We analyzed the mag-noise of fabricated CIP-GMR and TMR heads to clarify the properties of mag-noise and what influence it had on the head signal-to-noise ratio (SNR). We clarified that the measured mag-noise of CIP-GMR heads is quantitatively consistent with the calculated mag-noise. We found that when the MR ratio is small, the head-amp SNR increases as the MR ratio increases. The head-amp SNR saturates at a certain value of "mag-noise SNR" as the MR ratio increases. When the read head

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... small, the mag-noise SNR decreases. This is due to a large thermal fluctuation of the magnetization "mag-noise" in heads with a small volume. The mag-noise needs to be reduced to achieve high head-amp SNR. The volume of the free layer must be maintained at the highest possible level to reduce mag-noise.