1. A magnetic spin device comprising: a first ferromagnetic layer which has a changeable magnetization state; a second ferromagnetic layer with a fixed magnetization state; wherein the magnetic spin device has a spin resistance which is dependent on a relationship between said first ferromagnetic layer and said second ferromagnetic layer, including whether said changeable magnetization state and said fixed magnetization state are parallel or antiparallel; a write line for receiving a write signal adapted for altering said changeable magnetization state, said write signal having a first variable amplitude including a first current value and a second larger current value than said first current value for setting the magnetic spin device to a first logic state, and a second variable amplitude including a third current value and a fourth larger current value than said third current value for setting the magnetic spin device to a second logic state.