Journal of Magnetism and Magnetic Materials 310 (2007) 532–535 Magnetism and unconventional superconductivity in isostructural cerium and plutonium compounds J.D. Thompson , Tuson Park, N.J. Curro, F. Ronning, R. Movshovich, E.D. Bauer, J.L. Sarrao Los Alamos National Laboratory, MS K764, Los Alamos, NM 87545, USA Available online 10 November 2006 Abstract The heavy-fermion antiferromagnet CeRhIn 5 exhibits a complex interplay between magnetism and unconventional superconductivity (SC) as a function of applied pressure and magnetic field. This interplay leads to a line of magnetic quantum-critical points within the superconducting state. A comparison of nuclear spin-relaxation measurements on CeRhIn 5 to those made on CeCoIn 5 , PuCoGa 5, and PuRhGa 5 suggests that SC and magnetism also may be related closely in these isostructural superconductors. r 2006 Elsevier B.V. All rights reserved. PACS: 75.20.Hr; 74.70.Tx; 74.20.Mn; 75.30.Mb Keywords: Superconducting mechanisms; CeRhIn 5 ; PuCoGa 5 ; Pressure; Heavy fermion; NQR 1. Introduction Magnetism and unconventional superconductivity (SC) are closely coupled broken symmetries in heavy-fermion materials. The connection between these two states is most apparent in Ce- and U-based compounds in which magnetism and SC are invariably nearby each other as a function of some tuning parameter and often coexist [1]. CeRhIn 5 provides one of several examples of this interplay that suggests magnetic fluctuations play an essential role in creating unconventional SC [2]. On the other hand, Pu-based superconductors are rare, with only two exam- ples PuCoGa 5 [3] and PuRhGa 5 [4]. These materials form in the same tetragonal, HoCoGa 5 (1 1 5) structure type as CeRhIn 5 and have modestly enhanced electronic specific heats of order 100 mJ/mol K 2 [3,4]. So far, no magnetically ordered Pu-member of the 115 family has been found, which makes it less clear that their SC arises in proximity to magnetism. Nevertheless, relationships between the Ce- and Pu115s, discussed below, allow the reasonable plausibility that magnetic fluctuations are involved as well in Cooper pairing in the Pu superconductors. 2. Results and discussion CeRhIn 5 is an instructive starting point for considering the relationship between magnetism and SC in the 115 family of materials. At atmospheric pressure, neutron diffraction [5] finds an ordered moment (0.8 m B ) below a Ne´ el temperature of T N ¼ 3.8 K that is close to that expected for a localized 4f electron in a crystal-field doublet ground state. The Fermi-surface topology of CeRhIn 5 is nearly identical to its La-analog, additionally implying that the 4f electron is essentially localized [6]. The response of CeRhIn 5 to applied pressure is shown by data in the vertical plane in Fig. 1 [7]. T N decreases for P41 GPa and extrapolates to T ¼ 0 at P 2 E2.4 GPa; however, the pressure-induced superconducting transition temperature T c ¼ T N for P 1 E1.7 GPa, which hides evi- dence for coexistence of SC and magnetic order (MO) above P 1 and prevents a reliable extrapolation of T N (P) to T ¼ 0. Qualitatively, this T–P relationship between mag- netism and SC is typical of other Ce-based heavy-fermion systems [8]. Recent specific heat measurements have ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.138 Corresponding author. Tel.: +1 505 667 6416; fax: +1 505 665 7652. E-mail address: jdt@lanl.gov (J.D. Thompson).