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Magnetotransport in epitaxial films of the degenerate semiconductor Zn1−xCoxO

Budhani, R. C., Pant, Prita, Rakshit, R. K., Senapati, K., Mandal, Soumen, Pandey, N. K. and Kumar, Jitendra 2005. Magnetotransport in epitaxial films of the degenerate semiconductor Zn1−xCoxO. Journal of Physics: Condensed Matter 17 (1) , 75. 10.1088/0953-8984/17/1/008

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Magnetotransport measurements are performed over a broad range of temperature (T) and magnetic field (H) on highly degenerate n-type Zn1−xCoxO (0 \le x \le 0.30) epitaxial films. The cobalt-free samples are characterized by a metallic resistivity ρ(T) down to 2 K, a negative and predominantly isotropic magnetoresistance (MR) and optical transmission above 85% in the visible range of the electromagnetic spectrum. X-ray diffraction measurements show that while for x \le 0.20 , all cobalt atoms occupy the tetrahedral sites of the wurtzite structure of ZnO, a phase separation into CoO is seen for x>0.2. In the solution phase, we do not observe any signatures of a spontaneous ordering of the cobalt spins despite a large concentration of mobile electrons (>1020 cm−3). The absence of anomalous Hall resistance is consistent with this observation. The carrier concentration (n) over the entire range of x remains above the Mott limit for the insulator-to-metal transition in a doped semiconductor. However, while the Co-free samples are metallic (T>2 K), we see a resistivity (ρ) minimum followed by lnT divergence of ρ(T) at low temperatures with increasing x. The magnetoresistance of these samples is negative and predominantly isotropic. Moreover, the MR tends to follow a logH behaviour at high fields. These observations, including the Kondo-like minimum in the resistivity, suggest s–d exchange dominated transport in these dilute magnetic semiconductors.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Publisher: IOP Publishing
ISSN: 0953-8984
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Last Modified: 04 Jun 2017 04:57

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