Magnetic ordering in the high Tc superconductor Eu0.1Gd0.9Ba2Cu3Ox

Abstract

Hyperfine Interactions 42 (1988) 1257 MAGNETIC ORDERING IN THE HIGH T SUPERCONDUCTOR EuoAGdo.gBa2Cu3Ox t c R.D. TAYLOR, J.O. WILLIS and Z. FISK Physics Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Superconducting transition temperatures T c near 95 K have been found for a number os R Ba2ChaOx systems, where R includes most of the rare earths /1/. Even magnetic ions such as Gd a-e have little effect on T c . Heat capacity measurements of C, dBa2CuaOx show a k-like feature at 2.24 K thought to be associated with magnetic ordering, and superconductivity persists below this temperature /2/. We have made aStEu biossbauer Effect (ME) measurements on EuBa2CuaOx at temperatures down to 1.3 K. The isomer shift in EuBa2CuaO• clearly shows the Eu to be in the 3+ state, and the absence of any hyperfine field shows it to be non- magnetic at all temperatures studied. For Euo.lC, do.gBa2CuaO• we find a trans- ferred hyperfine field at the Eu-sites rn i f - ' ~ t ) developing below 2.1 K. These results Euo.lC~.aBa2CuaOx are shown in Fig. 1 from data fitted with a magnetic Hamiltonian for the unresolved hyperfine spectra. The curve shown is a Brillouin fit to the data assuming g = 2 and a moment of 7y~ for Gd . The fxt gives a saturation hyperfine field of 2.9(3) T and a mag- netic ordering temperature T. of peak in the heat capacity for EuoaGdo.gBa2Cha07 was determined to be 1.95(5)K. The measurements show that o EualC, doaBa2C~aO• becomes magnetically ordered below 2.1K with the tempera- K ture dependence expected foz spon- taneous ordering of Gd ~ ions. The Fig. 1. Transferred hyperfine field at magnitude of the hyperfine field tSiEu sites as a function of temperature. transferred to the ~StEu sites is roughly that expected from the dipole field from the Cd a~ neighbors; the Eu retains its Eu a§ nonmagnetic character. The ordering temperature T N and the heat capacity peak are of common origin. Super- conductivity masks the presence of magnetic ordering in magnetic susceptibility measurements, but a long extrapolation of the high temperature susceptibility of CdBa2CuaO v gives T O ~ -4.8 K. ;Below 2.1 K, magnetism and superconductivity coexist. Temperature, ~Work supported by Department of Energy, Basic Energy Sciences, Materials Science References Z. Fisk, J. D. Thompson, E. Zirngiebl, State Commun., 62 (1987) 743. J. O. Willis, Z. Fisk, J. D. Thompson, S-W. Cheong, R. M. Aikin, and E. Zirngiebl, J. biagn. Magn. Mat. 67 (1987) L139. J. L. Smith, and S-W. Cheong, Solid J.C. Baltzer A.G., Scientific Publishing Company J. L. Smith,