3 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
Altering the Static Dipole on Surfaces through Chemistry: Molecular Films of Zwitterionic Quinonoids
The adsorption of molecular films made of small molecules
with a large intrinsic electrical dipole has been explored. The data
indicate that such dipolar molecules may be used for altering the
interface dipole screening at the metal electrode interface in organic
electronics. More specifically, we have investigated the surface electronic
spectroscopic properties of zwitterionic molecules containing 12π
electrons of the <i>p</i>-benzoquinonemonoimine type, C<sub>6</sub>H<sub>2</sub>(<u>···</u>NHR)<sub>2</sub>(<u>···</u>O)<sub>2</sub> (R = H (<b>1</b>), <i>n</i>-C<sub>4</sub>H<sub>9</sub> (<b>2</b>), C<sub>3</sub>H<sub>6</sub>–S–CH<sub>3</sub> (<b>3</b>), C<sub>3</sub>H<sub>6</sub>–O–CH<sub>3</sub> (<b>4</b>), CH<sub>2</sub>–C<sub>6</sub>H<sub>5</sub> (<b>5</b>)), adsorbed on Au. These molecules are stable
zwitterions by virtue of the meta positions occupied by the nitrogen
and oxygen substituents on the central ring, respectively. The structures
of <b>2</b>–<b>4</b> have been determined by single
crystal X-ray diffraction and indicate that in these molecules, two
chemically connected but electronically not conjugated 6π electron
subunits are present, which explains their strong dipolar character.
We systematically observed that homogeneous molecular films with thickness
as small as 1 nm were formed on Au, which fully cover the surface,
even for a variety of R substituents. Preferential adsorption toward
the patterned gold areas on SiO<sub>2</sub> substrates was found with <b>4</b>. Optimum self-assembling of <b>2</b> and <b>5</b> results in ordered close packed films, which exhibit n-type character,
based on the position of the Fermi level close to the conduction band
minimum, suggesting high conductivity properties. This new type of
self-assembled molecular films offers interesting possibilities for
engineering metal–organic interfaces, of critical importance
for organic electronics
Spin-Dependent Hybridization between Molecule and Metal at Room Temperature through Interlayer Exchange Coupling
We
experimentally and theoretically show that the magnetic coupling at
room temperature between paramagnetic Mn within manganese phthalocyanine
molecules and a Co layer persists when separated by a Cu spacer. The
molecule’s magnetization amplitude and direction can be tuned
by varying the Cu–spacer thickness and evolves according to
an interlayer exchange coupling mechanism. <i>Ab initio</i> calculations predict a highly spin-polarized density of states at
the Fermi level of this metal-molecule interface, thereby strengthening
prospective spintronics applications