hcp Co80Pt20 films with (101̄0) orientation (a axis and c axis in plane) have been measured. A magnetostrictive stress tester with magnetic field up to 18 kOe was constructed based on the bending cantilever technique. The magnetoelastic coupling constants were directly extracted from the magnetostrictive stress data and no information on the mechanical properties of the Co80Pt20 film is needed. The magnetoelastic coupling constants along the a and c axes were B1′=15×106 and B2′=−80×106 erg/cc, respectively, which are much smaller than those of pure Co.
Surface morphology and molecular conformation for ultrathin lubricant films with functional end groups
Authors: Guo Qian , Izumisawa Satoru , Phillips David M. , Jhon Myung S.
Published: May 2003

Using molecular simulation techniques based on a coarse-grained, bead-spring model, we examined the static and dynamic properties of linear perfluoropolyethers (PFPEs) in a nanoscale lubricant film on a solid wall. The conformation of the PFPEs, as predicted by the anisotropic radius of gyration, exhibits an oblate structure near the wall, but recovers a spherical shape as the distance from the wall increases. The density profile of the functional end groups for the PFPE molecules shows a characteristic oscillation as a function of the distance from the wall, indicating molecular layering. We also used the simulated surface morphology to examine the PFPE film roughness. Our preliminary dynamic simulations indicate that the wall interaction produces an anisotropy in the self-diffusion coefficient.
Magnetic measurements on human erythrocytes: Normal, beta thalassemia major, and sickle
Authors: Sakhnini Lama
Published: May 2003

In this article magnetic measurements were made on human erythrocytes at different hemoglobin states (normal and reduced hemoglobin). Different blood samples: normal, beta thalassemia major, and sickle were studied. Beta thalassemia major and sickle samples were taken from patients receiving lifelong blood transfusion treatment. All samples examined exhibited diamagnetic behavior. Beta thalassemia major and sickle samples showed higher diamagnetic susceptibilities than that for the normal, which was attributed to the increase of membrane to hemoglobin volume ratio of the abnormal cells. Magnetic measurements showed that the erythrocytes in the reduced state showed less diamagnetic response in comparison with erythrocytes in the normal state. Analysis of the paramagnetic component of magnetization curves gave an effective magnetic moment of μeff=7.6 μB per reduced hemoglobin molecule. The same procedure was applied to sickle and beta thalassemia major samples and values for μeff were found to be comparable to that of the normal erythrocytes.
Interface characterization of magnetic tunnel junctions by using tunneling spectroscopy
Authors: Ando Y. , Hayashi M. , Oogane M. , Kubota H. , Miyazaki T.
Published: May 2003

Junctions doped with a small mount of Al between the top ferromagnetic electrode and the insulator were fabricated. The tunnel magnetoresistance (TMR) ratio increased at the doped Al thickness of 0.2 nm after annealing at 250 °C. Inelastic-electron-tunneling spectroscopy (IETS) has been applied to investigate the spin-dependent tunneling process for the tunnel junctions. The IET spectrum subtracting the spectrum at parallel magnetization configuration from that at antiparallel configuration showed a peak around 20 mV of the bias voltage especially for the junction after annealing at 250 °C. Over the corresponding voltage the TMR ratio as a function of the bias decreased; however, the influence was relatively small.