Volume 124, number 8 PHYSICS LETTERS A 12 October 1987 SUPERCONDUCTING AND MAGNETIC PROPERTIES OF THE OXIDE SUPERCONDUCTORS La~ 85Sro15Cu1~Fe~O4 J.M. MATYKIEWICZ, C.W. KIMBALL, J. GIAPINTZAKJS, A.E. DWIGHT Northern Illinois University ‘, DeKalb, IL 60115, USA M.B. BRODSKY, B.D. DUNLAP, M. SLASKI 2 and F.Y. FRADIN Argonne National Laboratory ~, Argonne, IL 60439, USA Received 8 June 1987; revised manuscript received 7 August 1987; accepted for publication 18 August 1987 Communicated by J.I. Budnick Mössbauer and magnetic measurements have been made in the perovskite superconductors La 1 35Sr01 5Cu1 57Fe~O 4for x= 0.0025, 0.005, 0.01, 0.05 and 0.10. The superconducting transition temperature is rapidly depressed as x increases, reaching T~ = 0 for x 0.03. Mössbauer data for x = 0.05 show behavior below 15 K which indicates magnetic ordering. Magnetic suscep- tibility data give an effective moment of 3—4 ~i5/Featom, and a band-like susceptibility which increases with x. 1. Introduction magnetic pairing of the superconducting electrons, polaron formation, or excitons [10—131.In order to Recent observations of very high superconducting further explore the electronic and magnetic proper- transition temperatures in oxide compounds have ties of these compounds, we have obtained magnetic focused renewed interest on oxide compounds [1—91. and Mössbauer measurements on superconducting The very high transition temperatures, ranging from La 85Sr01 5CuO4 compounds containing Fe additions. 40 to 100 K, have raised questions about the mech- anism responsible for the high superconductivity. The superconducting properties have been attributed to 2. Experimental conduction in Cu—O two-dimensional planes, with oxygen contributing substantially to the electron The compounds were synthesized by intimately density of states at the Fermi surface [5—7]. The mixing high purity oxides (5 or 6—9s pure) of the La, oxygen breathing modes are thought to play an Sr, Cu, and 57Fe constituents. The mixtures were important role if the mechanism for superconduc- pressed into pellets, sintered at 100°C for 48 hours tivity is due to electron—phonon coupling [61. How- and then annealed in an oxygen atmosphere at 550°C ever, electron—phonon interactions alone may not for 5 hours. X-ray analysis showed all compounds to produce transition temperatures as high as 100 K, be single phase and to have the tetragonal K 2NiF4 and several alternate mechanisms have been pro- structure at room temperature. For the x= 0 com- posed which involve either real space antiferro- pound, the lattice parameters are identical to those previously reported [4,5]. Superconducting transi- Work supported by the National Science Foundation (RUI) tion temperatures were obtained by ac susceptibility DMR8416695. measurements, and are listed in table 1. The mea- - Permanent address: Institute of Physics Polytechnic, Krakow, Poland. surements of magnetic properties were made by Work supported by the US Department of Energy, BES-Mate- means of a SQUID susceptometer and a Faraday rials Sciences, under Contract W-3 I - I 09-ENG-38. balance in fields up to 1 and 1.4 T, respectively. 0375-960l/87/$ 03.50 © Elsevier Science Publishers B.V. 453. (North-Holland Physics Publishing Division)