Magnetotransport properties of Co-C granular thin films depending on the carbon sputtering power
- PDF / 2,147,102 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 86 Downloads / 196 Views
Magnetotransport properties of Co-C granular thin films depending on the carbon sputtering power J.G Kang*, M. Mizuguchi, and K. Takanashi Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Abstract CoxC1-x granular films were deposited on Si substrates by a co-sputtering method. A large negative MR of 30.3% was obtained at 2 K for the sample prepared with the sputtering power of 50 W (C) and 4 W (Co). We have studied structural properties of Co-C granular films by Raman spectroscopy. Two peaks (D and G modes) from carbon bonds were clearly observed, and the intensity ratio of two peaks changed with the sputtering power, suggesting that the graphitization was promoted with the sputtering power. It was also revealed that the transport mechanism changed from tunneling to Mott’s variable range hopping and MR decreased with the sputtering power. Introduction Magnetotransport in magnetic nanostructures is one of the important issues for spintronics. Magnetic granular films consisting of nanometer-sized magnetic metal particles (Fe, Co, Ni..) embedded in an insulating matrix exhibit giant magnetoresistance (MR) due to spin dependent tunneling[1-11] and have received much attention. It has been well known that the tunneling magnetoresistance (TMR) effects are influenced by the kind of matrix materials. The magnetic granular films with carbon matrix have been investigated so far [11-16] and have large application potential as spin transport materials because long spin relaxation time is expected due to its weak spin-orbit interaction [14,15]. The films of amorphous carbon (a-C) have a mixture of graphite–like sp2 and diamond-like sp3 bond characteristics. The ratio of sp2 and sp3 orbitals in an a-C film can be changed with the deposition condition that results in different electronic properties. Therefore, interesting phenomena are expected in magnetic granular films with an aC matrix [16]. In this paper, systematic investigation has been performed on magneto-transport properties of Co-C granular films with different sputtering power.
Experimental Co-C granular films were deposited on Si (100) substrates by magnetron co-sputtering using high purity Co (> 99.9%) and C (> 99.999%) targets. Before deposition, the Si substrates were
ultrasonically cleaned in ethanol and then acetone, and rinsed in de-ionized water. The base pressure of the growth chamber was less than 2×10-5 Pa and the deposition was carried out in an Ar atmosphere of 2.1×10-1 Pa at room temperature. The film composition changed by setting the different sputtering powers for the Co and C target. A metal mesh was placed over the Co target to enable precise control of the Co content. The Co content (xCo) was determined with an electron probe micro-analyzer (EPMA). The resistance–temperature (R–T) relation and magnetotransport properties of the films were measured with a physical property measurement system (PPMS, Quantum Design) using a fourprobe method at temperatures ranging from 2 to 300 K. The sample size was 8 × 4 × t nm (length
Data Loading...
