Microstructural and magnetic evolution upon annealing of giant magnetoresistance melt-spun Co-Cu granular alloys (original) (raw)
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Journal of Applied Physics, 1997
The effects of annealing on the structural, magnetic, and magnetotransport properties of melt-spun Co 10 Cu 90 granular alloys were investigated. The interaction effects were studied from both remanent magnetization and magnetotransport data, using two different methods to reach the demagnetized state, ac and dc demagnetization. The analysis of the structural evolution and interaction strength between the magnetic clusters clearly shows the role of some structural parameters ͑particle size and density, interparticle distance͒ and the degree of magnetic correlation in the magnetic field response of the resistance in these inhomogeneous systems.
Europhysics Letters (EPL), 2002
In Co-Cu metastable alloys, suitable thermal treatments create Co nanoclusters that are responsible for the giant magnetoresistance phenomena. A detailed microscopic study by means of high-resolution X-ray diffraction and extended X-ray absorption spectroscopy has revealed an anomaly in the thermally induced segregation process, occurring at the same temperature regardless of the sample composition. This phenomenon roughens the nanocluster interface and degrades the sample magnetotransport properties.
Structure and magnetic properties in CoCu granular alloys
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003
Granular alloys, composed of magnetic clusters embedded in non-magnetic metallic matrices, can develop giant magnetoresistance effect after suitable preparation and thermal treatments. The structural effect of annealing on the structure of Co 10 Cu 90 samples has been directly probed by in situ time resolved X-ray diffraction (TR-XRD) during thermal treatment. TR-XRD definitively proves the occurrence of an anomalous behaviour in the thermally activated segregation process that is related to the evolution of magnetotransport properties in these materials.
Microstructural dependence of giant-magnetoresistance in electrodeposited Cu-Co alloys
Journal of Materials Science, 2004
The relationship between the microstructure and the magnetic properties of heterogeneous Cu-Co [Cu92.5-Co7.5] (at.%) thin films prepared by electrodeposition was studied. Electron spectroscopic imaging (ESI) studies clearly revealed the evolution of the cobalt microstructure as a function of thermal treatments. The as-deposited film is composed of more than one phase; metastable Cu-Co, copper and cobalt. During annealing the metastable phase decomposes into two fcc phases; Cu and Co. Grain growth occurs with increasing annealing duration, such that the cobalt grains are more homogeneously distributed in the copper matrix. A maximum GMR effect was found after annealing at 450 • C for 1.5 h, which corresponds to an average cobalt grain size of 5.5 nm according to magnetization characterization. A significant fraction of the cobalt in the Cu-Co film did not contribute to the GMR effect, due to interactions between the different magnetic grains and large ferromagnetic (FM) grains. The percolation threshold of cobalt in metastable Cu-Co alloys formed by electrodeposition is lower (less than ∼7.5 at.%) than that prepared by physical deposition methods (∼35 at.%).
Investigation of heterogeneous Cu1−xCox alloys with giant magnetoresistance
Ultramicroscopy, 1993
Dedicated to Professor John M. Cowley on the occasion of his seventieth birthday The decomposition kinetics of Cu l_.Co x alloys have been investigated based on the theory of spinodal decomposition. Microstructural parameters such as size and concentration of compositional modulations have been predicted for as-prepared and subsequently annealed CUslCOl9 and Cu65C035 samples. These predicted values have been compared with those determined experimentally from a combination of electron microscopy and field ion microscopy. The discussion emphasizes a possible application of a known decomposition mechanism and evaluated microstructural parameters to improve the amplitude of giant magnetoresistance in heterogeneous Cu~ _xCOx samples.
Journal of Applied Physics, 2010
A series of CoxCu100−x (x = 0, 40...75, 100) layers with thicknesses in-between 13 nm and 55 nm were prepared on silicon substrates using cross-beam pulsed laser deposition. Wide-angle X-ray diffraction (WAXRD), transmission electron microscopy (TEM) and electrical transport measurements revealed a structure consisting of decomposed cobalt and copper grains with grain sizes of about 10 nm. The influence of cobalt content and layer thickness on the grain size is discussed. Electron diffraction (ED) indicates the presence of an intermetallic Co-Cu phase of Cu3Au structuretype. Thermal treatment at temperatures between 525 K and 750 K results in the progressive decomposition of Co and Cu, with an increase of the grain sizes up to about 100 nm. This is tunable by controlling the temperature and duration of the anneal, and is directly observable in WAXRD patterns and TEM images. A careful analysis of grain size and the coherence length of the radiation used allows for an accurate interpretation of the X-ray diffraction patterns, by taking into account coherent and non-coherent scattering. The alloy films show a giant magnetoresistance of 1...2.3 % with the maximum obtained after annealing at around 725 K.
Magnetic properties and giant magnetoresistance of melt-spun granular Cu100-x-Cox alloys
Physical Review B, 1995
We report in this paper the first observation of giant magnetoresistance as high as 23% in electrodeposited [Fe/Pt]n granular multilayers with different thicknesses of bi-layers. [Fe/Pt]n multilayers were prepared by electrodeposition, through the single bath technique. Cu (100) textured polycrystalline foils were used as substrate. The composition of the studied samples is Cu:Pt(x nm)/[Fe(tFe nm)/Pt(x nm)]n, in which the thickness of the iron layer varied between 2.5÷12.5 nm while the thickness of the non-magnetic Pt layer is varied by changing the bottom Pt layer thickness x between 0.5÷3.0 nm. The SEM characterization of the multilayer revealed a granular structure of the deposit with the granule diameter in the range from 2 to 11 nm. These results are comparable with those obtained by the X-ray diffraction measurements of crystallites size obtained by the Scherer equation. The hysteresis loops showed that the magnetic properties are influenced both by the thickness of the bi-layer and by the number of periods (n). The coercivity (Hc) varied in the range 8÷21 kA•m -1 and the remanence ratio was M/Ms = 0.23÷0.81. The samples display out of plane anisotropy and anti-ferromagnetic type coupling between layers, as it was emphasized by means of the torsion magnetometer. [Fe/Pt]n electrodeposited multilayers display giant magnetoresistance effect which can be explained mainly by the exchange interaction among neighbouring layers and by the spatially inhomogeneous magnetic structure of the granular multilayer (favouring spin scattering at the interfaces between grains and layers).
Advances in Condensed Matter Physics
This work investigates the evolution of microstructures and magnetic properties during isothermal annealing of Cu-Fe-Co alloys, using electron microscopy and superconducting quantum interference device (SQUID) magnetometry. Small coherent granular precipitates composed of iron and cobalt formed in the copper matrix in the early stage of precipitation. As annealing proceeded, the precipitates lost coherency to the matrix after reaching a size of 15–20 nm and twin-like structures were consecutively introduced in the particles. The SQUID measurements revealed that the magnetic properties of the specimens correlated with the microstructural evolution. The coercive force initially increased with annealing time but decreased after reaching a peak. Lorentz Microscopy suggested that the initial large increase of magnetization was invoked by a structural transition from fcc to B2 in the precipitates.