Critical properties of the unconventional spin-Peierls system TiOBr

TL;DR

This study investigates the critical properties of the spin-Peierls transition in TiOBr, finding that its critical exponent aligns with 3D universality classes and noting differences from TiOCl.

Contribution

The paper provides detailed x-ray scattering analysis of TiOBr's critical behavior, clarifying its universality class and structural differences from related compounds.

Findings

Critical exponent beta consistent with 3D universality classes

Narrow asymptotic critical regime with beta_{asy} = 0.32

No evidence of commensurate fluctuations above Tc1

Abstract

We have performed detailed x-ray scattering measurements on single crystals of the spin-Peierls compound TiOBr in order to study the critical properties of the transition between the incommensurate spin-Peierls state and the paramagnetic state at Tc2 ~ 48 K. We have determined a value of the critical exponent beta which is consistent with the conventional 3D universality classes, in contrast with earlier results reported for TiOBr and TiOCl. Using a simple power law fit function we demonstrate that the asymptotic critical regime in TiOBr is quite narrow, and obtain a value of beta_{asy} = 0.32 +/- 0.03 in the asymptotic limit. A power law fit function which includes the first order correction-to-scaling confluent singularity term can be used to account for data outside the asymptotic regime, yielding a more robust value of beta_{avg} = 0.39 +/- 0.05. We observe no evidence of commensurate fluctuations above Tc1 in TiOBr, unlike its isostructural sister compound TiOCl. In addition, we find that the incommensurate structure between Tc1 and Tc2 is shifted in Q-space relative to the commensurate structure below Tc1.