Comparison of Temperature and Field Dependencies of the Critical Current Densities of Bulk YBCO, MgB$_2$, and Iron-Based Superconductors

We compare the temperature and field dependence of the critical current densities of high-T
_c
superconductor materials intended for various bulk applications such as trapped-field magnets. This comprises bulk samples of YBa
₂
Cu
₃
O
_x
(YBCO), MgB
₂
, and iron-based materials, including also various versions of the YBCO compound such as melt-textured ones, infiltration-growth processed ones, and YBCO foams. Critical current densities and flux pinning forces were obtained from magnetization loops measured using Quantum Design SQUID and physical property measurement system (PPMS) systems with applied magnetic fields of up to ±9 T. The obtained data are compared to each other with respect of the optimal cooling temperature possible using modern cryocoolers. Furthermore, we plot the temperature dependencies of the critical current densities versus the normalized temperature t = T/T
_c
. This enables a direct judgement of the performance of the material in the trapped-field applications.