Thermally activated magnetic noise and spectra in GMR heads

Summary form only given. Thermally activated ferromagnetic resonance in spin valve or CPP/GMR heads, referred to as mag-noise, results in significant additional noise in the read back voltage, further reducing already strained SNR at high area recording densities (N. Smith and P. Arnett, Appl. Phys. Lett., vol. 78, p. 1448, 2001). At 30 Gbits/in/sup 2/ density, i.e. a track width around W=200 nm, the mag-noise is at similar level as that of the head Johnson noise. In this paper, we present a combined micromagnetic modeling and experimental study of mag-noise magnitude and spectra for spin valve GMR heads. It is found that at W=200 nm and a nominal stripe height, the noise spectra exhibits multiple resonance frequencies, indicating a spatial non-uniformity of the magnetization precessions over the free layer. At a slightly narrower track width and a reduced stripe height, the multimode feature reduces to a virtually single mode resonance. Micromagnetic simulation shows that increasing sensor stripe height significantly yields a significant increase of mag-noise level in the low frequency region. Detailed micromagnetic modeling is presented in the paper on the multimode excitation conditions. Analysis on the head designs with multiple sense layers such as CPP/GMR head is also presented.