Antiferromagnetism of perovskite EuZrO 3 Yanhua Zong, Koji Fujita à , Hirofumi Akamatsu, Shunsuke Murai, Katsuhisa Tanaka Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan article info Article history: Received 22 July 2009 Received in revised form 19 October 2009 Accepted 22 October 2009 Available online 29 October 2009 Keywords: Orthorhombic perovskite Europium zirconate Antiferromagnetism Magnetic interaction M¨ ossbauer spectroscopy abstract Polycrystalline EuZrO 3 has been synthesized by the solid-state reaction between EuO and ZrO 2 , and its structural and magnetic properties have been investigated. Rietveld analysis of the X-ray diffraction pattern indicates that EuZrO 3 crystallizes in an orthorhombic perovskite structure. 151 Eu M¨ ossbauer effect measurement reveals that almost all the europium ions are present as the divalent state and occupy distorted sites with non-axial electric field gradients, in agreement with the orthorhombic structure. In contrast to previous reports, an antiferromagnetic transition was observed around 4.1 K. The magnetic structure below the Ne ´ el temperature has been discussed. & 2009 Elsevier Inc. All rights reserved. 1. Introduction Divalent europium (Eu 2+ )-bearing perovskite oxides, EuM 4+ O 3 (e.g. M=Ti, Nb), have been studied in the last several decades for their intriguing magnetic and electrical properties [1–7]. A variety of magnetic and electrical properties has been observed, depend- ing on the kind of M cations, oxygen non-stoichiometry, and aliovalent cationic substitution. For instance, europium niobate (EuNbO 3 ) behaves like a ferromagnetic (FM) metal [1,2], while the introduction of oxygen vacancies converts it into a superconduc- tor with a critical temperature of about 6 K [3]. On the other hand, europium titanate (EuTiO 3 ) is an antiferromagnetic (AFM) insulator with a Ne ´el temperature (T N ) of about 5.5 K, and quantum paraelectric properties with strong spin–lattice coupling are observed at low temperatures [4–7]. Our recent experimental results have demonstrated that the AFM state of EuTiO 3 is converted into a FM state through the lattice expansion in epitaxial thin films [8], which is in good agreement with the theoretical prediction proposed by Ranjan et al. [6]. In addition, it has been reported that partial substitution of trivalent rare-earth ions (e.g. La 3+ , Gd 3+ ) for Eu 2+ ions in EuTiO 3 introduces electrons into the conduction band of Ti 3d states, resulting in the occurrence of FM metals [9]. Compared with EuNbO 3 and EuTiO 3 , the structure and physical properties of europium zirconate (EuZrO 3 ) have been less investigated. Shafer [10] first prepared EuZrO 3 by a high- temperature solid-state reaction using ZrO 2 and EuO as starting materials and ascribed its crystal structure to a cubic perovskite. Recently, Viallet et al. [11] performed X-ray diffraction (XRD) pattern refinement on EuZrO 3 prepared by the same procedure in Ref. [10] and showed that it crystallizes in orthorhombic symmetry at room temperature. Namely, the previous reports on the crystal structure of EuZrO 3 are quite controversial. In addition, the magnetic ordering of EuZrO 3 has not been observed down to 4K [10,11] which was the lowest measurement temperature. Therefore, further investigation is necessary to clarify both the crystal structure and magnetism of EuZrO 3 . In this study, we have synthesized polycrystalline EuZrO 3 following the method described in Refs. [10,11], and examined its crystal structure and magnetic properties. Almost all europium ions are present as the divalent state in the synthesized EuZrO 3 , as revealed by 151 Eu M¨ ossbauer spectroscopy. The crystal structure is refined to an orthorhombic perovskite-type structure (Pbnm space group) through Rietveld analysis of the XRD pattern. In contrast to previous reports, measurements of magnetic suscept- ibility down to 2 K demonstrate that orthorhombic perovskite EuZrO 3 behaves as an antiferromagnet below about 4.1 K. This is the first observation of magnetic ordering in EuZrO 3 . 2. Experimental procedures Polycrystalline EuZrO 3 was prepared from reagent-grade Eu 2 O 3 , ZrO 2 , and graphite powders through the following two processes: (I) Eu 2 O 3 +C-CO+2EuO; and (II) EuO+ZrO 2 -EuZrO 3 . In the first step, Eu 2 O 3 and slightly excessive graphite were thoroughly mixed and pressed into a pellet. The pellet was then sintered at 1450 1C for 6 h in an Ar(95)/H 2 (5) (vol%) atmosphere. ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jssc Journal of Solid State Chemistry 0022-4596/$ - see front matter & 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.jssc.2009.10.014 à Corresponding author. E-mail address: fujita@dipole7.kuic.kyoto-u.ac.jp (K. Fujita). Journal of Solid State Chemistry 183 (2010) 168–172