Abstract
In this paper we verify that clustering of Mg-deficient regions in superconducting Mg1-xB2 samples, introduces random disorder into the system, sufficient to stabilize a vortex glass phase for small enough values of x. Employing harmonic susceptibility, among other experimental techniques, we have conducted a systematic investigation of the glass-liquid frontier in the magnetic field versus temperature phase diagram of vortex matter for three samples, corresponding to x=0.025, 0.075, and 0.100. Interestingly, the studied melting line presents a kink in the low-field/high-temperature region of the diagram, indicating that thermal disorder might become important at larger temperatures, anticipating the melting process of the vortex glass phase.