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Intrinsic and spatially nonuniform ferromagnetism in Co-doped ZnO films

Co doped ZnO films have been deposited by a laser-molecular beam epitaxy system. X-ray diffraction and UV spectra analysis show that Co effectively substitutes the Zn site. Transmission electron microscopy (TEM) and secondary ion mass spectroscopy analysis indicate that there are no clusters. Co dopants are uniformly distributed in ZnO film. Ferromagnetic ordering is observed in all samples deposited under an oxygen partial pressure, PO2=10-3, 10-5, and 10-7 torr, respectively. However, the magnetization of PO2=10-3 and 10-5 is very small at room temperature. At low temperature, the ferromagnetic ordering is enhanced. Muon spin relaxation (μSR) measurements confirm the ferromagnetism in all samples, and the results are consistent with magnetization measurements. From μSR and TEM analysis, the film deposited under PO2=10-7 torr shows intrinsic ferromagnetism. However, the volume fraction of the ferromagnetism phase is approximately 70%, suggesting that the ferromagnetism is not carrier mediated. Resistivity versus temperature measurements indicate Efros variable range hopping dominates the conductivity. From the above results, we can confirm that a bound magnetic polaron is the origin of the ferromagnetism. Disciplines Engineering | Physical Sciences and Mathematics Publication Details Tseng, L. T., Suter, A., Wang, Y. R., Xiang, F., Bian, P., Ding, X., Tseng, A., Hu, H. L., Fan, H. M., Zheng, R. K., Wang, X. L., Salman, Z., Prokscha, T., Suzuki, K., Liu, R., Li, S., Morenzoni, E. & Yi, J. B. (2017). Intrinsic and spatially nonuniform ferromagnetism in Co-doped ZnO films. Physical Review B: Condensed Matter and Materials Physics, 96 (10), 104423-1-104423-10. Authors L T. Tseng, A Suter, Y R. Wang, Feixiang Xiang, P Bian, X Ding, A Tseng, H L. Hu, Huiqing Fan, Rongkun Zheng, Xiaolin Wang, Z Salman, T Prokscha, Katsuaki Suzuki, R Liu, Sean Li, E Morenzoni, and Jiabao Yi This journal article is available at Research Online: http://ro.uow.edu.au/aiimpapers/2752 PHYSICAL REVIEW B 96, 104423 (2017) Intrinsic and spatially nonuniform ferromagnetism in Co-doped ZnO films L. T. Tseng,1 A. Suter,2 Y. R. Wang,1 F. X. Xiang,3 P. Bian,4 X. Ding,1 A. Tseng,1 H. L. Hu,1 H. M. Fan,5 R. K. Zheng,4 X. L. Wang,3 Z. Salman,2 T. Prokscha,2 K. Suzuki,6 R. Liu,7 S. Li,1 E. Morenzoni,2 and J. B. Yi1,* 1School of Materials Science and Engineering, UNSW, Sydney, NSW 2052, Australia 2Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, 5232 Villigen, Switzerland 3Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, New South Wales 2522, Australia 4School of Physics, The University of Sydney, NSW 2006, Australia 5College of Chemistry and Materials Science, Northwest University, Xi’an, Shaanxi 710069, China 6Department of Materials Science and Engineering, Monash University, 3800 Victoria, Australia 7SIMS Facility, Office of the Deputy-Vice Chancellor (Research and Development), Western Sydney University, Locked Bag 1797, Penrith, New South Wales 2751, Australia (Received 13 March 2017; published 18 September 2017) Co doped ZnO films have been deposited by a laser-molecular beam epitaxy system. X-ray diffraction and UV spectra analysis show that Co effectively substitutes the Zn site. Transmission electron microscopy (TEM) and secondary ion mass spectroscopy analysis indicate that there are no clusters. Co dopants are uniformly distributed in ZnO film. Ferromagnetic ordering is observed in all samples deposited under an oxygen partial pressure, PO2 = 10−3, 10−5, and 10−7 torr, respectively. However, the magnetization of PO2 = 10−3 and 10−5 is very small at room temperature. At low temperature, the ferromagnetic ordering is enhanced. Muon spin relaxation (μSR) measurements confirm the ferromagnetism in all samples, and the results are consistent with magnetization measurements. From μSR and TEM analysis, the film deposited under PO2 = 10−7 torr shows intrinsic ferromagnetism. However, the volume fraction of the ferromagnetism phase is approximately 70%, suggesting that the ferromagnetism is not carrier mediated. Resistivity versus temperature measurements indicate Efros variable range hopping dominates the conductivity. From the above results, we can confirm that a bound magnetic polaron is the origin of the ferromagnetism. DOI: 10.1103/PhysRevB.96.104423