The DMG says this about magic item durability:
Most magic items are objects of extraordinary craftsmanship. Thanks to a combination of careful crafting and magical reinforcement, a magic item is at least as durable as a nonmagical item of its kind. Most magic items, other than potions and scrolls, have resistance to all damage. Artifacts are practically indestructible, requiring extraordinary measures to destroy.
Antimagic field's interaction with magic items is defined as such:
The properties and powers of magic items are suppressed in the sphere. For example, a +1 long sword in the sphere functions as a nonmagical long sword.
So would an antimagic field suppress the damage resistance of magic items, allowing them to be destroyed more easily? If this is true, then destroying artifacts would be trivial with a high-level caster.