The present work shows that vortex pinning behaviour in NbTi is primar
ily a magnetic interaction. The vortex lattice under the action of pin
ning centres deforms and a vortex lattice dislocation(VLD) is stablish
ed. Using a Modified Collective Pinning Theory (MCPT), it can be shown
that when the quantity of VLD is maximum, the magnetic interaction is
larger than the core pinning interaction. Application of MCPT to arti
ficial pinning centre (APC) composite shows complete agreement between
theoretical and experimental results for the reduced pinning force de
nsity curve as a function of reduced magnetic field (F(p)xb).