Universality Class Transition Across the Helimagnetic Ordering in Te-doped Cu$_2$OSeO$_3$

TL;DR

This study investigates how Te doping in Cu$_2$OSeO$_3$ affects its magnetic phase transitions, revealing a transition in universality class from Heisenberg to Ising that is robust against chemical pressure, with implications for magnetic interaction strength.

Contribution

It provides the first analysis of universality class transition across helimagnetic ordering in Te-doped Cu$_2$OSeO$_3$, demonstrating robustness of the transition and linking doping to interaction strength changes.

Findings

Te doping lowers transition temperatures and critical fields.

Universality class transition remains Heisenberg to Ising despite doping.

Doping reduces Dzyaloshinskii-Moriya and symmetric exchange interactions.

Abstract

Cu$_2$OSeO$_3$ is a multiferroic insulating chiral magnet which exhibits various magnetic orderings at different conditions. The positions of these magnetic phase transitions are known to be sensitive to chemical substitution. Here, we present a universality class analysis of the Cu$_2$OSe$_{1-x}$Te$_x$O$_3$ with $(0\leq x \leq 0.1)$. Tellurium is a non-magnetic ion which, upon substitution into the selenium positions of the structure, applies a positive chemical pressure and expands the crystal lattice. Our SANS and magnetometry data indicate that Te inclusion lowers the paramagnetic to helical ordering temperature and the critical field required for the conical to field polarised phase transition. By using the Heat-map Modified Iteration Method that evaluates critical behaviour on both sides of the transition, we show that the Heisenberg to Ising universality class transition of the initial ordering is robust to internal chemical pressure. Additionally, we attribute the decreases with doping in both critical temperature and critical field to be due to decreases in the strength of the Dzyaloshinskii-Moriya and Symmetric Exchange Interactions.