Yukimi Jyoko

Preparation of Giant Magnetoresistance Co/Cu Multilayers by Electrodeposition

Reflection electron microscopy of electrodeposited Co, Cu/(111) Pt ultrathin layers and bilayers has revealed a heteroepitaxial and simultaneous multinuclear multilayer growth. Giant magnetoresistance and oscillatory antiferromagnetic interlayer coupling have been observed in a (111) textured Co/Cu multilayered nanostructure, which is compositionally modulated over nanometer length scales with distinct ferromagnetic Co-Cu alloy and nonmagnetic Cu layers, prepared by electrodeposition under potential control in the presence of a very slight amount of CrO{sub 3}. Such a multilayered structure containing a nominal Cu spacer layer thickness of 3.2 nm exhibits a large saturation magnetoresistance of more than 18% at room temperature. Currently the development of new magnetic multilayered nanostructures has attracted considerable attention for potential applicability to magnetoresistive sensor devices.

Characterization of electrodeposited magnetic Co/Pt multilayered nanostructures

Electrodeposition will prove to be promising for the preparation of magnetic metal nanostructures. Multilayered fcc Co/Pt nanostructures grown on a Pt(111) single-crystal substrate by electrodeposition under potential control exhibit a remanent perpendicular magnetization and a large magnetic coercivity, which depend on the multilayer growth mechanism. A possible interfacial alloying below the Pt overlayers induces a magnetic moment on the Pt atoms, leading to asymmetry between Pt/Co and Co/Pt interfaces of the multilayers. The role of the codeposition of Ni as an inhibitor for the nucleus growth process as well as for the dissolution of Co during the Pt deposition is of great importance for the occurrence of the multilayered nanostructure.

Characterization of electrodeposited Co/Cu ultrathin films and multilayers

Abstract Reflection electron microscopy (REM-RHEED) studies of electrodeposited Co,Cu/Pt(111) ultrathin layers have revealed a heteroepitaxial and simultaneous multinuclear mutilayer growth in a range from submonolayer up to some ten monolayer coverages. ‘Giant’ magnetoresistance and oscillatory antiferromagnetic interlayer coupling have been observed in a (111) textured Co/Cu multilayered nanostructure, which is compositionally modulated over nanometer length scales with distinct ferromagnetic Co Cu alloys and nonmagnetic Cu layers, prepared by electrodeposition under potential control. Such a multilayered structure containing a nominal Cu spacer layer thickness of 3.2 nm exhibits a large saturation magnetoresistance of more than 18% at room temperature. This value is nearly comparable to those previously reported in vapor-deposited multilayers.

Structure and magnetic properties of electrodeposited metallic multilayers

Abstract We have studied the structure and magneto-transport properties of Co/Cu multilayers prepared by electrodeposition. The oscillation of magnetoresistance ratio as a function of Cu-layer thickness is observed. The obtained values of magnetoresistance were 12% and 18% around 1st and 3rd peaks, respectively. The structure and magneto-transport properties of electrodeposited Co/Cu multilayers are discussed.

Preparation and characterization of electrodeposited Pt/Co multilayers

Abstract Reflection electron microscopy (REM) of electrodeposited Co/Pt(111) ultrathin layers and sandwiches has revealed a heteroepitaxial and simultaneous multinuclear multilayer growth up to coverages of some ten monolayers and an interfacial alloy formation. Cross-sectional transmission electron microscopy (TEM) has provided direct evidence for composition modulation across successive layers in a Pt/Co nanometer-multilayered structure prepared by electrodeposition under potential control.

Preparation of Giant Magnetoresistance Co‐Cu Heterogeneous Alloys by Electrodeposition

Reflection electron microscopy of electrodeposited Co, Cu/(111) Pt ultrathin layers has revealed a heteroepitaxial and simultaneous multinuclear multilayer growth or a three-dimensional island growth, which depends on the deposition overpotential. Giant magnetoresistance has been observed in heterogeneous Co-Cu alloy films, which consist of ultrafine fcc Co-rich clusters in a nonmagnetic polycrystalline Cu matrix, prepared by electrodeposition under potential control. Such a heterogeneous Co 0.2 Cu 0.8 alloy exhibits a large saturation magnetoresistance of more than 20% at room temperature.

Preparation and characterization of electrodeposited metallic multilayers

Abstract Multilayered films of Co/Pt were prepared by alternating electrodeposition of Co and Pt using two electrolytic baths. The structure of the electrodeposited multilayers was analyzed by reflection electron microscopy (REM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The magnetic anisotropy of the films was examined by changing the thickness of Co layers. Though the perpendicular magnetization characteristics are not good enough, electrodeposition may be feasible for multilayer deposition.

Characterization of electrodeposited magnetic multilayers

Electrodeposition will prove to be a promising candidate for the preparation of magnetic nanostructures. Multilayered Co/Pt nanostructures grown on a Cu(111) single-crystal substrate by electrodeposition under potential control exhibit a remanent perpendicular magnetization and a large coercivity, which depend on the deposition overpotential and hence the multilayer growth mechanism. Giant magnetoresistance and oscillatory antiferromagnetic interlayer coupling have been observed in a face-centered cubic (fcc) (111) textured Co/Cu multilayered nanostructure. Moreover, a large saturation magnetoresistance of more than 20% has been achieved at room temperature for a heterogeneous Co-Cu alloy, which consists of ultrafine fcc Co-rich clusters in a nonmagnetic Cu matrix.

Preparation of metallic multilayers by electrocrystallization

Abstract Reflection electron microscopy (REM) studies of Co electrocrystallization on Pt(111) surfaces under potential control have revealed a simultaneous multinuclear multilayer growth up to the coverage of some 10 monolayers. The feasibility of electrocrystallization to produce Co/Pt multilayers with comparable structures and magnetic properties to those by vapor-phase deposition is discussed.

Electrodeposition of amorphous Co-Ti alloys.

Amorphous Co-Ti alloys have been produced by both DC and pulse current plating from an acid sulfate bath, and their electrochemical properties in a sulfuric acid solution have been studied by means of electrochemical polarization measurements. X-ray intensities diffracted from the deposits were progressively lowered with increasing concentration of titanyl ion and faded away for DC-plated deposits containing 17.8mol% Ti. The pulse-plated Co-Ti alloys exhibited an amorphous phase with a high degree of homogeneity as well as high titanium content compared with DC-plated alloys. It is probable that the induced codeposition of amorphous Co-Ti alloys proceeds via the formation of a complex hydroxide, such as [Co⋅Tin(OH)2n+1]ad, as an adsorbed intermediate. The exchange current for catholic hydrogen evolution on the amorphous alloys was two orders of magnitude larger than that on pure cobalt deposits, whereas there were no differences in their corrosion resistance. This high activity for hydrogen evolution is ascribed to an increase in surface roughness caused by a selective dissolution of titanium from the amorphous alloy electrodes.