Evolution of the bulk properties, structure, magnetic order, and superconductivity with Ni doping in CaFe$_{2-x}$Ni$_{x}$As$_{2}$
ORAL
Abstract
Magnetization, susceptibility, specific heat, resistivity, neutron and x-ray diffraction have been used to characterize the properties of CaFe$_{2-x}$Ni$_{x}$As$_{2}$ as a function of Ni doping. The combined first-order structural and magnetic phase transition occur together in the undoped system, with a small decrease in the area of the $a-b$ plane along with an abrupt increase in the length of the $c$-axis in the orthorhombic phase. With increasing x the transition temperature decreases but remains sharp at modest dopings. At larger dopings the transition is more rounded, and decreases to zero for x$\approx $0.06 where superconductivity develops. The regime of superconductivity is quite restrictive, with a maximum T$_{C}$ of 15 K and an upper critical field H$_{C2}$=14 T. Superconductivity disappears in the overdoped region.
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