Abstract:In this paper, we present a comprehensive review of research on electrical and charge transport properties of spin crossover complexes. This includes both the effect of spin-state switching on the dielectric permittivity and electrical conductivity of the material and vice versa the influence of an applied electrical field (or current) on the spin-state of the system. The survey covers different size scales from bulk materials and thin films to nanoparticles and single molecules and embraces the presentation of several device prototypes and hybrid materials as well.

The fabrication of large-area vertical junctions with a molecular spin-crossover complex displaying concerted changes of spin degrees of freedom and charge-transport properties is reported. Fabricated devices allow spin-state switching in the spin-crossover layer to be triggered and probed by optical means, while detecting associated changes in electrical resistance in the junctions.

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Spin crossover compounds are considered to be a viable alternative for creating display, memory and switching devices due to the bistability of their magnetic, optical, mechanical and electrical properties. This Letter presents the study of the dielectric and transport properties of the [Fe(Htrz)2(trz)](BF4) (Htrz = 1H‐1,2,4‐triazole) complex in a wide temperature and frequency range. Our results reveal a singular behavior of the dielectric modulus upon the spin transition in conjunction with the switching of the conductivity between the high spin and low spin states. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 13962To link to this article :ABSTRACT: In this study we analyze the metal substitution effects on the structural, morphological, charge transport, and spin transition properties of the [Fe 1−x Zn x (Htrz) 2 (trz)](BF 4 ) (trz = triazole, x = 0, 0.26, or 0.43) compound using electron microscopy, powder X-ray diffraction, optical reflectivity, Raman, FTIR, 57 Fe Mossbauer, and broadband (10 −2 −10 6 Hz) dielectric spectroscopies. The crystal structure and the morphology of the objects remain nearly unaffected, whereas the thermal spin transition shifts from 362 to 316 K and the thermal hysteresis width decreases from 45 to 8 K for increasing values of x. For each compound the electrical conductivity drops when the iron(II) electronic configuration is switched from the low-spin to the high-spin state. A strong overall decrease in conductivity with increasing Zn concentration is also observed in both spin states. These results, together with the analysis of the charge carrier dynamics, suggest that the ferrous ions participate directly in the charge transport mechanism, explaining the strong spin-state dependence of the electrical properties in this compound.

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We studied the effect of light irradiation on the electrical conductance of micro-rods of the spin crossover [Fe(Htrz)2(trz)](BF4) network, organized between interdigitated gold electrodes. By irradiating the sample with different wavelengths (between 295 and 655 nm) either in air or under a nitrogen atmosphere we observed both a reversible and an irreversible change of the current flowing in the device. The reversible process consists of an abrupt decrease of the current intensity (ca. 10-50%) upon light irradiation, while the irreversible process is characterized by a slow, but continuous increase in time of the current, which persists also in the dark. These photo-induced processes were only detected in the high conductance low-spin (LS) state of the complex. On switching the rods to the high spin (HS) state the conductance decreases two orders of magnitude (at the same temperature) and - as a consequence - the photo-effect vanishes.

This paper illustrates quasi-static magnetization switching via vortex formation in soft magnetic nanoparticles of various shapes and sizes. The research is motivated by the rapid development of novel alternatives to the current paradigm of magnetic recording, which approaches its fundamental limits. The study is performed by using NMAG simulation environment which is a finite-element micro-magnetic simulation package based on Python scripts running on a Linux virtual machine. Various shapes and sizes are considered in this analysis of hysteresis phenomena and vortex formations in nanoparticles subject to different orientations of the magnetic field