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Insights into Magnetic Spots in HOPG: From Characterization to Resistance Behavior

Explore the characterization of magnetic spots in Highly Oriented Pyrolytic Graphite (HOPG) and understand the transition from ohmic to ballistic resistance. The study covers resistances, mean free paths, densities, and mobilities related to bombarded magnetic spots. Detailed analysis of potential changes within the spots is presented along with simulations and experimental results on resistance behavior at different temperatures.

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Insights into Magnetic Spots in HOPG: From Characterization to Resistance Behavior

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  1. Results from Madrid and Leipzig • 1. Characterization of magnetic spots in HOPG: Bombarded spots exhibiting magnetism are insulating. • From ohmic to Ballistic resistance in HOPG • Resistances,mean free paths, densities and gigantic mobilities.

  2. EFM in bombarded magnetic spots

  3. Profile of potential changes through the spots

  4. Theory of potential drops in the spots Ve is the electric potential variation through the spot and contains Vc(Coulomb interaction between charghes) Plus the work function change W Assuming that the change in W is constant through the spot the only change remaining is the Coulomb interaction.

  5. Profile of potential changes through the spots: λ =5 micrometers!

  6. Fig.2a Fig.2b Fig.2c Fig.3a

  7. L W W Ls

  8. Fabricated constriction

  9. Current and potential simulations

  10. Current versus constriction width • Rs2D=2/π(ρ/t)ln(Ω/W)+ (ρ/t)L/W. • Rs3D = ρ/W Maxwell´s result. L=1 micron 3D 2D 2D L=4microns

  11. Experiments as a function of T Resistance at 200K Logarithmic behaviour Theory

  12. Normalized resistances to the resistance • Without constriction. Ballistic term grows at low T

  13. Densities , resistivities and mobilities (2*107V-1s-1cm2!) Notice: density reduces with T but also resistivity.

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