Interest in metal-organic open-framework structures has increased enormously in the past few years because of the potential benefits of using crystal engineering techniques to yield nanoporous materials with predictable structures and interesting properties. Here we report a new efficient methodology for the preparation of metal-organic open-framework magnetic structures based on the use of a persistent organic free radical (PTMTC), functionalized with three carboxylic groups. Using this approach, we create an open-framework structure Cu3(PTMTC)2(py)6(CH3CH2OH)2(H2O), which we call MOROF-1, combining very large pores (2.8-3.1 nm) with bulk magnetic ordering. MOROF-1 shows a reversible and highly selective solvent-induced 'shrinking-breathing' process involving large volume changes (25-35%) that strongly influence the magnetic properties of the material. This magnetic sponge-like behaviour could be the first stage of a new route towards magnetic solvent sensors.

This critical review represents a concise revision of the different experimental approaches so far followed for the structuration of molecular nanomagnets on surfaces, since the first reports on the field more than ten years ago. Afterwards, a presentation of the different experimental approaches followed for their integration in sensors is described. Such work involves mainly two families of sensors and devices, microSQUIDs sensors and three-terminal devices for single-molecule detection. Finally the last section is devoted to a detailed revision of the different experimental techniques that can be used for the magnetic characterization of these systems on surfaces, ranging from magnetic circular dichroism to magnetic force microscopy. The use of these techniques to characterize other nanostructured magnetic materials, such as nanoparticles, is also revised. The aim is to give a broad overview of the last advances achieved with these techniques and their potential and evolution over the next years.

15] In order to form thin films for vitrification, it was necessary to load the grids with warm gelator solution that had not yet gelled. The solution was then allowed to cool slightly, beginning the gelation process, on the grid before blotting and plunging (see Experimental). In this way we were able to capture the initial aggregation before complete gelation made it impossible to form thin films. The use of glow-charged grids was found to facilitate the formation of uniformly thin, well-formed films.

Converse flexoelectricity is a mechanical stress induced by an electric polarization gradient. It can appear in any material, irrespective of symmetry, whenever there is an inhomogeneous electric field distribution. This situation invariably happens in piezoresponse force microscopy (PFM), which is a technique whereby a voltage is delivered to the tip of an atomic force microscope in order to stimulate and probe piezoelectricity at the nanoscale. While PFM is the premier technique for studying ferroelectricity and piezoelectricity at the nanoscale, here we show, theoretically and experimentally, that large effective piezoelectric coefficients can be measured in non-piezoelectric dielectrics due to converse flexoelectricity.

The high piezoelectricity found in PbZr 1− x Ti x O 3 (PZT) and related PbTiO 3 solid solutions materials originates in the existence of a monoclinic crystal structure and the formation of nanodomains at the morphotrophic phase boundary (MPB). [18][19][20] Ferroelastic nanodomain structures and low-symmetry monoclinic phases help accommodating the large elastic forces that develop at the MPB, providing elastic matching at the internal interfaces and inducing large piezoelectricity. In addition, the formation of ferroelastic nanodomains in thin fi lms gives rise to novel effects such as fl exoelectric polarization rotation in a/c domains, [ 1 ] enhanced piezoelectricity by the fl exoelectric effect in PZT nanostructures [ 21 ] or monoclinic areas of largely enhanced piezoresponse close to domain walls. [ 22 ] Thus, using epitaxial strain to induce different combinations of nanodomains with well-defi ned orientations and periodicities (domain engineering) opens a route to improved piezoelectrics, especially beneficial for the design of lead-free materials. [ 23,24 ] In classical lead-free ferroelectric BaTiO 3 single crystals, ferroelastic and ferroelectric 90° domains and nonferroelastic and ferroelectric 180° domains are observed at room temperature, [25][26][27][28][29] consistent with the tetragonal crystal structure of the bulk crystal. Predictions for epitaxially strained BaTiO 3 thin fi lms have resulted in different crystal symmetries and, thus, different domain structures. [30][31][32][33][34][35][36][37] Particularly interesting are the predictions for fi lms under low-strain values: even under zero nominal strain, the structure is modifi ed by the elastic constrains imposed by the substrate and the different thermal expansion of fi lm and substrate. Experimental realization of these phases is now becoming possible thanks to using substrates of the rare-earth scandate family. [ 38,39 ] In particular, using a Landau-Ginsburg-Devonshire-type nonlinear phenomenological theory, Koukhar et al. reported the BaTiO 3 phase diagram shown in Figure 1 . [ 30 ] This and other related works [ 32,40,41 ] have predicted a rich and fl at energy landscape with large variety of single-, multi-, and metastable domain phases. Next to these many phase transitions (around which the piezoelectric responses are expected to greatly increase), monoclinic aa*/ca* and ca 1 /ca 2 phases, not present in single crystals, have been predicted for low-strain values. In this paper we test those predictions experimentally. We have stabilized two different domain structures with long and well-ordered domains: a room temperature monoclinic ca 1 /ca 2 phase and either an a/c or an aa*/ca* phase above 50 °C.Epitaxial strain in ferroelectric fi lms offers the possibility to enhance the piezoelectric performance utilizing low crystal symmetries and high density of domain walls. Ferroelectric BaTiO 3 has been predicted to order in a variety of phases and domain confi gurations when grown under low strain on low mismatched substrates, but little ex...

Unveiling surface adsorbates under atmospheric conditions and in surface water redox reactions on TiO2 terminated surfaces and ferroelectric oxides, as studied by AP-XPS.

No abstract

We show that reducing the crystal size of ͓Mn 12 O 12 ͑O 2 C 6 H 5 ͒ 16 ͑H 2 O͒ 4 ͔ single-molecule magnets from 11.5 to 0.4 m strongly affects the molecular magnetic anisotropy and magnetic-relaxation rates. The effective activation energy for the spin reversal of the standard clusters decreases by 13% with decreasing size, whereas it remains approximately constant for the "fast relaxing" species. The pre-exponential factor 0 increases with decreasing crystal size for both. The observed decrease in the effective energy barrier for the slow relaxing species seems to be associated with the existence of a distribution of second-order transverse anisotropy terms, centered on E = 0, which broadens as the crystal size decreases. By contrast, the expected changes in the axial anisotropy parameter D with decreasing crystal size are too small to account for the change in U. The different effects that the reduction in crystal size has on the fast and slow relaxing species are discussed.