Angular dependent studies of vortex pinning and dynamics in RbEuFe₄As₄ single crystals with columnar defects

We performed studies of vortex pinning and dynamics in RbEuFe₄As₄ single crystals with different densities and orientations of aligned columnar defects (CDs) introduced by heavy ion irradiation, as a function of temperature (T) and magnetic field strength (H) and orientation (Θ). Pristine crystals have a superconducting transition temperature T_c~37K and a magnetic ordering transition of the Eu at T_m~15K, neither of which is changed by the irradiations. We developed a model to account for the modifications to the vortex critical state produced by the magnetic moments. Irradiated crystals exhibit large critical current densities (J_c) and a lock-in phase (where vortices remain fully trapped into the CDs even if H is tilted away from them), which is the fingerprint of correlated pinning. For large CDs densities (e.g. matching field B_Φ ~ 10T) the lock-in phase spans an unusually large angular range and extends to fields above 2T. This allows us to investigate the angular variations of J_c and the creep rates associated with the expansion of half-loops and double-kinks inside the lock-in region, due to the changes in the pinning energy arising from the –B●H/4π term in the free energy.