Sub-10 nm helices stabilized by single-ion anisotropy in the chiral Mott insulator Co$_5$TeO$_8$

TL;DR

This study predicts and experimentally confirms sub-10 nm helices in Co$_5$TeO$_8$, stabilized by single-ion anisotropy, revealing a new mechanism for magnetic texture control in correlated oxides.

Contribution

It introduces a density functional theory-guided approach to discover sub-10 nm helices stabilized by single-ion anisotropy, contrasting with Dzyaloshinskii-Moriya interaction dominance.

Findings

Neutron scattering reveals proper-screw helices with tunable pitch of 5.7-10 nm.

Site-dependent single-ion anisotropy exceeds Dzyaloshinskii-Moriya interactions.

Phase diagram shows eight distinct magnetic phases with magnetoelectric coupling.

Abstract

Narrow-gap Mott insulators promise exceptional opportunities for voltage-controlled magnetic textures in low-dissipation spintronics, although their prediction remains challenging. Here we employ a density functional theory-guided approach to predict a narrow charge-transfer gap (127 meV) in the chiral cubic frustrated oxide Co$_5$TeO$_8$. Comprehensive neutron scattering and magnetometry reveal proper-screw Bloch-type helices with field- and temperature-tunable pitch of 5.7-10 nm embedded in a complex phase diagram with eight distinct phases. Ab initio wavefunction calculations demonstrate site-dependent single-ion anisotropy exceeding Dzyaloshinskii-Moriya (DM) interactions by an order of magnitude, establishing the anisotropy-frustration interplay as the stabilization mechanism, contrasting starkly with DM-dominated cubic helimagnets. Sharp capacitance anomalies at phase boundaries confirm intrinsic magnetoelectric coupling throughout the phase diagram. Co$_5$TeO$_8$ thus provides a platform for voltage-tunable sub-10 nm magnetic textures, demonstrating effective theory-guided discovery of functional magnetic materials in correlated oxides.