Luciano Martini*, Danilo Zola**, Massimiliano Polichetti***, Sandro Pace*** Rivista: IEEE Transactions on applied Superconductivity Vol.17, N.2, Giugno 2007 USA * CESI RICERCA ** CNR-INFM *** UNIVERSITA’ DI SALERNO The magnetic instability in MgB2 monofilamentary tapes with nickel alloy matrix has been investigated by measuring hysteresis loops and magnetic relaxation. The measurements have been performed in the temperature range from 2 K up to 39 K, applying an external magnetic field up to 20 kOe both parallel and perpendicular to the filament direction.We have analysed the magnetic instability by using an adiabatic and dynamical approach and taking also into account the effects of the samples geometry on the magnetic properties. In this work we discuss the observed dependence of the flux jumps on the temperature and on the applied magnetic field taking into account the recent results on the magnetic instability in a superconductor placed in a perpendicular magnetic field. Index Terms—Flux jumps, magnetic instability, magnetic relaxation, superconducting tapes.