Spin Crossover Nanomaterials: From Fundamental Concepts to Devices

Abstract

Nanoscale spin crossover materials capable of undergoing reversible switching between two electronic configurations with markedly different physical properties are excellent candidates for various technological applications. In particular, they can serve as active materials for storing and processing information in photonic, mechanical, electronic, and spintronic devices as well as for transducing different forms of energy in sensors and actuators. In this progress report, a brief overview on the current state-of-the-art of experimental and theoretical studies of nanomaterials displaying spin transition is presented. Based on these results, a detailed analysis and discussions in terms of finite size effects and other phenomena inherent to the reduced size scale are provided. Finally, recent research devices using spin crossover complexes are highlighted, emphasizing both challenges and prospects.

Single‐Crystal X‐Ray Diffraction Study of Pressure and Temperature‐Induced Spin Trapping in a Bistable Iron(II) Hofmann Framework

“…Strong coupling between the active building blocks favours cooperative hysteretic behaviour, conferring bistability (memory effect) to the magnetic, optical, electrical, structural and mechanical properties of the material. These properties are promising for the application of SCO materials in data storage devices, sensors and actuators …”

Elucidating the Structural Chemistry of a Hysteretic Iron(II) Spin‐Crossover Compound From its Copper(II) and Zinc(II) Congeners

“…Spin‐crossover (SCO) compounds are metal/organic materials that switch between a high‐spin and low‐spin electronic configuration under a temperature, pressure or photochemical stimulus . Structural and electronic changes accompanying an SCO event perturb many other properties of the compound, including its colour, magnetic moment, conductivity, dielectric properties, and elastic moduli .…”

“…Structural and electronic changes accompanying an SCO event perturb many other properties of the compound, including its colour, magnetic moment, conductivity, dielectric properties, and elastic moduli . Recently proposed applications exploiting these properties of SCO materials include their use as bits in electronic memory devices, in micro‐cantilevers, and for barocaloric refrigeration . Most such applications require compounds exhibiting abrupt thermal SCO with significant thermal hysteresis, which are bistable at temperatures inside the hysteresis loop .…”

Direct Visualization of Local Spin Transition Behaviors in Thin Molecular Films by Bimodal AFM

“…With decreasing film thickness, the transition is slightly shifted to higher temperatures, which we attributed to the stabilization of the LS phase by surface energy and stress . The transition in the films is accompanied by a substantial spontaneous strain and associated changes of refractive index and electrical resistance, which gives rise to numerous potential applications of 1 in mechanical actuators, temperature sensors, photonic and electronic devices …”

“…[1][2][3] Recently, much attention has been attracted to emergent physical properties and potential applications of nanoscale SCO materials in the form of nanoparticles, thin films, and nano-heterostructures. [4][5][6] Many aspects of the related physics focus on the study of the effect of surfaces/interfaces on the phase stability and phase transition dynamics. [7][8][9][10][11][12] At reduced sizes, the increasing contribution of surfaces to the total free energy may give rise to structural and electronic changes in the material, which actually go beyond the surface layers.…”