  The performance of superconducting radiofrequency (SRF) cavities used for
particle accelerators depends on two characteristic material parameters: field
of first flux entry $H_{entry}$ and pinning strength. The former sets the limit
for the maximum achievable accelerating gradient, while the latter determines
how efficiently flux can be expelled related to the maximum achievable quality
factor. In this paper, a method based on muon spin rotation ($\mu$SR) is
developed to probe these parameters on samples. It combines measurements from
two different spectrometers, one being specifically built for these studies and
samples of different geometries. It is found that annealing at 1400{\deg}C
virtually eliminates all pinning. Such an annealed substrate is ideally suited
to measure $H_{entry}$ of layered superconductors, which might enable
accelerating gradients beyond bulk niobium technology.
