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.
Strain-mediated photomagnetic effects in heterostructured nanoparticles of Prussian blue analogues
The photomagnetic properties of cubic heterostructured nanoparticles of Prussian blue analogues (PBAs) are reported for various morphologies (with length scales of 100 nm < l < 1 µm) studied over a wide range of temperature (2 K < T < 300 K) and magnetic field (µ0H < 10 T). These results focus on heterostructures of a pressure-sensitive NiCr-PBA (A) and a photomagnetic CoFe-PBA (B) to illuminate the strain effects that are induced in the nonphotoactive A component up to its ferromagnetic ordering temperature (Tc ~ 70 K). A charge-transfer induced spin-transition(CTIST) generates a lattice contraction in B during slow-cooling, and after irradiation with white light, the resulting stress is released by the photoinduced expansion of the B component at low temperatures (T < 150 K). The core of this work addresses the mechanism and extent of the strain in the A component of the heterostructures. With this goal, a series of BA core@shell nanoparticles with the same B cores and varying A shell thicknesses was investigated.In addition, the series of cubic nanoparticles allows a straightforward calculation of the high-field magnetization in the A shell. Thus, by employing the conjectured mechanisms of the decreased magnetism, the depth of the induced strain is extracted from the high-field data, revealing a strain depth of nominally 20 nm, which is a recurrent length  scale appearing for the PBAs. To accompany the high-field analysis, the seemingly simple step of numerically differentiating the low-field susceptibility data provides further elucidation of the strain effects. Specifically, these derivatives expose a sharpening of the A ordering temperature in the light state of the core@shell nanoparticles, an effect which is found to be ubiquitous for all of the A-containing heterostructures. This finding asserts the understanding that the photoinduced expansion of the B core relieves the stress that is applied to the A shell in the dark state. These core@shell studies were initially guided by prior core@shell@shell findings, which reveal that, while a free surface of A is not needed, a stress-sensitivity must be established by growing the A material on an underlying phase possessing even a subtly disparate framework. Finally, studies which sought to achieve photoeffects at more practical temperatures incorporated a CrCr-PBA (C) with a high-Tc (220 K) in novel BC, CB, andCAB heterostructures. To complement the bulk magnetism results, electron magnetic resonance (EMR) studies reveal that demagnetizing effects from domains, which have previously been observed in A films, play a central role in the photoinduced strain in the A shells of theBA particles. Moreover, while the EMR results confirm overall decreases in the high-field magnetism of the A component of the heterostructures, this investigation also unveils a history dependence of the photoeffect, where the system must be cycled through the ordering temperature of the B core to allow the A domains to fully relax. In addition to the studies of the heterostructured PBAs, the…
Solitary Orbital Paget Disease: A Case Report
Purpose: To describe the clinical findings in a patient who had developed painless supraorbital prominence. Methods: Clinical and histopathological findings of the case are reviewed and presented. Results: The patient had an isolated histologically confirmed Paget disease of the orbit. Local excision of the lesion was performed. Conclusion: Paget disease can present not only as a diffuse process but also as a painless, solitary lesion of the orbit.