The cerium based ‘115’ materials, CeMIn 5 (M = Co, Rh, Ir), are highly unconventional metals that can display superconductivity, magnetism, or, as we found, a coexistence of both. There are several ways to explore the many degrees of freedom of these systems, including: alloying, dilution of the active cerium ion with a non- magnetic analog, and the suppression of super- conductivity with magnetic fields. We found in an alloying study of antiferromagnetic CeRhIn 5 and CeCoIn 5 that the antiferromagnetic character of CeRhIn 5 is retained throughout much of the alloy composition range, with the antiferromagnetism completely suppressed when the alloy is 75% CeCoIn 5 . However, the most surprising aspect is the coexistence of the normally competing phases of antiferromagnetism and superconductivity, an indication of the highly novel character of these fascinating materials. A second study we are currently pursuing shows a suppression of superconductivity as cerium is replaced with one of its non-magnetic analogs, yttrium. This behavior was further characterized by studying the effects of magnetic field on the super- conducting behavior. These materials are incredibly fascinating, with their exotic superconductivity, ‘tunable’ ground states, and unconventional metallic behavior. Aside from these, the ‘115’s’ may give us glimpses into the unconventional behavior of the high-T c cuprate superconductors. Exotic Superconductivity and Magnetism in Cerium Based ‘115’ Materials M. Brian Maple, University of California San Diego - DMR 0335173 a b c a - The two distinct electronic phases, antiferromagnetism (AFM) and superconductivity (SC), of the CeRh 1-x Co x In 5 system, including the region of the coexistence (SC/AFM). b - Suppression of T c in Ce 1-x Y x CoIn 5 with increasing yttrium concentration, x. c - Suppression of T c , in Ce Y CoIn for x = 0.1, 0.2, and 0.25, with Physical Review B 65, 014506 (2001) Physical Review B 72, 024551 (2005)