Dresden 2011 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 56: Graphene (jointly with DY, DS, HL, O, TT)
MA 56.6: Vortrag
Donnerstag, 17. März 2011, 16:30–16:45, HSZ 401
Anisotropic magnetoresistance observed in graphite flakes — •Jose Barzola-Quiquia, Andreas Schadewitz, Winfried Böhlmann, and Pablo Esquinazi — Division of Superconductivity and Magnetism, University of Leipzig, D-04103 Leipzig, Germany
The possibility to have magnetic order at room temperature in a system without 3d metallic magnetic elements attracts the interest of the solid state physics community. Experimental evidence for the existence of ferromagnetism in virgin and proton-irradiated graphite samples was published based on SQUID [1] and XMCD [2] measurements. An alternative method to detect magnetic order is to measure the magnetoresistance (MR). The MR develops a characteristic butterfly loop when measured vs. magnetic field. In this work we have studied the magnetotransport properties of micrometer-size and ~10 nm thick graphite flakes as a function of temperature, magnetic field applied in- and out-plane configurations. We investigated especially the MR as a function of the angle between current and applied field in order to study the anisotropic magnetoresistance (AMR). Virgin graphite flakes show a small AMR and flakes treated with H2SO4 show an increase in the AMR signal. The observed behavior provides evidence for intrinsic and induced ferromagnetism at the surface of graphite samples. This investigation also was complemented using SQUID magnetometry on graphite powder in virgin state and after treatment with H2SO4 resulting in a clear ferromagnetic signal. [1] P. Esquinazi et al., Phys. Rev. B 66, 024429 (2002), Phys. Rev Lett. 91, 227201 (2003). [2] H. Ohldag et al., Phys. Rev. Lett. 98, 187204 (2007).