arXiv subjects

D. Mertz

Publications and source records attributed to D. Mertz.

4 recordsLinked to original sources

arXiv2026

A low-tech solution to process entire metal/molecule heterostructure stacks into vertical nanopillar electronic devices

Quantum technologies aim to assemble devices whose operation is controlled by the quantum state of individual atoms. Achieving this level of control in a practical, scalable design remains, however, a major obstacle to mass societal adoption. By working at the level of interatomic bonding, molecular engineering has enabled exquisite control over the electronic properties of individual atoms and their interactions with neighboring atoms. This positions molecular electronics as a potentially disruptive quantum technology, but serious technological challenges have prevented it from being included in technical road maps. The main obstacle is that conventional, mass scalable nanodevice technologies utilize resists and solvents that can degrade molecules. Some approaches involve exposing junction interfaces to contaminants (e.g. air, resist etc...), which can be particularly problematic for spintronics. In this technical paper, we present our decade-long work into building a nanotechnological chain that can process entire metal/molecule heterostructures into vertical nanopillars electronic devices. We discuss the advantages and pitfalls of the various iterations of this process that were implemented. We also discuss outlooks for this unique technology.

cond-mat.mes-hall↗

arXiv2019

Magnetoresistance and spintronic anisotropy induced by spin excitations along molecular spin chains

Electrically manipulating the quantum properties of nano-objects, such as atoms or molecules, is typically done using scanning tunnelling microscopes and lateral junctions. The resulting nanotransport path is well established in these model devices. Societal applications require transposing this knowledge to nano-objects embedded within vertical solid-state junctions, which can advantageously harness spintronics to address these quantum properties thanks to ferromagnetic electrodes and high-quality interfaces. The challenge here is to ascertain the device's effective, buried nanotransport path, and to electrically involve these nano-objects in this path by shrinking the device area from the macro- to the nano-scale while maintaining high structural/chemical quality across the heterostructure. We've developed a low-tech, resist- and solvent-free technological process that can craft nanopillar devices from entire in-situ grown heterostructures, and use it to study magnetotransport between two Fe and Co ferromagnetic electrodes across a functional magnetic CoPc molecular layer. We observe how spin-flip transport across CoPc molecular spin chains promotes a specific magnetoresistance effect, and alters the nanojunction's magnetism through spintronic anisotropy. In the process, we identify three magnetic units along the effective nanotransport path thanks to a macrospin model of magnetotransport. Our work elegantly connects the until now loosely associated concepts of spin-flip spectroscopy, magnetic exchange bias and magnetotransport due to molecular spin chains, within a solid-state device. We notably measure a 5.9meV energy threshold for magnetic decoupling between the Fe layer's buried atoms and those in contact with the CoPc layer forming the so-called 'spinterface'. This provides a first insight into the experimental energetics of this promising low-power information encoding unit.

cond-mat.mes-hall↗

arXiv2001

Orbital frustration at the origin of the magnetic behavior in LiNiO2

We report on the ESR, magnetization and magnetic susceptibility measurements performed over a large temperature range, from 1.5 to 750 K, on high-quality stoichiometric LiNiO2. We find that this compound displays two distinct temperature regions where its magnetic behavior is anomalous. With the help of a statistical model based on the Kugel'-Khomskii Hamiltonian, we show that below T_of ~ 400 K, an orbitally-frustrated state characteristic of the triangular lattice is established. This then gives a solution to the long-standing controversial problem of the magnetic behavior in LiNiO2.

cond-mat.mtrl-sci↗

arXiv1999

Magnetic clusters formation in Li_{1-x}Ni_{1+x}O_2 compounds : experiments and numerical simulations

The magnetic properties of Li_{1-x}Ni_{1+x}O_2 compounds with x ranging between 0.02 and 0.2 are investigated. Magnetization and ac susceptibility measured at temperatures between 2 K and 300 K reveal a high sensitivity to x, the excess Nickel concentration. We introduce a percolation model describing the formation of Ni clusters and use an Ising model to simulate their magnetic properties. Numerical results, obtained by a Monte-Carlo technique, are compared to the experimental data. We show the existence of a critical concentration, x_c = 0.136, locating the Ni percolation threshold. The system is superparamagnetic for x x_c. The 180 Ni-O-Ni inter-plane super-exchange coupling J_\perp \simeq -110K is confirmed to be the predominant magnetic interaction. From the low temperature behavior, we find a clear indication of a 90 Ni-O-Ni intra-plane antiferromagnetic interaction $J_\parallel \simeq -1.5K$ which implies magnetic frustration.

cond-mat.mtrl-sci↗