The first-order reversal curve (FORC) diagram: Theory and case study
一阶反转曲线（FORC）图的原理及应用实例

The magnetic minerals in natural rocks can record variations in paleoenvironment.However,the magnetic properties of samples represent signals from the assemblage of various magnetic minerals and grain sizes of the measured samples.To circumvent this problem,the first-order reversal curve(FORC)diagram was designed recently to decode the magnetic properties of bulk samples.The FORC diagram can provide the distributions of both the coercivity spectrum and the magnetic interaction field.Moreover,it may also identify different magnetic minerals and characterize their domain status.In this paper,we firstly introduced the theory of the FORC diagram and its physical explanations.We then applied the method in detecting the thermal alteration of a basalt sample,which contains aluminum-substituted titanomagnetite.In order to further enhance the signal related to the thermal alteration upon heating,we constructed the difference of two FORC diagrams measured at two temperatures for the first time.The results show that the difference of two FORC diagrams is rather sensitive,and can diagnose even subtle changes in magnetic minerals upon heating.