Abstract
Magnetization, susceptibility, specific heat, resistivity, neutron and x-ray diffraction have been used to characterize the properties of single-crystalline as a function of Ni doping for varying from 0 to 0.1. The combined first-order structural and magnetic phase transitions occur together in the undoped system at 172 K with a small decrease in the area of the plane along with an abrupt increase in the length of the axis in the orthorhombic phase. With increasing the ordered moment and transition temperature decrease but the transition remains sharp at modest doping while the area of the plane quickly decreases and then saturates. Warming and cooling data in the resistivity and neutron diffraction indicate hysteresis of . At larger doping the transition is more rounded and decreases to zero for . The susceptibility is anisotropic for all values of . Electrical resistivity for and 0.06 shows a superconducting transition with an onset of nearly 15 K which is further corroborated by substantial diamagnetic susceptibility. For the fully superconducting sample there is no long-range magnetic order and the structure remains tetragonal at all temperature but there is an anomalous increase in the area of the plane in going to low . Heat-capacity data show that the density of states at the Fermi level increases for as inferred from the value of Sommerfeld coefficient . The regime of superconductivity is quite restrictive with a maximum of 15 K and an upper critical field . Superconductivity disappears in the overdoped region.
5 More- Received 14 August 2009
DOI:https://doi.org/10.1103/PhysRevB.80.144524
©2009 American Physical Society