the free layer in a magneto - resistive memory element is stabilized through being pinned by an antiferromagnetic layer . a control valve layer provides exchange coupling between this antiferromagnetic layer and the free layer . when writing data into the free layer , the control valve layer is heated above its curie point thereby temporarily uncoupling the free layer from said antiferromagnetic layer . once the control valve cools , the free layer magnetization is once again pinned by the antiferromagnetic layer .