Magnetic susceptibility of realistic superconducting samples

Finite element numerical exploration of the Meissner-London equations was performed for realistic three-dimensional (3D) superconducting samples of non-ellipsoidal shape and, also, having internal textures. The goal was to establish the connection between the effective finite-size magnetic susceptibility, geometric parameters of the model and the intrinsic parameters such as London penetration depth. Theoretical results are compared with the experiments where the total magnetic susceptibility was measured using tunnel-diode resonator and local first critical field was measured using NV-centers in diamond optical magnetometry. The observed differences are attributed to the specific morphological features of iron-based superconductors and high-T_c cuprates.