Shifted loops and coercivity from field imprinted high energy barriers in ferritin and ferrihydrite nanoparticles

TL;DR

This paper investigates how the coercive field and loop shifts in ferritin and ferrihydrite nanoparticles depend on the maximum magnetic and cooling fields, linking these effects to changes in intra-particle energy barriers.

Contribution

It introduces a model explaining the field-dependent coercivity and loop shifts based on intra-particle energy barriers imprinted by maximum and cooling fields.

Findings

Coercivity depends on maximum magnetic field in hysteresis loops.

Loop shifts are influenced by both maximum and cooling fields.

Magnetization time dependence varies with field history in ferritin.

Abstract

We show that the coercive field in ferritin and ferrihydrite depends on the maximum magnetic field in a hysteresis loop and that coercivity and loop shifts depend both on the maximum and cooling fields. In the case of ferritin we show that the time dependence of the magnetization also depends on the maximum and previous cooling fields. This behavior is associated to changes in the intra-particle energy barriers imprinted by these fields. Accordingly, the dependence of the coercive and loop shift fields with the maximum field in ferritin and ferrihydrite can be described within the frame of a uniform-rotation model considering a dependence of the energy barrier with the maximum and the cooling fields.