Spontaneous cycloidal order mediating a spin-reorientation transition in a polar metal

TL;DR

This paper demonstrates how complex magnetic order, specifically a cycloid, spontaneously forms in a polar metal due to competing magnetic interactions, leading to a temperature-dependent spin reorientation transition.

Contribution

It uncovers the emergence of a magnetic cycloid mediating spin reorientation in Ca$_3$Ru$_2$O$_7$, revealing the role of polar distortions and magnetic field sensitivity.

Findings

Identification of a temperature-evolving magnetic cycloid

Observation of higher harmonic modulations under magnetic fields

Unified understanding of magnetic phases in a polar metal

Abstract

We show how complex modulated order can spontaneously emerge when magnetic interactions compete in a metal with polar lattice distortions. Combining neutron and resonant x-ray scattering with symmetry analysis, we reveal that the spin reorientation in Ca$_3$Ru$_2$O$_7$ is mediated by a magnetic cycloid whose eccentricity evolves smoothly but rapidly with temperature. We find the cycloid to be highly sensitive to magnetic fields, which appear to continuously generate higher harmonic modulations. Our results provide a unified picture of the rich magnetic phases of this correlated, multi-band polar metal.