Heteromolecular Interface Design for Better Multiferroic Molecular Spintronics

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

Nontechnical Description This project focuses on the interface between a class of molecules which are magnetic, but where the magnetic properties can be turned on and off, and a different group of molecules whose properties are easily altered by voltage. The overall research goals are to better understand the mechanisms that dominate the voltage manipulation of an unusual class of molecules that can be flipped between being magnetic or not magnetic. There are good reasons to pursue this better understanding. Suitable combinations of molecules, that can be toggled between a state acting like a very small magnet and one having no magnetism, with molecules whose intrinsic properties can be controlled by an applied voltage make it possible to fabricate a molecular "switch" that requires very little power to turn on and off. By choosing the right molecule from each class, novel, low cost and extremely low power electronic devices can be made, that can be switched on and off billions of times without degradation. These are devices that can be reduced to the size of a virus particle, or even smaller, which could lead to super high dense computer memories. The cost is low since molecular films can be printed on a wide variety of surfaces. The investigators, having developed this new technology, intend to explore the principles for designing novel and even better molecular materials where magnetism and voltage are intertwined. Student training will include direct international experience in science. Other activities involve both undergraduate and graduate students, including visiting undergraduates, in cutting edge research at the interface of chemistry and physics and outreach activities where the students learn how to communicate cutting edge research to a nontechnical audience. Technical Description This research team has demonstrated voltage controlled nonvolatile transistor-like devices that use molecular spin crossover complexes as the conduction channel. In these systems, the molecular spin state can be tuned by the gate voltage, altering the magnetic properties and the conductance by orders of magnitude. This success opens the door to obtaining deeper insights into possible magneto-electric coupling in molecular systems. This research focuses on a better understanding of the mechanisms that dominate the voltage manipulation of the spin state of these metal-organic complexes. The ultimate aim of investigating suitable combinations of ferroelectric and local moment molecular systems is to find systems with super-large (large electric response to a small magnetic field) or super-small (large magnetic response to a small applied voltage) magneto-electric coefficients. But the core of this research is how intermolecular interaction affects intramolecular configurations, resulting in changes to the ligand field, the molecular dipole, and ultimately the spin state. To accomplish this goal, the investigators will (1) identify what determines the changes in spin crossover phenomenology with molecular film thickness; (2) determine the energy barriers to spin state switching; (3) learn how a heteromolecular system, where the spin state of the molecular overlayer is altered by an applied electric field, reacts to competing processes; (4) identify the smallest controllable domain size within a continuous film; and (5) identify whether or not a spin orientation anisotropy barrier exists. The combined molecular systems will be characterized by a variety of spectroscopic techniques, magnetometry and scanning probe techniques to determine spin state, ferroelectric polarization, as well as spin crossover activation energies, while thin film heterostructure conductance and magnetic moment will be characterized in the presence of applied magnetic and electric fields at various temperatures. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.