AVS 46th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Monday Sessions
       Session MI+VM+AS-MoA

Invited Paper MI+VM+AS-MoA9
Noise in GMR Recording Heads

Monday, October 25, 1999, 4:40 pm, Room 618/619

Session: Magnetic Recording: Media and Heads
Presenter: H.T. Hardner, Seagate Technology
Authors: H.T. Hardner, Seagate Technology
M.B. Hurben, Seagate Technology
Correspondent: Click to Email
Magnetoresistive sensors exploit a close coupling between magnetization and resistance to convert changes in magnetic field to an electrical signal. Thus, the enhanced sensitivity of the giant magnetoresistive (GMR) materials to magnetic field is accompanied by larger electrical noise due to magnetization noise. A magnetic contribution to 1/f noise originates in thermal fluctuations in magnetization. This is a concern for sensors intended for low frequency applications rather than for magnetic recording heads due to the very high frequencies at which the heads operate. However, discrete steps in the resistance can also appear due to large discrete changes in domain structure. When these steps occur as a continuous magnetic signal is applied to the device they are called Barkhausen noise. In small enough devices discrete magnetoresistive steps can be observed even at fixed magnetic field. While the sensitivity of the resistance to changes in magnetization is proportional to the magnetoresistance, the propensity for complex domain structure with fluctuations between multiple metastable states varies by material, processing, and design. The suppression of these fluctuations to create a device with a single stable magnetization state is a key goal in the design and manufacture of magnetoresistive recording heads. This talk will provide some brief background on how recording heads are stabilized as well as an overview of resistance noise data from GMR devices including comparisons of different materials and the use of resistance noise measurements to study domain structure. Recent results on resistance noise in spin-valve recording heads both at the finished stage and during wafer processing will be presented along with discussion of how a detailed study of electrical noise can help identify stability problems. Analysis of both time and frequency domain data will be considered.