Disentangling magnetic hardening and molecular spin chain contributions to exchange bias in ferromagnet/molecule bilayers

TL;DR

This study distinguishes between magnetic hardening and molecular spin chain effects in ferromagnet/molecule bilayers, demonstrating their additive nature and implications for organic spintronic devices.

Contribution

It experimentally separates and confirms the distinct and additive roles of magnetic hardening and spin chains in FM/molecule bilayers, advancing understanding of interfacial magnetic effects.

Findings

Both effects are distinct and additive.

Confirmed increase in anisotropy with molecular adsorption.

Spin chains can enhance magnetic exchange.

Abstract

We performed SQUID and FMR magnetometry experiments to clarify the relationship between two reported magnetic exchange effects arising from interfacial spin-polarized charge transfer within ferromagnetic metal (FM)/molecule bilayers: the magnetic hardening effect, and spinterface-stabilized molecular spin chains. To disentangle these effects, both of which can affect the FM magnetization reversal, we tuned the metal phthalocyanine molecule central site's magnetic moment to selectively enhance or suppress the formation of spin chains within the molecular film. We find that both effects are distinct, and additive. In the process, we 1) extended the list of FM/molecule candidate pairs that are known to generate magnetic exchange effects, 2) experimentally confirmed the predicted increase in anisotropy upon molecular adsorption; and 3) showed that spin chains within the molecular film can enhance magnetic exchange. This magnetic ordering within the organic layer implies a structural ordering. Thus, by distengangling the magnetic hardening and exchange bias contributions, our results confirm, as an echo to progress regarding inorganic spintronic tunnelling, that the milestone of spintronic tunnelling across structurally ordered organic barriers has been reached through previous magnetotransport experiments. This paves the way for solid-state devices studies that exploit the quantum physical properties of spin chains, notably through external stimuli.