1/f noise in anisotropic and giant magnetoresistive elements

Microfabricated magnetoresistive elements based on either the anisotropic or the giant magnetoresistance effect were tested for their frequency dependent resistance noise behavior at room temperature in a dc magnetic field, using a dc sense current. Thermal resistance noise was the dominant noise source above about 10 kHz. At low frequencies the resistance noise was found to be dominated by a $\text{1/f}$ contribution that depends on the applied magnetic field. The $\text{1/f}$ noise is relatively low and field independent when the element is in a saturated state and contains a relatively large and field dependent excess contribution when the magnetic field is in the sensitive field range of the element. The $\text{1/f}$ noise level observed in saturation is comparable to the $\text{1/f}$ noise level found in nonmagnetic metals; the excess noise has a magnetic origin. The variation of the excess noise level with the applied dc magnetic field can be explained qualitatively using a simple model based on thermal excitations of the magnetization direction.