Structural, Optical and Magnetic Properties of Co and Fe Doped ZnO Thin Films Grown by Radio Frequency Magnetron Sputter
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Structural, Optical and Magnetic Properties of Co and Fe Doped ZnO Thin Films Grown by Radio Frequency Magnetron Sputtering Luis M. Angelats1, Maharaj S. Tomar1, Rahul Singhal1, Oscar P. Perez2, Hector J. Jimenez1, and Ricardo Martinez1 1 Physics, University of Puerto Rico, P.O. Box 9016, Mayaguez, 00680, Puerto Rico 2 General Engineering, University of Puerto Rico, P.O. Box 9044, Mayaguez, 00680, Puerto Rico ABSTRACT Zn0.90Co0.10O and Zn0.85[Co0.50Fe0.50]0.15O targets were used to grow thin films by rf magnetron sputtering. XRD patterns of the films showed a strong preferred orientation along c-axis. Zn0.90Co0.10O film showed a transmittance above 75% in the visible range, while the transmittance of the Zn0.85[Co0.50Fe0.50]0.15O film was about 45%; with three absorption peaks attributed to d-d transitions of tetrahedrally coordinated Co2+. The band gap values for Zn0.90Co0.10O and Zn0.85[Co0.50Fe0.50]0.15O films were 2.95 and 2.70 eV respectively, which are slightly less than ZnO bulk. The Zn0.90Co0.10O film showed a relatively large positive magnetoresistance (MR) at the high magnetic field in the temperature range from 7 to 50 K, which reached 11.9% a 7K for the magnetoresistance. The lowest MR was found at 100 K. From M-H curve measured at room temperature shown a probable antiferromagnetic behavior, although was possible to observe little coercive field of 30 Oe and 40 Oe for Zn0.90Co0.10O and Zn0.85[Co0.50Fe0.50]0.15O films, respectively. INTRODUCTION There is interest in dilute magnetic oxide semiconductors for spin based devices. The ZnO is a II-VI compound semiconductor with the hexagonal wurtzite structure with band gap energy ~3.1 eV. It has interesting properties from the viewpoint of forming a transparent ferromagnetic material [1]. Several groups have reported room temperature ferromagnetism in transition-metaldoped ZnO [3-8]. ZnO films doped with Co and Fe have been reported to be ferromagnetic with a Curie temperature of about 280 K [7]. But, Kim et al. pointed out the presence of Co clusters in their films as a reason for room temperature ferromagnetism. Therefore, the origin and clear understanding of ferromagnetism in Co- and Fe-doped ZnO has not been clearly elucidated. It is known that rf magnetron sputtering offers higher density plasma and films of better stoichiometry were possible. In the present study, Co- and Fe-doped ZnO thin films were deposited on quartz substrate at 300o C using rf magnetron sputtering in pure argon atmospheres. Structural, optical and magnetic properties of the films were investigated. EXPERIMENTAL DETAILS The targets of pure ZnO, Zn0.90Co0.10O and Zn 0.85[Co 0.50 Fe 0.50 ]0.15O were to used for the growth of ZnO and Co- and Fe-doped ZnO films by rf magnetron sputtering on quartz substrate
at 300o C. The base pressure in the chamber was ∼ 1.0 x 10-4 Torr and the working pressure was 8.5 x 10-3 Torr, mainly consisting of high-purity Ar gas. During the sputtering (90 minutes), the experimental parameters, e.g. rf power (125 W), substrate-to-target distanc
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