Coexistence of antiferromagnetism and ferrimagnetism in adjacent honeycomb layers

TL;DR

This paper reports the discovery of a novel hybrid magnetic state in Co$_2$Mo$_3$O$_8$ where antiferromagnetic and ferrimagnetic layers coexist at the atomic scale, enabled by specific exchange interactions and anisotropies.

Contribution

It introduces an atomic-scale hybrid spin state with coexisting antiferromagnetic and ferrimagnetic layers stabilized by magnetic fields and specific exchange interactions.

Findings

Hybrid spin state stabilized in Co$_2$Mo$_3$O$_8$ by magnetic fields.

Layered structure of alternating antiferromagnetic and ferrimagnetic honeycomb layers.

The stability of the hybrid phase can be achieved at zero magnetic field.

Abstract

Antiferromagnetic and ferro/ferrimagnetic orders are typically exclusive in nature, thus, their co-existence in atomic-scale proximity is expected only in heterostructures. Breaking this paradigm and broadening the range of unconventional magnetic states, we report here on an atomic-scale hybrid spin state, which is stabilized in three-dimensional crystals of the polar antiferromagnet Co$_2$Mo$_3$O$_8$ by magnetic fields applied perpendicular to the \emph{Co} honeycomb layers and possesses a spontaneous in-plane ferromagnetic moment. Our microscopic spin model, capturing the observed field dependence of the longitudinal and transverse magnetization as well as the magnetoelectric/elastic properties, reveals that this novel spin state is composed of an alternating stacking of antiferromagnetic and ferrimagnetic honeycomb layers. The strong intra-layer and the weak inter-layer exchange couplings together with competing anisotropies at octahedral and tetrahedral \emph{Co} sites are identified as the key ingredients to stabilize antiferromagnetic and ferrimagnetic layers in such a close proximity. We show that the proper balance of magnetic interactions can extend the stability range of this hybrid phase down to zero magnetic field. The possibility to realize a layer-by-layer stacking of such distinct spin orders via suitable combinations of microscopic interactions opens a new dimension towards the nanoscale engineering of magnetic states.