Force field is a little to “scientific” for the fantasy book and to my understanding of SciFi also implies something outside surrounding the object being protected not part of it.
Magic OTOH is clearly acceptable in the Tolkien world and I would not argue that his mithril coat might have a protective spell though that was not clearly stated in the novel per se we do know the Nazgul fought with enchanted weaponry that almost turned the Hobbit into a Wraith.
🙂 Noted