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 H5Hr 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 H5Hr axis.