Optical evidence for a magnetically driven structural transition in the spin web $Cu_3TeO_6$

TL;DR

This study uses optical spectroscopy to reveal a magnetically driven structural transition in Cu3TeO6, evidenced by a new spectral mode appearing below 50 K, linked to magnetic ordering at 61 K.

Contribution

The paper provides optical evidence of a magnetically induced structural transition in Cu3TeO6, highlighting a new spectral mode associated with magnetic ordering.

Findings

A new mode at 208 cm^{-1} appears below 50 K.

Spectral weight of the new mode increases as (T*-T)^{1/2}.

Optical features relate to the magnetic phase transition at 61 K.

Abstract

$Cu_3TeO_6$ is a modest frustrated $S=1/2$ spin system, which undergoes an anti-ferromagnetic transition at $T_N\sim61$ $K$. The anti-ferromagnetic spin alignment in $Cu_3TeO_6$ below $T_N$ is supposed to induce a magneto-elastic strain of the lattice. The complete absorption spectrum of $Cu_3TeO_6$ is obtained through Kramers-Kronig transformation of the optical reflectivity, measured from the far-infrared up to the ultraviolet spectral range as a function of temperature ($T$). Below $T^*\sim 50$ $K$, we find a new mode at 208 $cm^{-1}$. The spectral weight associated to this additional mode increases as $\propto (T^*-T)^{1/2}$ with decreasing $T$ below $T^*$. The implication of the optical findings will be discussed in relation to the magnetic phase transition at $T_N$.