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-xCox)₂As₂ 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.