Journal of Magnetism and Magnetic Materials 272–276 (2004) e1383–e1384 Magnetic field induced percolation in Pr 0.67 Ca 0.33 MnO 3 by small angle magnetic neutron scattering Ch. Simon a, *, S. Mercone a , V. Hardy a , C. Martin a , D. Saurel b , A. Brulet b a Laboratoire CRISMAT, UMR 6508 du CNRS et de l’ENSICAEN, CAEN 14050, France b Laboratoire L ! eon Brillouin, CE SACLAY, Gif/Yvette, 91191 France Abstract We have studied by small angle neutron scattering the evolution induced by the application of magnetic field of the coexistence of ferromagnetism and antiferromagnetism in a crystal of Pr 0.67 Ca 0.33 MnO 3 . The results are compared to magnetic measurements, which provide the evolution of the ferromagnetic fraction. These results show that the growth of the ferromagnetic phase corresponds to an increase of the thickness of the ferromagnetic ‘‘cabbage’’ sheets. r 2003 Published by Elsevier B.V. PACS: 64.75. g; 71.12. Ex; 75 Keywords: Phase separation; Manganite; Small angle magnetic neutron scattering It was recently proposed that the ground state of manganites, which displays colossal magnetoresistive (CMR) properties, could be an electronic phase separa- tion [1]. This is a very elegant manner to interpret the CMR properties by percolation of a metallic ferromag- netic phase in an insulating antiferromagnetic matrix. A small change of the fraction or of the arrangement of the domains can induce percolation. Small angle neutron scattering (SANS) is a very powerful technique to study the phase separation between a ferromagnet and an antiferromagnet since the contrast between them is very large (the AF does not scatter at small angle) [2,3]. Among the manganites, Pr 1x Ca x MnO 3 series is one of prime interest, because Pr and Ca are about the same size and hence minimize the cationic size mismatch effect. The composition x ¼ 0:33; studied here, shows a mixing of F and AF phases as shown by neutron diffraction. Existence of the phase separation is now well proved by magnetoresistance, magnetization and specific heat studies. In Pr 0.67 Ca 0.33 MnO 3 , it was recently published that small angle magnetic neutron scattering is a good method to study the size and the shape of the domains of the phase separation [3]. At low temperature (30 K), the structure is that of a ‘‘cabbage’’ with 2D sheets (stripes) of about 15 ( A of thickness. We have studied by small angle neutron scattering the evolution induced by the application of magnetic field on the coexistence of ferromagnetism (F) and anti- ferromagnetism (AF) in a crystal of Pr 0.67 Ca 0.33 MnO 3 . The results are compared to magnetic measurements which provide the evolution of the ferromagnetic fraction (Fig. 1). Small angle neutron scattering was performed on PAXY spectrometer at the Orph! ee reactor. The sample was introduced in a cryostat with superconducting split coil and aluminum windows. The magnetic field is applied in a horizontal plane, perpendicular to the neutron beam. At 2 T, the signal is anisotropic because it is zero parallel to the magnetic moments (Fig. 2). The calibra- tion of the spectrometer was performed with a Plexiglas sample following the procedure given in. After subtrac- tion of the background, normalization by the Plexiglas sample, the scattering function is presented in absolute units (cm 1 ). The temperature of 30 K was chosen because the ferromagnetic fraction of the sample reaches 100% at 5.9 T. ARTICLE IN PRESS *Corresponding author. Tel.: 33 2 31 45 26 86; fax: 33 2 31 95 16 00. E-mail address: simon@ismra.fr (C. Simon). 0304-8853/$ - see front matter r 2003 Published by Elsevier B.V. doi:10.1016/j.jmmm.2003.12.441