Patent ID: 7990137

Claim:
A device of evaluating a magnetic read head having a magnetoresistive element including a magnetically free layer, and a magnetic bias layer that applies a bias magnetic field to the magnetically free layer, comprising: a measuring section measuring a ferromagnetic resonance frequency of the magnetically free layer under a condition of applying a predetermined external magnetic field to the magnetically free layer; and an operation section computing the bias magnetic field according to a conditional equation (1), Hb={ (2*π* f 0/γ) 2 /Ms}− ( Hk+Hm ) (1) where Hb is the bias magnetic field, f 0 is the ferromagnetic resonance frequency of the magnetically free layer, γ is a gyroscope constant, Ms is a saturation magnetic field of the magnetically free layer, Hk is a shape anisotropy magnetic field of the magnetically free layer, and Hm is the external magnetic field applied to the magnetically free layer.