Magnetic properties of (Y,Er)Ba2Co3O8

Proceedings of the 21st International Conference on Low Temperature Physics Prague, August 8-14, 1996 Part $3 - Superconductivity 2: HTS - Synthesis, etc.

LT 21 Magnetic

properties

of(Y,Er)Ba2Co308

1. Felner and J. Gersten Racah Institute of Physics, The Hebrew University, Jerusalem, 91904, Israel. The (Y,Er)Ba2Co30 8 compounds crystallize in a cubic perovskite-type (a=4.134A~ structure. DC magnetic susceptibility and Mossbauer-spectroscopy (MS) on 57Fe doped materials, show that the Co sublattice does not order magnetically doma to 1.5 K. MS reveal two inequivalent Co sites. Specific-heat and susceptibility studies show that Er in ErBa2Co30 8 orders magnetically at 3.2 K. The Cp(T) at H=0 T curves indicate a significant high electronic linear term of y~200 mJ/mol K2. INTRODUCTION Full substitution by Fe or Co for Cu in YBa2Cu307 (YBCO) leading to YBa2M308 has been reported recently [1-31. The crystal structure of the tetragonal RBa2Fe30 8 (RBFO) was studied in detail[I] The magnetic properties of RBFO (R=Y,Eu, Gd), studied by magnetic susceptibility and Mossbauerspectroscopy (MS) measurements, show that they exhibit an antiferromagnetically ordering of the iron moments, at TN~ 670 K regardless of R [2]. MS studies show two different subspoctra for the Fe(1) and Fe(2) sites below and above T N. The purpose of this paper, employing several complementary experimental techniques, is to compare the RBFO system to the RBa2CO30 8 (RBCoO) system for which a provskite cubic crystal structure was obtained [3]. Magnetic susceptibility and MS on 0.5 at % 57Fe doped materials reveal that the Co ions do not order magnetically down to 1.5 K. On the other 9 3oo.

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(at 0 T) on ErBCoO indicate, that Er is magnetically ordered at T=3.2 K. At H= 9 T, no anomaly is observed in the specific-heat. EXPERIMENTAL DETAILS AND RESULTS Ceramic samples with a nominal composition RBa2Co308 (R=Y and Er) were prepared by solid state reaction techniques, using the procedure given in ref. 2. Powder XRD measurements indicate that both materials are nearly single phase (Fig. 1) and have the perovskite cubic structure. For both materials we obtain a = 4.134(2) A ~ Attempts to prepare single phase materials with other R elements failed. The shortest Co-Co distance - 4.134(2) A ~ is longer by 5.5 % than the shortest Fe-Fe distance found in YBa2Fe308. Fig. 2 exhibits the tic magnetic measurements (M/H=z(T)) of RBCoO performed with a commercial (SQUID) magnetometer. For R=Er, one distinct anomaly is ~

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CzechoslovakJournal of Physics,Vol. 46 (1996), Suppl. $3

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Fig. 3) MS spectrum of Fe doped YBa2Co30 8 observed at T=3.2 K which is attributed to the magnetic ordering of the Er sublattice. In contrast to the high TN(Fe)=670 K obtained in RBFO [2], no anomaly is observed in the z(T) curve of YBCoO which indicates that the Co sublattice does not order magnetically down to 1.5 K. The z(T) of YBCoO obeys the Curie-Weiss (CW) law: Z=z0+C/(T-0) where Z0 is the temperature independent susceptibility, C is the molar Curie constant and 0 is the CW temperature. The fit at 2