insulating barrier layer such as mgo the free layer 810 has a magnetization that is biased in a direction parallel with the air bearing surface magnetic biasing is provided by hard magnetic bias layers 822 located at either side of the sensor stack the hard bias layers 822 are separated from the sensor stack 802 and from at least one of the shields by a thin electrically insulating layer 824 that can be constructed of a material such as alumina a capping layer 826 can be provided at the top of the sensor stack 802 to protect the under lying layers during manufacture and to magnetically de couple the free layer 810 from the upper shield 806 the pinned layer structure 808 includes first and second magnetic layers 814 816 that are anti parallel coupled across a non magnetic anti parallel coupling layer such as ru 818 the first magnetic layer 814 is exchange coupled with a layer of afm material such as irmn or ptmn 820 in order for the magnetic afm coupling to exhibit the necessary pinning strength the afm layer 820 must be relatively thick as can be appreciated the pinned layer structure 808 and afm 820 consume a large amount of read gap in addition in a.