* Corresponding author. Tel.: #33-1-69-08-96-85; fax: #33- 1-69-08-82-61. E-mail address: sidis@llb.saclay.cea.fr (Y. Sidis) Physica B 281&282 (2000) 967}968 Inelastic neutron scattering studies on Sr  RuO  Y. Sidis*, M. Braden, P. Bourges, B. Hennion, S. NishiZaki, Y. Maeno, Y. Mori Laboratoire Le & on Brillouin, C.E.A./C.N.R.S., F-91191-Gif-sur-Yvette Cedex, France Forschungszentrum Karlsruhe, INFP, Postfach 3640, D-76021 Karlsruhe, Germany Department of Physics, Kyoto University, Kyoto, 606-8502, Japan CREST, Japan Science and Technology Corporation, Kawaguchi, Saitama, 332-0012, Japan Abstract Inelastic neutron scattering measurements, performed in the normal state of Sr  RuO  , reveal the existence of signi"cant incommensurate magnetic spin #uctuations located at q  "($0.6/a, $0.6/a, 0), in agreement with dynamical nesting properties predicted from LDA calculations. This "nding points towards the possibility of a competi- tion between p-wave spin triplet and d-wave spin singlet superconductivity in Sr  RuO  .  2000 Elsevier Science B.V. All rights reserved. Keywords: Spin dynamics; Sr  RuO  ; Quasi 2D system; Superconductivity In the layered perovskite superconductor Sr  RuO  [1], there is now strong evidence for a p-wave spin triplet pairing [2}4], likely mediated by strong ferromagnetic (FM) #uctuations that disfavor both s- and d-wave spin singlet superconductivity [5}8]. Nevertheless, recent cal- culations have predicted a sizeable magnetic response, far away from the zone-center, at the incommensurate wave vector (2/3a, 2/3a, 0) [9], arising from pronounced nest- ing properties of the almost one-dimensional d  bands. Mazin and Singh discuss the possibility of a competition between p-wave and d-wave superconductivity in Sr  RuO  [9]. We report inelastic neutron scattering (INS) measure- ments carried out on single crystals of Sr  RuO  in the normal. Samples have been grown by a #oating zone method. The largest sample (¹  &0.62 K) has a cylin- drical shape (4 mm in diameter and 35 mm long). The INS experiments were performed on the triple axis spec- trometers 2T (thermal beam) at the Laboratoire Le H on Brillouin, Saclay, France. The experimental set up in- corporates PG002 monochromator and analyzer and 14.7 meV "xed "nal energy. Data were taken within the scattering plane spanned by (1, 0, 0) and (0, 1, 0) direc- tions. Hereafter, the wave vector Q"(H, K, ¸) is indexed in units of the reciprocal tetragonal lattice vectors 2/a"2/b"1.63 A s  and 2/c"0.49 A s  (I4/mmm space group) [1]. Fig. 1 shows representative constant- scans taken in the (H, K, 0)-plane: at "6.2 meV and around Q  " (1.3, 0.3, 0) along the (0, 1, 0) direction. At 10.4 K, a sharp maximum of intensity is peaked at Q  "(1.3, 0.3, 0) on top of a smooth background and it almost disappears at room temperature. At 10.4 K, several constant- scans, with 6.2 meV energy transfer and performed along di!er- ent directions ((1, 0 ,0), (0, 1, 0), (1, 1, 0), (1, !1, 0)) have revealed the existence of comparable peaks at Q  " q  #G, where q  "($0.3, $0.3, 0),($0.6/a, $0.6/a, 0) and G is a zone-center or a Z-point (0 0 1) in the (HK0)-plane. The best "t of the data to a Gaussian pro"le incorporating experimental resolution function demonstrates that the peak intensity is isotropic with an intrinsic q-width (FWHM), q"0.13$0.02 A s . This yields a correlation length,  ( "2/q), of about 15 A s . The scattering at q  decreases both at high temper- ature and at large wave vector, such that its intensity can be reasonably well described by the squared magnetic 0921-4526/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 0 9 0 6 - 0