The jamming transition—marked by dramatic changes in mechanical properties, such as stiffness and damping—enables programmable and adaptive structures for robotic applications. This phenomenon, driven by changes in the coupling between individual subunits of an aggregate, can be controlled through external actuation sources. Existing jamming actuation methods, such as applying a vacuum with an airtight envelope, pose significant limitations, as they require the structures to be tethered, limiting reconfigurability and scalability. Here, we introduce an untethered jamming mechanism based on magnetic interactions between soft-ferromagnetic composites. We establish composite design principles to program the magnetization of the subunits, demonstrate linear, planar, and volumetric jamming and shape-locking, and model the magneto-mechanical behavior. This approach contributes to the development of jamming-based materials in which the jamming directions and transition points can be tuned on-the-fly by adjusting the external magnetic field orientation and strength, respectively.