Coexistence of superconductivity and magnetic order in NdPt2B2C

In our single-phase samples of NdPt2B2C (nominal composition NdPt2.1B2.4C1.2) and nearly single-phase Au-substituted NdPt1.5Au0.6B2C, we have observed superconductivity (Tc,onset∼3 K), both in electrical resistance and low-field magnetization measurements. While zero resistance state is reached in Au-substituted sample at ∼2.8 K, it is below 1.6 K in the non-Au sample. AC susceptibility measurements down to 10 mK confirmed superconductivity in the non-Au sample with broader transition and having diamagnetic strength similar to that of a bulk superconductor. We also find that the Tc of La1-xNdxPt2.1B2.4C1.2 (∼10 K for x=0) alloys decreases gradually when La is replaced by Nd. Zero-resistance state in La0.3Nd0.7Pt2.1B2.4C1.2 occurs at 2.8 K. We do not observe the previously reported magnetic order around 9.5 K in NdPt2.1B2.4C1.2. Our heat capacity measurements performed down to 1.7 K in both NdPt2.1B2.4C1.2 and NdPt1.5Au0.6B2C, indicate the occurrence of bulk magnetic order below 1.7 K. A peak at 1.5 K in AC susceptibility data of NdPt2.1B2.4C1.2 in the presence of 300 Oe DC magnetic field confirms magnetic order. Results of our studies show that in NdPt2B2C, superconductivity and magnetism coexist below 1.5 K