First-order reversal-curve diagrams and reversible magnetization

First-order reversal curve (FORC) diagrams have recently been used for the characterization of magnetic systems in both geology and physics. However, the FORC distribution involves a mixed second derivative which reduces the reversible component of the magnetization to zero. As a result, the FORC distribution is not properly normalized. Furthermore, the calculation of the FORC distribution becomes unreliable near the axis where the reversible magnetization should be located (i.e., the H=H-r axis). We propose here a method of incorporating the reversible magnetization into the FORC distribution using "extended" FORC's. With extended FORC's, the FORC distribution is properly normalized and robust near the H=H-r axis.