The only way to base the feat Leadership on Intelligence rather than Charisma appears to be the wizard archetype instructor, which seems to be written for a single-class wizard rather than a 1-level dip for a magus. Nonetheless, the instructor's extraordinary ability apprentice says, in part, that...
Because cohorts are most interested in the instructor's magical ability, the instructor uses his Intelligence modifier, rather than Charisma, to determine his Leadership score. At 7th level, an instructor may select the Leadership feat—using his Intelligence modifier to determine his Leadership score—but doing so only provides followers, never a second cohort.
Because the extraordinary ability apprentice replaces arcane bond, the entirety of the extraordinary ability apprentice should be available with but one level in wizard, making it so that a magus 6/instructor wizard 1 can pick the feat Leadership and have the feat based on his Intelligence instead of Charisma. But, like in any such case that relies on careful reading, talk to the GM.
While many feats, traits, and even magic items add to a creature's leadership score, this is the only official Pathfinder tool that I've found that changes the ability score on which the feat Leadership is based. (There's apparently no feat like D&D 3.5's Might Makes Right (Rac 166) for Pathfinder, for example.) That the change happens to switch Charisma to Intelligence is just coincidence.