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.
Design of Bistable Gold@Spin‐Crossover Core–Shell Nanoparticles Showing Large Electrical Responses for the Spin Switching
A simple chemical protocol to prepare core–shell gold@spin‐crossover (Au@SCO) nanoparticles (NPs) based on the 1D spin‐crossover [Fe(Htrz)2(trz)](BF4) coordination polymer is reported. The synthesis relies on a two‐step approach consisting of a partial surface ligand substitution of the citrate‐stabilized Au NPs followed by the controlled growth of a very thin layer of the SCO polymer. As a result, colloidally stable core@shell spherical NPs with a Au core of ca. 12 nm and a thin SCO shell 4 nm thick, are obtained, exhibiting a narrow distribution in sizes. Differential scanning calorimetry proves that a cooperative spin transition in the range 340–360 K is maintained in these Au@SCO NPs, in full agreement with the values reported for pristine 4 nm SCO NPs. Temperature‐dependent charge‐transport measurements of an electrical device based on assemblies of these Au@SCO NPs also support this spin transition. Thus, a large change in conductance upon spin state switching, as compared with other memory devices based on the pristine SCO NPs, is detected. This results in a large improvement in the sensitivity of the device to the spin transition, with values for the ON/OFF ratio which are an order of magnitude better than the best ones obtained in previous SCO devices.
Direct observation of nonlinear four-magnon scattering in spin-wave microconduits
H. Schultheiss,1,2 K. Vogt,2,3 and B. Hillebrands2 1Materials Science Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois 60439, USA 2Fachbereich Physik and Forschungszentrum OPTIMAS, Technische Universitat Kaiserslautern, D-67663 Kaiserslautern, Germany 3Graduate School of Excellence Materials Science in Mainz, Gottlieb-Daimler-Strasse 47, D-67663 Kaiserslautern, Germany (Received 7 June 2012; revised manuscript received 27 July 2012; published 10 August 2012)