Ca 2 RuO 4 Thin Film Growth by Pulsed Laser Deposition
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Ca2RuO4 Thin Film Growth by Pulsed Laser Deposition Xu Wang1, Yan Xin2, Hanoh Lee3, Patricia A. Stampe4, Robin J. Kennedy4, Zhixian Zhou3, and Jim P. Zheng1 1 Department of Electrical and Computer Engineering, Florida A&M University and Florida State University, Tallahassee, FL 32310, USA 2 Magnet Science and Technology, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA 3 Department of Physics, Florida State University, Tallahassee, FL 32310, USA 4 Department of Physics, Florida A&M University, Tallahassee, FL 32307, USA
ABSTRACT Bulk Ca2RuO4 is an antiferromagnetic Mott insulator with the metal-insulator transition above room temperature, and the Neel temperature at 113 K. There is strong coupling between crystal structures and magnetic, electronic phase transitions in this system. It exhibits high sensitivity to chemical doping and pressure that makes it very interesting material to study. We have epitaxially grown Ca2RuO4 thin films on LaAlO3 substrates by pulsed laser deposition technique. Growth conditions such as substrate temperature and O2 pressure were systematically varied in order to achieve high quality single-phase film. Crystalline quality and orientation of these films were characterized by X-ray diffractometry. Microstructure of the thin films was examined by transmission electron microscopy. The electrical transport properties were also measured and compared with bulk single crystal.
INTRODUCTION Since the discovery of layered perovskite superconductor Sr2RuO4 (SRO) [1], it has attracted wide research interests because of its similar structure to the original high-Tc cuprate. Its closely related isomorph, Ca2RuO4 (CRO), is one of the Ruddlesden-Popper Ca-based series, Can+1RunO3n+1, with n = 1. Although CRO is not a superconductor, it has complex and interesting physical properties. It is found to be a Mott insulator with the metal-insulator transition at TMI = 357 K [2]. Its canted antiferromagnetic ordering occurs below 113 K [3]. Under pressure, it changes from a paramagnetic Mott insulator to a ferromagnetic metal at around room temperature [4, 5]. Since Mott metal-insulator transition is still one of the open problems in condensed-matter physics, the structure driven transition in CRO system makes it a very good research candidate. CRO exhibits high sensitivity to chemical doping. Small amount of trivalent La doping for divalent Ca in CRO drastically changes its transport and magnetic properties. Single crystal electron-doping system Ca2-xLaxRuO4 has been grown by Maeno et al. using floating zone method [6] and Cao et al. using flux method with Cl-flux [7]. With increasing La doping, TMI and electrical resistivity are both reduced while stronger ferromagnetism appears [6, 7]. The richness in their magnetic and electronic transport properties in this system provides the possibility of making useful devices if thin film fabrication of this system is successful. Lattice
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mismatch strain and stress between film and substrate and various defects are common in t
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