RESUMO
Single crystals of HfAs(1.7)Se(0.2) are grown by chemical transport reaction and their chemical composition characterized in detail by various analytical methods. Chemical analyses and crystal structure investigations by single-crystal X-ray diffraction as well as powder diffraction with synchrotron radiation reveal a tetragonal PbFCl structure type with strong disorder caused by a significant arsenic deficiency (As(0.9)) on the 2a site and mixed occupancy of the 2c site (As(0.8)Se(0.2)). HfAs(1.7)Se(0.2) is a diamagnetic metal which transforms into a superconducting state at T(c)=0.52 K. Similar to other PbFCl-type arsenide selenides, the title compound displays a magnetic-field-independent -AT(1/2) term in the low-temperature electrical resistivity. This unusual term presumably originates from the electron scattering of structural two-level systems. According to the experimental results, HfAs1.7Se0.2 appears to be a rare example of a nonmagnetic Kondo material.
RESUMO
We present the results of our comprehensive investigation on the antiferromagnetic heavy-fermion superconductor Ce3PtIn11 carried out by means of electrical transport, heat capacity and ac magnetic susceptibility measurements, performed on single-crystalline specimens down to 50 mK in external magnetic fields up to 9 T. Our experimental results elucidate a complex magnetic field - temperature phase diagram which contains both first- and second-order field-induced magnetic transitions and highlights the emergence of field stabilized phases. Remarkably, a prominent metamagnetic transition was found to occur at low temperatures and strong magnetic fields. In turn, the results obtained in the superconducting phase of Ce3PtIn11 corroborate an unconventional nature of Cooper pairs formed by heavy quasiparticles. The compound is an almost unique example of a heavy fermion system in which superconductivity may coexist microscopically with magnetically ordered state.