High Pressure Synthesis of RuSr 2 MeCu 2 O 8 (Me = Ho or Y)
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High Pressure Synthesis of RuSr2MeCu2O8 (Me = Ho or Y) R. Ruiz-Bustos1, J. M.Gallardo-Amores1 , E. Morán1, J. P. Attfield2, R. Sáez-Puche1 and M. A. Alario-Franco1* (1) Laboratorio Complutense de Altas Presiones and Departmento de Química Inorgánica. Facultad de Ciencias Químicas. Universidad Complutense. 28040. Madrid . Spain. EU. (2) Interdisciplinary Research Centre in Superconductivity. Madingley Road. Cambridge CB3 OHE and Department of Chemistry. University of Cambridge. Lensfield Road. Cambridge CB2 1EW. United Kingdom. EU. ABSTRACT The synthesis at high pressures ( ∼60 Kbar) and high temperatures (∼1100 ºC) of the title new ruthenates has been achieved and the materials compared to the gadolinium analogue. The structure remains tetragonal (S.G. P4/mmm) and the cell parameters linearly decrease following the lanthanide contraction. Preliminary results concerning the complex magnetic properties of these materials, where superconductivity, antiferromagnetism and a superimposed ferromagnetic ordering coexist, are presented.
INTRODUCTION
[Sr-O12] [Cu-O5] [Ru-O6] [RE-O6 ]
a b
y zcx
Figure 1. Structure of RuSr2RECu2O8 (Adapted from ref.6). On the right coner, the tilting of the RuO6 octahedra in the ab plane is highlighted.
Substitutional chemistry remains one of the most active avenues in the search for either new high Tc superconducting materials or variations in the properties of known ones; this has been specially fruitful in YBa2Cu3O7 (YBCO) where most of the lanthanides replace ytrium (1). If, at the beginning of the "superconducting rush" the copper in the chains was substituted by -simply- some of the so-called representative elements, such as Bi, Pb or Tl, more recently, and often with the support of high pressures and high temperatures, a priori unlikely substitutes for copper, such as carbon, boron, phosphorous or sulfur, have been successfully introduced in this so-called reservoir plane; as expected this process do affect the superconducting properties such as Tc and others (2, 3). If the structure is flexible enough, that is, some chemical bonds can be modified, either by compression or tension, high pressure can be used to accommodate different species in a particular crystallographic site
II11.6.1
replacing the species existing at room pressure. Therefore, high pressure and high temperature techniques are an important tool to expand the search for new materials, in general and, in particular, new superconductors (5). Quite recently, one of the most intriguing materials derived from YBCO by cationic substitution is, undoubtedly, RuSr2GdCu2O8, sometimes called the ferromagnetic superconductor in which the charge reservoir layer is composed of [RuO6] octahedra, the remaining of the structure being essentially identical to that of YBCO, see figure 1. It has been reported that the ruthenium atoms, which seem to be in an oxidation state intermediate between 4+ and 5+, order ferromagnetically below a Curie temperature of ∼130-140 K while the material becomes superconducting below a critical temper
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