Patent ID: 8460805

Claim:
An apparatus, comprising: a first magnetic layer comprising a plurality of grains, the first magnetic layer having a first anisotropy value (H k ); a second magnetic layer comprising a plurality of grains and having stronger inter-granular exchange coupling than the first magnetic layer and a third magnetic layer, the second magnetic layer having a second anisotropy value (H k ) that is less than the first anisotropy value (H k ) and a third anisotropy value (H k ); an exchange tuning layer comprising a plurality of grains and located between the first and second magnetic layers, the exchange tuning layer having stronger inter-granular exchange coupling than the first and second magnetic layers, the exchange tuning layer having an anisotropy value (H k ) less than the first and second anisotropy values; the third magnetic layer comprising a plurality of grains, the third magnetic layer having the third anisotropy value (H k ); and a second exchange tuning layer comprising a plurality of grains and located between the second and third magnetic layers.