Magnetoresistance and tunnel effect of some multilayer thin film structures

Full text: The magneto-transport properties of ferromagnetic/nonmagnetic/ferromagnetic multilayers are dependent of the thickness of thin films and the roughness, but the nature of thin film interlayer is very important factor for interface scattering process. In this study we develop a fast and reliable method to characterise the electric and magnetic properties of some complex multilayer structures. Using magnetoresistance (MR), Hall effect and tunnelling effect we can estimate the quality and other properties of the deposited films. We report the magnetic properties and magnetoresistance of magnetic thin film multilayers in correlation with microstructural properties. The multilayer films were characterized atomic force microscopy (AFM) for surface texture, grain size and roughness. Samples investigated in this paper were prepared by d.c. magnetron sputtering, at Ar pressure during the deposition: 29 mPa. The samples were denoted with S1, S2, S3 and S4: - 1:Si/SiO2/Py(10 nm)/Co(3 nm)/Al2O3(1 nm)/Co(3 nm)/Py(10 nm)/FeMn(10 nm)/Py(8 nm) - 2:Si/SiO2/Py(10 nm)/Co(3 nm)/Cu(2 nm)/Co(3 nm)/Py(10 nm)/FeMn(10 nm)/Py(8 nm) - 3: Si/SiO2/Py(10 nm)/Al2O3(1 nm)/Py(10 nm)/FeMn(10 nm)/Py(8 nm) - 4: Si/SiO2/Py(20 nm)/Al2O3(2 nm)/Py(20 nm). Two types of configurations were obtained: unpatterned films for magnetoresistance (MR) and Hall effect measurements and cross-stripe structures for tunnel effect measurements. For electrical conductivity, Hall effect and tunnel effect measurements we used the dc four point technique. All these configurations are connected through a switching box to a system composed by an instrumentation amplifier (EI-1040) and an external DAQ board (LabJack U12). The effective thicknesses of the oxide layers were estimated by tunnel effect measurements. At low Ar pressure we obtained structures that are rather granular films than well defined multilayer structures. On the other hand we obtained an increase of the Hall resistivity, which can be very attractive in the field of the magnetic sensors. The saturation fields obtained when the magnetic field is applied normal to the film plane are less than the values predicted from the shape anisotropy and give us information regarding the films roughness. Using tunnelling experiments we can estimate the thickness and the quality of the oxide layer. References: 1. . S. Plasket, P. P. Freitas, N. P. Barradas, M. F. da Silva and J. C. Soares, J. Appl. Phys. 76 (1994) 6104 2. . S. Moodera, G. Mathon, J. Magn. Magn. Mater. 200 (1999) 524 3. . Volmer, J. Neamtu, J. Magn. Magn. Mater. 272-276 (2004) 1881