Magnetic structure driven by monoclinic distortions in the double perovskite Sr2YRuO6

TL;DR

This study reveals that monoclinic distortions in Sr2YRuO6 influence its magnetic ground state, showing a transition from a spin structure similar to K2NiF4 to a canted superstructure, driven by structural symmetry breaking.

Contribution

It provides a new interpretation of the magnetic structure in Sr2YRuO6, linking monoclinic distortions to reorientation of magnetic moments and resolving previous discrepancies.

Findings

Low-temperature spin structure resembles K2NiF4

Transition to a canted super-structure near magnetic transition

Correlation between canting angle peaks and thermal anomalies

Abstract

The monoclinic double-perovskite Sr2YRuO6 has recently gained a renewed interest in order to get a deeper insight into the exotic magnetic ground states associated with geometric frustration. Striking discrepancies between the spin order derived from the neutron diffraction refinements and the macroscopic magnetic and thermal responses is a major challenge that must be addressed. In this work, detailed neutron diffraction measurements as a function of temperature yield a completely different interpretation of the patterns. We show that at low temperatures a spin structure of the K2NiF4-type is an accessible configuration for the magnetic ground state. In the neighborhood of the magnetic transition this configuration evolves into a canted super-structure. The deduced temperature dependence of the canting angle exhibits two closely spaced peaks, which are in excellent agreement with the double peaks in the magnetic contribution to the specific heat and in the thermal expansion coefficient. We explain these features in terms of reorientation of the net ferromagnetic moment of the noncollinear spin state, due to the local breaking of the inversion symmetry promoted by the monoclinic distortions, with structural changes acting as the driving force.