Diamagnetism of Bulk Graphite Revised

Abstract

Recently published structural analysis and galvanomagnetic studies of a large number of different bulk and mesoscopic graphite samples of high quality and purity reveal that the common picture assuming graphite samples as a semimetal with a homogeneous carrier density of conduction electrons is misleading. These new studies indicate that the main electrical conduction path occurs within 2D interfaces embedded in semiconducting Bernal and/or rhombohedral stacking regions. This new knowledge incites us to revise experimentally and theoretically the diamagnetism of graphite samples. We found that the c-axis susceptibility of highly pure oriented graphite samples is not really constant, but can vary several tens of percent for bulk samples with thickness t 30 µm, whereas by a much larger factor for samples with a smaller thickness. The observed decrease of the susceptibility with sample thickness qualitatively resembles the one reported for the electrical conductivity and indicates that the main part of the c-axis diamagnetic signal is not intrinsic to the ideal graphite structure, but it is due to the highly conducting 2D interfaces. The interpretation of the main diamagnetic signal of graphite agrees with the reported description of its galvanomagnetic properties and provides a hint to understand some magnetic peculiarities of thin graphite samples.

Magnetization of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ micrometer thin ring and its depinning line

“…In order to estimate the deflection at the edge of the cantilever tip ∆x, the calibration of the cantilevers were performed. The gauge factor GF of the cantilever, that was used for the Bi-2212 ring, was mechanically determined by a manipulator from SU-RUGA SEIKI CO., LTD, using the method described elsewhere [43,63]. Further calibration of the GF was performed in the SQUID magnetometer by measuring the magnetization of the Bi-2212 flake S7, that has the identical geometry ratio [65] as the Bi-2212 sample S1, see Figure 4.…”

Magnetization of Bi2Sr2CaCu2O8+δ Micrometer Thin Ring and Its Depinning Line

“…Four piezoresistors on the cantilevers are part of a Wheatstone bridge, with 2 piezoresistors placed at the edge (which measures the cantilever deflection) and 2 piezoresistors on the base of the cantilever (for current compensation) [42]. Such configuration compensates the magnetic field influence on the piezoresistors, increasing the sensitivity of the system to magnetic moments of the order of m ∼ 5•10 −10 emu at 0.1 T applied field [43]. The cantilever was fixed in a holder inside a continuous He-flow cryostat equipped with a superconducting solenoid powered by a IPS120-10 (Oxford) power supply.…”

“…In order to estimate the deflection at the edge of the cantilever tip Δx, the calibration of the cantilevers was performed. The gauge factor GF of the cantilever that was used for the Bi-2212 ring was mechanically determined by a manipulator from SURUGA SEIKI CO., LTD., using the method described elsewhere [43,63]. Further calibration of the GF was performed in the SQUID magnetometer by measuring the magnetization of the Bi-2212 flake S7 that has the identical geometry ratio [65] as the Bi-2212 sample S1, see Fig.…”

Influence of surface band bending on a narrow band gap semiconductor: Tunneling atomic force studies of graphite with Bernal and rhombohedral stacking orders

“…[16] Kelvin force microscopy studies of the surface of well-oriented graphite samples, done in air as well as in inert atmosphere, revealed the coexistence of insulatingand conducting-like regions, [17] whose origin can also be related to the presence of ideal graphite and regions with SF at or near the surface, respectively. These highly conducting 2D SF are the origin for the metallic-like behavior in the temperature dependence of the resistance [2,11], for the low temperature Shubnikov-de Haas and de Haasvan Alphen quantum oscillations [10,11], and also for the huge diamagnetism of graphite [18] at fields applied parallel to the c−axis [19]. In other words, the proposed Fermi surface [3] does not correspond to ideal graphite, in contradiction to the semimetal picture proposed more than 60 years ago.…”