MICROSTRUCTURE, MAGNETIC AND MAGNETOTRANSPORT PROPERTIES OF Co-C NANOCOMPOSITE THIN FILMS
TANG Ruihe1), YANG Zhigang1), ZHANG Chi1), YANG Bai2), LIU Xiaofang2), YU Ronghai2)
1) Key Laboratory of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084
2) School of Materials Science and Engineering, Beihang University, Beijing 100191
Cite this article:
TANG Ruihe YANG Zhigang ZHANG Chi YANG Bai LIU Xiaofang YU Ronghai. MICROSTRUCTURE, MAGNETIC AND MAGNETOTRANSPORT PROPERTIES OF Co-C NANOCOMPOSITE THIN FILMS. Acta Metall Sin, 2011, 47(4): 469-474.
Abstract Co-C nanocomposite thin films with a Co atomic content of 13.0% were fabricated onto Si (100) substrates by magnetron co-sputtering technique. Post annealing was carried out in vacuum at annealing temperature ranging from 473 K to 773 K for 30 min. TEM images indicate that the Co nanoparticles are dispersed uniformly in an amorphous carbon matrix for the as-deposited samples, and Co particle size is in a range of 1.5-3.0 nm. After annealing at 673 K, the average Co particle size is enlarged distinctly. Magnetization hysteresis loops reveal that the as-deposited thin films show low magnetization. As annealing temperature is increased, both magnetization and coercivity are enhanced significantly. The samples annealed at 673 K and 773 K show ferromagnetic behaviors at low temperature, and superparamagnetic behaviors at room temperature, which are characteristic magnetic features for granular system. A negative magnetoresistance (MR) of 1.33% is observed for the as-deposited Co-C thin films at 4.2 K in the applied magnetic field of 3980 kA/m. The MR value decreases with increasing annealing temperature. Resistance (R) versus temperature (T) curves exhibit a good linear relationship of lnR-T-1/4 at a broad low temperature range, suggesting that the conduction in Co-C nanocomposite thin films follows the variable range hopping transport mechanism.
Supported by National Natural Science Foundation of China (Nos.50771058 and 50729101) and the National Major Fundamental Research Program of China (No.2010CB934602)
