Synchrotron X-ray Spectroscopy Study on the Valence State in alpha- and beta-YbAlB4 at Low Temperatures and High Magnetic Fields

TL;DR

This study investigates the valence state of Yb ions in alpha- and beta-YbAlB4 at low temperatures and high magnetic fields using synchrotron X-ray spectroscopy, revealing temperature-dependent valence fluctuations and magnetic field effects.

Contribution

It provides detailed measurements of Yb valence states and their fluctuations in YbAlB4 compounds under varying temperature and magnetic field conditions, highlighting new insights into valence behavior.

Findings

Yb valence is approximately 2.78 at 2 K in beta-YbAlB4.

Valence increases gradually with temperature, reaching near trivalent around 290 K.

Application of 32 T magnetic field causes a small valence increase (~0.002) at 40 K.

Abstract

The valence state of Yb ions in beta-YbAlB4 and its polymorph alpha-YbAlB4 has been investigated by using X-ray absorption and emission spectroscopy in SPring-8 at temperatures from 2 to 280 K. The observed Yb valence is 2.78 +- 0.01 in beta-YbAlB4 at 2 K by using the X-ray emission spectroscopy. The valence is found to gradually increase with increasing temperature toward the trivalent state, and the characteristic temperature of the valence fluctuation is expected to be about 290 K. We also found a small increase in the Yb valence (~0.002) by applying a magnetic field of 32 T at 40 K to beta-YbAlB4.