Magnetoresistance studies of discontinuous multilayer thin Co/Ag films (original) (raw)
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Acta Physica Polonica A, 1997
The as-deposited and annealed Co/Ag discontinuous multilayer-like structures were examined. Discontinuous Co sublayers are thought to consist of fine superparamagnetic and ferromagnetic grains. Using the bimodal superparamagnetic grain sizes distribution the GMR(H) dependencies were successfully modelled with the use of two Langevin functions simulating the magnetization of the superparamagnetic grains.
Preparation and giant magnetoresistance of electrodeposited Co–Ag/Ag multilayers
Thin Solid Films, 2009
Electrodeposition of Co-Ag/Ag multilayers along with their giant magnetoresistance (GMR) was investigated. The electrodeposition process was optimized for both minimizing the dissolution of the Co layer and achieving a high magnetoresistance. Structural analysis of Co-Ag/Ag deposits revealed that silver has an fcc structure, whereas cobalt crystallizes in the hcp structure. No solid solution of Co and Ag was detected. The X-ray diffraction study did not show any satellite reflection. A GMR of the order of 0.5% and 2% could be observed at room temperature and at 20 K, respectively, with both superparamagnetic and ferromagnetic GMR contributions throughout the temperature range studied.
Structural evolution and magnetic behavior of Co/Ag multilayers submitted to thermal annealing
Journal of Magnetism and Magnetic Materials, 1998
We report on the structural evolution and the magnetic behavior of the Co/Ag multilayered films deposited in a UHV chamber at room temperature, submitted to 10 min thermal annealing at temperatures ranging from 100 to 600°C. The structural characterization was performed using X-ray diffraction and X-ray absorption spectroscopy techniques. Magnetoresistance and magnetization measurements were used to study the evolution and magnetic behavior of the samples. The results show that, besides the roughness at the interfaces and the structural disorder of the Co layers, the as-deposited sample has a compressive stress at Ag-Co interface originated by the difference between the surface energies of Ag and Co. After annealing at 400°C, there is a breakup of the layers accompanied by a relaxation of the stress and defects as well as partial crystallographic ordering of the Co clusters. The room-temperature magnetoresistance change from anisotropic magnetoresistance to giant magnetoresistance with a sharp maximum, reaching 4.5%.
Current-perpendicular and current-parallel giant magnetoresistances in Co/Ag multilayers
Physical Review B, 1995
We report results of measurements of the perpendicular [current perpendicular to the layer planes (CPP)] and parallel [current in the layer planes (CIP)] magnetoresistances (MRs) of Co/Ag multilayers having Co and Ag thicknesses tc, and tAs ranging from 1.5 to 60 nm. (1) We find the variations of the CPPand CIP-MRs with tAg and tc, to be qualitatively similar to each other, suggesting that the parameters determining both may also be similar. (2) In accord with predictions that CPP-MR)CIP-MR, we find their ratio m=CPP-MR/CIP-MR to range from about 3 to at least 6. (3) We analyze current perpendicular to the layer plane (CPP) specific resistances, Ar, , of Co/Ag multilayers having a wide range of Co and Ag thicknesses tc, and tAg in terms of a two-current, series resistor model based upon the assumption that the spin-diffusion lengths in the Co and Ag are much longer than t«and tAg, respectively. We show first that a six parameter fit gives rather good agreement with four data sets, with the three parameters that can be separately checked agreeing within experimental uncertainties with independent measurements of the same quantities. We then examine the ability of these fits to predict the behavior of additional sets of data. Here we find some agreements and some disagreements. Possible reasons for the disagreements are examined.
Journal of The Electrochemical Society
In order to explore the possible surfactant effect of Ag on the formation of electrodeposited multilayers, Co/Cu(Ag) multilayers were prepared by this technique and their structure and giant magnetoresistance (GMR) were investigated. The multilayers were deposited from a perchlorate bath with various amounts of Ag + ions in the solution for incorporating Ag atoms into the multilayer stack. Without Ag addition, secondary neutral mass spectroscopy (SNMS) indicated a well-defined composition modulation of the undermost Co/Cu bilayers. However, already at an Ag content as low as 1.8 at.% incorporated, SNMS showed a deterioration of the periodic multilayer structure. In agreement with the SNMS results, superlattice satellites were visible in the X-ray diffraction (XRD) patterns of the multilayers with up to 0.3 at.% Ag. The satellites were, however, very faint even for multilayers without Ag addition, indicating that the multilayers have high interface roughness and/or poor periodicity. In the absence of Ag and at the smallest Ag content investigated by XRD, a strong central multilayer peak and the weak superlattice satellites were complemented by weak diffraction maxima from non-periodic Co and Cu domains. In the Co/Cu(Ag) multilayer containing about 25 at.% Ag, i.e., nearly as much as Cu, XRD found a separate Ag(Cu) phase. In spite of the imperfect layered structure, a multilayer-type GMR behavior was observed in all samples up to about 10 at.% Ag incorporated in the multilayer stack. The GMR magnitude increased for Ag contents up to about 1 at.%, which implies that a small amount of Ag may have a beneficial effect through a slight modification of the layer growth and/or interface formation. However, for higher Ag contents beyond this level, the GMR was reduced in line with the structural degradation revealed by XRD and SNMS. For the highest Ag contents (above about 10 at.%), the GMR exhibited a behavior characteristic of a granular magnetic alloy, in agreement with the results of the structural study.
Magnetooptical spectra of discontinuous multilayers Co/SiO2 with tunnel magnetoresistance
Physica B: Condensed Matter, 2001
Magnetooptical spectra of Co(x)/SiO 2 (y) bilayers and [Co(x)/SiO 2 (y)] n multilayers consisting of discontinuous ultrathin Co layers, are studied in the geometry of transverse Kerr effect (TKE). It is found that: (a) the sign, magnitude and spectral shape of the TKE signal strongly depend on the size of Co particles when Co volume fraction is close to the percolation threshold (x varying between 1.3 and 1.8 nm); (b) the TKE signal in [Co (1.6 nm)/SiO 2 (3.0 nm)] 6 multilayers at 3.0 eV has the record-high magnitude for Co-based systems, 3 Â 10 À2 , which exceeds that measured in bulk Co about in a factor of five and in factor of 50 that corresponding to homogeneous Co film of equivalent thickness; (c) the TKE signal of multilayers is nonlinear with respect to both the thickness of the SiO 2 spacer y and the number of periods n. To explain this anomalous behavior we have calculated magnetooptical spectra of bilayers in the framework of macroscopic Fresnel magnetooptics and modified effective medium approach for discontinuous Co layers, considering them as nanocomposites Co-SiO 2 . It is shown that magnetooptical properties dramatically change when Co volume fraction approaches the percolation threshold. #
An interplay between the structure and giant magnetoresistance in laser treated Ag/Co multilayers
An interplay between the structure and giant magnetoresistance (GMR) evolution in Ag/Co multilayers exposed to excimer XeCl laser pulses with the fluences of (0.1-0.25) Jcm -2 for (1-200) times is studied. Two samples with different layer thickness ratios, Ag 4 Co 1 and Ag 6 Co 1 , were electron-beam evaporated on Si(100) substrate. X-ray diffraction revealed polycrystalline face-centered cubic structure of the Ag layers which is strongly textured in Ag 4 Co 1 multilayer while in other sample the layers are not structurally coherent. A strong texture in Ag 4 Co 1 stabilizes the multilayer structure in the irradiation regime without melting and the GMR varies non-systematically in a rather narrow interval around the original value. Contrarily, the grain boundary diffusion of Ag into Co layers occurs due to laser treatment in Ag 6 Co 1 leading to the formation of a discontinuous multilayer which enhances the GMR ratio more than twice. When the Ag melting threshold is reached, rapid solidification produces a granular-like structure irrespective of the structural character of the original multilayer and the GMR value changes unpredictably in a broad interval. The conclusions are supported by the hard X-ray reflectivity and diffuse scattering measurements as well as by transmission electron microscopy observations .
Magnetoresistance in nanostructured Co-Ag prepared by mechanical-alloying
Magnetics, IEEE …, 1994
ball-milled to yield a granular solid of composition CoSoAg7a in the form of coarse powder. The material is an intimate mixture of grains of fcc CO in a silver matrix. The cobalt is in the single-domain size range, and the samples exhibit coercivity (0.07 T at 296 K) and unusual thermomagnetic effects, including field-induced unidirectional anisotropy. There is a large, isotropic negative magnetoresistance, which exceeds 10 95 at 4.2 K.
We have investigated the relationship between the magnetism and the magnetoresistance effect in the Co/Au, Ag multilayer films with layers produced in the atomic level by pulse electrodeposition method. The magnetoresistance effect is dependent on both the thickness of Co ferromagnetic layer and Ag,Au non-magnetic layers. The magnetization of these films shows the minimum value against the Ag and Au layer thickness. The Ag and Au layer thickness showing the maximum of MR ratio is not of necessary in agreement with the Ag and Au layer thickness showing the minimum of magnetization. Antiparallel alignment of magnetic spin is a necessary but not sufficient condition in order to generate the GMR of multilayer films. For the Co/Au multilayer films, the Au layer thickness showing the minimum of the magnetization shifts to higher side of the Au layer thickness.