The magnetoelectrochemical switch

Abstract

In the field of spintronics, the archetype solid-state two-terminal device is the spin valve, where the resistance is controlled by the magnetization configuration. We show here how this concept of spin-dependent switch can be extended to magnetic electrodes in solution, by magnetic control of their chemical environment. Appropriate nanoscale design allows a huge enhancement of the magnetic force field experienced by paramagnetic molecular species in solutions, which changes between repulsive and attractive on changing the electrodes' magnetic orientations. Specifically, the field gradient force created within a sub-100-nm-sized nanogap separating two magnetic electrodes can be reversed by changing the orientation of the electrodes' magnetization relative to the current flowing between the electrodes. This can result in a breaking or making of an electric nanocontact, with a change of resistance by a factor of up to 10 3 . The results reveal how an external field can impact chemical equilibrium in the vicinity of nanoscale magnetic circuits.magnetohydrodynamics | supramolecular chemistry | electrochemistry S pintronics (1, 2) is a mature research field in solid-state physics, with important electronic device applications. Spindependent transport studies in a liquid environment are much scarcer, and still rely on solid-state spintronics devices concepts. For example, giant magnetoresistance or tunnel magnetoresistance spin valves (3) are used for detecting the stray magnetic field (4) of nearby micrometer-sized (bioactive) magnetic beads (5). The objects studied are significantly larger than the molecular scale, owing to the predominant concentration gradient and Brownian forces exceeding by orders of magnitudes the magnetic force experienced by paramagnetic molecules (6). However, miniaturization of ferromagnetic elements below the micrometer range provides opportunities for enhancing the magnetic force field, making the detection of single spin possible (7). We propose here to use such a nanoscale enhancement strategy to investigate how the realization of very large magnetic field gradients can impact the properties of paramagnetic molecules, in particular by modifying their chemical equilibrium. An external magnetic field controls the magnetization direction of ferromagnetic immersed electrodes, with a related large change of the magnetic forces in their vicinity. This modifies accordingly the chemical stability of the solution, in the interesting case where paramagnetic molecules are essential to the construction of a conductive molecular-sized system. The resulting metallic nanobridge therefore exhibits electrical properties tunable through a change of magnetic orientations of the electrodes. While it relies on a totally different physical origin, this is the chemical analog of a solid-state spin valve device.We illustrate this concept by presenting magnetoresistance (MR) results for a Ni-based nanobrige separating two nearby Ni electrodes immersed in an electrochemical solution. The experiments are based up...

Highlighting spin selectivity properties of chiral electrode surfaces from redox potential modulation of an achiral probe under an applied magnetic field

“…The study of the mutual influence between chirality, electron spin and magnetism is a well-documented field of research 1–7. Implications span from pure fundamental research, to chemical applications of both analytical and synthetic character, to multidisciplinary purposes such as the development of computing oriented electronics 8,9. In this context the interrelated disciplines of magnetoelectrochemistry, spintronics and Spin Dependent Electrochemistry (SDE) play a crucial role.…”

“… 1 – 7 Implications span from pure fundamental research, to chemical applications of both analytical and synthetic character, to multidisciplinary purposes such as the development of computing oriented electronics. 8 , 9 In this context the interrelated disciplines of magnetoelectrochemistry, spintronics and Spin Dependent Electrochemistry (SDE) play a crucial role. Actually, magnetic effects in electrochemical systems have been investigated since the XIX century, particularly focusing on Lorentz and Kelvin force effects.…”

Multilevel Resistance Switching and Enhanced Spin Transition Temperature in Single- and Double-Molecule Spin Crossover Nanogap Devices

“…In this study we use the electromigration method, [12][13][14] which has the advantage of scalability and a rigid silicon wafer substrate for better device stability. This is particularly important in the case of magnetic electrodes, 15 where SCO compounds have the potential to be used as highly efficient spin-filters, [16][17][18] as it can eliminate effects from magnetostriction. 19 DFT modelling of isolated SCO compounds in contact with metallic electrodes predicts that in general there will be a change in conductance associated with the spin transition.…”