It was recently found that disordered graphen is characterized by a non-saturating linear magnetoresistance with increasing value as the temperature rises. This effect can be used for the development of the magnetic field sensors. The structural, electrical properties and magnetoresistance of disordered mosaic-like graphen are presented in this study.
Graphen was synthesized by Chemical Vapor Deposition method on Cu foil at the temperature of 1000 °C in a mixture of Ar (90.9 %), H₂ (9 %) and CH₄ (0.1 %). A standard technique was used to transfer graphene layers onto glass substrates. The characterization of the structure of graphen layers was carried out by means of Raman spectroscopy with laser source with λ=532 nm. The measurements of the dependences of the resistance on temperature and magnetic fields (R(T) and R(B)) of the graphen layers were done in the temperature range 2‑300 K and in magnetic field up to 8 T.
According to the analysis of Raman spectra, synthesized graphen is characterized by mosaic-like structure with different thickness varied from 1 to 6 layers. It was found that the ratio between the intensities of 2D and G lines (I_2D/I_G) was varied in the range of ~ 1.98‑3.37 in different points of the samples. Besides G and 2D peaks D, D', and D + D' lines (with high intensity of the D line) were registered indicating thus inhomogeneity and defectness of the samples. Negative magnetoresistance (MR) with crossover to positive one was observed in the temperature range of 2‑50 K at the inreasing of the magnetic field. As a result of analysis of R(B) curves at T > 50 K it was found that the quadratic positive MR dependence (R ~ B²) for the low magnetic fields was changed to linear MR (R ~ B) as the induction of the magnetic field B was increased. Negative MR is induced by weak localization effects. Positive MR can be explained by the dominating of the defects induced charge carriers scattering mechanism.

Keywords: graphen, magnetoresistance, Raman spectroscopy, inhomogeneity, defect

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