Evolution of the bulk properties, structure, magnetic order, and superconductivity with Ni doping in CaFe2xNixAs2

Neeraj Kumar, Songxue Chi, Ying Chen, Kumari Gaurav Rana, A. K. Nigam, A. Thamizhavel, William Ratcliff, II, S. K. Dhar, and Jeffrey W. Lynn
Phys. Rev. B 80, 144524 – Published 29 October 2009

Abstract

Magnetization, susceptibility, specific heat, resistivity, neutron and x-ray diffraction have been used to characterize the properties of single-crystalline CaFe2xNixAs2 as a function of Ni doping for x 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 ab plane along with an abrupt increase in the length of the c axis in the orthorhombic phase. With increasing x the ordered moment and transition temperature decrease but the transition remains sharp at modest doping while the area of the ab plane quickly decreases and then saturates. Warming and cooling data in the resistivity and neutron diffraction indicate hysteresis of 2K. At larger doping the transition is more rounded and decreases to zero for x0.06. The susceptibility is anisotropic for all values of x. Electrical resistivity for x=0.053 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 ab plane in going to low T. Heat-capacity data show that the density of states at the Fermi level increases for x0.053 as inferred from the value of Sommerfeld coefficient γ. The regime of superconductivity is quite restrictive with a maximum TC of 15 K and an upper critical field Hc2=14T. Superconductivity disappears in the overdoped region.

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  • Received 14 August 2009

DOI:https://doi.org/10.1103/PhysRevB.80.144524

©2009 American Physical Society

Authors & Affiliations

Neeraj Kumar1, Songxue Chi2,3, Ying Chen2,3, Kumari Gaurav Rana1, A. K. Nigam1, A. Thamizhavel1, William Ratcliff, II2, S. K. Dhar1, and Jeffrey W. Lynn2,*

  • 1Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India
  • 2NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
  • 3Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA

  • *Corresponding author.

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Issue

Vol. 80, Iss. 14 — 1 October 2009

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