# Thermal discrete dipole approximation for the description of thermal emission and radiative heat transfer of magneto-optical systems

## TL;DR

This paper generalizes the thermal discrete dipole approximation (TDDA) to model near-field radiative heat transfer and thermal emission in magneto-optical and anisotropic materials of arbitrary shapes, enabling active control studies.

## Contribution

It introduces a generalized TDDA method for magneto-optical and anisotropic materials, with simplified formulas and rigorous validation of Kirchhoff's law for such systems.

## Key findings

- Validated the generalized TDDA for MO systems.
- Derived simple formulas for thermal quantities.
- Confirmed Kirchhoff's law for MO objects.

## Abstract

We present here a generalization of the thermal discrete dipole approximation (TDDA) that allows us to describe the near-field radiative heat transfer between finite objects of arbitrary shape that exhibit magneto-optical (MO) activity. We also extend the TDDA approach to describe the thermal emission of a finite object with and without MO activity. Our method is also valid for optically anisotropic materials described by an arbitrary permittivity tensor and we provide simple closed formulas for the basic thermal quantities that considerably simplify the implementation of TDDA method. Moreover, we show that employing our TDDA approach one can rigorously demonstrate Kirchhoff's radiation law relating the emissivity and absorptivity of an arbitrary MO object. Our work paves the way for the theoretical study of the active control of emission and radiative heat transfer between MO systems of arbitrary size and shape.