What is ZFC-FC?

Answer 1

Zero Field Cooling - Field Cooling

Measuring an effect from a field in the two following ways:

ZFC- Applying the field at a relatively low temperature compared to a characteristic temperature and continuously measuring the effects of the field as you raise the temperature to a level well above the characteristic level.

FC - Applying the field at a relatively high temperature compared to a characteristic temperature and continuously measuring the effects of the field as you lower the temperature to a level well below the characteristic level.

FC can be thought of as the reverse process to ZFC. If the effect you're measuring doesn't reverse using ZFC-FC, then you have something interesting on your hands.