Miniature Hall-probe arrays were used to measure the critical current densities for the three main directions of vortex motion in the stoichiometric LiFeAs superconductor. These correspond to vortices oriented along the c-axis moving parallel to the
ab-plane, and to vortices in the ab-plane moving perpendicular to, and within the plane, respectively. The measurements were carried out in the low-field regime of strong vortex pinning, in which the critical current anisotropy is solely determined by the coherence length anisotropy parameter, {epsilon}_{xi}. This allows extraction of {epsilon}_{xi} at magnetic fields far below the upper critical field B_c2. We find that increasing magnetic field decreases the anisotropy of the coherence length.
A miniature Hall sensor array was used to detect magnetic induction locally in the vortex states of the $beta$-pyrochlore superconductor KOs$_2$O$_6$. Below the first-order transition at $T_{rm p}sim 8$ K, which is associated with a change in the rat
tling motion of K ions, the lower critical field and the remanent magnetization both show a distinct decrease, suggesting that the electron-phonon coupling is weakened below the transition. At high magnetic fields, the local induction shows an unexpectedly large jump at $T_{rm p}$ whose sign changes with position inside the sample. Our results demonstrate a novel redistribution of vortices whose energy is reduced abruptly below the first-order transition at $T_{rm p}$.
