Magnetization and magnon excitation energies of the magnetic semiconductors EuTe and EuO on the basis of the renormalized spin wave theory

TL;DR

This paper derives analytic expressions for temperature-dependent magnetization and magnon energies in EuTe and EuO using renormalized spin wave theory, matching experimental data and revealing characteristic features like energy gaps in AFM EuTe.

Contribution

It provides the first full analytic expressions for sublattice magnetization and magnon energies in EuTe and EuO considering magnon interactions with the renormalized spin wave theory.

Findings

Magnetization curves agree well with experimental data.

Magnon excitation energies match inelastic neutron scattering results.

EuTe exhibits a characteristic maximum in magnon energies and an energy gap due to AFM interactions.

Abstract

We present analytic expressions for the temperature dependent magnetization and magnon dispersion relation of the antiferromagnetic (AFM) EuTe and the ferromagnetic (FM) EuO. These bulk semiconductors represent concentrated spin systems for which the interaction between magnons has to be taken into account. We do this using the renormalized spin wave theory. A higher order Green's function according to Tjablikov is used for their description. As a result, we obtain a modified Bloch- T3/2 law, for low temperatures and high magnetic fields. A full analytic expression is given for the sublattice magnetization of the AFM EuTe (B0=0), with a N\'eel temperature of TN = 9.81 K. The magnetization curves {\sigma}N(T) of EuO (for 0 \leq T \leq 0.68TC) and {\sigma}R(T) (for 0.82TC < T < TC) agree well with experiment. The spin wave excitation energy perfectly matches experimental data from inelastic neutron scattering. In the case of EuTe the magnon excitation energies exhibit a characteristic maximum. For q = 0, an energy gap Eg occurs in the spin wave spectrum, a consequence of the AFM exchange interaction J2(T). Such energy gaps exist in the spectrum of magnon excitation energies only in systems with AFM interactions.