2 research outputs found
Disentangling magnetic hardening and molecular spin chain contributions to exchange bias in ferromagnet/molecule bilayers
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.Comment: Non
Magnetic Properties of Mono- and Multilayer Assemblies of Iron Oxide Nanoparticles Promoted by SAMs
Owing
to the wide scope of applications of magnetic nanoparticle
assembling, the aim of this study is to evaluate the influence of
nanoparticle aggregates on the magnetic properties of 2D assemblies.
Magnetic iron oxide nanoparticles (NPs) have been synthesized by the
coprecipitation (NP<sub>cop</sub>) and thermal decomposition (NP<sub>dec</sub>@OA) methods, and were assembled on self-assembled monolayers
of organic molecules decorated by a phosphonic acid terminal group
at their surface (SAM-PO<sub>3</sub>H<sub>2</sub>). The nanostructure
and magnetic properties of assemblies depend directly on the aggregation
of NP suspensions. NP<sub>cop</sub> result in an unstable suspension
and were assembled into a non-homogeneous monolayer of aggregates.
The post-functionalization of NP<sub>cop</sub> with oleic acid after
synthesis (NP<sub>cop</sub>@OA) favors a better stability of the suspension
and enhances the nanostructure of the assembly, although smaller NP
aggregates remain. In contrast, NP<sub>dec</sub>@OA which are functionalized <i>in situ</i> by oleic acid during the synthesis step were assembled
as individual nanomagnets and result in a dense monolayer. Multilayer
assemblies were also prepared from NP<sub>cop</sub>@OA and NP<sub>dec</sub>@OA by performing the alternative deposition of these NPs
with (1,4-phenylene)Âbisphosphonic acid. The nanostructure of assemblies
has been studied by scanning electron microscopy (SEM) and atomic
force microscopy (AFM). The magnetic properties of monolayer and multilayer
assemblies have been studied by using a SQUID magnetometer. While
assemblies of individual NPs enhance dipolar interactions in-plane
as a result of shape anisotropy, assemblies of NP aggregates favor
stronger dipolar interactions with random orientation. The magnetic
properties of monolayer and multilayer assemblies have also been compared.
The dimensionality (2D vs 3D) has a strong effect on the dipolar interactions
when individual NPs are considered in contrast to aggregated nanoparticles