Magnetic properties and giant magnetoresistance of melt-spun granular Cu100-x-Cox alloys (original) (raw)
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Giant magnetoresistance and magnetic properties of electrodeposited Cu–Co granular films
Journal of Alloys and Compounds, 2001
The effect of NaOH with different concentrations on CoFe/Cu multilayer films was studied between pH = 3.70 and pH = 2.70. The effect of different electrolyte pH from 3.7 to 2.7, which was obtained at various NaOH concentrations, on CoFe/Cu multilayer films was studied. The structural studies by x-ray diffraction (XRD) revealed that the multilayers have face-centered cubic structure. The preferential orientation of the multilayer is in the (220), (111), (111), and (222) direction at pH = 3.7, 3.3, 3.0 and 2.7, respectively. It was observed that at pH = 3.0, the film composition, by energy dispersive x-ray spectroscopy (EDX), contains 3.22 at. Co % and 96.78 at. Cu %, and at low pH (2.7), 10.58 at. Co %, 4.18 at. Fe % and 85.24 at. Cu %. Magnetoresistance measurements made at room temperature showed that all films exhibited giant magnetoresistance (GMR), which was affected by the electrolyte pH. The observed GMR values are 4.0 %, 4.6 %, 4.2 %, and 12 % at the pH values of 3.7, 3.3, 3.0 and 2.7, respectively. Magnetic measurements of the films were made at ±20 kOe by using ADE EV 9 model a vibrating sample magnetometer. The magnetic measurements revealed that the coercivity of the films increased from 70 Oe to 93 Oe and stayed there, and the saturation magnetization monotonically increased form T. Sahin ( ) · 7.40 emu/g to 17.05 emu/g with decreasing electrolyte pH from 3.7 to 2.7.
CoFe–Cu granular alloys: From noninteracting particles to magnetic percolation
Journal of Applied Physics, 1999
CoFe-Cu granular films with ferromagnetic content ranging from 0.10 to 0.33 by volume were prepared by radio frequency sputtering. As-cast samples were rapidly annealed at various temperatures up to 750°C to promote the segregation of CoFe particles within the metallic matrix. Magnetic and transport properties suggested that this family of samples may be classified into three groups: ͑i͒ below about 0.20 volume content of CoFe, all samples display the typical features of a granular solid constituted by a random distribution of nanometric CoFe particles within a Cu matrix, and the maximum magnetoresistance is about 20% at low temperature ͑giant magnetoresistance͒; ͑ii͒ for as-cast samples within 0.20 and 0.30 of volume concentration, magnetoresistance and magnetization display complex bimodal behavior and large metastable effects associated with the interparticle interactions, which stabilize a domain-like microstructure well below the volume percolation threshold ͑0.55͒, as already observed in CoFe-Ag͑Cu͒ granular alloys. As a consequence of the large magnetic correlations, magnetoresistance is very low ͑1%-3%͒. Through annealing, the microstructure and therefore the transport properties evolve to those of a classical giant magnetoresistance system with large particles; and ͑iii͒ above about 0.30 of volume content ͑and still below the volume percolation threshold͒, as-cast samples display both anisotropic and giant magnetoresistance, as also observed in other granular alloys. Annealing leads to complete segregation and to the formation of large magnetic particles, which results in a transition from mixed behavior of both anisotropic and giant magnetoresistance ͑GMR͒ regimes to a giant magnetoresistance regime, with a maximum GMR of about 7%.
Journal of The Electrochemical Society, 2020
Detailed new results are reported on the preparation and giant magnetoresistance (GMR) of electrodeposited Co-Fe/Cu multilayer films by using four different baths (sulfamate, sulfate, ammonium chloride and sodium citrate type solutions). Two-pulse plating was applied for Co-Fe(5nm)/Cu(5nm) multilayer preparation by using galvanostatic pulses for the deposition of the magnetic layer. The Cu layer deposition potential was electrochemically optimized for each bath formulation by analyzing the current transients during the deposition of the non-magnetic layers. The optimal Cu deposition potential was found to be dependent both on the bath formulation and the Fe2+/Co2+ ion concentration ratio. The results of X-ray diffraction (XRD) measurements were in agreement with the composition of the samples. At low Fe content (about 10 at.% Fe) in the magnetic layer, an fcc structure was formed (in some cases, even multilayer satellites were observed). In samples with high Fe content (about 33 at....
IEEE Transactions on Magnetics, 2018
Giant magnetoresistance (GMR) behavior in electrodeposited N[Fe/Cu/Ni] multilayered (ML) structures is investigated as a function of non-magnetic (Cu) and ferromagnetic (Fe and Ni) layers' thicknesses. Detailed structural and magnetic analyses of the ML structures are studied before looking into the GMR behavior. Structural analyses reveal that all peaks are well matched with Ni (face-centered cubic) being the top most layer during ML deposition. Shifting of preferred orientation, between (220) and (111) planes, is observed with the thickest layer of copper spacer. Refined structural parameters are calculated and details of fittings are discussed with reference to layer thicknesses. Crystallite size, dislocation density, stacking fault probability, and strain all show oscillatory behavior with variation in thicknesses. Magnetic behavior shows strong dependence of magnetization on thickness of each layer. Saturation magnetization (M s) increases up to a value of 10.12 emu/cm 3 with increasing Fe and Ni layer thicknesses. Whereas, oscillatory behavior of magnetization is observed with variation in Cu layer thickness. Magnetoresistance (MR) measurements show oscillatory GMR behavior as a function of intervening layer thickness. Highest value of GMR ∼12% is observed at a Cu layer thickness of 9.6 nm. Structural, magnetic, and MR properties of N[Fe/Cu/Fe] are observed on the basis of variation of thicknesses of non-magnetic (Cu) and ferromagnetic (Fe and Ni) layers. It is observed that layer thicknesses play a dominant effect on the nature (i.e., oscillatory) and on the value of GMR.
Magnetic properties of Fe∕MgO granular multilayers prepared by pulsed laser deposition
Journal of Applied Physics, 2009
Granular multilayers ͓Fe͑t nm͒ / MgO͑3 nm͔͒ N with 0.4 nmഛ t ഛ 1.5 nm were prepared by sequential pulsed laser deposition. Transmission electron microscopy ͑TEM͒ images show that increasing t causes the growth of the sizes of Fe nanoparticles and broadening of the particle size distribution. For t Ͼ 0.81 nm, continuous Fe layers are formed. The evolution of the shapes and sizes of the particles is reflected in the magnetic properties of the investigated films. A crossover from superparamagnetic to ferromagnetic behavior upon formation of a continuous Fe layer is observed. The fit of zero field cooled and field cooled susceptibility measurements and magnetization curves using Curie-Weiss law and a weighted sum of Langevin functions, respectively, allows the estimation of the average granule size for the films with t Ͻ 0.61 nm. The results of the estimations correlate with the data obtained from TEM images. Reduction of saturation magnetization for Fe nanoparticles and an increase of the coercivity up to 1200 Oe at low temperatures were found. It is attributed to the formation of Fe-core/FeO x-shell structured nanocrystals. The oxide shell gives rise to a strong contribution of surface anisotropy. Isotropic tunneling magnetoresistance up to ϳ3% at room temperature and in magnetic field up to 18 kOe was found for the film with t = 0.61 nm. For higher t, an anisotropic magnetoresistance typical for continuous ferromagnetic films was observed.
Physics of the Solid State, 1998
A phenomenological model is developed for the giant magnetoresistance of granular media comprising ferromagnetic granules in a nonmagnetic metal matrix. Both volume and surface spindependent scattering by the ferromagnetic granules are taken into account. The internal electric fields are inhomogeneous because of the different conductivities of the granules and the matrix. The dependence of the effective conductivity of the medium on the average magnetization is calculated and used to explain the giant magnetoresistance effect. The magnetoresistance is plotted as a function of the volume concentration of ferromagnetic granules and the granule radius. Experiments on Co-Cu and Co-Ag granular films are discussed.
Journal of The Electrochemical Society, 2016
In an effort to see the possible surfactant effect of Pb on the formation of electrodeposited multilayers, Co/Cu(Pb) 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 Pb 2 + ions in the solution. The composition analysis by energy dispersive X-ray spectroscopy revealed that the Pb mole fraction in the deposit varies in a non-monotonous manner with Pb 2+ ion concentration. By fitting the measured X-ray diffraction patterns, superlattice satellites could be identified in some of these multilayers. A ferromagnetic-type GMR behavior was observed for Co/Cu(Pb) deposits prepared from baths with small Pb 2+ ion concentration, corresponding to the formation of a layered structure. The GMR magnitude decreased from 8 to 10 % with increasing Pb concentration and, also, changed to a superparamagnetic-type GMR; finally, for high Pb 2+ ion concentrations, the magnetoresistance behavior turned over to anisotropic magnetoresistance characteristic of bulk materials.