The Effect of Doping on the Magnetic Properties in ${\rm Ba}{({\rm Fe}_{1-x}{\rm Co}_{x})}_{2}{\hbox {As}}_{2}$ Polycrystalline Samples

We performed an extensive characterization of Co-doped polycrystalline 122 iron pnictide samples, Ba(Fe
_1-
x
Co
x
)
₂
As
₂
with
x
=0.07, 0.09, 0.1, 0.12, by means of high-field
dc
magnetization and
ac
1st and 3rd harmonic susceptibility response measurements. From
M
(
H
) loops through the Bean model formula both the magnetic field and
T
dependences of the
J
_c
are derived. From the 3rd harmonic response of the
ac
susceptibility as a function of the
dc
magnetic field up to 10 T recorded at different temperatures, we determined the irreversibility line, using the onset criterion. From these analyses, 7% and 9% of Co-doped samples showed the best
J
_c
performances.