Appl. Phys. A 74 [Suppl.], S637–S639 (2002) / Digital Object Identifier (DOI) 10.1007/s003390201569 Applied Physics A Materials Science & Processing Detailed magnetic structure of the coupled edge-sharing CuO 2 chains in Ca 2 Y 2 Cu 5 O 10 M. Matsuda 1, ∗ , K. Kakurai 1 , H. Yamaguchi 2 , T. Ito 2 , C.H. Lee 2 , K. Oka 2 1 Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan 2 National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan Received: 18 July 2001/Accepted: 13 November 2001 –  Springer-Verlag 2002 Abstract. Elastic neutron scattering experiments were per- formed on the quasi-one-dimensional magnet Ca 2 Y 2 Cu 5 O 10 , which consists of the ferromagnetic edge-sharing CuO 2 chains. This compound shows an antiferromagnetic long- range ordering below T N = 29.5 K. It is found that the mag- netic moments are not localized at Cu sites but 22 ± 4% of the total moments exist at oxygen sites in the ordered phase. This behavior is similar to that observed in La 9 Ca 5 Cu 24 O 41 . PACS: 75.25.+z; 75.40.Cx Copper oxides with edge-sharing CuO 2 chains, in which copper spins are coupled by the nearly 90 ◦ Cu-O-Cu in- teraction, are found to exhibit various interesting phenom- ena. Ca 2 Y 2 Cu 5 O 10 , which consists of the edge-sharing CuO 2 chains, is a S = 1 2 quasi-one-dimensional Heisenberg ferro- magnet [1]. The magnetic excitations from the coupled edge- sharing CuO 2 chains show an anomalous behavior [1]. The excitation peak width in energy becomes broader with in- creasing Q along the chain although sharp excitations are ob- served around the zone center and perpendicular to the chain. It is revealed that the anomalous broadening on the magnetic excitations is caused mainly by the interchain interactions. Another interesting feature in the edge-sharing CuO 2 chain is that the magnetic moments can be induced at oxy- gen sites because of a strong Cu d -O p hybridization in the CuO 2 chains. It was predicted theoretically by Weht and Pick- ett that large moments lie on the oxygen ions in the CuO 2 chains in Li 2 CuO 2 [2]. In La 9 Ca 5 Cu 24 O 41 , which consists of the ferromagnetic edge-sharing CuO 2 chains as in Li 2 CuO 2 , it was observed that the magnetic moments exist at oxygen sites (∼ 0.02 μ B ) as well as at Cu sites (∼ 0.2 μ B ) [3]. From a powder diffraction study [4], a possibility of a small amount of the magnetic moments at oxygen sites is suggested. However, the number of the magnetic Bragg peaks used for the magnetic structural analysis is only 5 and er- rors of the magnetic intensities are rather large because the ∗ Corresponding author. (Fax: +81-29/282-5939, E-mail: matsuda@neutrons.tokai.jaeri.go.jp) magnetic intensities are weak except an intense (0,0,1) peak. As the result, the statistics are not enough to be analyzed quantitatively. In this study, we performed neutron diffrac- tion measurements using a single crystal in order to elucidate the magnetic moment at oxygen sites in the ferromagnetic edge-sharing CuO 2 chains Ca 2 Y 2 Cu 5 O 10 . We observe 12 in- dependent magnetic Bragg reflections with small errors so that a quantitative analysis is possible. It is found that about 22 ± 4% of the total magnetic moments exist at oxygen sites. 1 Experimental details The single crystal of Ca 2 Y 2 Cu 5 O 10 was grown using a travel- ing solvent floating zone method in air. The dimensions of the rod shaped crystal were ∼ 6Φ × 25 mm 3 . The effective mosaic of the single crystal is less than 0.4 ◦ with the spectrometer con- dition as described below. Detail of the crystal characteriza- tion is described elsewhere [5]. The crystal used in this study is the one that was used to study the magnetic excitations [1]. The neutron scattering experiments were carried out on the 3-axis spectrometer TAS-2 installed at the guide hall of the JRR-3M at Japan Atomic Energy Research Insti- tute (JAERI). The horizontal collimator sequences were guide-80 ′ – S–80 ′ –80 ′ with the fixed initial neutron energy E i = 30.5 meV. Contamination from higher-order beams was effectively eliminated using PG filters. The single crys- tal, which was oriented in the (hhl) scattering plane, was mounted in a closed cycle refrigerator. In the magnetic struc- tural analysis, the absorption correction is not applied since the absorption cross-sections for Ca, Y, Cu, and O are small. The extinction effect is considered to be prominent only in the (0,0,1) reflection since the intensity is comparable to the in- tense nuclear Bragg intensities [4, 6]. Other magnetic Bragg reflections are so weak that the extinction effect is considered to be negligible. 2 Results and discussion The magnetic Bragg reflections are expected at (even, even, odd) and (odd, odd, even) from the magnetic structure