Question Author
Thanks for replying maxi, but unfortunately i can't speak german!
I originally found the phrase "free baron" in reference to the memoirs of an Englishman in the early 18th c, who described himself as "the free baron of Devon".
After a bit of research, although i didn't find an exact definition, i think a 'free baron' is probably a 'baron' who severed his financial ties (land) and political affiliations with the king, but kept the title and some of the priviledges.
Thanks anyway!