Nonlinear high-frequency magnetic response of magnetoferritin metacrystals governed by spin thermodynamics

TL;DR

This paper develops a thermodynamic theory to describe the nonlinear high-frequency magnetic response of magnetoferritin metacrystals, which are complex superstructures with potential biological magnetoreception functions.

Contribution

It introduces a novel thermodynamic model for the dynamic magnetization of large superparamagnetic nanoparticle assemblies under high-frequency fields.

Findings

Predicts the high-frequency magnetic response dependence on static magnetic fields.

Provides a theoretical basis for experimental detection of magnetoferritin in tissues.

Links magnetic response to potential biological functions in navigation.

Abstract

A theory is developed of the time-dependent magnetization of the metacrystal composed of magnetoferritin macromolecules. Such superstructures, comprising up to several millions of superparamagnetic nanoparticles encapsulated in protein shells, can be created artificially using biochemical assembling technologies. They have been also shown to occur naturally in sensitive cells of the inner ear of birds, which suggests their possible involvement in the detection of the geomagnetic field for orientation and navigation of migratory animals. The dynamics of the magnetic system of the magnetoferritin metacrystal, comprising a very large number of magnetic moments coupled by long-range dipole forces, is exceedingly complex. In order to find the response of the metacrystal to high-frequency magnetic fields, we used a thermodynamic approach borrowed from the theory of nuclear spin systems of solids. The resulted theory yields the time-dependent superspin temperature and magnetization induced by oscillating magnetic fields of arbitrary strength. The predicted dependence of the high-frequency response on the static magnetic field can be used for experimental detection and characterization of magnetoferritin metacrystals in biological tissues.