Magnetoresistance in Spin Valves Based on Organic Semiconductors with Ferromagnetic Electrodes
- PDF / 361,438 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 68 Downloads / 184 Views
1033-J04-05
Magnetoresistance in Spin Valves Based on Organic Semiconductors with Ferromagnetic Electrodes Hirokazu Tada1, Motoyasu Kakita1, Tomonori Ikegami1, Tomohiro Nagano1, Iwao Kawayama2, and Masayoshi Tonouchi2 1 Department of Materials Physics, Osaka University, 1-3 Machikaneyama, Toyonaka, 560-8531, Japan 2 Institute of Laser Engineering, Osaka University, 2-6 Yamadagaoka, Suita, 565-0871, Japan ABSTRACT We have prepared layered sandwich structures composed of Co / organic materials (OMs) / La0.67Sr0.33MnO3 and measured the magnetic field effect on electrical resistance. We inserted various OMs including pentacene, C60, 8-hydroxy-quinoline aluminum and titanylphthalocyanine with a thickness in the range from 200 nm to 1,000 nm. All devices prepared showed clear spin-valve characteristics with magneto-resistance (MR) ratios of approximately a few to 10% at low temperature. It was found that spins were transported in rather thick organic films, and the polarity of MR depended upon materials inserted and their film thickness.
INTRODUCTION Spin-injection and transport properties in organic materials (OMs) have recently been intensively studied utilizing sandwich structures composed of ferromagnetic (FM) metal / OMs / FM metal. Since the first report of spin-valve behaviors in layered sandwich structure composed of Co / 8-hydroxy-quinoline aluminum (Alq3) / La0.67Sr0.33MnO3 (LSMO) [1], some groups have discussed about magnetic field effect on the electrical properties of the layered devices based on poly-3-hexylthiophene (P3HT) [2] and tetraphenyl-porphyrin (TPP) [3] as well as Alq3 [4, 5]. There are, however, still some arguments whether spins are transported in OMs or are just tunneling through thin layers of OMs. This argument is coming from the fact that it is very difficult to prepare the well-defined interface between OMs and upper FM electrodes. In most cases, metal atoms and/or clusters penetrate into OMs when we deposit metal materials on OMs[6]. This results in the increase of probability of tunneling of carriers and short circuits between electrodes. In the present study, we have prepared layered spin-valve devices based on pentacene (Fig. 1(a)), C60 (Fig. 1(b)), Alq3 (Fig. 1(c)) and titanyl-phtahlocyanine (TiOPc, Fig. 1(d)) with Co and LSMO electrodes, and discussed about the thickness dependence of magneto-resistance (MR).
EXPERIMENT Figure 1(e) shows a schematic illustration of the device prepared. LSMO films were grown epitaxially on MgO by pulsed laser deposition [7] and patterned on a rectangular electrode with dimensions of 1 mm x 2 mm x 100 nm by photolithography and dry etching. OMs were purified by vacuum sublimation prior to use. Thin films of OMs were prepared by thermal
evaporation in a vacuum chamber with a base pressure of approximately 2 x 10-6 Pa. The thickness of the films was monitored with a quartz oscillator and was controlled to be in the range from 200 nm to 1000 nm. The specimen was then transferred into another vacuum chamber without breaking the vacuum, where the upper C
Data Loading...
