Unusual Galvanomagnetic Properties of Pyrolytic Graphite

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In this communication we want to report three unusual features observed in galvanomagnetic behavior of "straight" and nitrogen-doped pyrolytic graphite (P.G.): (1) Negative magneto-resistance is found also in n-type as well as in p-type materials at 77°K. (2) The field dependence of the negative magneto-resistance does not only obey the quadratic law, but it even changes the sign to positive in the higher field region. (3) The Hall coefficient has opposit signs in two principal axes. Summary of the preparation history and properties of some of the P.G. specimens is given in Table I. The magneto-resistance was measured along the layer plane of the samples at room temperature and liquid nitrogen temperature. Most of our specimens show negative magneto-resistance in the lower field range at liquid nitrogen temperature as shown in Fig.1. Though a negative magneto-resistance in carbonaceous material is not an entirely new phenomenon, its appearance has been regarded to occur only in p-type materils^<1),2),3)>. Our experiments show clearly for No. R-22 show the negativecharacter regardless of their conduction type. Only in the methane cracked deposits No. R-22 the negative character disappeared upon heat treatment in accordance with Klein's result^<1)>. It is not the effect of conduction type conversion induced by hear-treatment as Klein suggests that is essential in the disappearance of the negative character.
社団法人日本物理学会の論文
1964-01-05

Unusual Galvanomagnetic Properties of Pyrolytic Graphite

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