Control of the Speed of a Light-Induced Spin Transition through Mesoscale Core-Shell Architecture.
The rate of the light-induced spin transition in a coordination polymer network solid dramatically increases when included as the core in mesoscale core-shell particles. A series of photomagnetic coordination polymer core-shell heterostructures, based on the light-switchable Rb aCo b[Fe(CN)6] c· mH2O (RbCoFe-PBA) as core with the isostructural K jNi k[Cr(CN)6] l· nH2O (KNiCr-PBA) as shell, are studied using temperature-dependent powder X-ray diffraction and SQUID magnetometry. The core RbCoFe-PBA exhibits a charge transfer-induced spin transition (CTIST), which can be thermally and optically induced. When coupled to the shell, the rate of the optically induced transition from low spin to high spin increases. Isothermal relaxation from the optically induced high spin state of the core back to the low spin state and activation energies associated with the transition between these states were measured. The presence of a shell decreases the activation energy, which is associated with the elastic properties of the core. Numerical simulations using an electro-elastic model for the spin transition in core-shell particles supports the findings, demonstrating how coupling of the core to the shell changes the elastic properties of the system. The ability to tune the rate of optically induced magnetic and structural phase transitions through control of mesoscale architecture presents a new approach to the development of photoswitchable materials with tailored properties.
Molecular Spin Crossover Materials: Review of the Lattice Dynamical Properties
The lattice dynamical aspects of the spin crossover phenomenon in molecular solids—displaying intricate couplings between the electronic spin state of the molecules and the lattice properties—are reviewed. Emphasis is on experimental and theoretical approaches giving access to the vibrational spectra and to key properties, such as the heat capacity, vibrational entropy and enthalpy, lattice rigidity, elastic constants, and elastic interactions. Recent results in relation to surface and finite size effects as well as with ultrafast out‐of‐equilibrium phenomena are also covered.
Magnetic structures of Ising and vector spins monolayers by Monte-Carlo simulations
Abstract We derive the optimal magnetic structures for monolayers of either square or triangular lattice symmetry with evidence for morphological differences. The interplay between short-range exchange and long-range dipolar forces leads to quite different results for Ising spins and vector spins. For the Ising model, spin domains with parallel stripes, chevron patterns and labyrinths at different scales and with thermal disorder are deduced. For the vector model with a weak perpendicular anisotropy, the spins are planar and form a lattice of vortices of both signs. Such a structure remains stable even under a large perpendicular magnetic field, whereas a weak in-plane magnetic field is sufficient to obtain a uniform magnetic domain. For a sufficiently large perpendicular anisotropy, a mixed structure appears that includes spin vortex areas surrounding spin-up and spin-down areas.