Pinning Properties of 1144 Polycrystalline Samples With Aliovalent Doping

The 1144 Iron-Based Superconductors (IBSC), characterized by the A
₁
AE
₁
Fe
₄
As
₄
chemical composition (A = Alkaline, AE = Alkaline-Earth), has gained significant interest in the recent years due to their crystalline structure characterized by an intrinsic modulation of the strain along the
c
-axis and by the proneness in forming crystalline defects with a positive impact on flux pinning. Moreover, it has been proved that the compound is compatible with the cost-effective powder-in-tube (PIT) manufacturing process. In our recent experiments, we have showed that the A
₁
AE
₁
Fe
₄
As
₄
structure can be tailored to obtain a 1144 compound characterized by different (A
_x
AE
_1-x
)(AE
_y
A
_1-y
)Fe
₄
As
₄
chemical formulae without any depression in the critical temperature value. On the other hand, it has been recently shown that the doping with selected elements on both A and AE sites has a clear influence on the pinning and the grain boundary properties of poly-crystalline samples. In this work we report the results of the extensive magnetic characterization performed on pristine Ca
₁
K
₁
Fe
₄
As
₄
and doped (A
_x
Ca
_1-x
)(AE
_y
K
_1-y
)Fe
₄
As
₄
with Ba as dopant on the K site and either La or Na as dopant on the Ca site. In particular, the magnetization hysteresis loops recorded at different temperatures
M
(
H, T
) and the critical current density dependences extracted from the
M
(
H
) using the Bean model,
J
_c
(
B
,
T
), have been analyzed in order to assess the effect of aliovalent doping on the quality of the produced samples in terms of grain boundary properties and pinning efficiency.