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We introduce an implementation of magnetophoresis to measure the absolute magnetization of ferromagnetic nanorods dispersed in fluids, by analyzing the velocity of single nanorods under an applied magnetic field gradient. A microfluidic guideway prevents aggregation of nanorods, isolates them, and confines their motion for analysis. We use a three-dimensional imaging system to precisely track nanorod velocity and particle-surface proximity. We test the effect of the guideway on nanorod velocity under field gradient application, finding that it guides magnetophoresis, but imposes insignificant drag beyond that of a planar surface. This result provides insight into the transport of magnetic nanorods at microstructured interfaces and allows the use of an analytical model to accurately determine the reacted viscous drag in the force balance needed for quantitative magnetometry. We also estimate the confining potential of the guideway with Brownian motion measurements and Boltzmann statistics. We use our technique to measure the magnetization of ferromagnetic nanorods with a noise floor of 8.5 × 10-20 A·m2·Hz-½. Our technique is quantitative, rapid, and scalable for determining the absolute magnetization of ferromagnetic nanoparticles with high throughput. [ABSTRACT FROM AUTHOR]

A spin wave Doppler technique is used to measure the spin transfer velocity and the current polarization in current-carrying (Ni0.80Fe0.20)1-xGdx alloy wires. Reduced magnetization values with Gd doping suggest possible increases in the spin transfer velocity. Contrary to these expectations, we measured a decrease in the spin transfer velocity upon introducing Gd dopants. For a current density of 1011 A/m2, the measured velocities range from 6.0 m/s ± 0.6 m/s for pure Permalloy (Ni0.80Fe0.20) to 2.6 m/s ± 0.3 m/s for (Ni0.80Fe0.20)0.945Gd0.055. Interpretation of these values yields a current polarization ranging from 0.71 ± 0.02 to 0.30 ± 0.01 for the same compositions. These results reveal that Gd dopants in Permalloy have a more significant impact on the current polarization than on the material's magnetization for these alloy compositions. [ABSTRACT FROM AUTHOR]

This paper reports effects of inter-film interactions on static and dynamic magnetization behavior at film edges in magnetic trilayer stripe arrays under transverse applied fields. The trilayers consist of two magnetic films of Ni80Fe20, 10 nm and 20 nm thick that interact via dipolar fields across thin, nonmagnetic spacers from 1 nm to 20 nm thick. These trilayer films are patterned into stripe arrays by optical interference lithography. Ferromagnetic resonance spectra exhibit separate edge modes that are identified as excitation of edge modes primarily in one magnetic film or the other. When interlayer exchange is negligible, we observe several effects of dipolar edge-edge coupling including shifts of the edge saturation fields and changes in the mode intensity ratio relative to single-film edges. These interaction effects are reproduced by micromagnetic modeling and explained by simple models. [ABSTRACT FROM AUTHOR]

We use “edge mode” ferromagnetic resonance to probe the magnetic properties of oxidized Ni80Fe20 (Py) nanostripe edges. The oxidation is carried out using either oxygen plasma or thermal annealing in an oxygen ambient. We find that for both treatments the edge saturation field decreases systematically with increasing oxidation due to reduced magnetization near the edges. However, the change of effective out-of-plane anisotropy field shows opposite trends for these two oxidation methods. Micromagnetic simulations suggest that thermally annealed samples may have an additional reduction in the bulk magnetization, possibly due to a compositional change in Py stripes. The two distinct oxidation profiles also result in different changes in resonance linewidth; we find little damping change for plasma treatment but an enhanced effective damping for thermal annealing. [ABSTRACT FROM AUTHOR]

The buildup of stress with increasing thickness of magnetic thin films is a common phenomenon that often induces undesirable anisotropies that can convert an otherwise magnetically soft film into a magnetically hard one. We found that by interlayering such a magnetic thin film with films that are either not lattice matched or have a different crystal structure, reductions in the saturation field as large as 400-fold can be achieved. Differences in grain size appear to be responsible. [ABSTRACT FROM AUTHOR]

The spin dynamics of sub-100-nm Ni80Fe20 nanomagnets are directly measured using the magneto-optic Kerr effect and a broadband detection scheme. Elliptical dots approximately 68 nm in diameter and 10 nm thick were fabricated in 20×20 μm2 arrays. There is approximately a factor of 2 increase in the effective linewidth when compared to a 20 μm diameter continuous disk of the same material. Using micromagnetic simulations, we model the effect of dot-to-dot size variation on the effective linewidth and find that 2 nm size variations are more than sufficient to account for the effective increase in linewidth. [ABSTRACT FROM AUTHOR]

The effects of edge roughness on vortex nucleation field and its distribution are measured in Permalloy nanostructured arrays. Teardrop-shaped elements, 250 nm wide and 30 nm thick, were fabricated using electron beam lithography and lift-off. Roughness variations were created by varying the electron dose during patterning, and measured by analysis of in-focus transmission electron microscopy (TEM) images. In situ measurements of the vortex nucleation fields and the nucleation field distributions of the dose arrays were performed with Lorentz mode TEM. In combining the measurements of edge roughness with measurements of nucleation field and its distribution, we show that edge roughness increases the probability for vortex nucleation and thus permits vortices to nucleate at larger applied fields, but at the same time, edge roughness broadens the nucleation-field distribution in magnetic nanostructured arrays. [ABSTRACT FROM AUTHOR]

The effect of doping on the magnetic damping parameter of Ni80Fe20 is measured for 21 transition metal dopants: Ti, V, Cr, Mn, Co, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, and Au. For most of the dopants, the damping parameter increases linearly with dopant concentration. The strongest effects are observed for the 5d transition metal dopants, with a maximum of 7.7×10-3 per atomic percent osmium. [ABSTRACT FROM AUTHOR]

We have carried out an extensive search for credible evidence to support the existence of a ballistic magnetoresistance (BMR) effect in magnetic nanocontacts. We have investigated both thin-film and thin-wire geometries for both mechanically formed and electrodeposited nanocontacts. We find no systematic differences between mechanically formed and electrodeposited nanocontacts. The samples we have investigated include mechanical contacts between ferromagnetic wires, electrodeposited nanocontacts between ferromagnetic wires, ferromagnetic nanocontacts electrodeposited on Cu wires, nanocontacts electrodeposited between ferromagnetic films anchored on wafers, ferromagnetic nanocontacts electrodeposited on Cu films anchored on wafers, nanocontacts between two ferromagnetic films connected by a pinhole through an insulating film, and nanocontacts formed by focused ion-beam etching. In none of these samples did we find credible evidence for a BMR effect. However, we did find a number of artifacts due to magnetostrictive, magnetostatic, and magnetomechanical effects that can mimic BMR. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Grazing incidence x-ray reflectometry has been used to study surface oxidation as a diffusion barrier for Al deposited on ferromagnetic metals (Co, Fe, Ni, and Ni[sub 80]Fe[sub 20]). Samples of the form SiO[sub 2]\10 nm X\4 nm Al with X=(Co, Fe, Ni, and Ni[sub 80]Fe[sub 20]) were investigated for X\Al intermixing. Surface oxidation was achieved by exposing the ferromagnetic layer to O[sub 2] to oxidize the top two or three atomic layers before depositing the Al layer. Specular x-ray scans were used for the analysis. Samples of the form SiO[sub 2]\10 nm X\4 nm Au were used to separate topographical roughness from intermixing. Surface oxidation was found to suppress the diffusion of Al into Co, Ni, and Ni[sub 80]Fe[sub 20] but not into Fe. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on strong anisotropy in thin magnetic films deposited on obliquely sputtered tantalum underlayers. Fitting the angular dependence of the ferromagnetic resonance field to obtain values of anisotropy field; Microstructure of spin valve; Magnetoresistive measurements of the dispersion of the hard axis directions.

A 'trapped spin wave' or edge modes of magnetic precession are used to probe the magnetic environment near magnetic film edges magnetized perpendicular to the edge. Results reveal that micromagnetic models of dynamics in stripes show that the edge mode frequency-field relationship depends on whether the edge surface is vertical or tapered, while the 'bulk' modes are nearly unaffected.

Presents an overview of a study on dynamics and self-organized criticality in magnetic materials. Equations of motion for the normal modes of normally magnetized thin films; Involvement of parametrically excited modes in features of the domain of auto-oscillation; Effects of degeneracy breaking in pairs of hidden modes.

Focuses on a study which investigated the use of lead and gold as surfactants in an attempt to achieve smoother and sharper interfaces in giant magnetoresistance spin valve multilayers. Experimental details; Results and discussion; Conclusions.

Provides information on a study that investigated the possible extensions to the limits of the compromise in giant magnetoresistance by using alternatives to pure cobalt as the center film in symmetric spinning valves. Experimental procedure; Results and discussion on the study; Conclusions.

Presents a study which optimized the values of the giant magnetoresistance in symmetric and bottom spin valves. Results; Discussion; Conclusions.

Provides information on a study that investigated the use of indium as a surfactant to achieve smoother interfaces in giant magnetoresistance spin valves. Experimental procedure; Results and discussion on the study; Conclusions.

Presents information on a study which investigated the dependence of the giant magnetoresistance effect, the coercivity, the coupling field, and the resistivity on film deposition at low-substrate in spin valve multilayers of the general type metallic glass. Methodology of the study; Results and discussion; Conclusions.

Presents a study that determined the giant magnetoresistance (GMR) values exceeding 21% in symmetric spin valves. Reason for the interest in symmetric spin valves; Details of the magnetoresistance measurements performed; Temperature dependence of the GMR of a typical sample; Dependence of the GMR in the symmetric spin valve structures on the thickness of the cobalt layers.

Examines the magnetic and optical properties of γ-ferrous oxide nanocrystals. Details of the magnetization susceptibility data from the experiment and computer simulations; Information on the calculated magnetic anisotropy for the particles; Description of the red shifting of the optical absorption edge.

The mechanism of switching of uniaxial, single domain, single crystalline epitaxiai garnet particles on a 2D square array was investigated. The anisotropy field of the sample is 2 kOe, while the gaussian switching field distribution is 280 [+ or -] 85 Oe. The dominant contribution to the incoherent switching is from inhomogeneous internal fields and canted moments at the corners and edges, where the switching starts. The interaction field with the surrounding particles, reduced nucleation barriers at crystalline defects, thermal activation, and dynamical effects in FMR also contribute to the observed switching field and its standard deviation. Index terms - coercivity, magnetization switching, single domain particles

In our Al2O3 magnetic-tunnel junction (MTJ) samples that have a Neel coupling equal to or larger than their easy-axis coercivities, we found that the hysteresis loop totally collapses into a near-linear response upon rotating the easy axis of the sample off the applied field axis. A very high magnetic field sensitivity of 138%/mT (13.8%/Oe), which is among the highest reported so far, with near-linear response, was exhibited by Al2O3 MTJs using this loop collapsing technique. This phenomenon can be explained by the switching astroid curve. In order to make this technique applicable in an actual sensor, we devised a two-step procedure whereby both easy-axis and hard-axis fields are used to accomplish the same loop collapsing effect as rotation. These result is one of the best combinations of saturation field and tunneling magnetoresistance ever achieved for MTJs, in addition to the linear nonhysteretic response at zero field that is so important for magnetic sensors. [ABSTRACT FROM AUTHOR]

Micromagnetic calculations are used to determine the eigenfrequencies and precession patterns of some of the lowest-frequency magnetic normal modes of submicron patterned elements. Two examples are presented. For a Permalloy-like ellipse, 350 nm × 160 nm × 5 nm thick in zero field, the lowest frequency normal mode at 4 GHz corresponds to precession in the "ends" of the ellipse. Other resonant frequencies are compared with the frequencies of spinwaves with discrete wave vectors. For a normally magnetized 50 nm diameter × 15 nm thick cobalt disk, the calculated eigenfrequencies increase linearly with applied field, mimicking the behavior of the experimental critical current for spin transfer instabilities in an experimental realization of this disk. [ABSTRACT FROM AUTHOR]

We have achieved excellent exchange decoupling of grains in CoPd multilayers by annealing in air at 300 °C. Samples exhibit a slope in the hysteresis loop close to 1.0, nucleation fields as large as 11 kOe, and coercivities as large as 16 kOe. These are among the best properties ever achieved for CoPd multilayers. In samples of the general type seed layer\ (0.3 nm Co\1 nm Pd)×15\capping layer, it appears that atoms diffuse rapidly up and down the grain boundaries at 300 °C. From x-ray photoelectron and Auger depth profiling, we have found that when Co atoms arrive at the surface they become oxidized and remain at the surface, leaving the grain boundaries depleted in Co and apparently nonmagnetic. If the annealing is carried out in vacuum, exchange decoupling of the grains does not occur. This result supports our conclusion that the presence of oxygen plays a crucial role. When Au or Pt atoms are present in the seed layer or capping layer, they diffuse into the CoPd grain boundaries and apparently enhance the exchange decoupling of grains. [ABSTRACT FROM AUTHOR]

We measure surface anisotropy in permalloy sPyd deposited between two layers of normal metal (NM=Ag, Cu, or Ta) by measuring the total perpendicular anisotropy with the angular dependence of the ferromagnetic resonance (FMR) field in a resonant cavity. Comparisons are made with the frequency dependence of a broadband FMR technique and vibrating sample magnetometry, and neither match the sensitivity and range of the cavity technique. We see there is a difference between the surface anisotropy at the interfaces: Py-Ta has a surface anisotropy of (0.078±0.009) mJ/m2 and the Py-Ag and Py-Cu interfaces have surface anisotropies of (0.10±0.007) mJ/m2. [ABSTRACT FROM AUTHOR]

The ferromagnetic resonance linewidth is a result of both intrinsic damping and contributions from inhomogeneities, which in thin films can be dominated by the roughness. Microstructural measurements and magnetization dynamics are reported here for 50-nm films of Permalloy deposited on substrates with controlled roughness. Ferromagnetic resonance measurements reveal a strong linewidth broadening that peaks when the magnetization is approximately 30° from the in-plane direction. These results are compared with a recently developed two-magnon theory of resonance broadening due to inhomogeneous demagnetizing fields in a rough film. [ABSTRACT FROM AUTHOR]

The extrinsic ferromagnetic resonance linewidth is modeled in a perpendicular recording media with inhomogeneous uniaxial anisotropy field Hu and with tilting of the easy axes from the film normal. The linewidth is calculated using both a local resonance model and a classical equivalent of the two-magnon model. Variations in Hu and easy axis tilting are shown to produce very different angular dependence of the linewidth, and when the two-magnon models are valid, the linewidth is also shown to depend on inter-granular exchange coupling. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Detailed ferromagnetic resonance measurements on thin Ni[SUB80]Fe[SUB20] films are described that determine characteristics of intrinsic damping and the effects of intentionally created defects on linewidth. Measurements are made as a function of frequency with magnetization oriented in-plane and normal to the plane. For nominally uniform films, the ferromagnetic resonance linewidth is linear in frequency for both in-plane and normal magnetization and is well described by Landau-Lifshitz damping with a constant damping parameter. The effect of inhomogeneity was investigated by depositing the Ni[SUB80]Fe[SUB20] films on specially prepared substrates, one with parallel, random grooves and one with polycrystalline, antiferromagnetic NiO. The linewidth in these samples is generally larger with magnetization in-plane than it is with magnetization normal. In the NiO/Ni[SUB80]Fe[SUB20] film, the in-plane linewidth is linear in frequency with a significant zero-frequency linewidth. In the Ni[SUB80]Fe[SUB20] sample on the grooved substrate, the linewidth has a more complicated frequency dependence. [ABSTRACT FROM AUTHOR]

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 2p[SUB&frac32; 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. [ABSTRACT FROM AUTHOR]

HITPERM/SiO[SUB2] single and multilayer thin films have been produced using a target composition of Fe[SUB]70Co[SUB30])[SUB88]Zr[SUB7]B[SUB4]Cu[SUB1]. The as-deposited HITPERM film contains small bcc (or B2) nanocrystals of volume fraction less than 10% surrounded by an amorphous matrix. The lattice parameter of the nanocrystal is about 5% larger than an equilibrium FeCo phase. The saturation induction determined from FMR measurements (1.53±0.08 T) is consistent with VSM and SQUID measurements (1.45-1.5 T) and also with as-spun amorphous ribbons (1.55-1.62 T). The Landé g-factors (2.15±0.05) are typical of transition metals, particularly, of Fe. The Landau-Lifshitz-Gilbert damping parameters of the single and multilayered films are small (α=5 0.005±60.0004) with each layer acting almost independently. Neither thickness variation of each layer nor the number of stacking significantly affects the damping process in a range of film thicknesses of 50-150 nm, while the coercivities are strongly dependent on those parameters. This supports a notion that the damping parameter is an intrinsic property. [ABSTRACT FROM AUTHOR]

An anomalous Hall effect (AHE) and a planar Hall effect (PHE) represent a perpendicular component and an in-plane component of the magnetization in the double-layered media. Since AHE and PHE have different symmetries regarding to the applied magnetic field H, it is easy to distinguish the AHE component, which is proportional to M, and PHE component, which is proportional to M², from the measured Hall voltage V[sub H]. The Hall voltage of the double-layered film composed of Co-Cr-Ta and Ni-Fe layers was observed when the magnetic field is applied at an angle (α) of 30° from the normal to the film plane. The perpendicular and the in-plane components, which are regarded as the magnetization process of Co-Cr-Ta and that of the Ni-Fe layer, respectively, can be easily determined from these characteristics. The Hall measurement is useful to study the magnetization characteristics in the double-layered media. [ABSTRACT FROM AUTHOR]

The magnetic field determined from vanishing rotational hysteresis loss of CoCrPtB perpendicular thin film media was experimentally investigated. It was clarified that (1) in Co[sub 72]Cr[sub 16]Pt[sub 8]B[sub 4] media with d[sub mag] of less than 200 nm and Co[sub 64]Cr[sub 24]Pt[sub 8]B[sub 4] media with d[sub mag] of less than 100 nm, a homogeneous structure was realized, except for the existence of an initial growth region. (2) For both media, the perpendicular rotational hysteresis loss, W[sub r], the maximum field of W[sub r], H[sub p], and the field where W[sub r] = 0, H[sub W][sub r=0], increased with an increase in d[sub mag]. (3) For both media, H[sub W][sub r = 0] / H[sup grain][sub k] increased with an increase in d[sub mag] and saturated at a magnitude of about 1. (4) For the medium with thin magnetic film thickness, at applied field of H[sub W][sub r=o] < H < H[sup grain][sub k], a multidomain state was realized in the torque measurement in spite of no observation of loss of rotational hysteresis. This is considered to be due to the existence of thermal agitation between the multidomains. [ABSTRACT FROM AUTHOR]

The details of the magnetization reversal in coupled ferromagnetic Co/Ru/Co trilayers deposited on obliquely sputtered Ta underlayers were studied using the magneto-optical indicator film technique. The ground states of the sandwich are characterized by noncollinear magnetization orientations in the two Co layers, which can be remagnetized by the motion of 180° and non-180° domain walls. In the latter case, the angle between the magnetization vectors in the adjacent domains was revealed to be about ± 100°, and an anomalous magnetization reversal was observed. The canted magnetization states and their mutual transformations are discussed in terms of the competition between ferromagnetic coupling through pinholes and antiferromagnetic coupling across the Ru layer. [ABSTRACT FROM AUTHOR]

The magnetic domain structure, magnetic properties, and thermal stability of IrMn biased top spin valves containing Co and NiFe have been investigated. The magneto-optical indicator film pictures of Ni-Fe biased IrMn spin valve show the formation and motion of domain walls that separate large domains in the free film unlike the Co biased IrMn spin valve structure with many small microdomains. From the angular dependence of the ferromagnetic resonance linewidth (ΔH) and resonance field (H[sub res]) it was found that the IrMn biased Co film is very different from the behavior of a NiO biased Permalloy film which exhibits two-magnon scattering. To investigate the thermal stability two kinds of magnetoresistance measurements at anneal temperature (T [sub Anm]) and room temperature (T[sub RT]) following anneals were accomplished. [ABSTRACT FROM AUTHOR]

We present the dependence of the magnetostriction in Ni[sub 0.8]Fe[sub 0.2] films on Tb and Gd doping concentration and compare with the measured doping dependence of the high-frequency damping. While the magnetostriction and the high-frequency damping are correlated, the dependence is complicated. In particular, the high-frequency damping parameter α increases rapidly (α=0.008–0.84) with a modest increase in the magnetostriction (λ[sub s]=-0.6×10[sup -6] to 5.7×10[sup -6]) for Tb doping concentrations up to 10%. For Gd doping, the high-frequency damping changes slowly (α=0.008–0.02) as the doping concentration is increased to 10%, whereas the increase in magnetostriction is similar to that observed in the Tb-doped films. Further, it is possible to achieve low magnetostriction (λ[sub s]=2×10[sup -6]) near the region of critical damping. Measurements of the angular dependence of the ferromagnetic resonance linewidth in Tb-doped Ni[sub 0.8]Fe[sub 0.2] films show little change similar to the behavior observed in undoped Ni[sub 0.8]Fe[sub 0.2] films, although the linewidths are considerably larger. This is in contrast to systems such as Ni[sub 0.8]Fe[sub 0.2] on NiO, which have a large angular dependence indicating that the relaxation process proceeds through the generation of spin waves. The enhanced damping in the Tb-doped films appears, therefore, to be mediated through direct phonon generation. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It has recently been found that large uniaxial anisotropy fields in excess of 120 kA/m (1500 Oe) can be created in thin (3-5 nm) films of Co by obliquely sputtered Ta underlayers. This anisotropy can be used to pin the bottom film of a spin valve while having only a modest effect on the top "free" film, separated by a 2.5 nm Cu spacer layer. This article describes measurements of thermal stability in these Ta-pinned spin valves. Using room temperature giant magnetoresistance (GMR) as a measure, we find that the structure is stable under cumulative 20 min anneals at 25 °C intervals up to 300 °C; GMR decreases to zero upon further anneals up to 450 °C. Measurements taken at elevated temperatures reveal that GMR decreases linearly with temperature, extrapolating to zero at approximately 425 °C, while the anisotropy field is much less temperature dependent, remaining nearly constant up to 150 °C and gradually decreasing to 50% of its room temperature val! ue at 325 °C. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]