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In orthogonal frequency-division multiple access (OFDMA), closely spaced multiple subcarriers are assigned to different users for parallel signal transmission. An interleaved subcarrier-assignment scheme is preferred because it provides maximum frequency diversity and increases the capacity in frequency-selective fading channels. The subcarriers are overlapping, but orthogonal to each other such that there is no intercarrier interference (ICI). Carrier-frequency offsets (CFOs) between the transmitter and the receiver destroy the orthogonality and introduces ICI, resulting in multiple-access interference. This paper exploits the inner structure of the signals for CFO estimation in the uplink of interleaved OFDMA systems. A new uplink signal model is presented, and an estimation algorithm based on the signal structure is proposed for estimating the CFOs of all users using only one OFDMA block. Diversity schemes are also presented to improve the estimation performance. Simulation results illustrate the high accuracy and efficiency of the proposed algorithm.

In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle αR (associated with an inflection in the lattice constant aR) near 400 and 350 °C in BiFeO3 (BFO) and (BiFeO3)0.95(BaTiO3)0.05 (BFO-5%BT), respectively. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic-paramagnetic transition, which is responsible for the broad frequency-dependent dielectric maxima. A rhombohedral (R)-orthorhombic (O)-cubic (C) transition sequence takes place near 820 and 850 °C in BFO upon heating. BFO-5%BT exhibits a R-C transition near 830 °C. The BaTiO3 substitution can enhance dielectric and ferromagnetic responses and reduce electric leakage. The dielectric loss of BFO-5%BT remains less than 0.04 below 150 °C. [ABSTRACT FROM AUTHOR]

Cupric oxide (CuO) nanoparticles with different morphologies were synthesized by thermal annealing of the copper hydroxide at various temperatures. Significant changes in both the particle size and the morphology with the annealing temperature (TA) were observed. The average particle size (d) increases from 13 to 33 nm and the morphology varies from ellipsoidal to rodlike as TA increases from 150 to 550 °C. The formation of these morphologies is explained in terms of the variation in the interplanar H-bonds breaking rate with different temperatures. The magnetic measurements reveal the presence of weak ferromagnetic interaction and the blocking behavior in these nanoparticles. The magnetic field dependence of the superparamagnetic blocking temperature (TB) follows the Brown equation. In addition, the linear variation in zero field cooled susceptibility with particle size is consistent with the predictions of Néel model for the uncompensated spins. These surface spins are responsible for the observed anomalous magnetic properties of CuO nanoparticles. [ABSTRACT FROM AUTHOR]

Step edge growth of Co nanoislands on Cu(111) surface have been investigated by scanning tunneling microscopy (STM). The cobalt atoms cluster at the upper step edges and form bilayer islands of 2 nm in diameter (about nine Co atoms in width) initially during the initial stage of Co deposition. This result is in accordance with the total energy calculations within density functional theory. Besides, the size and amount of nanoislands increase with increasing coverage. The average number of Co atoms contained in one island increases with a rate of 375 atoms per monolayer (ML). The statistics data on the STM images indicate that the cobalt nanoislands preferentially grow at the upper step edge during the first stage of Co deposition, then toward terrace, and finally, the growth rate of islands in edge is almost the same as that in terrace for Co thickness above 0.78–1.42 ML. [ABSTRACT FROM AUTHOR]

CoFeB films were deposited on glass substrate by the sputtering method. From x-ray-diffraction and electron-diffraction-ring patterns, the major phase in the as-deposited CoFeB film is amorphous (or nanocrystalline). However, we could also identify a minor CoFe(110) crystalline phase in the film. We have tried to suppress this crystalline phase by changing the Ar partial pressure (PAr) during deposition and found that the optimal condition is PAr=5×10-3 Torr. Because the electrical resistivity value (ρ) of the film is in general larger than 100 μΩ cm, it also indicates that the amorphous phase is dominant. From the temperature coefficient of resistance measurement, we learn that the amorphous phase in the CoFeB film crystallizes in succession at two higher temperatures (Tcr1 and Tcr2) than the room temperature (RT). Besides the electrical properties, the film thickness (tf) dependence of saturation magnetization (Ms), saturation magnetostriction (λs), and coercivity (Hc) has also been discussed. From the Auger-depth profile analysis, it is found that there is one CoOx (with 0.4<=x<1) oxide layer, about 15 Å in thickness, lying on the top surface of the CoFeB film, and another CoOx oxide layer, about 20 Å, lying near the CoFeB/glass interface. At RT CoOx is supposed to be paramagnetic. However, due to the proximity effect between CoOx and CoFeB, the CoOx layers may become ferromagnetic with the average magnetization Mox. By fitting the Ms data as a function of (1/tf), we can show that the last conjecture is correct, and Mox is not zero. The CoOx layer plays an important role on Ms,λs, and Hc of the CoFeB films with tf ranging from 50 to 503 Å. [ABSTRACT FROM AUTHOR]

This article correlated Nd2Fe14B single-layer and [(Nd2Fe14B)x/Nb]n multilayer film magnetization reversal processes to the observed microstructure image. Coercivity temperature dependence was fitted to modified nucleation and pinning models. The microstructure parameter (αK) describes the deteriorating effect of Nd2Fe14B grain anisotropy on coercivity in the nucleation model. For a single layer with 400 nm thickness, the αK values change from 0.18 to 0.43 when annealing temperature increases from 550 to 903 K. The highest values of single- and multilayer films are 0.46 and 0.70, respectively. Film magnetization reversals were predominant and fitted the reverse domain nucleation model well. The Nb spacer layer enriched the grain boundaries of the Nd2Fe14B phase, which in turn inhibited the grain growth. [ABSTRACT FROM AUTHOR]

Superconducting transition temperatures T[sub c] of sputtered Co/SC/Co trilayers and SC/Co bilayers with SC= Nb and NbTi were studied by the electrical resistivity and magnetic susceptibility. For a fixed Co layer thickness, T[sub c] decreases with decreasing SC layer thickness. By applying a published model for the effects of pair breaking, the critical SC layer thickness d[sub SC] was deduced. The effect of interface roughness on T[sub c](d[sub SC]) is discussed from the viewpoint of the superconducting coherence length. [ABSTRACT FROM AUTHOR]

Spin-dependent tunnel junctions, Co/Al[sub 2]O[sub 3]/Co (CoFe)/NiFe, were fabricated to investigate the effect of the additional Co (CoFe) interlayer on tunneling magnetoresistance. The quality of the junction was examined with a cross-sectional image generated by high-resolution transmission electron microscopy, and an electron energy loss spectra map. For junctions with a Co (CoFe) interlayer in the top electrode thinner than 0.8 nm (1.0 nm), the tunneling magnetoresistance ratio increases with interlayer thickness. For junctions with a 0.8–2.0 nm Co (1.0–2.0 nm CoFe) interlayer in the top electrode, the tunneling magnetoresistance ratio reaches the maximum value of 2.16 (4.45) times that without any Co (CoFe) interlayer in the top electrode. The increase in the tunneling magnetoresistance ratio may be attributed to the increased effective ferromagnetic electrode polarization and the various spin-flip scattering factors. [ABSTRACT FROM AUTHOR]

A series of Permalloy films, of various shapes such as a square, a rectangle, a circle, and a rhombus, was made. The sample length to width ratio L/w varied from 1 (i.e., square) to 29 (i.e., rectangle). We studied how the planar Hall effect (PHE) signal was affected by adding a transverse field H[sub y] along the easy-axis direction of the sample. It was found that in a certain range of H[sub y], the PHE sensitivity S might become inoperative, i.e., S changed linearly as a function of H[sub y] from -S[sub max] to + S[sub max] (or vice versa), where S[sub max] was the maximum sensitivity. This phenomenon is explained by considering the Zeeman-energy and the single-domain-rotation effects. In particular, for the square sample, the following data exist: (1) S[sub max] is as high as 310 Ω/T at the film thickness t= 500 Å, and (2) the inoperative range for H[sub y] is the narrowest among all the samples. From this study, we conclude that the field of the Earth H[sub e]—as long as its horizontal component is larger than 0.25 Oe—can be employed to stabilize the magnetic structure of a Permalloy element and to achieve the best PHE performance with S[sub max]. [ABSTRACT FROM AUTHOR]

The magnetic characteristics of BaFe12-2xCoxSnxO19 powders prepared by the chemical coprecipitation annealing technique were investigated. The results showed that as x was increased, the saturation magnetization gradually decreased although the coercivity underwent a rapid deterioration. When x=0.8, the coercivity went below 1,000 Oe and the saturation magnetization was approximately 52 emu/g.

Presents a study which investigated the changes in various superconducting properties as a function of silver substitution in the bulk granular. Problems concerning the location of silver atoms and formation of silver clusters; Background on magnetic field dependence; Importance of impurity control and stoichiometric variation in tailoring the various superconducting properties.

Nanometer size [Fe.sub.3][O.sub.4] particles were fabricated by chemical coprecipitation technique. The particle shape and size are affected by the PH value of the reactive solutions. The ferrofluids were fabricated with the [Fe.sub.3][O.sub.4] particles as magnetic particles, ammonium oleate as surfactant, and de-ionized water as solvent. Optical transmission of [Fe.sub.3][O.sub.4] nanoparticle ferrofluids was investigated as a function of incident optical wavelengths between 450 and 750 nm and applied magnetic fields up to 150 Oe. In general, for samples with lower PH value, the particles are small and agglomerate together, however, for samples with higher PH value, the particles are larger and distributed uniformly. Samples precipitated with higher PH value show larger variation of the transmittance ([Delta]T). This can be understood by our transmission electron microscope and X-ray diffraction pattern studies. The behavior of agglomeration for samples with lower PH value relates to the smaller variation of the optical transmission to the magnetic field. Index Terms--Chemical coprecipitation, [Fe.sub.3][O.sub.4], nanoparticle ferrofluid.

The magnetic properties of ultrathin Co/Ag/Si(111) films were studied by surface magneto-optic Kerr effect. A magnetic phase diagram for binary-metal Co/Ag films deposited on Si(111) surfaces has been successfully established. The phase diagram can be divided into four regions: nonferromagnetic Co-Si compound; low Curie temperature Co film; canted out-of-plane anisotropy; in-plane anisotropy. The ferromagnetic inactive layers at the Co/Si interface are formed due to intermixing of Co and Si; and can be efficiently reduced by the Ag buffer layer. We have demonstrated that the inactive layer thickness is reduced from 2.1ML for Co/Si(Ill), to 1.0 for Co/2.8MLAg/Si(111), and 0.0 for Co/5.6MLAg/Si(111). Index Terms--cobalt, magneto-optic Kerr effect, ultrathin film

The thermal stability, interlayer diffusion, and magnetic properties of FePt(100 nm) single-layer and multilayer [Os(5 nm) /FePt(25 nm)]4 films on a Si(100) substrate with/without a 10-nm-thick Os underlayer have been studied as functions of the annealing temperatures between 400 and 800 °C. The insertion of a thin Os layer into the FePt and Si(100) interface results in better thermal stability. No diffusion evidence was found in samples with an Os underlayer for annealing temperatures up to 700 °C, as seen from x-ray, transmission electron microscopy, and magnetic studies. We have experimentally demonstrated that the Os underlayer can effectively prevent the diffusion of the intermixing between the FePt layer and the Si(100) substrate for temperatures up to 700 °C. As a result of this study, the Os has potential to be a better diffusion barrier to prevent the diffusion of the FePt film on a Si(100) substrate from forming an ordered face centered tetragonal (fct) L10 hard magnetic phase. [ABSTRACT FROM AUTHOR]

The spin damping behavior of the bismuth-substituted yttrium iron garnets (BixY3-xFe5O12) prepared by the coprecipitation process was investigated using the ferromagnetic resonant (FMR) in this study. By analyzing the FMR responses, the spin damping coefficient of the x=0.25-1.25 in polycrystalline Bi:YIG (yttrium aluminum garnet) samples was obtained from the 3 dB linewidth of their FMR spectra. The data demonstrated that the damping coefficient started from 3.21×10-3 for x=0.25 and went to its minimum value of 0.31×10-3 for x=0.75. However, the damping coefficient enhanced to 8.55×10-3 with increasing of the bismuth concentration to x=1.25. The results revealed that the spin damping behavior of the Bi:YIG garnets was strongly dependent on a YFeO3 (111) phase. [ABSTRACT FROM AUTHOR]

In this study, the influence of the addition of carbon nanotube (CNT) (0, 0.5, 1.0, and 2.0 wt %) on complex permittivity, complex permeability, and reflection loss for La0.7Sr0.3MnO3-δ (LSMO)/ polymer composites was investigated. Microwave absorbing composites were prepared by molding and curing a mixture of LSMO powders, CNTs, and epoxy resin. The complex permittivity and complex permeability for LSMO/CNT composites were examined by a cavity perturbation technique. The experimental results showed that the complex permittivity increased with increasing CNT addition and the imaginary part of the permeability decreased with rising frequency. In the present study, a microwave absorbing composite filled with 80 wt % LSOM powders and 2 wt % CNTs exhibited the optimum performance, that is, the microwave absorbing peak was -22.85 dB at 9.5 GHz and the -10 dB absorbing bandwidth reached 3.3 GHz for the sample with a matching thickness of 3 mm. [ABSTRACT FROM AUTHOR]

The optical transmittance increases with decreasing the concentration of FePt in both water-based and hexane-based ferrofluids. However, under an applied magnetic field H, the transmittance T increases with increasing H field. The variation in transmittance ΔT increases rapidly for samples in hexane at H=182 Oe. However, ΔT is very small for samples in distilled water. This can be explained due to the different aggregation ability of magnetic particles in ferrofluid. For the samples in hexane, its larger aggregation ability makes the magnetic particles easier to agglomerate and becomes much more chainlike elongated along the perpendicular magnetic field. Thus, it makes the area covered by the droplets per unit area in ferrofluid decrease and the ΔT increases with increasing the magnetic field. However, for samples in hexane, the optical properties may also be related with the Mie resonance. At H>60 Oe, the particle aggregation occurs and elongates more along the magnetic fields. This would cause the longitudinal plasmon resonance absorption to shift to a longer wavelength. Therefore, the absorption increases and the variation in transmittance ΔT decreases with increasing the incident wavelength. [ABSTRACT FROM AUTHOR]

Results on both field driven and current induced domain wall motion in Co/Cu/Ni80Fe20 trilayered half-ring in-series wires with different linewidths were presented. The switching behavior depends linearly on the linewidth of Co/Cu/Ni80Fe20 trilayered half-ring structures. A larger bias field (Hb) applied to the samples results in a smaller critical current needed to reverse magnetization. The critical current density was observed to be 3×107 A/cm2 for Ni80Fe20 and 2×108 A/cm2 for Co at zero field. The results of the numbers of giant magnetoresistance jump (digital) versus external magnetic field and current densities (analog) of this design have potential utility as an analog-digital converter. [ABSTRACT FROM AUTHOR]

The magnetic-induced dielectric responses of BiFeO3 (BFO) thin films were measured at the X-band microwave frequency ranged from 7 to 12.5 GHz. The measurement was given initially by a high-precision cavity microwave resonator without magnetic field. Both the real and imaginary parts of the permittivity showed its dielectric property as a function of the measuring frequency. The X-band dielectric responses of the BFO thin film were then measured by a controlled magnetic field at room temperature. The data demonstrated up to 2.2% dielectric tunability by using only 3.46 kOe magnetic field at TE107 mode (9.97705 GHz). [ABSTRACT FROM AUTHOR]

The crystal structures, magnetic properties, and the behaviors of ferromagnetic resonance of the GaAs(001)/Fe/Ag/Fe multilayers with different thicknesses of the Fe seeding layer are investigated. For the first time, a transformation from polycrystal into nearly bcc (001) single-crystal structure is observed in the top Fe layer while the thickness of the Fe seeding layer increases. The frequency of ferromagnetic resonance in Fe/Ag/Fe multilayers can be tuned by varying the strength of the external magnetic field and the thickness of the Fe seeding layer. Also it can be well fitted by the resonance equation. The correlation between crystal structures and ferromagnetic resonance manifests itself. [ABSTRACT FROM AUTHOR]

A cavity perturbation resonance technique is used to determine the complex permittivity and permeability of iron-based composite absorbers prepared by mixing various weight percentages of carbonyl iron powder with epoxy as the matrix. The complex permittivity ([variant_greek_epsilon]′-j[variant_greek_epsilon]″) and permeability (μ′-jμ″) are measured around X-band (7–12.5 GHz for permittivity and 7.5–14 GHz for permeability) by the cavity perturbation resonance technique and the results are compared with those obtained by the transmission/reflection method. Experimental results show that the average differences of real parts of permittivity ([variant_greek_epsilon]′) and real and imaginary parts of permeability (μ′ and μ″) measured by these two techniques are less than 10%. The differences in [variant_greek_epsilon]″, however, is apparently higher than the others. As a general trend, the difference increases with increasing weight percentage of carbonyl iron. [ABSTRACT FROM AUTHOR]

We demonstrate detecting chirality of vortex state in a magnetic ring by lateral nonlocal spin-valve (NLSV) measurement. A Permalloy (Py) ring, a Py narrow wire, and copper contacts were used as spin injector, detector, and the normal-metal diffusive channel, respectively. By comparing the anisotropic magnetoresistance loop of the individual ring with NLSV loop, the vortex chirality and the related switching field of the ring can be determined. Both onion-to-vortex transition field and vortex chirality were found to alternate in both the same and different current probe arrangements on the magnetic ring. [ABSTRACT FROM AUTHOR]

NiFe inserted layer with different thicknesses on the dielectric properties of multiferroic AlN/NiFe/AlN multilayer films fabricated on the B270 glass substrates by the reactive sputtering technique was studied. The variation of dielectric constant for multilayer films is dependent on the thickness of the NiFe inserted layer observed from 40 Hz to 30 MHz. In this work, single AlN layer exhibits dielectric constant value of around 6.5. However, we find that the dielectric constant of the AlN/NiFe/AlN multilayer films is raised up to 60 for even with a 1 nm thick NiFe inserted layer. Additionally, this work also indicates that the dielectric tunability of AlN/NiFe/AlN films is dependent on the external magnetic field. These results conclude some magnetoelectric properties of AlN films those in relation to the NiFe ferromagnetic inserted layer. Possible mechanisms for the enhanced dielectric constant in the AlN/NiFe/AlN films have been discussed in the paper. [ABSTRACT FROM AUTHOR]

Cross-strip magnetic tunnel junctions (MTJs) were fabricated following this sequence: Si(100)/Ta(30 Å)/CoFeB(80 Å)/AlOx(to)/Co(70 Å)/IrMn(90 Å)/Ta(100 Å), under an in-plane deposition field (h)=500 Oe, where to=12, 17, 22, and 26 Å is the thickness of the AlOx layer. From the resistance (Ro) versus to plot, Ro increases from 255 to 1138 Ω exponentially, as to increases from 12 to 26 Å. This indicates that the quantum tunneling mechanism is valid in our case. Furthermore, the tunneling magnetoresistance (TMR) increases initially from 49% to 63% and then decreases to 33%, as to increases monotonically. This shows that with the increase of the barrier thickness, to>=17 Å, the spin polarization in the current after tunneling is weakened eventually. The microstructure of the to=17 Å MTJ observed under high-resolution cross-sectional transmission electron microscope shows that the interfaces between CoFeB/AlOx and AlOx/Co are smooth, resulting in the high TMR ratio observed. Saturation magnetostriction (λs) of this series of CoFeB/AlOx/Co MTJs ranges from -5 to -2 ppm. The λs versus to plot also shows the concave-up feature. Finally, we find that the optimal MTJ has the following properties: TMR=63% and λs=-5 ppm. [ABSTRACT FROM AUTHOR]

Magnetic properties, phase evolution, and microstructure of melt-spun (Sm1-xPrx)Co7-yHfyCz ribbons have been investigated. For (Sm1-xPrx)Co7-yHfy (x=0–1; y=0.1–0.3) ribbons, the magnetization increases, but coercivity decreases, with increasing Pr content. However, the phase constitution and microstructure have not been influenced by modifying Pr content x. The attractive magnetic properties of Br=6.5 kG, iHc=6.1 kOe, and (BH)max=7.2 MG Oe could be obtained for (Sm0.8Pr0.2)Co6.9Hf0.1 ribbons. A slight addition of C in (Sm0.8Pr0.2)Co6.9Hf0.1Cz (z=0.06–0.14) ribbon not only refines the microstructure, but also induces nanoscale fcc-Co precipitation in the matrix, leading to the stronger exchange-coupling effect between magnetic grains and the enhancement of remanence and magnetic energy product. As a result, the improved magnetic properties of Br=7.1 kOe, iHc=8.5 kOe, and (BH)max=11.2 MG Oe can be achieved for (Sm0.8Pr0.2)Co6.9Hf0.1C0.12 ribbons. [ABSTRACT FROM AUTHOR]

The effect of microstructure refinement on magnetic properties in single-phase Ll0 Fe58Pt42 films was studied. Samples with thickness t of 100, 200, and 300 nm were sputtering deposited on glass substrate with elevated temperatures Ta of 400 and 800 °C. In the t=300 series of films, the order parameter of films with Ta=400 and 800 °C were identical, about 0.663, but the average grain size is different by approximately eight times in diameter (from ∼75 to ∼610 nm). Comparing to the film of Ta=800 °C with large grains, significant enhancement in remanence of about 32% was obtained in the 400 °C annealed film (∼880 emu/cm3) and the energy density was achieved an increment of about 72% (19.6 MG Oe), which exceeds the theoretical preditions. The reasonable explanations are summarized as the dimension confinement of interactions and the degradation of anisotropy. [ABSTRACT FROM AUTHOR]

FePt thin films with the addition of Ag layers have been fabricated in order to study the microstructure and magnetic properties via a molecular beam epitaxy technique on MgO (001) single-crystal substrates at 350 °C. The enhancement of the coercivity is due to the film structures changed from continuous state to an isolated particulate character, not an ordering enhancement of FePt films with Ag addition. Studies of angular dependent coercivity show a tendency of a domain-wall motion shift toward rotation of reverse-domain type with the addition of Ag layers into the FePt films. The intergrain interaction was confirmed from the Kelly-Henkel plot that indicated FePt films with Ag addition can lead to the reduction of intergrain exchange coupling. [ABSTRACT FROM AUTHOR]

Spin accumulation effect and anomalous magnetoresistance resulting in spin dependent transport in NiFe/Al/NiFe single-electron transistors have been studied. The magnetic tunneling process is strongly influenced by the charging energy and a superconducting gap. The magnetoresistance is enhanced with decreasing bias voltage. In addition, a suppressed superconducting gap caused by spin accumulation was experimentally demonstrated. For higher bias voltage, the spin accumulation induced by the spin-valve effect is seen as periodic oscillation in a Coulomb blockade region. Below the critical voltage, which is the sum of the superconducting gap and charging energy, spin accumulation can suppress the superconductivity and induce anomalous magnetoresistance. [ABSTRACT FROM AUTHOR]

Magnetic interactions between permalloy elliptical rings in different arrangements of two-dimensional arrays were investigated. The edge-to-edge distances between units along the long axis were changed from 2 μm down to 100 nm. Formation of domain walls during magnetization reversals results in magnetostatic coupling between adjacent units. When two neighboring rows were shifted one-half pitch along the short axis to form a shift-type array, large stable field range for vortex states was obtained. [ABSTRACT FROM AUTHOR]

The effects of underlayer on the microstructure and magnetic characterizations of epitaxial FePt films were studied. Enhanced out-of-plane coercivity and ordering were obtained in the Pt-underlayered FePt samples, which may be due to the proper lattice strain from the Pt underlayer. The larger lattice parameter of Pt may enlarge the a axis and reduce the c axis of the L10 FePt phase and result in low-temperature ordering. However, such an effect does not appear in Fe-underlayered samples because of the smaller lattice parameter and the considerable interdiffusion. The angular dependence coercivity revealed that the dominant reversal mechanism of the FePt films changed from domain-wall motion to rotation, which is caused by the formation of L10 island structures induced by the Pt underlayer. On the other hand, the Fe-underlayered FePt films showed a broad peak roughly at 45°, implying the tilt of the easy axis about 45° away from the film normal. [ABSTRACT FROM AUTHOR]

Fe/Pt multilayer films capped with an amorphous SiO2 layer have been fabricated in order to study the microstructure and magnetic properties via a molecular beam epitaxy technique at 400 °C. The formation of granularlike FePt films was obtained with this process due to the interpenetration of SiO2 which has a lower surface energy. Studies of angular dependent coercivity show a tendency of a domain-wall motion weaken toward rotation of reverse-domain type upon thickness of SiO2 capping layer atop the Fe/Pt multilayer films. The intergrain interaction was confirmed from the Kelly–Henkel plot that indicated the exchange coupling between neighboring grains in the uncapped FePt films. On the other hand, negative δM value was obtained when the FePt films capped with SiO2 layer, indicating that the SiO2 capping layer can lead to the reduction of intergrain exchange coupling in SiO2/FePt films. [ABSTRACT FROM AUTHOR]

Mn-doped CuO nanoparticles were synthesized using a coprecipitation method. Powder x-ray analysis reveals that all the samples crystallize into a monoclinic-type structure. Significant changes occur in both the microstructure and particle size with calcination temperature TA. The average particle size d increases from 11 to 85 nm as the TA increases from 250 to 850 °C. For particles of size d≤22 nm, energy dispersive spectroscopy indicates the existence of a crystalline Cu1-xMnxO core surrounded by an amorphous CuO shell. M(T) curves reveal a spin-glass behavior for the 11 and 22 nm particles and a ferromagnetic behavior for particles of size d>=35 nm. The observed ferromagnetic behavior is attributed to the coexistence of Mn2+ and Mn3+ ions. [ABSTRACT FROM AUTHOR]

Magnetic properties, phase evolution, and microstructure of melt spun SmCo7-xHfxCy (x=0–0.5; y=0–0.14) ribbons via direct quenching have been investigated. For SmCo7-xHfx series ribbons, proper volume fraction of Hf is effective to stabilize and increase the magnetocrystalline anisotropy field of the TbCu7-type structure. Accordingly, the optimal magnetic properties of Br=6.4 kG, iHc=7.3 kOe, and (BH)max=8.7 MG Oe could be obtained for x=0.1. Furthermore, a slight C addition to above alloys is helpful in refining the grain size of the ribbons from 100–400 nm for C-free to 10–80 nm for C-containing samples. As a result, the magnetic properties are further improved to Br=6.9 kG, iHc=11.8 kOe, and (BH)max=10.6 MG Oe for SmCo6.8Hf0.2C0.12 nanocomposite ribbons. [ABSTRACT FROM AUTHOR]