Magnetic tunnel junction magnetic device (16) for writing and reading uses a reference layer (20c) and a storage layer (20a) separated by a semiconductor or insulating layer (20b), which can include an antiferromagnetic layer adjacent the storage layer. The blocking temperature of the magnetisation magnetization of the storage layer is less than that of the reference layer. The storage layer is heated (22, 24) above the blocking temperature of its magnetisation magnetization. A magnetic field (34) or a magnetic torque created by the injection of spin polarized electrons is applied (26) to it orientating its magnetization with respect to that of the reference layer without modifying the orientation of the reference layer.