So, to start, I'm aware of the feat Dimensional Agility, but that doesn't seem exactly right with how it works with Spell Combat. Dimensional Agility makes Dimension Door basically not count as your move action, as well as your standard. But, if it's used in sync with the Magus's Spell Combat class feature which states:
A magus can choose to cast the spell first or make the weapon attacks first, but if he has more than one attack, he cannot cast the spell between weapon attacks.
… and the only restriction on Spell Combat is:
…can also cast any spell from the magus spell list with a casting time of 1 standard action (any attack roll made as part of this spell also takes this penalty).
While the Dimension Door spell itself is, indeed, a standard action, but the spell forces you to not take any other actions afterwards. But what if it's used first or second as a part of Spell Combat, as a part of a full attack?
Because it's part of a full-round action (full attack), there wouldn't technically be any "other actions" besides the full attack. I guess this question boils down to "What is a full-round action, and is it made up of other actions?".
Say a Magus starts 50 feet from the enemy. He uses Spell Combat as a full-attack to use Dimension Door behind the enemy and get all of his attacks. Would this be legal according to RAW, or would the spell description overwrite it?
In either case, I believe there would be nothing stopping you from casting Dimension Door at the end of your attacks to teleport away from any threatening enemies, except a failed Concentration check.
Best Answer
Yes, a Magus can use Dimension Door as part of Spell Combat
A full-round action is one of several different actions, but none of them are specifically broken up into standard-move action pairs, so there is no reason why Dimension Door's action restriction should apply beginning in the middle of any full-round action.
As in your question the magus would be able to begin the full-round action, cast the spell, attack, then end the full-round action without taking any "other actions" after casting the spell.