Spin crossover with thermal hysteresis: practicalities and lessons learnt

Abstract

The observation of spin crossover with thermal hysteresis loops of more than a few Kelvin remains relatively uncommon and unpredictable, so is a relatively underdeveloped, but important, area of spin crossover, particularly for memory applications. Lessons learnt regarding the origins, and the practicalities of the proper study and reporting, of thermal hysteresis loops are considered and explained, from a synthetic chemists perspective, after a general introduction to the field of spin crossover.

Switching Magnetic Properties by a Mechanical Motion

“…Spin-crossover complexes [16][17][18][19][20] are particularly interesting for such purpose, as they can exist in two stable spin states and have been largely studied. Even if spin-crossover behavior is theoretically expected to occur in octahedral complexes with 3d 4 to 3d 7 electronic configurations, most spin-crossover complexes are based on Fe(III), Fe(II), and Co(II), with only few reported examples of compounds of Mn(II), Mn(III), Cr(II), and Co(III).…”

“…Several stimuli have been used to trigger magnetic properties changes [3] in three main areas: (i) changing the spin state of a transition metal in spin crossover (SCO) systems [4][5][6][7][8][9][10][11]; (ii) switching the exchange interaction between different spin carriers [12,13]; and (iii) switching single-molecule magnet (SMM) properties [14,15]. Spin-crossover complexes [16][17][18][19][20] are particularly interesting for such purpose, as they can exist in two stable spin states and have been largely studied. Even if spin-crossover behavior is theoretically expected to occur in octahedral complexes with 3d 4 to 3d 7 electronic configurations, most spin-crossover complexes are based on Fe(III), Fe(II), and Co(II), with only few reported examples of compounds of Mn(II), Mn(III), Cr(II), and Co(III).…”

Synthesis of 4-Hydroxy-2,6-di(pyrazol-1-yl)pyridine, and the Spin State Behaviour of Its Iron(II) Complex Salts

“…that was used in the DSC experiments [33]. The errors on the measured thermodynamic parameters will also be relatively large, because the transitions lie near the lower temperature limit for our calorimeter (Figure 4).…”

High-Temperature Wide Thermal Hysteresis of an Iron(II) Dinuclear Double Helicate

“…In particular, dinuclear species have received much attention since they are a simple model for revealing intra-and intermolecular interactions for enhancing cooperativity [25][26][27][28][29][30][31][32][33][34]. From a more practical point of view, the importance of studying the reproducible nature and scan rate dependence of the hysteresis loop and high-temperature SCO with sufficient thermal stability has recently been pointed out in order to define the limiting characteristics of SCO materials [33,[35][36][37][38][39].…”

“…In particular, dinuclear species have received much attention since they are a simple model for revealing intra-and intermolecular interactions for enhancing cooperativity [25][26][27][28][29][30][31][32][33][34]. From a more practical point of view, the importance of studying the reproducible nature and scan rate dependence of the hysteresis loop and high-temperature SCO with sufficient thermal stability has recently been pointed out in order to define the limiting characteristics of SCO materials [33,[35][36][37][38][39]. Recently, we have focused on SCO molecules with 1-R-1H-1,2,3-triazole-containing Schiff-base (1-R-1H-1,2,3-triazolimine; R = Me and Ph) ligands since the ligand system can easily modify its structure with the choice of a substituent R of a precursor, 1-R-1H-1,2,3-triazole-4-carbaldehyde, and another amino precursor by simple click reaction [40][41][42], Schiff-base reaction [43] and replacement of R using the method reported by L'abbé and coworkers [44,45].…”