Evolution of Magnetic and Superconducting States in UCoGe With Fe and Ni Substitution
- PDF / 357,215 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 50 Downloads / 156 Views
1264-Z12-04
Evolution of Magnetic and Superconducting States in UCoGe With Fe and Ni Substitution J. J. Hamlin, R. E. Baumbach, K. Huang, M. Janoschek, N. Kanchanavatee, D. A. Zocco, and M. B. Maple Department of Physics, University of California, San Diego La Jolla, CA 92122, U.S.A. ABSTRACT The very small number of known ferromagnetic superconductors places the study of such compounds at the frontier of superconductivity research. Recently, UCoGe has emerged as a new member of the class of materials exhibiting coexistence of ferromagnetism and superconductivity (Curie temperature TCurie = 3 K; superconducting critical temperature Ts = 0.8 K). This compound has generated much excitement, in part because it has been proposed that the superconductivity derives from spin triplet pairing mediated by ferromagnetic interactions. Therefore, a key question is how changes in the magnetic state of UCoGe affect the superconducting properties. We have carried out a comprehensive study of the UCo1-xFexGe and UCo1-xNixGe series of compounds across the entire range of composition 0 ≤ x ≤ 1. We report the results of x-ray diffraction, electrical resistivity, and magnetization measurements to elucidate the magnetic and superconducting phase diagram of the U[Fe, Co, Ni]Ge system. Substitution of either Ni or Fe into UCoGe initially results in an increase in the Curie temperature. At higher dopant concentrations (x), the ferromagnetic state crosses over to paramagnetism in UCo1-xFexGe and antiferromagnetism in UCo1-xNixGe. INTRODUCTION Materials such as ErRh4B4 [20,21,1] and HoMo6S8 [22,2], which display the coexistence of superconductivity (SC) and ferromagnetism (FM), have been known for over three decades. In these two compounds, the latter compounds TCurie lies below Ts and the superconductivity vanishes at a second, lower critical tempearture Ts' < TCurie. Within the temperature interval between Ts' and TCurie, the ferromagnetism and superconductivity coexist macroscopically (in a spatially inhomogeneous manner), whereas a new sinusoidally-modulated state with a wavelength ~ 100 Å and superconductivity coexist microscopically (within the same volume element) [3]. In contrast, the recently discovered uranium-based compounds UCoGe [8], UGe2 (under pressure) [4], UIr (under pressure) [5], and URhGe [6] appear to exhibit the microscopic coexistence of superconductivity and itinerant electron ferromagnetism. Such a coexistence is intriguing since, in a conventional superconductor, the large internal field generated by the ferromagnetic order would be expected to destroy the superconducting state by breaking the spin-singlet Cooper pairs [7]. It is thus often suggested that the superconducting electrons in such compounds may pair in triplet states, mediated by critical fluctuations associated with a ferromagnetic quantum critical point (QCP) [8-10]. A key question for any magnetic superconductor is how changes in the magnetic state effect the superconducting critical temperature. For UCoGe, both chemical substitution and pressure hav
Data Loading...
