Magnetic properties of RE-Ba-Cu oxides in the normal and superconducting states
- PDF / 408,831 Bytes
- 5 Pages / 613 x 788.28 pts Page_size
- 1 Downloads / 154 Views
Magnetic Properties of RE-Ba-Cu Oxides in the Normal and Superconducting States H. L. LUO, S.M. GREEN, C. JIANG, YU MEI, and C. POLITIS The magnetic properties of single-phase superconducting RBa2Cu307_ x (R = Y, Nd, Sin, Eu, Gd, Dy, Ho, Er, Tm) with resistive Tc - 95 K are summarized. The normal state susceptibilities of these compounds are classified into three groups: (1) Pauli paramagnetic R = Y, (2) the light rare-earths R = Nd, Sm, Eu, and (3) the heavy rare-earths R = Gd, Dy, Ho, Er, Tm. For the YBa2Cu307_~, susceptibility, Meissner, and shielding effects were carefully analyzed. For the light rare-earth compounds, the normal state susceptibility cannot be fitted to the Curie-Weiss law, x(T) = N/x2ff/3kB (T - 0). In this report, the susceptibilities of SmBazCU3OT_x and EuBa2Cu307_x are analyzed within the framework of the Van Vleck-Frank theory. A systematic study has also been carried out on the magnetic properties of the heavy rare-earth compounds in the normal and superconducting states. The data from several research groups are collected for comparison. For our group, the normal state susceptibilities closely follow the Curie-Weiss law. The effective moments determined from the experimental data are in agreement with those expected from Hund's rule for the free R 3+ ions. In all cases, the value of 0 is negative (except for Gd, 0 --- 0), revealing the presence of antiferromagnetic interactions. After the discovery of YBazCU3OT_x with a superconducting transition temperature (To) in the range of 90 to 95 K l it was soon learned that, in the compound, the element Y played only a passive role in the superconductivity. In fact, Y can be completely replaced by any rare-earth (R) elements (except Sc, Ce, Pr, and Tb) without adversely affecting the superconducting characteristics despite the large magnetic moments associated with some of the R 3+ ions such as Gd, Dy, etc. Magnetic properties of RBazCu307_ x H.L. LUO, Professor, S.M. GREEN, Graduate Research Assistant, C. JIANG, Visiting Scholar from Shanghai Institute of Metallurgy, Academia Sinica, People's Republic of China, and YU MEI, Postdoctoral Researcher, are with the Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, CA 92093-0114. C. POLIT1S is Adjunct Professor at UCSD and Group Leader, Institute for Nuclear Solid State Physics, Kernforschungszentrum Karlsruhe, West Germany. Manuscript submitted October 19, 1987. 734--VOLUME 19A, MARCH 1988
(RBCO) have been studied by several groups of researchers 2~5 In this report, we present our latest systematic study of the magnetic properties of well-characterized RBazCU3OT_x with R = Nd, Sm, Eu, Gd, Dy, Ho, Er, and Tm. On one hand, data indicate that all these R 3+ ions essentially possess their full free ion moments. On the other hand, there are subtle differences among them. The commonly practiced calcination method was used for the preparation of all samples; namely, appropriate amounts of well-ground and well-mixed oxide powders were reacted at - 9 0 0 ~ for
Data Loading...
