It would not automatically fly into your hand, however what exactly happens is up to the DM/GM
Antimagic Field says the following for Magic Items:
The properties and powers of magic items are suppressed in the sphere.
For example, a longsword, +1 in the sphere functions as a nonmagical
A magic weapon's properties and powers are suppressed if it is used
against a target in the sphere or wielded by an attacker in the
sphere. If a magic weapon or a piece of magic ammunition fully leaves
the sphere (for example, if you fire a magic arrow or throw a magic
spear at a target outside the sphere), the magic of the item ceases to
be suppressed as soon as it exits. Emphasis mine.
Based on this description, the Dwarven Thrower would no longer be suppressed once it leaves the antimagic field, however once it re-enters it would be. The Dwarven Thrower would begin to return to the thrower, however what happens once it re-enters is uncertain and most likely up to the DM.
Based on this answer to a similar question, the returning feature of the Dwarven Thrower is magical due to the Dwarven Thrower being a magical item. (See Pg 17 of Sage Advice Compendium under Is the breath weapon of a dragon magical?)
Is the breath weapon of a dragon magical?
Determining whether a game feature is
magical is straightforward. Ask yourself these questions
about the feature:
- Is it a magic item?
- Is it a spell? Or does it let you create the effects of a spell
that’s mentioned in its description?
- Is it a spell attack?
- Is it fueled by the use of spell slots?*
- Does its description say it’s magical?
If your answer to any of those questions is yes, the feature
As a result, the Dwarven Thrower would not automatically fly into your hand, but what exactly happens when re-entering the Antimagic Field is up to the DM.
Some possible interpretations could be:
- It continues flying, but you may have to try and catch it, rather than it flying into your hand.
- It just drops because it was magically flying and had no actual momentum behind it (Unlikely)
I would most likely go with option 1. Depending on how much of the Antimagic field the hammer flies through before reaching you could decide if a check is needed to catch it.