Negative Transverse Magnetoresistance of Boron-doped Graphite at Liquid-nitrogen Temperature in Relation to 3D Weak Loca
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K. Sugihara College of Pharmacy, Nihon University, 7-7-1 Narashinodai, Funabashi, 274-8555, Japan (Received 26 July 2001; accepted 16 October 2001)
The negative transverse magnetoresistance of boron-doped graphite at liquidnitrogen temperature has been studied in detail using 3000 °C-treated Grafoil (commercially available graphite foil), with the measurements of interlayer spacing d002 at room temperature, the Hall coefficient and electrical resistivity at liquidnitrogen temperature, and temperature dependence of the resistivity in a temperature range 1.7–273 K. The negative transverse magnetoresistance can be measured for the specimens with hole carriers having the Fermi energy lower than −0.07 eV, estimated by the Slonczewski–Weiss–McCure (SWMcC) band model using the Hall coefficient data. Characteristic feature of the negative transverse magnetoresistance has been investigated in terms of the SWMcC band model and a weak localization theory obtained by extending Kawabata’s theory.
I. INTRODUCTION
Boron atoms dissolve into graphite lattice substitutionally, of which maximum solid solubility for natural Madagascar graphite is 2.35 at.% at 2350 °C.1 The interlayer spacing d002 decreases linearly with atomic fraction of boron, and the lattice constant a0 increases linearly as boron enters the lattice. The boron atom plays a role of an acceptor. Sugihara et al. reported the electrical resistivity and negative transverse magnetoresistance for boron-doped natural graphite compacts.2 They measured the resistivity in a temperature range 1.7–273 K and the transverse magnetoresistance at 4.2 K and in magnetic fields up to 6.5 T. The dependence of the resistivity on temperature was very weak and expressed by (T) ⳱ (0) − a√T ,
(1)
while the transverse magnetoresistance was written ⌬/0 ⳱ −b√B ,
(2)
where (T) and (0) are the resistivity at temperature T and that at 0 K, a is a positive constant, B is the magnetic field, and b is a positive constant. The √T dependence of the resistivity and negative √B dependence of the
a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 1, Jan 2002
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magnetoresistance at low temepratures have been observed in doped semiconductors and many amorphous alloys.3 However, with an assumption that the lattice disorder was introduced by dissolved boron atoms, Sugihara et al. explained the results in terms of the Slonczewski–Weiss–McCure (SWMcC) band model and a weak localization theory obtained by extending Kawabata’s theory in a regime of an intermediate atomic fraction of boron of 1 at.%.4,5 Hishiyama et al. prepared boron-doped specimens using a commercially available graphite foil named Grafoil and measured the temperature dependence of the resistivity in a range 4.2–300 K and the transverse magnetoresistance at 4.2 K in magnetic fields up to 6.5 T.6 They observed similar behaviors of the resistivity and the negative transverse magnetoresistance. Recently, Hishiyama e
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