Magnetization of the virgin HOPG sample (G-pure) at T = 30 K in fields applied (a) parallel and (b) perpendicular to the c-axis. The inset magnifies the ferromagnetic-like hysteresis cycle observed in the low-field magnetization perpendicular to the c-axis.
Hysteresis cycles measured in fields varying between −2 T and +2 T when applied perpendicular to the c-axis of the studied Na implanted HOPG samples. The diamagnetic background is subtracted.
Saturation magnetization at T = 30 K (represented as squares) of the ferromagnetic-like response for the pure and Na-implanted HOPG samples and the corresponding planar magnetoresistance magnitudes (circles) measured in = 5 T at the same temperature.
Magnetoresistance perpendicular to the c-axis as a function of the applied field for the quoted samples. The measurements were performed at T = 2 K. The inset shows the configuration adopted for attaching the electrical contacts and schematizes the expected current flow.
Shubnikov-de Haas oscillations in the magnetoresistance of the virgin HOPG sample at the quoted temperatures. The temperature dependence of the oscillation amplitudes labelled as I and II were analysed with Eq. (3) for samples GNa-1 and GNa-2.
Shubnikov-de Haas oscillations in the magnetoresistance of the virgin and Na implanted GNa-1 and GNa-2 HOPG samples at T = 2 K. The inset shows the amplitude of the fast Fourier transform applied to results for the G-pure sample.
Fitting of the Lifshitz-Kosevich factor (see Eq. (3)) to the temperature dependent amplitude of the oscillation denoted as II in Fig. 5, but for the GNa-1 sample.
Parameters for Na implantation in HOPG.
Cyclotron frequencies and effective masses corresponding to oscillations III and IV in the SdH spectra for the samples G-pure, G(Na)-1, and G(Na)-1.
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