Magnetic structure of Ba(TiO)Cu$_4$(PO$_4$)$_4$ probed using spherical neutron polarimetry

TL;DR

This study used spherical neutron polarimetry to determine the non-collinear in-out magnetic structure of Ba(TiO)Cu$_4$(PO$_4$)$_4$, revealing the role of Dzyaloshinskii-Moriya interactions in its antiferromagnetic order.

Contribution

The paper provides the first detailed magnetic structure determination of Ba(TiO)Cu$_4$(PO$_4$)$_4$ using spherical neutron polarimetry, highlighting the non-collinear spin arrangement and the influence of Dzyaloshinskii-Moriya interactions.

Findings

Cu$^{2+}$ spins form a non-collinear in-out structure

Strong Dzyaloshinskii-Moriya interaction explains the spin arrangement

Magnetic structure identified for future theoretical studies

Abstract

The antiferromagnetic compound Ba(TiO)Cu$_4$(PO$_4$)$_4$ contains square cupola of corner-sharing CuO$_4$ plaquettes, which were proposed to form effective quadrupolar order. To identify the magnetic structure, we have performed spherical neutron polarimetry measurements. Based on symmetry analysis and careful measurements we conclude that the orientation of the Cu$^{2+}$ spins form a non-collinear in-out structure with spins approximately perpendicular to the CuO$_4$ motif. Strong Dzyaloshinskii-Moriya interaction naturally lends itself to explain this phenomenon. The identification of the ground state magnetic structure should serve well for future theoretical and experimental studies into this and closely related compounds.