S.R. Teixeira

Giant magnetoresistance in electrodeposited Co87Fe13/Cu compositionally modulated alloys

In this paper we report on the giant magnetoresistance effect and oscillatory exchange coupling in electrodeposited Co87Fe13/Cu compositionally modulated alloys. The alloys are compositionally modulated over nanometre length scales with ferromagnetic Co87Fe13 (Cu) alloy layers and non-magnetic Cu layers. Co87Fe13/Cu multilayered thin films were electrodeposited from a single sulfate plating solution containing all metallic ions of interest under computer-controlled potentiostat switching on (111)-textured Cu buffers previously evaporated on Si(111). Electrodeposits present a polycrystalline character with coexistence of face-centred cubic (fcc) and hexagonal close-packed (hcp) structures. Magnetoresistance effects as high as 8% were observed at room temperature. The dependence of the magnetoresistance effect on Cu spacer layer thickness shows an oscillation period around 1.0 nm.

Microstructure and magnetoresistance of electrodeposited (Co0.87Fe0.13)xCu1−x granular alloys

Abstract Heterogeneous (Co 0.87 Fe 0.13 ) x Cu 1− x alloys were electrodeposited with various additives from a single sulfate plating solution under potentiostatic conditions on Cu substrates. The alloys are polycrystalline with a predominant face-centered cubic structure and for x

Change of the electrical properties in Fe-Al2O3 granular films

A systematic study of the electrical resistance as a function of the temperature was performed in Fe-Al2O3 granular thin films. Our findings revealed a nonlinear dependence of the current versus voltage in the low field regime at low temperature. The variable range hopping mechanism is the best description of the behavior of our samples. A change of the electronic properties can be observed depending on the direct current applied to the sample’s plane, and is related to different localization lengths.

Structural evolution of FexCo1−x/NM (NM=Ag, Cu, Al2O3) discontinuous multilayers by XAS

Abstract We discuss the specific features of the K-edge X-ray absorption spectroscopy (XAS) at the Fe and Co K-edges in Fe x Co 1− x /NM discontinuous multilayers with NM=Ag, Cu, and Al 2 O 3 . Thermal treatments lead to the breakup of the layers forming a heterogeneous alloy with magnetic clusters of the FeCo embedded in a nonmagnetic (NM) matrix. Stabilization of the BCC phase of the FeCo alloy is directly evidenced by XAS. Differences among Fe and Co K-edge signatures indicate a strong dependence on the chemical nature of the absorbing atom for annealed samples. The amplitude of the extended X-ray absorption fine structure signal higher at the Co K-edge than at the Fe one reflect a smaller structural disorder in the Co environment. This behavior depends neither on the composition of the alloy nor on the NM material. In the case of Al 2 O 3 a higher disorder around Fe atoms is observed also in the as-deposited sample. All these results indicate that the Fe segregates at the interface of the magnetic clusters/NM matrix after thermal annealing.

Magnetoresistance dependence on Co composition in discontinuous CoxFe1−x/Ag multilayers

Abstract We report on the structural evolution and magnetic behavior of Co x Fe 1 −x /Ag discontinuous multilayers with x =0, 0.3, 0.7 and 1. The structural characterization was performed using X-ray absorption spectroscopy (XAS). It is found from XAS measurements that there is a better ordered structure around Co than Fe absorbing atoms. For CoFe alloys, we conclude that Co atoms are within the core of the magnetic particles, while Fe atoms preferentially occupy the interfacial positions near Ag. The magnetoresistance increases when Co is added to Fe.

Solid-state reaction in Fe/V multilayers by ion beam mixing with thermal annealing

Abstract We report a study on the structural and magnetic properties of iron–vanadium thin films, originally grown in multilayer form [Fe(20 A)/V(20 A)]20, and mixed by ion beam mixing (IBM) and a subsequent thermal treatment. The samples were structurally characterised by X-ray diffraction (XRD) in the θ–2θ geometry and X-ray absorption spectroscopy (XAS). The magnetic characterisation was made using conversion electron Mossbauer spectroscopy (CEMS). The XRD result for the as-deposited multilayer shows a high-degree crystallinity, while CEMS suggests abrupt interface, since no significant contribution from vanadium in iron is observed. After the IBM and thermal treatment, the results from XRD show an FeV solid solution indexed as a bcc-disordered structure (α phase). XAS structural results are consistent with the XRD observations. CEMS results show a magnetic moment reduction for mixed samples.