PACS 75.70.Cn The influence of In surfactant on the giant magnetoresistance (GMR) effect and magnetization processes has been investigated in Co/Cu thermally evaporated multilayers (MLs) with sublayer thicknesses of Co and Cu corresponding to the second antiferromagnetic maximum of interlayer coupling. Based on the Xray reflectivity (XRR) and atomic force microscopy (AFM) measurements it has been shown that In added in small amount at MLs interface leads to well ordered structures with small roughness (a few Å). This fact was reflected in magnetoresistivity values that were also larger for samples with In in comparison to pure Co/Cu multilayers. However, the magnetization hysteresis loops demonstrated the very small fraction of antiferromagnetic coupling in the investigated samples. These results indicate that the role of chemical roughness is not equivalent to the role of magnetic roughness. 1 Introduction GMR has recently received extensive attention due to its great potential in the field of magnetic sensors, high-density read-out heads and other magnetic storage technologies. One of the most promising candidate materials for devices reading/writing the magnetic information are Co/Cu multilayers [1], because of the very large GMR effect even at room temperature [2]. However, a wide variation of results for Co/Cu multilayers has been observed, indicating sensitivity of magnetic and transport properties to the preparation conditions [3,4]. The growth mode of films is determined by a combination of experimental parameters like the deposition rate and the orientation and temperature of the substrate, as well as by a number of fundamental energy parameters of the deposited material. The most important material parameter that is involved in the growth process is the adatom diffusion barrier. If, at given temperature and deposition flux the ratio of the adatom diffusion coefficient to the deposition flux is sufficiently large, deposited adatoms will not form stable nuclei and will only attach to steps. In this case the film growth process always proceeds in a smooth layer-by-layer way. However, additional barriers to interlayer transport are present, like the Ehrlich-Schwoebel barrier (ES) [5,6], that an adatom has to overcome to diffuse down a surface step. It is already known [7] that the presence of an ES barrier can lead to a growth instability, i.e. rough growth on an initially flat terrace. A high Ehrlich-Schwoebel barrier hinders the interlayer mass transport so that newly deposited adatoms cannot diffuse down when they have landed on top of an island. This process leads to the 3-dimensional growth of films.
We have studied the influence of the Pb buffer layer thickness in the Co/Cu multilayers on the magnetoresistance of the system. Co/Cu multilayers (ML) were thermally evaporated at very low deposition rates on Si substrates covered with Pb buffer layer of different thickness (5, 10, 20, 30, 40 nm). The structural characterisation of samples was performed by X-ray reflectometry (XRR) and Scanning Force Microscopy (SFM). Using ex situ scanning force microscopy we have measured directly the topography of the top surface of the multilayered structure as well as the top surface of buffer layer. Quantitative estimates of the character of sample surface have been done using dynamic-scaling theory. Magnetoresistance measurements were carried out at room temperature using a standard four-probe dc method with current in the plane of the sample. We have found that Pb buffer layer strongly influences the magnetotransport properties of Co/Cu multilayers. Since the thickness of single layers is of similar magnitude as the interfacial roughness in our samples the nature of the coupling is still not clear, but we suggest the creation of granular entities which are the main source of MR in these samples.
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