Simulation of Remanent, Transient, and Induced FORC Diagrams for Interacting Particles With Uniaxial, Cubic, and Hexagonal Anisotropy

The diagnostic power of first-order reversal curve (FORC) diagrams has recently been enhanced by an extended measurement protocol that yields three additional FORC-like diagrams: the remanent (remFORC), induced (iFORC), and transient (tFORC) diagrams. Here, we present micromagnetic simulations using this extended protocol, including numerical predictions of remFORC, iFORC, and tFORC signatures for particle ensembles relevant to rock magnetism. Simulations are presented for randomly packed single-domain (SD) particles with uniaxial, cubic, and hexagonal anisotropy, and for chains of uniaxial SD particles. Noninteracting particles have zero tFORC, but distinct remFORC and iFORC signals, that provide enhanced discrimination between uniaxial, cubic, and hexagonal anisotropy types. Increasing interactions lessen the ability to discriminate between uniaxial and cubic anisotropy but reproduces a change in the pattern of positive and negative iFORC signals observed for SD-dominated versus vortex-dominated samples. Interactions in SD particles lead to the emergence of a bi-lobate tFORC distribution, which is related to formation of flux-closure in super-vortex states. A predicted iFORC signal associated with collapsed chains is observed in experimental data and may aid magnetofossil identification in sediments. Asymmetric FORC and FORC-like distributions for hexagonal anisotropy are explained by the availability of multiple easy axes within the basal plane. A transition to uniaxial switching occurs below a critical value of the out-of-plane/in-plane anisotropy ratio, which may allow FORC diagrams to provide insight into the stress state of hexagonal minerals, such as hematite.