Reversal of Magnetic Fields
"The force necessary to flip a bit from the down to the up state is known as the coercive force and is a strong function of temperature. At room temperature, a normal magnet is too weak to flip the bits because the coercive force required is too high. Thus all the bits remain in the north-pole-down state in spite of the presence of the north-pole-up bias magnet in the drive. But at 150°C, the coercive force required to flip a domain falls almost to zero, and the bias magnet field is strong enough to record a north-pole-up state."
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