Appl. Phys. A 74 [Suppl.], S683–S685 (2002) / Digital Object Identifier (DOI) 10.1007/s003390201571 Applied Physics A Materials Science & Processing Structural and magnetic properties in bidimensional manganites C. Autret 1,2∗ , G. Andr´ e 2 , F. Bour´ ee 2 , C. Martin 1 , M. Hervieu 1 , A. Maignan 1 , R. Retoux 1 , B. Raveau 1 1 Laboratoire Crismat, UMR 6508 associ´ ee au CNRS, ISMRA, 6 boulevard du Mar´ echal Juin, 14050 Caen Cedex, France 2 Laboratoire L´ eon Brillouin, CEA-CNRS, Centres d’ ´ Etudes de Saclay, 91191 Gif-sur-Yvette Cedex, France Received: 18 July 2001/Accepted: 13 November 2001 –  Springer-Verlag 2002 Abstract. The Ln y−x Ca 2−x MnO 4 series, with a K 2 NiF 4 structure, has been studied by neutron powder diffrac- tion and electron microscopy in connection with the mag- netic and transport properties. We report here the results of the structural and magnetic study of two compounds, Pr 0.25 Ca 1.75 MnO 4 and Ho 0.08 Ca 1.92 MnO 4 , for which the Mn valency is 3.75 and 3.92 respectively and consequently that show different magnetic and transport behaviours. At room temperature (RT), the average structure of both compounds is orthorhombic with lattice parameters a p √ 2, 12 Å, a p √ 2, and Cmca space group. With decreasing temperature, the Ho 0.08 Ca 1.92 MnO 4 compound exhibits two magnetic phase transitions: antiferromagnetism appears at T N ≈ 165 K and ferromagnetism at T C ≈ 75 K. The two phases coexist below T C without any structural transition. The Pr 0.25 Ca 1.75 MnO 4 compound exhibits charge ordering below T CO ≈ 275 K, char- acterised by superlattice reflections clearly evidenced by electron diffraction. Neutron diffraction pattern refinements show a partial structural transition from Cmca (RT) to C2/c (low temperature) around the charge-ordering temperature and antiferromagnetism below T N ≈ 150 K. PACS: 75.25.z; 61.12.q The various physical properties of manganese perovskites (Ln 1−x Ae x MnO 3 , Ln lanthanide, Ae divalent alkaline-earth element) have recently been under active investigation be- cause of the interesting interplay between their magnetic, electronic and structural properties. To modify and un- derstand the properties of these three-dimensional com- pounds, much attention has been focused on the Ruddlesden– Popper two-dimensional phases (Ln, Ae) n+1 Mn n O 3n+1 [1, 2]. The investigation of the n = 1 member of this series, Ln x Ca 2−x MnO 4 , was previously reported [3]. It was shown that for all lanthanides the magnetic behaviour of the com- pounds changes from ferromagnetic to antiferromagnetic at ∗ Corresponding author. (Fax: +33-2/3195-1600, E-mail: cecile.autret@ismra.fr) x ≈ 0.2. For the low-x values, the Ho 0.08 compound was se- lected because the higher M value was registered (in all x and Ln series) and the Pr 0.25 sample was first studied by elec- tron microscopy and charge ordering evidenced. In this brief paper, we compare neutron diffraction versus temperature re- sults of Pr 0.25 Ca 1.75 MnO 4 and Ho 0.08 Ca 1.92 MnO 4 . 1 Experiments The samples were prepared using the standard high-tempera- ture solid-state-reaction technique as described in [4]. Neu- tron powder diffraction experiments were carried out at the Laboratoire Leon Brillouin (CEA/Saclay). The room- temperature (RT) and 10-K neutron-diffraction patterns were recorded on the high-resolution 3T 2 instrument in the range 6 ◦ < 2θ< 125.6 ◦ by a step of 0.05 ◦ (λ = 1.2251 Å) and the temperature-dependent diffraction patterns were recorded on the G4.1 diffractometer between 1.5 and 300 K in the range 8 ◦ < 2θ< 87.9 ◦ for Pr 0.25 Ca 1.75 MnO 4 and in the range 17 ◦ < 2θ< 96.9 ◦ for Ho 0.08 Ca 1.92 MnO 4 by a step of 0.1 ◦ (λ = 2.4266 Å). The data were analysed by the Rietveld method, using the Fullprof program [5]. 2 Results and discussion 2.1 Room-temperature structure The neutron powder diffraction study of Pr 0.25 Ca 1.75 MnO 4 and Ho 0.08 Ca 1.92 MnO 4 compounds performed at room tem- perature shows that these compounds have a slightly dis- torted orthorhombic structure, in agreement with the electron- microscopy observations. The high-resolution neutron-dif- fraction patterns on 3T 2 show that, for both compounds, all peaks are indexed in the Cmca space group with lat- tice parameters close to a ≈ a p √ 2, b ≈ 12 Å, c ≈ a p √ 2 (where a p is the parameter of the ideal perovskite struc- ture). For Pr 0.25 Ca 1.75 MnO 4 , the atoms are in the Cmca space group positions: Mn in 4(a) at 000; Ca and Pr in 8( f ) at 0 yz ; O(1) in 8( f ) at 0 yz ; O(2) in 8(e) at 1/4 y1/4