Anuj Kumar, Rajveer Jha, Shiva Kumar, Jagdish Kumar, P. K. Ahluwalia, R. P. Tandon, V. P. S. Awana
We report synthesis, structural, magnetic, specific heat and Density
Functional Theory (DFT) studies on MgCNi3 superconductor. Polycrystalline
MgCNi3 samples are synthesized through standard solid state reaction route and
found to crystallize in cubic perovskite structure with space group Pm3m,
without any detectable trace of Ni impurity. Both AC and DC magnetization
exhibited superconducting transition (Tc) at around 7.25 K. The lower critical
field (Hc1) and irreversibility field (Hirr) are around 140 Oe and 11 kOe
respectively at 2 K. The upper critical field (Hc2) being determined from
in-field AC susceptibility measurements is 11.6 kOe and 91.70 kOe with 50% and
90% diamagnetism criteria respectively. Heat capacity (Cp) measurements are
carried out under applied field of up to 140 kOe and down to 2 K. The
Sommerfeld constant ({\gamma}) and Debye temperature ({\Theta}D) as determined
from low temperature fitting of Cp(T) data to Sommerfeld-Debye model are 36.13
mJ/mole-K2 and 263.13 K respectively. The Bardeen-Cooper-Schrieffer (BCS)
parameter (2{\Delta}/KBTc) is around 3.62, suggesting MgCNi3 to be an
intermediate coupled BCS superconductor with value {\lambda} = 0.69. Although
the density functional theory (DFT) calculations exhibited the compound to be
non-magnetic but with spin fluctuations, the experimental isothermal
magnetization MH loops at 20, 50, 100, 200 and 300 K showed some ferromagnetic
nature in this compound with coercive field (Hc) of around 50 Oe at 20 K. The
Ni3d states play dominant roles near the Fermi levels and there is strong
hybridization between Ni3d and C2p states. It seems that MgCNi3 is
superconducting in close proximity of ferromagnetism.
View original:
http://arxiv.org/abs/1105.0482
No comments:
Post a Comment