DOI: 10.1002/adma.200601621 Epitaxial Stabilization of a New Multiferroic Hexagonal Phase of TbMnO 3 Thin Films** By Jung-Hyuk Lee, Pattukkannu Murugavel, Hyejin Ryu, Daesu Lee, Ji Young Jo, Jae Wook Kim, Hyung Jin Kim, Kee Hoon Kim, Younghun Jo, Myung-Hwa Jung, Young Hwa Oh, Young-Woon Kim, Jong-Gul Yoon, Jin-Seok Chung, and Tae Won Noh* Recently, multiferroic materials have provoked a renaissance because of the prospect of controlling both the dielectric and magnetic properties of these materials using a magnetic or an electric field. [1–6] Yet there are few materials that are simulta- neously ferroelectric and ferromagnetic in the same phase. [7,8] The orthorhombic TbMnO 3 phase has attracted much attention owing to its intriguing coupling between spin and charge degrees of freedom, but its ferroelectricity emerges at tempera- tures below 27 K. [1] Here, we report on the multiferroic proper- ties of a hexagonal TbMnO 3 metastable phase that was epitaxi- ally stabilized in thin-film form on substrates with hexagonal in-plane symmetry. In contrast to the bulk orthorhombic phase, [1] the hexagonal TbMnO 3 films display ca. 20 times larg- er remnant polarization with the ferroelectric ordering temper- ature shifted to ca. 60 K. In addition, a newly discovered anti- ferroelectric-like phase and a clear signature of magnetoelectric effects suggest its uniqueness in the class of hexagonal manga- nites. Here we demonstrate a promising way to synthesize new multiferroic materials that do not exist in bulk form. Among the known multiferroic materials, the rare-earth manganites RMnO 3 are very intriguing material systems that can have two kinds of crystal structure. Depending on the size of the R ion, [9] RMnO 3 forms either an orthorhombic (R = La–Dy) or a hexagonal (R = Ho–Lu) structure. All of the hexagonal rare-earth manganites show multiferroic behaviors with high ferroelectric ordering temperatures, T C , (typically, above 590 K) and magnetic ordering temperatures T N ∼ 70– 120 K. [3] The origin of the ferroelectric (FE) ordering in hex- agonal manganites is related to the tilting of the rigid MnO 5 trigonal bipyramid. [10] By contrast, among the orthorhombic RMnO 3 , only the three compounds containing rare-earth ele- ments near Ho (i.e., R = Dy, Tb, and Gd) show multiferroic behavior with a relatively low ferroelectric ordering tempera- ture (ca. 27 K). [1,11] In this case, the ferroelectricity originates from the magnetic-frustration-induced lattice modulation. These facts imply that there is a possibility of controlling the multiferroic properties by modifying the structural phase of the rare-earth manganites. Since the orthorhombic TbMnO 3 is near the hexagonal RMnO 3 series, the formation energy difference between the orthorhombic and hexagonal TbMnO 3 could be small. There- fore, it is a worthwhile attempt to stabilize it in a hexagonal phase and explore its multiferroic properties. We fabricated TbMnO 3 in a new hexagonal phase by laser ablating the bulk orthorhombic materials into thin films on either Pt(111)//Al 2 O 3 (0001) or YSZ(111) (YSZ: yttria-stabilized zir- conia) substrates. Note that the atomic arrangement on the surfaces of both substrates has hexagonal in-plane symmetry. In bulk, the TbMnO 3 exists in the distorted orthorhombic (GdFeO 3 -type) structure, as shown schematically in Fig- ure 1a. The hexagonal in-plane symmetry on the substrate surfaces could ensure that the TbMnO 3 films grow epitaxially in the hexagonal phase by maintaining the coherent film/sub- strate interface and thereby minimizing the surface energy, as represented schematically in Figure 1b. The top view of the possible atomic arrangements for the hexagonal TbMnO 3 on the Pt surface is also shown in Figure 1c. Figure 2a shows the X-ray diffraction (XRD) h–2h scan of a TbMnO 3 film on a Pt(111)//Al 2 O 3 (0001) substrate. Apart from the substrate peaks, all of the observed peaks are in- dexed to the (000l) planes of the hexagonal TbMnO 3 , con- firming that a phase-pure hexagonal TbMnO 3 film with the c-axis normal to the film surface is obtained. The rocking COMMUNICATION Adv. Mater. 2006, 18, 3125–3129 © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 3125 – [*] Prof. T. W. Noh, J.-H. Lee, Dr. P. Murugavel, H. Ryu, D. Lee, J. Y. Jo ReCOE & FPRD, School of Physics and Astronomy Seoul National University Seoul 151-747 (Korea) E-mail: twnoh@snu.ac.kr J. W. Kim, H. J. Kim, Prof. K. H. Kim CSCMR & FPRD, School of Physics and Astronomy Seoul National University Seoul 151-747 (Korea) Dr. Y. Jo,Dr. M.-H. Jung Quantum Materials Research Team, Korea Basic Science Institute Daejeon 305-333 (Korea) Y. H. Oh,Prof. Y.-W. Kim Department of Materials Science and Engineering Seoul National University Seoul 151-747 (Korea) Prof. J.-G. Yoon Department of Physics, University of Suwon Suwon, Gyunggi-do 445-743 (Korea) Prof. J.-S. Chung Department of Physics and CAMDRC, Soongsil University Seoul 156-743 (Korea) [**] This research was financially supported by Creative Research Initia- tives (Functionally Integrated Oxide Heterostructure) of MOST/ KOSEF. The experiments at PLS were supported by MOST and POSTECH. K. H. K. is supported by MOST through the National Re- search Laboratory program and KOSEF through CSCMR. J. W. K. and J.-S. C. are supported by Seoul R & BD. Supporting Information is available online from Wiley InterScience or from the author.