Femtosecond Spin-State Switching Dynamics of Fe(II) Complexes Condensed in Thin Films.

The tailoring of spin-crossover films has made significant progress over the past decade, mostly motivated by the prospect in technological applications. In contrast to spin-crossover complexes in solution, the investigation of the ultrafast switching in spin-crossover films has remained scarce. Combining the progress in molecule synthesis and film growth with the opportunities at X-ray free-electron lasers, we study the photoinduced spin-state switching dynamics of a molecular film at room temperature.

Residual Ferromagnetic Regions Affecting the First-Order Phase Transition in Off-Stoichiometric Fe-Rh.

Among the magnetocaloric materials featuring first-order phase transitions (FOPT), FeRh is considered as a reference system to study the FOPT because it is a "simple" binary system with a CsCl structure exhibiting a large adiabatic temperature change. Recently, ab initio theory predicted that changes in the Fe/Rh stoichiometry in the vicinity of equiatomic composition strongly influence the FOPT characteristics. However, this theoretical prediction was not clearly verified experimentally.

Table-top source for x-ray absorption spectroscopy with photon energies up to 350 eV.

We present a table-top setup for x-ray absorption spectroscopy (XAS) based on high harmonic generation (HHG) in noble gases. Using sub-millijoule pump pulses at a central wavelength of 1550 nm, broadband HHG in the range of 70-350 eV was demonstrated. The HHG coherence lengths of several millimeters were achieved by reaching the nonadiabatic regime of harmonic generation.

Multicaloric Cryocooling Using Heavy Rare-Earth Free La(Fe,Si)-Based Compounds.

The transition toward a carbon-neutral society based on renewable energies goes hand in hand with the availability of energy-efficient technologies. Magnetocaloric cooling is a very promising refrigeration technology to fulfill this role regarding cryogenic gas liquefaction. However, the current reliance on highly resource critical, heavy rare-earth-based compounds as magnetocaloric material makes global usage unsustainable.

Lattice solvent- and substituent-dependent spin-crossover in isomeric iron(II) complexes.

Spin-state switching in iron(II) complexes composed of ligands featuring moderate ligand-field strength-for example, 2,6-bi(1-pyrazol-1-yl)pyridine (BPP)-is dependent on many factors. Herein, we show that spin-state switching in isomeric iron(II) complexes composed of BPP-based ligands-ethyl 2,6-bis(1-pyrazol-1-yl)isonicotinate (BPP-COOEt, L1) and (2,6-di(1-pyrazol-1-yl)pyridin-4-yl)methylacetate (BPP-CHOCOMe, L2)-is dependent on the nature of the substituent at the BPP skeleton. Bi-stable spin-state switching-with a thermal hysteresis width (Δ) of 44 K and switching temperature () = 298 K in the first cycle-is observed for complex 1·CHCN composed of L1 and BF counter anions.