Formation of hexagonal phase of TbMnO 3 thin film and its multiferroic properties
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Pattukkannu Murugavel Department of Physics, Indian Institute of Technology-Madras, Chennai 600-036, India
Jae Wook Kim and Kee Hoon Kim Center for Strongly Correlated Materials Research (CSCMR) & Frontier Physics and Research Division (FPRD), School of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
Younghun Jo and Myung-Hwa Jung Quantum Materials Research Team, Korea Basic Science Institute, Daejeon 305-333, Korea
Jong-Gul Yoon Department of Physics, University of Suwon, Suwon Gyunggi-do 445-743, Korea
Jin-Seok Chung Department of Physics and CAMDRC, Soongsil University, Seoul 156-743, Korea (Received 19 December 2006; accepted 11 April 2007)
TbMnO3 exists in an orthorhombic phase in nature. Recently, we successfully grew TbMnO3 thin films in the hexagonal phase using epitaxial stabilization techniques. In this article, we will show the details of the deposition conditions that allow us to fabricate the hexagonal TbMnO3 films on Pt–Al2O3(0001) substrates. The artificial hexagonal phase can be easily formed above 850 °C, irrespective of the oxygen partial pressure. The hexagonal TbMnO3 films showed ferroelectric properties, which are significantly enhanced compared to those of the orthorhombic TbMnO3 bulk phase. We find interesting anomalies in the magnetic and magnetodielectric properties of the TbMnO3 films at around 45 K, which should be related with the Mn3+ spin reorientation. We also find spin-glass-like behaviors in the magnetic susceptibility, which could be attributed to the geometric frustration of antiferromagnetically coupled Mn spins with an edge-sharing triangular lattice. This work shows details of the growth and properties of hexagonal TbMnO3 films.
I. INTRODUCTION
Recently, multiferroic materials have caused a revival of intensive research activities due to their prospective application possibilities and intriguing physical phenomena.1,2 Among them, orthorhombic RMnO3 (R ⳱ Gd, Tb, and Dy) has been widely investigated to understand the origin of its strong magnetoelectric couplings.3 Because its ferroelectric (FE) origin is related to the magnetic frustrations, the FE property (TC) emerges only at very low temperatures. In contrast, hexagonal RMnO3 (R ⳱ Ho, . . . , Lu) has a high FE ordering temperature (typically above 590 K). Recently, we succeeded in fabricating a metastable hexagonal phase of TbMnO3 by epitaxially stabilizing it a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0270 2156 J. Mater. Res., Vol. 22, No. 8, Aug 2007 http://journals.cambridge.org Downloaded: 13 Mar 2015
in thin-film form on substrates with hexagonal in-plane symmetry.4 As shown in Fig. 1, the hexagonal symmetry of the Pt(111) surface, grown on the Al2O3(0001) substrate, could be used to stabilize the metastable hexagonal phase of TbMnO3 using the structure–strain relationship. Compared to the bulk orthorhombic phase, its FE properties were significantly enhanced. In addition, we reported a dielectric anomaly at the Néel temperature (TN; 70 K) a
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