Theoretical considerations on the anhysteretic remanent magnetization of interacting particles with uniaxial anisotropy

Abstract

[1] The anhysteretic remanent magnetization (ARM) is widely used in rock magnetism and paleomagnetism because of its sensitivity to the domain state of magnetic particles and the close analogy to natural remanent magnetizations. On the other hand, the ARM shares with other weak-field magnetizations the property of being extremely sensitive to magnetostatic interactions. Therefore it is desirable to model the effects of interactions on natural assemblages of magnetic particles. Direct micromagnetic calculations of the ARM acquisition process are not practicable; therefore an analytical approach is used calculate the ARM susceptibility of a system of interacting single-domain (SD) particles. The model is based on a statistical description of the interaction field. The equations obtained have been used to evaluate the dependence of the ARM on the packing fraction of the magnetic particles. The effect of interactions on the anisotropy of ARM (AARM) was evaluated as well. The AARM of densely packed particles is complex and depends critically on the microcoercivity. A physical interpretation of the AARM of highly interacting particles is therefore difficult.

First‐order reversal curve (FORC) diagrams of natural and cultured biogenic magnetic particles

“…As demonstrated by Egli [2004], ARM measurements are better suited to the identification of authigenic components in sediments, however, the interpretation depends on the presence of interactions. The comparison of χ ARM / M rs of authigenic components with the values predicted for noninteracting SD particles by Egli and Lowrie [2002], together with the predicted onset of significant interaction effects at p > 10 −3 [ Egli , 2006b], indicates that the magnetic particles are generally extremely well dispersed in sediments. While this can be expected of the case intact chains of magnetosomes, it is not obviously true of other magnetic components, which are not surrounded by cell material that prevents aggregation.…”

“…On the other hand, ARM is much more sensitive to magnetostatic interactions. Egli [2006b] calculated the factor r i by which the ARM of interacting particles is lowered, with respect to the noninteracting case. For uniaxial SD particles ( M rs / M s = 0.5, χ ARM /IRM = 2.77 mm/A), r i = 0.95 when p = 1.3 × 10 −4 , and r i = 0.5 when p = 2.6 × 10 −3 .…”

“…The amplitudes of the two functions used for the fit give us the relative magnetic contributions of the two groups: m A = 0.4 and m B = 0.6. We use the predicted ratio r i = χ ai ( p )/ χ a of the ARM of interacting particles with respect to their noninteracting counterpart given by Egli [2006b] to estimate the ARM ratio of BAIK. This requires the ARM ratio of the noninteracting case, which is unknown for this particular sample.…”

Changes in lake stratification and oxygen distribution inferred from two contrasting records of magnetotactic bacteria and diatoms

“…Another condition that can affect the ARM/SIRM ratio is potential magnetostatic interactions among grains, as this is known to weaken the ARM signal [ Egli , 2004, 2006]. The reason for increased interaction can be related to oxidation of the magnetosomes leading to the formation of superparamagnetic (SPM) particles.…”

Application of magneto-optical Kerr effect to first-order reversal curve measurements

“…It is wide spread in the geomagnetism and paleomagnetism sciences, [1][2][3] but is also used in thin film physics, 4 material sciences, and research into nanostructured systems. 5 Since the introduction of the scalar hysteresis model by Preisach 6 and further developments by Mayergoyz,7 theoretical description and mathematical modeling of FORC has significantly improved for particles, 8,9 multi-component samples, 10 or nanostructures 5 in recent years.…”