Thermally induced magnon accumulation in two-sublattice magnets

We present a temperature-dependent study of the thermal excitation of a magnon accumulation in two-sublattice magnetic materials. Using atomistic spin model simulations, we study the local magnetization profiles sublattice-wise in the vicinity of a temperature step in antiferromagnets, as well as in ferrimagnets. It is shown that the strength of the magnon accumulation in these systems scales with the derivative of the magnetization with respect to the temperature. These results give an insight into the complex temperature dependence of the magnon accumulation by making a direct link to the macroscopic behavior of the magnetization.

Figure 1

Absolute value of the normalized magnetization $m$ and the magnon accumulation $\mathrm{\Delta }m$ versus the space coordinate $z$ of the single sublattices of an antiferromagnet around a temperature step exemplary for a damping constant of $\alpha =0.01$, and an anisotropy constant of $d_z=0.01J$.

Figure 2

Illustration of the two magnon modes in an antiferromagnet with degenerated dispersion relation. The magnetic moments of the single sublattices can either precess left- or right-handed leading to magnon modes transporting opposite angular momentum.

Figure 3

Normalized magnetization component $m_z/m_0$ of the single sublattices A and B, and of the total system versus temperature $T$ in thermal equilibrium.

Figure 4

Magnon accumulation due to a temperature step for different temperature levels. (Top) Magnon accumulation $\mathrm{\Delta }{m}_z/m_0$ versus the space coordinate $z$ of the single sublattices and the total magnon accumulation due to a temperature step. (Bottom) Total magnon accumulation $\mathrm{\Delta }{m}_z/m_0$ versus the space coordinate $z$ for different temperature levels $T_2$.

Figure 5

Strength of the magnon accumulation $\mathrm{\Delta }{m}_z\left(T\right)$ at the temperature step as a function of the temperature in comparison with the derivative of the magnetization with respect to the temperature $\partial m_z/\partial T$ as a function of the temperature $T$.

Figure 6

Magnon accumulation due to a temperature step as a function of the position $z$ for different temperature levels close to the compensation point of magnon accumulation.