Magnetic layer thickness dependence of magnetization reversal in electrodeposited CoNi/Cu multilayer nanowires

The magnetization reversal of electrodeposited CoNi/Cu multilayer nanowires patterned in an array using a hole template has been investigated. The reversal mode is found to depend on the CoNi layer thickness t(CoNi); with increasing t(CoNi) a transition occurs from coherent rotation to a combination of coherent and incoherent rotation at around t(CoNi)=51 nm. The reversal mode has been identified using the magnetic hysteresis loops measured at room temperature for CoNi/Cu nanowires placed at various angles between the directions of the nanowire axis and external fields using a vibrating sample magnetometer. The nanowire samples have a diameter of ∼250 nm and constant Cu layer thickness of 4.2 nm with various t(CoNi) ranging from 6.8 nm to 7.5 μm. With increasing t(CoNi), the magnetic easy axis moves from the direction perpendicular to nanowires to that parallel to the nanowires at around t(CoNi)=51 nm, indicating a change in the magnetization reversal mode. The reversal mode for the nanowires with thin disk-shaped CoNi layers (t(CoNi)=6.8, 12 and 17 nm) is of a coherent rotation type, while that for long rod-shaped CoNi layers (t(CoNi)=150 nm, 1.0, 2.5 and 7.5 μm) can be consistently explained by a combination of coherent rotation and a curling mode. The effects of dipole–dipole interactions between nanowires and between adjacent magnetic layers in each nanowire on the reversal process have been discussed.     

Electrodeposition and characterization of Cu/Co multilayers: Effect of individual Co and Cu layers on GMR magnitude and behavior

The present work discusses the successful electrodeposition of Cu/Co multilayers, exhibiting appreciable GMR of 12-14% at room temperature. The effect of individual Cu and Co layers on the magnitude and behavior of GMR has been studied. By varying the thickness of individual layers the field at which saturation in GMR is observed can be controlled. It was observed that for lower thicknesses of Co layer, the saturation fields are reduced below 1 kOe. The Cu layer thickness seems to control the nature of magnetic coupling and the saturation field, with the two showing a correlation.     

Influence of superparamagnetic regions on the giant magnetoresistance of electrodeposited Co–Cu/Cu multilayers

The room-temperature magnetoresistance (MR) of electrodeposited Co–Cu/Cu multilayers was investigated. Samples were prepared on either a polycrystalline Ti foil or on a silicon wafer covered with a Ta buffer and a Cu-seed layer. The field dependence of the magnetoresistance was analyzed by decomposing the GMR into ferromagnetic (FM) and superparamagnetic (SPM) contributions, whereby the field dependence of the latter could be described by a Langevin function. In order to better understand the influence of the deposition conditions on the GMR in electrodeposited multilayers, the evolution of the relative importance of the two GMR contributions is discussed in terms of the Co dissolution process during the Cu deposition pulse.     

Effect of organic additives on characterization of electrodeposited Co-W thin films

Co-W thin films were electrodeposited from aqueous bath with different organic additives. Electrochemical analysis showed that the transient state was limited and polarization behaviors were more evident during Co-W electrodeposition in the presence of organic additives. SEM measurement indicated that the surface morphology was affected by the nature of the organic additives to a large extent. Homogeneous Co-W thin films were obtained from the solutions containing ethyl methacrylate. Moreover, it was obvious that the presence of organic additives, in the electroplating bath, modified the structure and magnetic properties of the Co-W thin films according to the XRD and VSM measurements.     

Influence of complexing agent on the electrodeposited Co-Pt-W magnetic thin films

Complexing agents are often used to improve the quality of electrodeposited alloys. Influence of different complexing agents with hydroxycarboxylic acid group on the electrodeposited Co-Pt-W thin films has been investigated. Cathodic polarization curves show that the polarization behaviors of electroplating bath with different complexing agents are very different. Surface morphology, phase composition and magnetic properties are observed by means of FESEM, XRD and vibrating sample magnetometer (VSM), respectively. It has been found out that, if citrate was used as complexing agent, the Co-Pt-W thin films were homogeneous and the granular crystals with the average grain size of 2 μm have been observed. Co-Pt-W thin films exhibited hexagonal close packed (hcp) lattice and strong perpendicular anisotropic magnetic behavior (H_c⊥ = 215.5 kA/m; H_c∥ = 55.4 kA/m). In the presence of gluconate, needle-like deposits were obtained and a strong face centered cubic (fcc(1 1 1)) texture was measured. The Co-Pt-W thin films showed isotropic magnetic behavior. In the case of tartate and malate, the coexistence of needle-like deposits and cellular deposits appeared. The XRD patterns showed that the mixed fcc and hcp phase formed. Perpendicular anisotropic magnetic behaviors of thin films, from malate or tartate baths, were not obvious.     

Bi surfactant effects of Co/Cu multilayered films prepared by sputter deposition

The influence of a Bi surfactant layer on the structural and magnetic properties of Co/Cu multilayers grown onto Cu(1 1 0) buffer layer by RF magnetron sputtering has been studied. The results of X-ray diffraction revealed the initial deposition of a 2.0 Å-thick Bi layer onto the Cu buffer layer prior to the deposition of the Co/Cu multilayer yielded high-quality fcc-(1 1 0) oriented epitaxial films. The X-ray photoelectron spectra revealed that Bi was segregated at around the top of the surface. Therefore, Bi was concluded to be an effective surfactant to enhance the epitaxial growth of Co/Cu(1 1 0) multilayer. The maximum giant magnetoresistance and antiferromagnetic interlayer coupling ratios of the Co/Cu multilayers were increased by using the Bi surfactant layer.