Mechanical detwinning device for anisotropic resistivity measurements in samples requiring dismounting for particle irradiation

Uniaxial stress is used to detwin the samples of orthorhombic iron based superconductors to study their intrinsic electronic anisotropy. Here, we describe the development of a new detwinning setup enabling variable-load stress-detwinning with easy sample mounting/dismounting without the need to re-solder the contacts. It enables the systematic study of the anisotropy evolution as a function of an external parameter when the sample is modified between the measurements. In our case, the external parameter is the dose of 2.5 MeV electron irradiation at low temperature. We illustrate the approach by studying resistivity anisotropy in single crystals of Ba1-xKxFe2As2 at x = 0.25, where the much discussed unusual re-entrance of the tetragonal C-4 phase, C-4 -> C-2 -> C-4, is observed on cooling. With the described technique, we found a significant anisotropy increase in the C-2 phase after electron irradiation with a dose of 2.35 C/cm(2).