A magnetic device for magnetically coupling to a ferromagnetic body, comprising: a housing having a central bore; a plurality of pole sectors arranged within an envelope of the central bore and forming a workpiece contact interface of the magnetic device, each of the plurality of pole sectors comprising a plurality of spaced-apart pole portions arranged at respective distances, wherein a recess of a plurality of recesses separates each pole portion of the plurality of pole portions, wherein a first sector of the plurality of sectors form a first pole of the magnetic device and a second sector of the plurality of sectors form a second pole of the magnetic device; at least one first permanent magnet supported by the housing and having an active N-S pole pair; at least one second permanent magnet supported by the housing and having an active N-S pole pair, the at least one second permanent magnet being moveable relative to the first permanent magnet; and an actuator operatively coupled to the at least one second permanent magnet to move the at least one second permanent magnet relative to the at least one first permanent magnet, wherein the magnetic device establishes a first magnetic circuit with the at least one first permanent magnet and the at least one second permanent magnet through the plurality of pole sectors when the at least one second permanent magnet is positioned by the actuator in a first position relative to the at least one first permanent magnet and a second magnetic circuit with the first permanent magnet and the second permanent magnet when the second permanent magnet is positioned by the actuator in a second position relative to the at least one first permanent magnet. a housing having a central bore; a plurality of pole sectors arranged within an envelope of the central bore and forming a workpiece contact interface of the magnetic device, each of the plurality of pole sectors comprising a plurality of spaced-apart pole portions arranged at respective distances, wherein a recess of a plurality of recesses separates each pole portion of the plurality of pole portions, wherein a first sector of the plurality of sectors form a first pole of the magnetic device and a second sector of the plurality of sectors form a second pole of the magnetic device; at least one first permanent magnet supported by the housing and having an active N-S pole pair; at least one second permanent magnet supported by the housing and having an active N-S pole pair, the at least one second permanent magnet being moveable relative to the first permanent magnet; and an actuator operatively coupled to the at least one second permanent magnet to move the at least one second permanent magnet relative to the at least one first permanent magnet, wherein the magnetic device establishes a first magnetic circuit with the at least one first permanent magnet and the at least one second permanent magnet through the plurality of pole sectors when the at least one second permanent magnet is positioned by the actuator in a first position relative to the at least one first permanent magnet and a second magnetic circuit with the first permanent magnet and the second permanent magnet when the second permanent magnet is positioned by the actuator in a second position relative to the at least one first permanent magnet.