Memory storage devices comprising different ferromagnetic material layers, and methods of making and using the same

A method comprising:

• forming a memory storage element comprising at least a plurality of alternating first and second ferromagnetic layers, wherein each of the first ferromagnetic layers has a first critical current density (JC1), wherein each of the second ferromagnetic layers has a second critical current density (JC2), wherein JC1<JC2, wherein said memory storage element further comprising a plurality of alternating magnetic domains of opposite directions that are separated from each other by domain walls located therebetween, and wherein data is stored in said memory storage element as locations of magnetic domains and domain walls;
• applying a driving current to the memory storage element to effectuate movements of the magnetic domains and domain walls past a reading or writing device, wherein the driving current has a constant current density (JCconstant) that is greater than JC2, wherein the domain walls have a first velocity (VA) in the first ferromagnetic layers under the driving current and a second velocity (VB) in the second ferromagnetic layers under the driving current, wherein VB<VA;
• and
• selectively reading data from, or writing data into, said memory storage element when the domain wall velocity is equal to VB.