Mitchell, 22, is a former Chelsea academy graduate who signed professional terms for the Premier League champions in 2013.
He joined Chesterfield in 2016 going on to make thirty-two League appearances for the Spireites – twenty-eight of those in League One.
Barnes (pictured) joins on a month`s loan from SkyBet League One side Charlton Athletic.
With the Valiants since 2013, Barnes was rewarded for the progress he has made at Charlton by being handed his first-team debut against Swindon Town in April 2017.
A versatile and attack-minded full-back, Barnes, who was previously on the books of Arsenal, captained the Addicks’ under-23s to the Professional Development League 2 South title in 2016/17.
He lifted the national title with Charlton`s under-18s in 2014/15 and has been a stand-out performer for Jason Euell’s development squad ever since.
He has made three first-team appearances to date this term.