bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferromagnetic resonance and electric characterization in double perovskite Sr2FeMoO6
Authors: Flores A. G. , Zazo M. , Raposo V. , Íñiguez J. , de Francisco C. , Hernández-Gómez P.
Published: May 2003

In this work the study of the ferromagnetic resonance (FMR) and of the electrical conductivity in the perovskite sample, Sr2FeMoO6, is presented. The sample has been manufactured by conventional ceramic method sintering in inert gas atmosphere. Electrical conductivity, of about 1000–1200 S/m, has been measured in the 125–300 K temperature range. FMR linewidths have been measured at 9.48 GHz from 125 to 300 K. A decrease of the linewidth with increasing temperature has been obtained. This behavior has been attributed to the presence of valence exchange mechanism, which takes places in samples with Fe2+ cations. In this way, FMR linewidth analysis has been revealed like a useful and clear technique in determining the cation distribution of the sample showing the presence of Fe2+ ions. This technique has also shown data about the microstructure of the sintered polycrystalline sample finding the porosity value of the sample.
Oxygen vacancies effect on phase separation in Pr0.5Ca0.2Sr0.3MnO3−δ
Authors: Niebieskikwiat D. , Caneiro A. , Sánchez R. D.
Published: May 2003

We study the effect of the introduction of a controlled amount of oxygen vacancies on the magnetic and transport properties of the phase separated manganite Pr0.5Ca0.2Sr0.3MnO3−δ, for δ=0 and 0.01. This compound presents a paramagnetic to ferromagnetic (FM) transition below TC∼240 K, and then to a charge-ordered (CO) and antiferromagnetic (AFM) phase at TCO∼175 K. However, below TCO an appreciable FM component (∼20%) still survives, related to a FM volume immersed within the CO/AFM matrix. At low temperatures, in the mainly CO phase, the introduction of oxygen vacancies enhances the FM ordering, with the consequent decrease of resistivity and magnetoresistance (MR). On the contrary, in the FM phase (in the range TCO<T<TC) the magnetization is reduced and the resistivity and MR increase. These results are discussed in the frame of percolative transport in metal–insulator mixtures, and frustrated double exchange interaction due to the interruption of some Mn–O–Mn chains.
Room temperature coercivities of Tb1−xDyxFe2 (110) molecular beam epitaxy grown films
Authors: Beaujour J-M. L. , Bowden G. J. , Zhukov A. A. , Rainford B. D. , de Groot P. A. J. , Ward R. C. C. , Wells M. R.
Published: May 2003

It has been known for many years that the rare-earth intermetallic compound terfenol (Tb0.3Dy0.7)Fe2 is characterized by “giant magnetostriction,” which has found practical applications. In this article we report the magnetic properties of a series of molecular beam epitaxially (MBE) grown (110) Tb1−xDyxFe2 alloy films, on sapphire substrates. All the measurements were performed at room temperature with the field applied along an in-plane [1̄10] axis. However, unlike bulk Tb1−xDyxFe2, it is shown that the coercivity does not fall to zero at the magic ratio of x∼0.7. Instead, the coercivities fall almost on a straight line, with the maximum coercivity for pure TbFe2 (0.64 T) and the smallest for DyFe2 (0.22 T). The difference between the bulk and MBE films is attributed to the presence of a magnetoelastic strain term, induced during crystal growth by the sapphire substrate. In practice, the measured coercivities can be described, approximately, with a modified Stoner–Wohlfarth model.
Exchange through nonmagnetic insulating matrix
Authors: Skomski R. , Kashyap A. , Qiang Y. , Sellmyer D. J.
Published: May 2003

Exchange interactions between hard-magnetic particles in a nonmagnetic matrix are investigated by model calculations. A Landau–Ginzburg approach is developed to describe the net exchange interactions between spheres of arbitrary diameters. Introducing cylindrical coordinates and integrating over the surfaces of the adjacent spheres yields an exchange coupling which decreases with a decay length depending on interatomic exchange, intra-atomic exchange, and temperature. Typically, the decay length does not exceed a few interatomic distances. The decay is exponential but also contains a prefactor depending on the surface curvature of the grains. It increases with decreasing curvature, but this dependence is only a small correction to the leading exponential term.
Remagnetization processes in SmCo/NdCo exchange springs
Authors: Vlasko-Vlasov V. K. , Welp U. , Guo Z. J. , Jiang J. S. , Pearson J. E. , Liu J. P. , Miller D. J. , Tang Y. , Bader S. D.
Published: May 2003

Remagnetization processes in a SmCo/NdCo exchange spring system are studied using superconducting quantum interference device magnetometry and magneto-optical imaging. The magneto-optical images reveal that the reversal of the soft NdCo layer and its return to the polarized state at cycling around the exchange bias field occur due to the asymmetric nucleation and growth of twisted-phase domains. The observed peculiarities of the domain-wall kinetics are discussed and a way of tailoring exchange biased systems by regulating the motion of the twisted-phase domains is suggested.
Magnetoresistive signal isolators employing linear spin-valve sensing resistors
Authors: Qian Zhenghong , Wang Dexin , Daughton Jim , Tondra Mark , Lange Erik , Nordman Cathy , Popple Anthony , Myers John , Schuetz Jim
Published: May 2003

Feasibility of fabricating low power, high-speed, magnetoresistive signal isolators employing linear spin-valve resistors as sensing elements has been demonstrated. In the fabricated prototype digital isolators, linear spin-valve resistors are physically isolated from an on-chip coil by an 11 μm BCB isolation barrier, which provides the galvanic isolation with a breakdown voltage larger than 2000 V. The devices are high speed (>50 MHz), small size, and low power consumption. Only a 4.5 mA coil driving current is required for the device to be fully functional. The power consumption is estimated to be ∼1/6 of NVE’s present isolator products, which requires a 50 mA coil driving current. Besides digital signal isolators, linear spin-valve resistors can also be used in analog signal isolators. The response of the linear spin-valve resistors to the current passing through the coil has been demonstrated to have a very good linearity, with a linearity error less than 0.05%.
Magnetic properties of iron-rich Nd2−yDyyFe17−xSix mixed rare-earth system
Authors: Kamaraju K. , Yang J. B. , Yelon W. B. , Pringle O. A. , James W. J. , Cai Q. , Chu Z. , I’Heritier Ph.
Published: May 2003

A series of Nd2−yDyyFe17−xSix solid solutions with x=0, 1, 2, and 3 and y=0, 0.5, 1.0, 1.5, and 2.0 were prepared by induction melting stoichiometric amounts of high-purity elements. The x-ray diffraction data confirmed that the postannealed samples are 2:17 intermetallics of the R3̄m space group. The lattice parameters and unit-cell volumes were calculated using FULLPROF to analyze the neutron diffraction (ND) data. It was observed that for a particular y, the unit-cell volume decreased almost linearly with increasing silicon content (x⩽3), as is observed for single rare-earth 2:17 intermetallic compounds. For a given x, the cell volume decreased almost linearly with the increasing replacement of neodymium with dysprosium. The ND studies revealed additional density along the c-axis chains of Fe dumbells and rare-earth atoms. The perfect a-b-c stacking of the CaCu5 layers with a regular one third replacement of the rare-earth atoms by Fe dumbells appear to be broken, resulting in a disordered rhombohedral structure. The Curie temperature measurements showed no particular kind of dependence with increasing y. For a fixed content of Dy, an increase in Curie temperature from 61.46 °C to 236 °C for y=0, 69.3 °C to 241 °C for y=0.5, 76 °C to 227 °C for y=1, 95.45 °C to 224 °C for y=1.5, and 94.19 °C to 226 °C for y=2 was observed with increasing x (x⩽3). With increasing y, there was almost a linear decrease in magnetization of about 46% for x=0, 49% for x=1, 52% for x=2, and 50% for x=3. For a particular y with increasing x, the magnetization appears to reach saturation between x=1 and x=2.
Spin waves in random spin chains
Authors: Wan Xin , Yang Kun , Zhou Chenggang , Bhatt R. N.
Published: May 2003

We study quantum spin-1/2 Heisenberg ferromagnetic chains with dilute random antiferromagnetic impurity bonds with the modified spin-wave theory. By describing thermal excitations in the language of spin waves, we observe a low-temperature Curie susceptibility due to the formation of large spin clusters first predicted by the real-space renormalization-group approach, as well as a crossover to a pure ferromagnetic spin-chain behavior at intermediate and high temperatures. We compare our results of the modified spin-wave theory to quantum Monte Carlo simulations.
Effects of surface step and substrate temperature on nanostructure of L1–FePt nanoparticles
Authors: Sato Kazuhisa , Kajiwara Takenori , Fujiyoshi Masaru , Ishimaru Manabu , Hirotsu Yoshihiko , Shinohara Tadashi
Published: May 2003

The variation of the particle size, particle density, and its relation to the hard magnetic properties of FePt nanoparticles with respect to substrate temperatures and substrate surface morphologies has been investigated. On geometrically flat surfaces, densely dispersed FePt nanoparticles with a particle density of 1012 cm−2 were obtained at a substrate temperature below 573 K, while substrate temperatures between 623 and 823 K are necessary for obtaining well-oriented and well-isolated L10–FePt nanoparticles with large coercivity. Isolated particles fabricated above 573 K did not coalesce largely upon annealing at 873 K, which can be attributed to the “anchoring effect” of Pt “seed” particles. The coercivity of FePt nanoparticles was measured at 300 K damped with decreasing particle sizes below 10 nm. High-density areal packing of Fe/Pt nanoparticles could be fabricated at 673 K on a slightly inclined NaCl(001) substrate with surface steps. These particles coalesced easily upon annealing along the 〈100〉 step edges.
Magnetic properties of Sr-ferrite dot arrays by electron beam lithography
Authors: Liu Xiaoxi , Itoh Fumitake
Published: May 2003

We have successfully prepared Sr-ferrite dot arrays with perpendicular magnetic anisotropy by electron beam lithography. Virgin magnetic configurations detected by magnetic force microscopy (MFM) show single domain configuration for a 0.5 μm dot, while multidomain configurations are found for larger dots. The magnetization reversal mechanism in dots larger than 0.5 μm is found to be domain wall motion. While the magnetization reversal mechanism in 0.5 μm dots is found to be magnetization rotation. A normalized dc demagnetization remanence curve (DCD) measured by a superconducting quantum interference device (SQUID) indicates that with a decrease of dot size, the DCD curve is approaching the curve predicted by the coherent rotation model. Both MFM and SQUID results indicate that the single-domain dots reversed individually free from interdot magnetostatic coupling.
Modeling of hysteresis and magnetization curves for hexagonally ordered electrodeposited nanowires
Authors: Fodor P. S. , Tsoi G. M. , Wenger L. E.
Published: May 2003

A computational model has been developed to investigate how the magnetostatic interactions affect the hysteresis and magnetization curves for hexagonal arrays of magnetic nanowires. The magnetization coupling between nanowires arises from the stray fields produced by the other nanowires composing the array such that the field at each nanowire is the sum of the external field and the interaction field with the other nanowires. Using only two adjustable parameters: the interaction between nearest neighbors and the width of the Gaussian distribution in switching fields centered around the measured coercivity, simulations are compared with the experimentally measured hysteresis and magnetization curves for electrodeposited Co0.45Fe0.55 alloy nanowires with diameters from 12 to 48 nm. Excellent agreement is found for all nanowire systems except for the largest diameter arrays where deviations from the Gaussian distribution of switching fields need to be considered.
Monte Carlo simulations of phase transitions in Rb2MnF4
Authors: Lee H. K. , Landau D. P. , Schulthess T. C.
Published: May 2003

Rb 2 MnF 4 is believed to consist of very weakly coupled magnetic layers with isotropic superexchange between nearest neighbor Mn2+ ions in the same plane. To test this conjecture, Monte Carlo simulations were performed on a theoretical model consisting of stacked, nearest neighbor Heisenberg square lattices coupled by dipolar interactions. Simulation parameters such as the lattice constants and the superexchange constant were taken from experimental measurements, and periodic boundary conditions were used in all directions. We succeeded in achieving an algorithmic speed up from O(N2) to O(N ln N) through the combination of fast Fourier transforms for the evaluation of the dipolar interactions and global updates in the Monte Carlo steps. Our simulations reproduced very well the behavior observed in experiments with Rb2MnF4 crystals.
Magnetic domain structure of Fe–55 at. %Pd alloy at different stages of atomic ordering
Authors: Wang Lisha , Laughlin David E. , Wang Y. , Khachaturyan Armen G.
Published: May 2003

In this work, we use Lorentz microscopy imaging technique to study the magnetic domain structure of Fe–55 at %Pd alloy at different stages of atomic ordering. The underlying microstructure is characterized by using conventional transmission electron microscopy. At low annealing temperature, a tweed microstructure is formed. The ordered c variants in the tweed microstructure align along {110} plane traces. At higher annealing temperatures, a polytwinned structure is formed. The increase in the coercivity of the tweed structure is related to the density of magnetic macrodomain intersection with the tetragonal variants. After long time annealing, coarsened L10 grains are formed. Two types of magnetic domains are found in these coarsened grains. One is the “stripe” magnetic domain where the magnetization direction or the c axis of the L10 grain is perpendicular to the surface orientation. The other is “plate-like” magnetic domain; the magnetization direction of the L10 grain is found to be parallel to the specimen surface orientation.
Role of the Fe sublattice on the Invar anomaly in R2Fe14B compounds
Authors: Yang Ning , Dennis K. W. , McCallum R. W. , Kramer M. J. , Zhang Yuegang , Lee Peter L.
Published: May 2003

Thermal expansion anomalies of Nd2Fe14B and Y2Fe14B stoichiometric compounds have been studied by x-ray diffraction with high energy synchrotron radiation using a Debye–Scherrer geometry from room temperature to 1000 K. Y2Fe14B and Nd2Fe14B have similar temperature dependence of lattice parameters and bond distances up to their Curie temperatures Tc. The volumetric spontaneous magnetostriction at room temperature for Nd2Fe14B and Y2Fe14B were determined to be 1.49% and 1.45%, respectively. Among the Fe–Fe bonds, those bonds containing Fe(j2), whose projections are dominantly in the basal plane, have the highest contribution to the Invar effect. These bonds have magnetostrictive strain ranging from 0.4% to 0.8% at room temperature. Above the Curie temperature, Y2Fe14B has an isotropic thermal expansion, while Nd2Fe14B exhibits slightly anisotropic thermal expansion. The iron sublattices dominate the spontaneous volumetric magnetostriction of Y2Fe14B and Nd2Fe14B compounds.
Processing induced changes in Curie temperature of Nd2Fe14B melt-spun ribbons
Authors: Xu Youwen , Yang Ning , Dennis K. W. , McCallum R. W. , Kramer M. J. , Zhang Yuegang , Lee Peter L.
Published: May 2003

Changes of the Curie temperature Tc in Nd2Fe14B (2-14-1) can arise from changes in crystal chemistry or can be induced by compressive stresses. We have recently observed decreases in the Tc up to 30 K in nanocomposite melt-spun ribbons of 2-14-1 and α-Fe. The starting materials contain about 6.5%–15% additional Fe, while some samples had 3 wt % Ti–C added to control grain growth. Spin reorientation temperatures Ts measured on the samples with or without Ti–C are from 120 to 122 K depending on the wheel speed and composition, suggesting that changes in Tc are due to microstructure. X-ray diffraction dilatometry using the α-Fe lattice suggests that at 300 K the iron is under tension but switches sign due to differences in coefficients of thermal expansion between the α-Fe and 2-14-1. Similar d spacing of the (110) of α-Fe and (006) of 2-14-1 suggest that changes in Tc may in part be due to epitaxial stresses affecting the exchange coupling in the nanocomposite alloys.
Structure and magnetic properties of nanostructured Pr1−xGdxCo5 (x=0–1) powders prepared by mechanical alloying
Authors: Zhao X. G. , Zhang Z. D. , Cui B. Z. , Ren W. J. , Liu W. , Geng D. Y.
Published: May 2003

The phase components, structures, and magnetic properties of Pr1−xGdxCo5 (x=0–1) powders synthesized by mechanical alloying and subsequent annealing have been investigated systematically. The optimal magnetic properties, with a coercivity of 12.5 kOe, a remanence ratio of 0.72, and a maximum energy product of 12.7 MGOe, have been obtained from PrCo5 powders milled for 5 h and annealed at 700 °C for 2 min. The remanence and maximum energy product were decreased monotonically with increasing Gd content, whereas the coercivity was increased, reaching a maximum of 23.7 kOe in Pr0.2Gd0.8Co5 powders. X-ray diffraction and transmission electron microscopy observations reveal that an uniform (Pr,Gd)Co5/(Pr,Gd)2Co17 nanostructure with an average grain size of 20–30 nm forms in the powders annealing at 700 °C. The obtained magnetic hardening apparently originates from the high anisotropy field of the hard (Pr,Gd)Co5 phase and the uniform nanostructure developed by mechanical alloying and subsequent annealing.
Magnetic interaction effects on the hard magnetic properties of ball-milled SmCo5+NiO and SmCo5+CoO composites: A ΔM plot study
Authors: Sort J. , Suriñach S. , Muñoz J. S. , Baró M. D. , Nogués J. , de Brion S. , Chouteau G.
Published: May 2003

The effects of magnetic interactions on the hard magnetic properties of SmCo5 ball milled with NiO [antiferromagnetic (AFM) at room temperature] or with CoO [paramagnetic (PM) at room temperature] have been studied. The FM–AFM system exhibits improved magnetic properties (coercivity and squareness) for all compositions. The effects of magnetic interactions on the magnetic properties are analyzed in terms of classical ΔM plots. The plots show that in both systems magnetizing-like FM–FM exchange interactions are predominant for fields μ0H<μ0HC, while long-range dipolar interactions prevail for μ0H>μ0HC. The different types of magnetic interactions are found to depend on the degree of SmCo5 dispersion in the AFM (NiO) or PM (CoO) matrices. Moreover, the role of the AFM appears to be to enhance both the dipolar and exchange-like interactions, although the exchange effects appear to be responsible for the improvement of the magnetic properties.
Magnetic phase transitions in (Tb,Y)Mn2M2 (M=Ge and Si) systems
Authors: Dubenko I. S. , Gaidukova I. Yu. , Granovsky S. A. , Inoue K. , Markosyan A. S. , Roy S. , Ali N.
Published: May 2003

The temperature- and field-induced magnetic phase transitions in pseudoternary systems Tb1−xYxMn2Ge2 and Tb1−xYxMn2Si2, which are characterized by a separate magnetic ordering of the Mn and Tb subsystems, have been studied on strongly textured samples by magnetization and thermal expansion measurements. In the concentration region 0.4⩽x⩽1.0, where the Mn moments are ordered only, the magnetic structure is antiferromagnetic. The magnetic ordering in the Tb subsystem is accompanied by a transformation of the Mn magnetic structure. As a result, the compounds show a spontaneous magnetization. This transition is of a first-order type. In both systems the transition temperature for the Tb subsystem TC(Tb) decreases linearly with increasing Y concentration and goes to zero at about x=0.40. Canted phases and field-induced first-order transitions into the collinear phase have been observed in both systems below this temperature. It is concluded that the f–d exchange interaction is the primary factor governing the value of TC(Tb).
Crystal orientation control of multipole ring magnets for a surface permanent magnet rotor
Authors: Komuro M. , Kitamura M. , Kuriyama Y. , Masuzawa M.
Published: May 2003

The effects of the crystal orientation on the surface magnetic flux density and cogging torque were investigated for multipole ring magnets. A high magnetic field was applied to pole positions during the pressing process for the fabrication of ring magnets using anisotropic NdFeB powders. The radial orientation of the c axis of these ring magnets is 10% higher than that of previous ring magnets at pole positions. The ring magnets with a high orientation at the pole positions show a smaller distortion wave form of the surface magnetic flux density and a 20% higher surface magnetic flux density than previous ring magnets. The surface permanent magnet rotors using these ring magnets have a 75% smaller cogging torque with a basic period.
Developing highly coercive microstructures in Pr–Co magnets by Gd substitution
Authors: Meacham B. E. , Branagan D. J.
Published: May 2003

While permanent magnets based on Sm1Co5 are technologically important, magnets made from isostructural Pr1Co5 are not commercially significant even though Pr1Co5 has better intrinsic magnetic properties. The biggest problem is the formation of unfavorable phase equilibria which leads to an inability to develop high coercivity in binary Pr–Co alloys. A proposed solution was to make a hyperstoichiometric alloy with Gd as a substitute, in addition to carbon, to inhibit the formation of the deleterious phases leading to a predominantly single magnetic phase composition. An enhancement was observed in the coercivity. This result is perhaps surprising considering that the Gd atom, with a spherical 4f electron shell, is not expected to contribute to the magnetocrystalline anisotropy. Thus, the expectation was that the coercivity increase was caused by the microstructure but no distinguishing feature of microstructure was observed in transmission electron microscopy. It appears that Gd substitution instead affects the intrinsic magnetocrystalline anisotropy by reducing the effect of the small canting of the Pr moment through dilution.
A general approach for overwrite spectra
Authors: Li Shaoping , Zhang Huaan , Zhu W.
Published: May 2003

A generalized analysis has been presented for describing the influence of overwrite (or reverse overwrite) interferences on the spectra of readback signal, which extends the previous theory in describing the spectra characteristics caused by the hard–easy transition shift. Interestingly, it also suggests that the residual signal from the overwritten data pattern could be periodic as well. Essentially, an imprint effect arising from old data pattern could also create an amplitude-modulated signal that generates sidebands around the fundamental and odd harmonics of the overwriting signal.
Cryogenic pulsed inductive microwave magnetometer
Authors: Kos A. B. , Nibarger J. P. , Lopusnik R. , Silva T. J. , Celinski Z.
Published: May 2003

A cryogenic pulsed inductive microwave magnetometer is used to characterize the switching dynamics in thin-film magnetic materials at low temperatures and microwave frequencies. The system is contained inside a 20-cm-diam ultrahigh vacuum chamber and cooled by a cryopump that allows measurements between 20 and 350 K. A temperature controller regulates the sample temperature using two silicon diodes as sensors. Applied magnetic fields of up to 36 kA/m (450 Oe) are generated by a four-pole, water-cooled electromagnet with independent control of each axis. Magnetic switching in the sample is driven by high-speed current step pulses in a coplanar waveguide structure with the sample placed in a flip-chip configuration. A 20 GHz sampling oscilloscope is used to record the dynamics of the magnetic reorientation. The switching dynamics are given for a 10-nm-thick Ni–Fe film at 30 K in response to a 1 kA/m field step.
Exchange anisotropy and spin-wave damping in CoFe/IrMn bilayers
Authors: Rezende S. M. , Lucena M. A. , Azevedo A. , de Aguiar F. M. , Fermin J. R. , Parkin S. S. P.
Published: May 2003

The magnetic properties and the spin-wave damping in FM/AF bilayers of CoFe/IrMn have been investigated with magneto-optic Kerr effect magnetometry, ferromagnetic resonance (FMR), and Brillouin light scattering (BLS). As observed in other systems, the values of the interlayer exchange field obtained with different techniques are discrepant, but they all exhibit the expected t−1 dependence with the FM film thickness t. On the other hand the spin-wave relaxation rates measured by BLS and FMR are fit with a t−2 dependence plus a constant term. This is interpreted as the sum of two independent contributions, an intrinsic mechanism dominated by Gilbert damping and an extrinsic mechanism dominated by two-magnon scattering due to fluctuations of the interlayer exchange coupling caused by interface roughness.
Growth and characterization of BSTO/hexaferrite composite thin films
Authors: Hajndl R. , Sanders J. , Srikanth H. , Dudney N. J.
Published: May 2003

Ferroelectric/ferrite composite films are excellent systems in which the electromagnetic material properties can be tuned through changes in composition as well as microstructure. We report on our studies of the structural and magnetic properties of Ba0.5Sr0.5TiO3/BaFe12O19 (BSTO/BaM) composite thin films deposited on Al2O3 substrates using magnetron sputtering. Optimizing the sputtering conditions and postdeposition annealing lead to high-quality films without any impurity phases. Magnetic measurements yield saturation magnetization values in the range of 100 to 200 emu/cm3. Hysteresis loops exhibit a double transition that is observed only in the composite films and not in pure hexaferrite films grown under identical deposition conditions. The unusual feature in the M–H data is ascribed to the possibility of magnetodielectric effects associated with intergranular magnetic coupling mediated by the BSTO polarization layer.
Effect of NiAl intermediate layer on structural and magnetic properties of L1 FePt films with perpendicular anisotropy
Authors: Chen J. S. , Lim B. C. , Wang J. P.
Published: May 2003

The effect of NiAl intermediate layer on structural and magnetic properties of L10 FePt films with perpendicular anisotropy has been investigated. It is found that the crystallographic (001) texture of face-centered tetragonal-FePt films is improved after introducing a NiAl intermediate layer. The degree of the ordering and the coercivity of the fct-FePt films increase with NiAl intermediate layer thickness. The improvement of the crystallographic texture and magnetic properties may be attributed to the effective suppression of Cr diffusion from the underlayer. The grain size of FePt films with 4 nm of NiAl intermediate layer is about half of that of FePt film without NiAl intermediate layer.
Preparation of nanometric CuxFe1−xOFe2O3 for treatment of tumor
Authors: Huang Yuqiang , Kim Jong-Hee , Park Sang-Im , Shao Huiping , Kim Chong-Oh
Published: May 2003

The nanometric particles possess some physical and chemical properties different from the bulk. The water-based magnetic fluids with nanometric CuxFe1−xOFe2O3 particles were prepared by the two-step method, in which the x value varied from 0.1 to 0.4. The experiment results showed the magnetization decreased with increasing x values. The copper element was partly coprecipitated with iron oxides. These phenomena are ascribed to excess ammonia water in the precipitation. The decanoic acid and the nonanoic acid were selected as the first and second surfactants. The optimal reaction temperatures for the first and second surfactants were 80 and 60 °C respectively with the holding time of 30 min.
Analysis of repulsive interactions in chains of superparamagnetic colloidal particles for magnetic template-based self-assembly
Authors: Yellen Benjamin B. , Friedman Gary
Published: May 2003

A numerical model for magnetic template-based self-assembly of superparamagnetic colloidal particles is presented. It is shown that microwells positioned over the edges of magnetized template islands and application of external uniform magnetic field can control the number of particles deposited at each template site. The model includes statistical variations in particle sizes and magnetic moments and takes into account particle magnetization saturation effects.
Mn–Zn ferrite with higher magnetization for temperature sensitive magnetic fluid
Authors: Jeyadevan B. , Chinnasamy C. N. , Shinoda K. , Tohji K. , Oka H.
Published: May 2003

A growth-assisted coprecipitation process is proposed to achieve highly magnetic Mn–Zn ferrite particles. In this method, first, the particles were synthesized by coprecipitation under optimum condition. Then, further enhancement in particle size was obtained by using the already prepared particles as seed. The average crystallite size of the particles prepared by the proposed method was 12 nm. Furthermore, the magnetization at 1 T applied field was 50 emu/g compared to 37 emu/g of coprecipitated particles. It should be noted that the Curie temperature of the particles remained similar to the coprecipitated particles suggesting that the composition of the Mn–Zn ferrite particles has not been affected by the modified synthesis technique. The gradient of the magnetization-temperature curve was enhanced as a consequence of the rise in magnetization. These particles could be used for the synthesis of temperature sensitive magnetic fluid with higher magnetization and magnetization-temperature gradient.
Role of dynamic exchange coupling in magnetic relaxations of metallic multilayer films (invited)
Authors: Heinrich B. , Woltersdorf G. , Urban R. , Simanek E.
Published: May 2003

The relaxation processes were investigated by ferromagnetic resonance (FMR) using magnetic single, Au/Fe/GaAs(001), and double layer, Au/Fe/Au/Fe/GaAs(001), structures prepared by molecular beam epitaxy. These structures provided an excellent opportunity to investigate nonlocal damping which is caused by spin transport across a nonmagnetic spacer. In the double layer structures thin Fe layers F1 were separated from a second thick Fe layer F2 by a Au(001), normal metal spacer. The interface magnetic anisotropies separated the FMR fields of F1 and F2 by a big margin which allowed us to investigate FMR in F1 while F2 had a negligible angle of precession. The main result is that the ultrathin Fe films in magnetic double layers acquire a nonlocal interface Gilbert damping. Several mechanisms have been put forward to explain the nonlocal damping. A brief review of each mechanism will be presented. They will be compared with the experimental results allowing one to critically assess their applicability and strength. It will be shown that the precessing layers act as spin pumps and spin sinks. This concept was tested by investigating the FMR linewidth around an accidental crossover of the resonance fields for the layers F1 and F2.
Magnetism of the trigonal B12 cluster compound REB17CN (RE=Er, Ho)
Authors: Mori Takao , Leithe-Jasper Andreas
Published: May 2003

Magnetic properties of trigonal B12 cluster compounds REB17CN (RE=Er, Ho) were investigated. The structure (space group P-3m1) is composed of a three dimensional network based on interconnected B12 icosahedra and B6 octahedra. The rare earth atoms reside in voids of the boron framework, while C–B–C chains and nitrogen atoms bridge the icosahedra. Peaks in the zero field cooled magnetic susceptibility are observed at 29 and 6 K for HoB17CN and ErB17CN, respectively. Divergences are observed between the zero field cooled and field cooled susceptibilities, while the isothermal remanent magnetization shows a time dependent relaxation over several decades of time. The results are indicative of spin glass-like behavior. The spin glass-like behavior is thought to be caused by disorder from partial occupancy of the rare earth atomic sites and also possible frustration of magnetic interactions. These results are also of interest in the context of the ongoing investigation into the magnetism discovered in nonmetallic B12 icosahedral compounds of which it has been found that the B12 clusters are indicated to mediate the interaction.
As-quenched and nanocrystallized structure for Nb-poor Fe–Nb–B–P–Cu soft magnetic alloys melt spun in air
Authors: Makino A. , Bitoh T.
Published: May 2003

The as-quenched and nanocrystallized structures for Nb-poor Fe–Nb–B(–P–Cu) alloys melt spun in air have been investigated. The Nb-poor Fe85Nb6B9 alloy has the as-quenched structure composed of an amorphous phase and large α-Fe grains with 20–45 nm in size. The large α–Fe grains should remain after crystallization and result in a nonuniform nanocrystalline structure with the low permeability (μe) of 14 000 at 1 kHz. The simultaneous replacement of B by 1 at % P and Fe by 0.1 at % Cu for the alloy decreases the α-Fe grain size to nanoscale in an as-quenched state, and realizes a uniform crystallized nanostructure and good magnetic properties (μe=41 000 at 1 kHz and Bs=1.61 T) comparable to those of the typical Fe–M–B nanocrystalline alloys with a fully amorphous phase in an as-quenched state produced in a vacuum or Ar atmosphere. This result indicates that the precursor to the uniform nanostructure with high μe is not always a fully amorphous phase, and there is a possibility to realize the higher Bs materials with higher Fe contents.
Pulsed laser deposition of Y3Fe5O12 and Bi3Fe5O12 films on garnet substrates
Authors: Kahl S. , Grishin A. M.
Published: May 2003

We prepared Y3Fe5O12 (YIG) and Bi3Fe5O12 (BIG) films by pulsed laser deposition and present some practical aspects here. Low laser repetition rates result in a loss of oxygen and reduce the saturation magnetization of YIG by a factor of 5. Small changes of deposition conditions and lattice match for BIG films have little influence on the spectra of Faraday rotation but change magnetic coercivities by a factor of 10. Thin BIG films show higher coercivities than thick films. Coercivities increase with lattice mismatch between film and substrate. The wavelength of maximum Faraday rotation for BIG films in visible light depends on film thickness: We observed a redshift of almost 40 nm for a 2.6 μm thick film as compared to a 470 nm thick film.
More evidence for a distribution of tunnel splittings in Mn12–acetate
Authors: Mertes K. M. , Suzuki Yoko , Sarachik M. P. , Myasoedov Y. , Shtrikman H. , Zeldov E. , Rumberger E. M. , Hendrickson D. N. , Christou G.
Published: May 2003

In magnetic fields applied parallel to the anisotropy axis, the magnetization of Mn12 has been measured in response to a field that is swept back and forth across the resonances corresponding to steps N=4,5,…9. The fraction of molecules remaining in the metastable well after each sweep through the resonance is inconsistent with expectations for an ensemble of identical molecules. The data are consistent instead with the presence of a broad distribution of tunnel splittings. A very good fit is obtained for a Gaussian distribution of the second-order anisotropy tunneling parameter XE=−ln(|E|/2D). We show that dipolar shuffling is a small effect and is not responsible for the nonexponential relaxation.
Anomalous Hall resistivity due to grain boundary in manganite thin films
Authors: Taniyama T. , Hamaya K. , Kitamoto Y. , Yamazaki Y.
Published: May 2003

Anomalous Hall resistivities of polycrystalline manganite thin films with different grain sizes are reported. Positive anomalous Hall coefficients due to grain boundaries are clearly observed besides a negative contribution in the bulk manganite. The positive contribution becomes pronounced with decreasing grain size in the polycrystalline samples, reaching up to 4.2 μΩ cm at 5 K. The temperature dependence of the anomalous Hall resistivity is in good agreement with its magnetoresistive feature. Possible causes for the anomalous contribution are discussed within existing models for granular magnetoresistive thin films or multilayers.
Current-induced switching in low resistance magnetic tunnel junctions
Authors: Liu Yaowen , Zhang Zongzhi , Wang Jianguo , Freitas P. P. , Martins J. L.
Published: May 2003

Current-induced magnetization switching (CIMS) in low resistance tunnel junctions is reported at critical current densities of 1.9×106 A/cm2 for tunnel junction areas ranging from 2 to 3 μm2, and junction resistances from 6 to 20 Ω μm2. Typical tunnel magnetic resistance values for these junctions range from 15% to 21% (measured in an external magnetic field) and 10% to 14% resistance changes are obtained by CIMS. Micromagnetic simulation indicates that vortex fields and spin transfer effects cannot fully account for the observed current-induced switching. Although able to explain the observed transition from a parallel or antiparallel state to a vortex state, it fails to explain the switch back to the original state, at a comparable but symmetrical critical current density.
Magnetostrictive properties of polymer-bonded Fe–Co based alloy composites
Authors: Na S. M. , Suh S. J. , Shin K. H. , Lee Y. S. , Lim S. H.
Published: May 2003

Polymer-bonded composites of a Fe–Co based alloy are fabricated and their magnetic and mechanical properties are characterized. The use of flake-type powders with a thickness of 3–5 μm, instead of conventional spherical powders, is the key to good magnetostrictive properties and this is made possible by suitable design of the alloy (Fe36Co62Ge2) and the development of a pulverization process. The composites exhibit high magnetostriction of 105 ppm measured at an applied field of 4.3 kOe (70 ppm at 1 kOe). Large compressive strength of 42 MPa is also obtained for the composites, indicating solid bonding of flake-type powders by the polymer.
Fabrication condition effects on the magnetic and magnetostrictive properties of sputtered Tb-Fe thin films
Authors: Na S. M. , Suh S. J. , Lim S. H.
Published: May 2003

Magnetic and magnetostrictive properties of amorphous Tb-Fe thin films are investigated as functions of sputtering conditions such as the substrate thickness, input power, sputtering time, and coverage area ratio of coated thin film to substrate. The observed magnetic and magnetostrictive properties are well explained in terms of the macroscopic tensile stress, which is formed due to the difference of the thermal expansion coefficients between the thin film and substrate, and an annealing effect. The macroscopic tensile stress enhances in-plane anisotropy, and the annealing effect mainly reduces local residual stress introduced during sputtering. At sputtering conditions corresponding to a high thin-film/substrate temperature, the macroscopic tensile and an annealing effect are high, causing the magnetostriction sensitivity to increase at low magnetic fields, coercivity, and remanence ratio.
Magnetic force microscopy evaluation of written track distortions induced by media stray fields
Authors: Li Shaoping , Zhu Wenzhong , Wang Lei , Palmer Dean
Published: May 2003

The precise examination of the written track distortions induced by stray fields from media can help in understanding the magnetic recording process in many ways so as to optimize recording components/subsystem performance. In this work, the edge distortion, amplitude asymmetry, and transition shift of written tracks, which are induced by the media magnetostatic field, are characterized using the magnetic force microscope via a special analysis procedure. The written track distortions on different media erasure backgrounds and track edge environments were evaluated with the measurement accuracy as low as ±2 nm.
Fe
3
Pd
ferromagnetic shape memory alloys
Authors: Stern R. A. , Willoughby S. D. , MacLaren J. M. , Cui J. , Pan Q. , James R. D.
Published: May 2003

Fe 3 Pd alloys are potentially useful ferromagnetic shape memory materials with a maximum predicted strain of up to 6.8%. Currently, however, there are difficulties with fabrication of the desired fct-ordered martensitic phase. The experimentally observed ground state of Fe3Pd is a nonreversible bct phase, and a rapid quench is required to form the martensitic. This quench freezes substitutional disorder into the crystal, reducing the maximum obtainable strain to about 1%. Thus, discovering how to stabilize an ordered fct phase of Fe3Pd is of paramount importance if this is to become a usable shape memory material. Electronic structure calculations indicate the ordered fct phase can be energetically stabilized by decreasing the c/a ratio below the equilibrium value. This might be achieved by doping with materials containing a lone valence p-electron, such as B or Al. Furthermore, a rigid band analysis suggests that addition of electrons to the system through alloying slightly favors the ordered phase.
Thin Al, Au, Cu, Ni, Fe, and Ta films as oxidation barriers for Co in air
Authors: Gan L. , Gomez R. D. , Powell C. J. , McMichael R. D. , Chen P. J. , Egelhoff W. F.
Published: May 2003

We have investigated the effectiveness of Al, Au, Cu, Ni, Fe, and Ta films with thicknesses up to 4 nm for protecting a Co surface from oxidation in air at room temperature. The distinct change in the Co 2p3/2 core-level line shape observed by x-ray photoelectron spectroscopy upon the oxidation of Co makes it a simple matter to identify the fractions of the Co that are in the metallic state and in the oxidized state. We find that the best choices for protecting Co from oxidation are Al and Ta. We found that Au, which is one of the most popular choices, is not particularly effective for protecting Co.
Surface, interface and bulk studies of NiFe nanometer films for magnetoresistive heads
Authors: Hollingworth M. P. , Gibbs M. R. J. , Hill E. W.
Published: May 2003

Polycrystalline Ni81Fe19 films have been vapor-deposited in a forming field onto a 100-μm-thick borosilicate glass. The free surface and film/substrate interface magnetization has been probed using magneto-optical Kerr effect (MOKE) magnetometry, and bulk measurements have been taken using an alternating gradient force magnetometer. Saturation magnetostriction constants were derived from the strain dependence of the anisotropy field in the MOKE measurements, separating out for the first time free surface and interface effects. The free surface showed a clear uniaxial anisotropy with a low dispersion, while the interface showed a mixture of domain switching and moment rotation. We interpret the data in terms of a gradient in magnetic properties through the sample, and discuss consequences for magnetoresistive heads.
Resonant magnetic x-ray and neutron diffuse studies of transition metal multilayers
Authors: Hase T. P. A. , Buchanan J. D. R. , Tanner B. K. , Langridge S. , Dalgliesh R. M. , Foster S. , Marrows C. H. , Hickey B. J.
Published: May 2003

Electron scattering mechanisms within metallic multilayers are affected by both structural and magnetic disorders. Off-specular x-ray scattering has long been used to probe the structural interfaces, and it is only recently that it has been applied to the study of magnetic disorder. We compare the resonant magnetic x-ray scattering with off-specular neutron studies from magnetron-sputtered Co/Cu and Co/Ru multilayers grown at the second antiferromagnetic coupling peak. Both techniques yield similar results for the Cu system, and a simple domain model can be applied to extract the magnetic interface morphological parameters. For the Cu system, the in-plane correlation length is field dependent and is 880±20 Å after saturation along the hard axis, but increases to 7000±100 Å after saturation along the orthogonal easy axis. Both systems show strong out-of-plane correlations in both the structural and magnetic disorders. In all cases, the out-of-plane correlation length for the structural interfaces is 200–250 Å, but the ratio of the magnetic to structural correlations length is dependent on the magnitude of the exchange coupling and ranges from 0.4 to 1.4.
Exchange bias in Co/Co3O4 bilayers
Authors: You Biao , Wang Yixing , Zhao Yanling , Sun Liang , Sheng Wenting , Pan Minghu , Du Jun , Hu An , Lu Mu
Published: May 2003

Exchange biasing effect in Co/Co3O4(t) bilayers was carefully investigated by a vibrating sample magnetometer. It was surprising that a significant exchange bias effect appeared when the temperature varied from 90 to 220 K. In this temperature range bulk Co3O4 should be in a paramagnetic state because its Néel temperature is about 40 K. The exchange bias field (HE) of Co/Co3O4 fluctuated in the range of 110–130 Oe with various thickness of Co3O4 at 90 K and HE was zero when the temperature was above 220 K. X-ray photoelectron spectroscopy results indicated that a thin CoO layer formed near the interface, which may be due to the interdiffusion between Co and Co3O4 layers. Therefore, the exchange bias effect in Co/Co3O4 bilayers is thought to be dominated by the exchange coupling between the Co and CoO layers. Using the finite-size effect theory, we evaluated the average thickness of interfacial CoO layer to be 39 Å. The fluctuation of HE in Co/Co3O4 is probably due to thickness fluctuations of the CoO. Assuming that HE is inversely proportional to the thickness of CoO, we can conclude that the approximate thickness range of CoO is from 36 to 43 Å.
Structural and magnetic characterization of ion-beam deposited NiFe/NixFe1−xO composite films
Authors: Lin K.-W. , Gambino R. J. , Lewis L. H.
Published: May 2003

Nanocomposite films of Ni80Fe20/NixFe1−xO were prepared by a dual ion-beam deposition technique. The structural and magnetic properties of nanocomposite films fabricated with oxygen content in the deposition assist beam ranging from 0% to 55% were studied. The dependence of the resistivity on oxygen percent shows that the compositions with exchange-enhanced coercivity are close to a percolation threshold. A strong temperature dependence of coercivity Hc and exchange bias field Hex is found in these composite films. Films prepared with 46% O2 in the assist beam exhibit an enhanced Hc relative to Permalloy (Ni80Fe20) and a characteristic shifted hysteresis loop indicative of exchange coupling between the constituent metal and oxide phases. At T=10 K, films prepared with 44% O2 in the assist beam have an exchange shift Hex∼−225 Oe with a blocking temperature TB∼100 K that reflects the low Néel temperatures of FeO-rich NixFe1−xO solid solutions.
Control of exchange bias by diluting the antiferromagnetic layer
Authors: Misra A. , Nowak U. , Usadel K. D.
Published: May 2003

The domain state model for exchange bias is used for an investigation of recent experiments where the magnitude and direction of the exchange bias was controlled by He ion irradiation of an FeNi/FeMn sample. The defects in the sample which result from the irradiation are modeled as diluting the antiferromagnet (AFM) after the initial cooling procedure. This late dilution, carried out in presence of a field, leads to a rearrangement of the original domain structure of the AFM resulting in an enhancement or reduction in the bias field.
Simple iterative calculation of micromagnetic kernels
Authors: Apalkov D. M. , Visscher P. B.
Published: May 2003

To calculate the magnetostatic field in a micromagnetic calculation, it is customary to use a stored “kernel,” which is the average field in a cubic cell due to a uniform magnetization in some other cell. This can be calculated from a dipole approximation if the cells are far apart, but is obtained from a table of stored kernels for a finite set of small cell-separation vectors. The kernel is usually calculated numerically or analytically, either of which is laborious and error-prone. We have found an iterative method that requires almost no coding beyond what is already present in a micromagnetic code, and converges much more rapidly than finite-element integration.