Patent ID: 9548083
Date: 2017-01-17
CPC Classifications: G11B

Claim:
1. A method comprising: applying a first external magnetic field to a read sensor comprising a free layer having a free layer magnetic orientation in a longitudinal direction that is parallel to an air bearing surface of the read sensor when no external magnetic field is applied and a reference layer having a magnetic orientation that is perpendicular to the longitudinal direction and perpendicular to the air bearing surface of the read sensor, the first external magnetic field having an orientation that is parallel to the magnetic orientation of the reference layer of the read sensor; measuring a first thermal magnetic fluctuation noise spectrum from the read sensor when the first external magnetic field is applied to determine a first ferromagnetic resonance peak; applying a second external magnetic field to the read sensor, the second external magnetic field having an orientation that is anti-parallel to the magnetic orientation of the reference layer of the read sensor; measuring a second thermal magnetic fluctuation noise spectrum from the read sensor when the second external magnetic field is applied to determine a second ferromagnetic resonance peak; comparing at least one of respective frequencies and amplitudes of the first ferromagnetic resonance peak and the second ferromagnetic resonance peak to determine a strength value of the reference layer, wherein the strength value is a measure of a relative change in the magnetic orientation of the reference layer caused by the anti-parallel orientation of the second external magnetic field with respect to the parallel orientation of the first external magnetic field; storing the strength value of the reference layer.