The barrier change of Magus isnt a protection against spell he know. It is a protection that absorb all magic energy and the only reason he isnt able to block/absorb the spell he cast is because if his barrier would the spell wouldnt be able to go out of the barrier and would actualy heal him. So Magus could keep his distance easily considering the size of the arena and his speed while he cast spell to destroy Raziel.

Edit:

Spirit based weapon are always magic based wich would render Raziel totaly useless even Robo laser spin are absorbed by the barrier of Magus so it would mean his barrier block anything not pure physical that isnt the same element of his barrier.

Edit:

Oh, and if your wondering. Sword that does damage from wrong element would heal too. Here is an example. If Crono use Ice Sword or Ice Swirl and Magus isnt at *Ice Only* Well it would heal him.