an exercise about a kish graphite.

After a study of some quantity of graphites, graphites with microcrystalline and nanostructure, which negative magnetoresistance have shown sometimes some kind of strange dynamics under pressure and magnetic field influence, or have not showing any strange behavior at all, because the question may be asked about the normal behavior of graphite, the question of some ordinary graphite sample as a basis, as a picture in the book. An ideal case is been of interest. A kish sample, presented from Donetsk Institute of Organic Chemistry NASU is the most interesting example – the only kind of graphite studied, with hysteresis loop by temperature, rising under pressure, revealing by the pressure and potentiated by the pressure. Very weak effect as it may be seen when it happens at all – like it may be seen for thermoexpanded graphite, when resistivity dependence change it form. Kish resistivity dependence consists of two parts, linear and nonlinear one, and the different parts have shown different behavior under pressure influence.

Nonmagnetic high pressure cell was used to obtain hydrostatic pressure up to 1,7 GPa shown on fig. 1. Basal plane resistivity of kish-graphite presented from L. M. Litvinenko Institute of Physical-Organic Chemistry and Coal Chemistry N.A.S.U. was studied at fixed pressures in the 77-300 K temperature range in zero magnetic field and weak magnetic field of 1 T. Electric contacts were made by silver paste. Measurements performed in basal plane by a four-probe method. About two millimeters in diameter disks and 40 microns sick discs of kish graphite were used in experiment.

Magnetic field induces positive magnetoresistance in the kish sample within all temperature and pressure range studied. Magnetoresistance have an exponential form in the studied temperature range, and reducing of the magnetoresistance, as it may be seen in fig 2. may be due to the exponent shift to the lowest temperatures. Is it about an exitonic gap?  

Linear shift under pressure, but with a different sign for nitrogen and room temperature, almost about zero dot five slope, but with some difference, and the difference is of some different kind when the slope in nitrogen is higher than room temperature slope.