Effects of Ru vacancies and oxygen synthesis pressures on the formation of nanodomain structures in SrRuO 3 thin films
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Effects of Ru vacancies and oxygen synthesis pressures on the formation of nanodomain structures in SrRuO3 thin films
Y. Z. Yoo, O. Chmaissem, S. Kolesnik, B. Dabrowski, C. W. Kimball
Institute of NanoScience, Engineering and Technology (INSET), Physics Department, Northern Illinois University, DeKalb, Illinois 60115 L. McAnelly, M. Haji-Sheikh, A. P. Genis INSET, Electrical Engineering Department, Northern Illinois University, DeKalb, Illinois 60115
ABSTRACT SrRuO3 (SRO) thin films were grown on SrTiO3 (100) substrates using the pulsed laser deposition method.
The films’ growth properties widely changed in response to different
working oxygen partial pressures. An island growth mode was dominant for low pressures up to 10 mTorr followed by a step flow growth mode at 60 mTorr and step flow plus 2 D growth at 200 mTorr then reverting back to island growth at 300 mTorr. Significant out-of-plane strains of SRO films were observed for low growth pressures (up to 10 mTorr) but became notably reduced at 60 mTorr and continued to decrease gradually with further pressure increases. Formation of Ru vacancies occurs regardless of the working pressure values and appears to be minimized at 60 mTorr. Highest TC’s were obtained in films exhibiting the step flow growth mode. The role of Ru deficiencies in relation to strain, growth mode, and magnetic properties is discussed.
INTRODUCTION
SrRuO3 (SRO), a ferromagnetic metal oxide with curie temperature of 163 K, crystallizes the perovskite structure of the GaFeO3 orthorhombic family and has a pseudocubic lattice constant of ~ 0.393 nm that is nearly the same as that of cubic SrTiO3 (a ~ 0.391 nm). The structural,
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magnetic and transport properties of SRO make the material suitable as an electrode candidate for perovskite and spin-based ferroelectronics. SrRuO3 films grown on SrTiO3 (STO) substrates exhibit interesting properties that are different than the corresponding bulk properties. For example, SRO thin films grown on STO are compressively strained owing to its in-plane lattice matching to that of STO. The presence of such strains is known to negatively interfere with the spontaneous magnetization process, thus, resulting in a reduction of the ferromagnetic critical temperature TC. In addition, SRO films typically show the evolution of unique terrace and step structures in a narrow region of growth conditions on STO substrates presenting surface step and terrace structures, which is also related to the magnetic properties and microstructure of the films. 1 , 2 These properties cannot be considered separately because they correlate to each other.
Thus, in order to study the
relationship among the various above-mentioned physical properties, SRO films with different surface structures should be fully investigated for a better understanding of their magnetic, transport and structural properties. In this paper, SRO thin films have been grown with systemically modified physical properties by changing the working oxygen partial pressure. This work addre
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