Journal of Magnetism and Magnetic Materials 272–276 (2004) 162–164 Susceptibility studies of the electron-doped high-T C superconductors Nd 2x Ce x CuO 4 and Pr 2x Ce x CuO 4 C. Mennerich a,1 , D. Baabe a , D. Mienert a , F.J. Litterst a , P. Adelmann b , H.-H. Klauss a, * a Institut f . ur Metallphysik und Nukleare Festk . orperphysik, TU Braunschweig, Mendelssohnstr. 3, D-38106 Braunschweig, Germany b Institut f . ur Festk . orperphysik, Forschungszentrum Karlsruhe, D-76021 Karlsruhe, Germany Abstract We report magnetic susceptibility studies of the electron doped high-T C superconductors Nd 2x Ce x CuO 4 and Pr 2x Ce x CuO 4 with various xp0:1575: The temperature dependence of the susceptibility for all compounds is governed by the rare-earth magnetic moment under the presence of a crystalline electric field. Isothermal magnetisation studies reveal the decrease of the effective moments of Pr 3þ and Nd 3þ : The Meissner-fraction and critical field B C1 of the superconducting compounds are shown. r 2003 Elsevier B.V. All rights reserved. PACS: 71.70.Ch; 74.25.Ha; 74.72.h Keywords: Electron-doped high-T C superconductor; Cuprate; Crystalline electric field The compounds R 2 CuO 4 (R ¼ Nd; Pr) crystallize in the tetragonal body centered T’ structure [1] and show Cu 2þ antiferromagnetic order below T N ¼ 255 K [2]. Its Ce-doped derivates Nd 2x Ce x CuO 4 (NCCO) and Pr 2x Ce x CuO 4 (PCCO) are prototypes of electron doped high-T C superconductors [3,4]. Early investiga- tions of the electronic phase diagram revealed long- range antiferromagnetic order for xp0:13 [3,5] adjacent to a narrow superconducting doping range 0:13pxp0:18 with a maximum T C of 24 K for x ¼ 0:15 [4]. In contrast, recent investigations by Brinkmann et al. [6], using an alternative reduction procedure, indicate a much broader superconducting regime ex- tending to lower Ce-concentrations ð0:04pxp0:17Þ: Polycrystalline specimens of NCCO and PCCO with x ¼ 0:05; 0.1, 0.125, 0.15 and 0.1575 were prepared by standard ceramic techniques. Several steps of heat treatment procedures in air at temperatures between 950  C and 1100  C were performed, followed by a final reduction step at 925  C in Ar atmosphere. A phase purity better than 2% was checked by X-ray diffracto- metry. Figs. 1 and 2 show the temperature-dependent susceptibility wðT Þ of NCCO and PCCO for x ¼ 0:05; 0.1, 0.125 and 0.15 in 1 T field cooling. NCCO shows a remarkable uniform behavior, whereas in PCCO distinct differences are observed below 30 K: Above 30 K wðT Þ is governed by the rare-earth paramagnetic moments with a negligible contribution of the Cu 2þ spin system. The reciprocal wðT Þ (shown in the insets for NCCO and PCCO with x ¼ 0:1) follow a Curie–Weiss law above 50 K for NCCO (80 K for PCCO) from which we deduce an effective moment m eff ¼ 3:63 m B (and y ¼54 K) for Nd and m eff ¼ 3:61 m B (y ¼86 K) for Pr in good agreement with the free-ion-moments of m eff ¼ 3:62 m B for Nd 3þ and m eff ¼ 3:58 m B for Pr 3þ : To describe the behavior at lower temperatures, crystalline electric field (CEF) effects on the R 3þ ions have to be considered. Although the R 3þ ions occupy sites of tetragonal symmetry [7,8], a cubic CEF serves as ARTICLE IN PRESS *Corresponding author. Tel.: +49-531-392-5128; fax: +49- 531-391-5129. E-mail addresses: c.mennerich@tu-bs.de (C. Mennerich), h.klauss@tu-bs.de (H.-H. Klauss). 1 Also for Correspondence. 0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.11.063