Journal of Crystal Growth 220 (2000) 480–487 Crystal growth and characterization of the CMR compound La 1.2 (Sr,Ca) 1.8 Mn 2 O 7 M. Vela´zquez a, *, C. Haut a , B. Hennion b , A. Revcolevschi a a Laboratoire de Physico-Chimie de l’Etat Solide, UMR 8648, Universite ´ de Paris-Sud, 91405 Orsay Cedex, France b Laboratoire Le ´on Brillouin, CEA-Saclay, 91191 Gif-sur-Yvette, France Received 8 June 2000; accepted 18 September 2000 Communicated by L.F. Schneemeyer Abstract High-quality centimeter-sized single crystals of La 1.2 Sr 1.8y Ca y Mn 2 O 7 (0.04y40.2) were successfully grown using a floating zone method associated with an image furnace. We present the growth conditions together with a characterization of the single crystals by means of optical and electron microscopy, EDX and ICP@AES analysis, DTA- TGA measurements and redox titration, X-ray powder diffraction, Laue X-ray back-reflection and neutron diffraction. We also stress the main aspects of the complex thermodynamical and kinetic behaviors of these compounds. # 2000 Published by Elsevier Science B.V. PACS: 72.80.Ga; 81.10.Fq; 64.70.Dv; 81.30.Fb Keywords: Colossal magnetoresistance (CMR); La 1.2 (Sr,Ca) 1.8 Mn 2 O 7 ; Single crystal; Floating zone method; Incongruency; Nonconservativity; Metastability 1. Introduction In the last few years, the revival of interest for compounds exhibiting high magnetoresistance (MR) values has led to extensive studies of several manganite systems; the most dramatic results were obtained with thin films grown in the La–Ca– Mn–O perovskite-like system, with colossal mag- netoresistance (CMR) values (defined as (R(H,T )2R(0,T ))@R(H,T )) culminating at 127 000% at 77 K for an applied magnetic field value of 6 T [1,2]. The MR effect in this type of systems was previously described, in the simplest picture, by the double-exchange model, in which the e g -like electron, ferromagnetically coupled with the on- site localized t 2g -spin (Hund’s rule coupling), jumps in a spin-conserving process from the Mn 3+ site to the neighboring Mn 4+ site across *Corresponding author. Tel.: +33-01-69-15-65-78; fax: +33- 01-69-15-40-00. E-mail address: matias.velazquez@lpces.u-psud.fr (M. Vela´zquez). 0022-0248/00/$ - see front matter # 2000 Published by Elsevier Science B.V. PII:S0022-0248(00)00873-3