Twenty-one-year-old midfielder Jack Thomas, who worked under Murray at SkyBet League Two side Mansfield Town, has put pen-to-paper on an initial month-long loan deal.
He has permission from his parent club to feature for the Pilgrims in the Emirates FA Cup.
Twenty-three-year-old free agent Liam Wakefield (pictured) has also joined up with the United squad.
The former Doncaster Rovers, Accrington Stanley and Morecambe defender, with forty-seven Football League appearances to his name, is available with immediate effect.