The emergence of the local moment molecular spin transistor

Abstract

Local moment molecular systems have now been used as the conduction channel in gated spintronics devices, and some of these three terminal devices might even be considered molecular spin transistors. In these systems, the gate voltage can be used to tune the molecular level alignment, while applied magnetic fields have an influence on the spin state, altering the magnetic properties, and providing insights to the magnetic anisotropy. More recently, the use of molecular spin crossover complexes, as the conduction channel, has led to devices that are both nonvolatile and have functionality at higher temperatures, indeed some devices have now been demonstrated to work at room temperature. Here, several molecular transistors, including those claiming to use single molecule magnets, are reviewed.

Nonvolatile Voltage Controlled Molecular Spin-State Switching for Memory Applications

“…The successes with organic electronics, combined with indications of success in addressing the complex grand challenge of manipulating magnetically ordered states by electrical means, suggest new approaches and applications to develop novel spintronics. In molecular systems, the spin crossover (SCO) relates to the transition between a low spin (LS) of the metal ion (indeed, diamagnetic state in the case of the Fe 2+ system) to a high-spin (HS) paramagnetic state in 3D transition metal compounds, and for quite some time now, it has been suggested that the spin crossover (SCO) phenomenon has potential applicability in molecular spintronic devices [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. In such device elements, based on the molecular spin state, is very likely that state switching may be accomplished without large current densities or power consumption.…”

“…Such devices work where the voltage control of the molecular spin states leads to nonvolatile conductance changes [13,14]. From these many perspectives of memory devices [1][2][3][4][5][6][7][8][9][10][11][12][13][14] made possible by the molecular spinstate transition, we can construct a list of some of the key elements needed to make a competitive nonvolatile molecular device for memory applications.…”

“…Spin crossover molecular systems have a long history [16][17][18][19][20][21], but as successful nonvolatile devices that can be manipulated by voltage alone, the success is much more recent [12][13][14]. Nonetheless, a picture has emerged [5,7,8,12,22,23] of some of the key criteria needed to make a molecular spintronic device, based on spin crossover complexes, competitive with silicon technology. These identified criteria are as follows:…”

“…Figure 1 shows a schematic of a plausible nonvolatile memory element cell. This memory cell is based on the field effect voltagecontrolled spin state molecular transistor described elsewhere [12][13][14] and could exploit the difference between the low-resistance and high-resistance states of a voltage-controlled spin-state molecular memory device fabricated from spin crossover complexes. However, unlike DRAM (dynamic random-access memory), where charge storage on the cell must be refreshed periodically, molecular spin-state memory is nonvolatile, as noted above and elsewhere [12][13][14], and the output is resistive.…”

Probing the unpaired Fe spins across the spin crossover of a coordination polymer

“…2,3,5,6,[8][9][10][11][12][13][14][15][16][17]22,23 Bistability is an essential ingredient for implementing a spin crossover complex into a molecular device. 24 For a successful realization of such devices, it is important to investigate the impact of different characterization methods on the spin crossover properties of promising candidates. In this regard, the spin crossover coordination polymer [Fe(L1)(bipy)] n (where L1 is a N 2 O 2 2− coordinating Schiff base-like ligand bearing a phenazine fluorophore and bipy = 4,4′-bipyridine), of Figure 1a, is particularly interesting.…”