Mansfield Town midfielder Jack Thomas (21), who worked under Murray at Field Mill, 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.
Free agent Liam Wakefield (23) has also joined up with the United squad.
The former Doncaster Rovers, Accrington Stanley and Morecambe defender, with 47 Football League appearances to his name, is available with immediate effect.