Deteriorated Interlayer Coupling in Twisted Bilayer Cobaltites

TL;DR

This study investigates how twisting bilayer cobaltites affects their magnetic coupling, revealing a decrease in Curie temperature and suggesting new ways to control magnetic properties in layered quantum materials.

Contribution

It demonstrates the impact of twist angles on interlayer magnetic coupling in van der Waals cobaltites, a previously unexplored area in magnetic heterostructures.

Findings

Curie temperature decreases by ~13 K in twisted regions

Moire patterns are clearly observed and relate inversely to twist angle

Orbital hybridization weakening may cause magnetic changes

Abstract

A wealth of remarkable behaviors is observed at the interfaces between magnetic oxides due to the coexistence of Coulomb repulsion and interatomic exchange interactions. While previous research has focused on bonded oxide heterointerfaces, studies on magnetism in van der Waals interfaces remain rare. In this study, we stacked two freestanding cobaltites with precisely controlled twist angles. Scanning transmission electron microscopy revealed clear and ordered moir\'e patterns, which exhibit an inverse relationship with the twist angle. We found that the Curie temperature in the twisted region is reduced by approximately 13 K compared to the single-layer region using nitrogen-vacancy (NV) magnetometry. This phenomenon may be related to the weakening of the orbital hybridization between oxygen ions and transition metal ions in the unbonded interfaces. Our findings suggest a potential avenue for modulating magnetic interactions in correlated systems through twist, providing opportunities for the discovery of unknown quantum states.