Journal of Crystal Growth 273 (2004) 207–212 Growth of Sr 3 Fe 2 O 7x single crystals by the floating zone method A. Maljuk à , J. Strempfer, C. Ulrich, M. Sofin, L. Capogna, C.T. Lin, B. Keimer Max-Planck-Institut fu¨r Festko¨rperforschung, Heisenbergstrasse 1, D-70569, Stuttgart, Germany Received 10 July 2004; accepted 28 July 2004 Communicated by M. Schieber Available online 30 September 2004 Abstract We report the successful growth of high-quality Sr 3 Fe 2 O 7x single crystals with volumes of up to 0.3cm 3 by using the floating zone method. Compositional homogeneity of the crystals was verified by powder X-ray diffraction, optical and electron microscope measurements. The X-ray rocking curves of the Sr 3 Fe 2 O 7x single crystal gave a full-width at half- maximum (FWHM) of Bragg reflections of 0.02–0.031. The influence of the growth rate on the crystal size and quality was demonstrated. The effect of oxygen annealing was studied by magnetic susceptibility and Raman light scattering experiments. The Fe(+3)/Fe(+4) ratio was determined both from the magnetization and thermo-gravimetric data. r 2004 Elsevier B.V. All rights reserved. PACS: 81.10.Fq; 81.30.Dz Keywords: A2. Floating zone technique; B1. Oxides 1. Introduction It is well known that iron ions in compounds are usually divalent or trivalent. In combination with strontium several compounds have been synthe- sized with iron in the tetravalent state: SrFeO 3x , Sr 3 Fe 2 O 7x and Sr 2 FeO 4x [1,2]. All of them demonstrated exciting physical properties like a giant magnetoresistance associated with the order- ing of spin and charge degrees of freedom [3,4]. Since the growth of single crystals of tetravalent iron oxide is quite difficult, these compounds are predominantly studied in form of powder samples [1–6]. Thus, high-quality and large-size single crystals are in great demand for reliable physical and structural measurements. Sr 3 Fe 2 O 7 consists of isolated double sheets of FeO 6 octahedra, which is called a layered per- ovskite structure. Preparation of Sr 3 Fe 2 O 7x crystals is not obvious due to the question of the ARTICLE IN PRESS www.elsevier.com/locate/jcrysgro 0022-0248/$-see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2004.07.091 à Corresponding author. Tel.: +49-711-689-1405; fax: +49- 711-689-1093. E-mail address: a.maliouk@fkf.mpg.de (A. Maljuk).