10 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
Exchange Coupling of Spin-Crossover Molecules to Ferromagnetic Co Islands
The
properties of Fe(1,10-phenanthroline)<sub>2</sub>(NCS)<sub>2</sub> (Fe-phen) molecules deposited on Co/Cu(111) are studied with
scanning tunneling microscopy (STM) operated in ultrahigh vacuum at
low temperature (4 K) and ab initio calculations. Both the experimental
and theoretical results are used to identify the high-spin (HS) state
of Fe-phen. Additionally, the calculations reveal a strong spin-polarization
of the density of states (DOS) and is validated experimentally using
the spin sensitivity of spin-polarized STM. Finally, it is shown that
the magnetic moment of the Fe-ion within HS Fe-phen is strongly magnetically
coupled to the underlying magnetic Co through the NCS groups. These
findings enable promising spintronic perspectives
Ligand-Induced Energy Shift and Localization of Kondo Resonances in Cobalt-Based Complexes on Cu(111)
Magnetic
sandwich complexes are of particular interest for molecular
spintronics. Using scanning tunneling microscopy, we evidence the
successful deposition of 1,3,5-tris(η<sup>6</sup>-borabenzene-η<sup>5</sup>-cyclopentadienylcobalt) benzene, a molecule composed of three
connected magnetic sandwich units, on Cu(111). Scanning tunneling
spectra reveal two distinct spatial-dependent narrow resonances close
to the Fermi level for the trimer molecules as well as for molecular
fragments composed of one and two magnetic units. With the help of
density functional theory, these resonances are interpreted as two
Kondo resonances originating from two distinct nondegenerate d-like
orbitals. These Kondo resonances are found to have defined spatial
extents dictated by the hybridization of the involved orbitals with
that of the ligands. These results opens promising perspectives for
investigating complex Kondo systems composed of several “Kondo”
orbitals
Interconnected Cobaltocene Complexes on Metal Surfaces
Interconnected
molecular magnetic centers on metallic surfaces
are of interest for molecular spintronics. Complexes composed of two
or three cobaltocene units linked by naphthalene or benzene groups
are successfully deposited on Au(111) and Cu(111) by sublimation and
electrospray deposition. Low-temperature scanning tunneling microscopy
and spectroscopy are employed to investigate the deposited compounds
and their spin state. Although all molecules are composed of the same
magnetic cobaltocene unit, only one compound shows a zero-bias feature
compatible with a Kondo resonance, whose amplitude varies from molecule
to molecule. The amplitude variation and its absence for the other
investigated complexes are attributed to different molecule–substrate
coupling, which is strongly influenced by the linker. Parameters influencing
the molecule–substrate coupling and molecular properties are
extracted from the experimental data. These key parameters should
be considered for future strategies of interconnected magnetic centers
on metallic substrates
Robust and Selective Switching of an Fe<sup>III</sup> Spin-Crossover Compound on Cu<sub>2</sub>N/Cu(100) with Memristance Behavior
The
switching between two spin states makes spin-crossover molecules
on surfaces very attractive for potential applications in molecular
spintronics. Using scanning tunneling microscopy, the successful deposition
of [Fe(pap)<sub>2</sub>]<sup>+</sup> (pap = <i>N</i>-2-pyridylmethylidene-2-hydroxyphenylaminato)
molecules on Cu<sub>2</sub>N/Cu(100) surface is evidenced. The deposited
Fe<sup>III</sup> spin-crossover compound is controllably switched
between three different states, each of them exhibiting a characteristic
tunneling conductance. The conductance is therefore employed to readily
read the state of the molecules. A comparison of the experimental
data with the results of density functional theory calculations reveals
that all Fe(pap)<sub>2</sub> molecules are initially in their high-spin
state. The two other states are compatible with the low-spin state
of the molecule but differ with respect to their coupling to the substrate.
As a proof of concept, the reversible and selective nature of the
switching is used to build a two-molecule memory
Deposition of a Cationic Fe<sup>III</sup> Spin-Crossover Complex on Au(111): Impact of the Counter Ion
Spin-crossover
molecules on metallic substrates have recently attracted
considerable interest for their potential applications in molecular
spintronics. Using scanning tunneling microscopy, we evidence the
first successful deposition of a charged Fe<sup>III</sup> spin-crossover
complex, [Fe(pap)<sub>2</sub>]<sup>+</sup> (pap = <i>N</i>-2-pyridylmethylidene-2-hydroxyphenylaminato), on Au(111). Furthermore,
the bulk form of the molecules is stabilized by a perchlorate counterion,
which depending on the deposition technique may affect the quality
of the deposition and the measurements. Finally, we evidence switching
of the molecules on Au(111)
Power-to-Gas through High Temperature Electrolysis and Carbon Dioxide Methanation: Reactor Design and Process Modeling
This
work deals with the coupling between high temperature steam
electrolysis using solid oxide cells (SOEC) and carbon dioxide methanation
to produce a synthetic natural gas (SNG) directly injectable in the
natural gas distribution grid via a power-to-gas (P2G) pathway. An
intrinsic kinetics obtained from the open literature has been used
as the basis for a plug flow reactor model applied to a series of
cooled multitube fixed bed reactors for methane synthesis. Evaporating
water has been considered as coolant, ensuring a high heat transfer
coefficient within the shell side of the reactor. A methanation section
has been designed and optimized in order to moderate the maximum temperature
within the catalytic bed and to minimize the catalyst load. Then,
process modeling of a plant coupling high temperature electrolysis
and methanation is presented: the main goal of this analysis is the
calculation of overall plant efficiency (in terms of electricity-to-SNG
chemical energy). Plant size has been set considering a 10 MW<sub>el</sub> SOEC-based electrolysis unit; heat produced from the exothermal
methanation is entirely used for water evaporation before the steam
electrolysis. A heat exchanger network (HEN) has been designed in
order to reduce the number of components, resulting in an external
heat requirement equal to 185 kW (≈1.9% of the electrolysis
power). The SOEC-based power-to-gas system presented a higher heating
value based efficiency equal to ≈86% (≈77% if evaluated
on lower heating value basis)
Light-Induced Spin Crossover in an Fe(II) Low-Spin Complex Enabled by Surface Adsorption
Understanding
and controlling the spin-crossover properties of
molecular complexes can be of particular interest for potential applications
in molecular spintronics. Using near-edge X-ray absorption fine structure
spectroscopy, we investigated these properties for a new vacuum-evaporable
Fe(II) complex, namely [Fe(pypyr(CF<sub>3</sub>)<sub>2</sub>)<sub>2</sub>(phen)] (pypyr = 2-(2′-pyridyl)pyrrolide, phen = 1,10-phenanthroline).
We find that the spin-transition temperature, well above room temperature
for the bulk compound, is drastically lowered for molecules arranged
in thin films. Furthermore, while within the experimentally accessible
temperature range (2 K < <i>T</i> < 410 K) the bulk
material shows indication of neither light-induced excited spin-state
trapping nor soft X-ray-induced excited spin-state trapping, these
effects are observed for molecules within thin films up to temperatures
around 100 K. Thus, by arranging the molecules into thin films, a
nominal low-spin complex is effectively transformed into a spin-crossover
complex
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
High Spin Polarization at Ferromagnetic Metal–Organic Interfaces: A Generic Property
A high
spin polarization of states around the Fermi level, <i>E</i><sub>F</sub>, at room temperature has been measured in
the past at the interface between a few molecular candidates and the
ferromagnetic metal Co. Is this promising property for spintronics
limited to these candidates? Previous reports suggested that certain
conditions, such as strong ferromagnetism, i.e., a fully occupied
spin-up d band of the ferromagnet, or the presence of π bonds
on the molecule, i.e., molecular conjugation, needed to be met. What
rules govern the presence of this property? We have performed spin-resolved
photoemission spectroscopy measurements on a variety of such interfaces.
We find that this property is robust against changes to the molecule
and ferromagnetic metal’s electronic properties, including
the aforementioned conditions. This affirms the generality of highly
spin-polarized states at the interface between a ferromagnetic metal
and a molecule and augurs bright prospects toward integrating these
interfaces within organic spintronic devices