Is Transition Metal Incorporated ZnO an Intrinsic Ferromagnetic Semiconductor?
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1074-I07-05
Is Transition Metal Incorporated ZnO an Intrinsic Ferromagnetic Semiconductor? Kanwal P Bhatti1, Sujeet Chaudhary2, Dinesh K Pandya2, and Subhash C Kashyap2 1 Department of Applied Physics, Guru Nanak Dev University, Amritsar, 143005, India 2 Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India
ABSTRACT Studies on Mn, Ni and Co doped ZnO systems have revealed that the RTFM present in these systems can be both intrinsic and extrinsic depending on the choice of TM ion incorporated, technique of preparation and post-synthesis processing. Choice of such a technique that ensures better homogeneity and incorporation of TM ions in the ZnO host, leads to the occurrence of intrinsic, stable and robust RTFM. The air ambient processing eliminates the chances of any metallic cluster inclusions, and instead such TM oxide phases are formed that are nonferromagnetic. However, post synthesis processing like vacuum annealing of ZnO:Co samples under some situations can give rise to occurrence of extrinsic RTFM. But, this can be overcome by certain additional processing step. ZnO:Co samples with intrinsic RTFM (stable upto 900°C annealing) and Curie temperatures in excess of 450°C have successfully been prepared. INTRODUCTION Spintronics includes the study and investigation of material related aspects of the potential devices which specifically exploit the so far underutilized degree of freedom of the carriers, i.e., their spin. This has provided a worldwide research impetus to look for materials with stable and intrinsic ferromagnetic ordering at room temperature, e.g. transition metal (TM) incorporated IIVI oxides, which are potential candidates for spintronic devices [1]. At present, the experimental findings on the room temperature ferromagnetism (RTFM) in ZnO:TM (Mn, Co and Ni etc.) are at large variance, and both the nature and origin of RTFM are being debated. In case of the ZnO:Mn system, the samples prepared by solid state reaction method at 900°C, are reported to result in the phase pure paramagnetic samples [2]. The RTFM observed in Mn-substituted (≤5%) bulk ZnO synthesized at low (1021 Co ions/cm3, much greater than the concentration of charge carriers. Thus, the overlapping polarons (or the so called BMP) might correlate, and give rise to FM contribution. However, at the same time, the isolated polarons associated with the non-interacting Co ions (which are not taking part in the formation of BMPs) can contribute to the PM fraction of the
overall PM contribution of the Zn1-xCoxO samples. Alternatively, the observed FM in the present case could also be defect-mediated as suggested by Coey et al. [28]. This possibility stems from the fact that as the sintering temperature is increased to 800-900ºC range, the defects anneal out, thus explaining the decrease in FM in the present ZnO:Co samples. However, we do not completely rule out any other alternative explanation of the origin of FM in this system. Further studies based on microscopic investigations are required t
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