An apparatus comprises a ferromagnetic free layer having a first magnetic
moment and having a magnetization that rotates in response to an external
magnetic field, a first ferromagnetic reference layer positioned adjacent
to a first side of the ferromagnetic free layer and having a second
magnetic moment that is greater than the first magnetic moment of the
ferromagnetic free layer, a second ferromagnetic reference layer
positioned adjacent to a second side of the ferromagnetic free layer and
having a third magnetic moment that is greater than the first magnetic
moment of the ferromagnetic free layer, a first non-magnetic spacer layer
positioned between the ferromagnetic free layer and the first
ferromagnetic reference layer, a second non-magnetic spacer layer
positioned between the ferromagnetic free layer and the second
ferromagnetic reference layer, and a source of magnetic field for biasing
the first and second ferromagnetic reference layers.