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In this work we report the structural and magnetic characterization of a new three-dimensional porous metal–organic framework (MOF) based on iron(iii) and the formate anion, [Fe(HCO2)3]n·nHCO2H (1), which was obtained by solvothermal synthesis. The tridimensional structure crystallizes in the trigonal space group R3̅c and is formed by highly regular octahedral Fe(OHCO)6 units. These units contain six equal Fe–O distances, with angles slightly different from 90° or 180°. The packing of 1 corresponds to a 3D covalent network defined by face sharing between the parallelepipeds, which are formed by the interactions of Fe(OHCO)6 units through formate ligands, thus generating a 41263 topology. This topology contains channels in the three spatial directions, in which it is possible to find guest molecules of formic acid. The thermogravimetric analysis shows that 1 remains stable till 180 °C; after this temperature the decomposition of 1 begins. From a magnetic point of view, the reported MOF presents an antiferromagnetic behaviour in the 296 to 20 K range. The fit of the experimental data between room temperature and 50 K, using the high temperature series model (HTS model), permits us to estimate a J value of −1.01 cm−1, which is in agreement with the reported values for analogous systems based on transition metal ions and formate ligands. Below this temperature, a weak ferromagnetism as a product of spin canting was observed due to the anti–anti coordination mode of the bridging ligand, which satisfies the requirement for Dzyaloshinsky–Moriya antisymmetric interactions between the FeIII ions. The isothermal magnetization obtained at 2 K shows that the magnetization increases linearly with the applied magnetic field, reaching a value of 0.49Nβ at the highest applied field of 50 kOe, indicating the antiferromagnetic character of the ground state. DFT calculations using a dinuclear fragment confirm the magnitude and nature of the magnetic phenomena of this extended system at high temperatures. [ABSTRACT FROM AUTHOR]

Herein, we describe the combination of polyoxometalates (POMs) with a polynuclear metallic cluster Mn4 {Mn4 = [Mn4(OAc)2(pdmH)6]2+, (pdmH = deprotonated pyridine-2,6-dimethanol; C7H8NO2)} for the construction of ionic crystals with layered architectures. Choosing a POM with the appropriate charge and size not only allows for the fine tuning of the stacking periodicity, but it also allows modifying the in-plane packing motif and density of the cationic metallic clusters. The isolation of differently layered hybrid crystals with the same Mn4 single-molecule-magnet (SMM) system allowed for the direct comparison of the magnetic properties of such materials. The variation of the slow relaxation properties of the SMM clusters may be attributed to the variability of the low-energy spin states, which are particularly sensitive to the specific counternanion used. [ABSTRACT FROM AUTHOR]

It is demonstrated how local oxidation nanolithography performed with an atomic force microscope (AFM-LON) may be successfully employed for the nanopatterning of insulating regions of Ta2O5 on TaS2 ultrathin metallic layers. This provides a simple approach for the fabrication of electronic devices, such as single-electron transistors, at the nanoscale. [ABSTRACT FROM AUTHOR]

Abstract: Layered Double Hydroxides (LDH) containing paramagnetic NiII and FeIII ions in the hydroxide layers and chromium or rhodium oxalate complexes at the interlayer space were prepared by ion exchange from a NiFe-LDH precursor with sebacate anions between the hydroxide layers. The precursor was synthesized by coprecipitation at controlled pH in order to avoid the formation of solid phases different from LDH. Magnetic studies demonstrated that both LDHs, NiFe–Cr(ox)3 and NiFe–Rh(ox)3, exhibited a behaviour similar to the precursor. Nevertheless, the substitution of intercalated sebacate anions with oxalate complexes compresses the LDH basal spacing, increasing the intensity of dipolar interactions between the ferrimagnetic sheets, which promoted a small increment in the critical temperatures. With respect to variations of the magnetic properties between the oxalate intercalated materials, neither critical temperature nor coercive fields showed any remarkable difference. These systems though, represent the initial step in the design of new magnetic hybrid materials. [Copyright &y& Elsevier]

Higher-order exchange interactions and quantum effects are widely known to play an important role in describing the properties of low-dimensional magnetic compounds. Here, the recently discovered 2D van der Waals (vdW) CrI 3 is identified as a quantum non-Heisenberg material with properties far beyond an Ising magnet as initially assumed. It is found that biquadratic exchange interactions are essential to quantitatively describe the magnetism of CrI 3 but quantum rescaling corrections are required to reproduce its thermal properties. The quantum nature of the heat bath represented by discrete electron-spin and phonon-spin scattering processes induces the formation of spin fluctuations in the low-temperature regime. These fluctuations induce the formation of metastable magnetic domains evolving into a single macroscopic magnetization or even a monodomain over surface areas of a few micrometers. Such domains display hybrid characteristics of Néel and Bloch types with a narrow domain wall width in the range of 3-5 nm. Similar behavior is expected for the majority of 2D vdW magnets where higher-order exchange interactions are appreciable., (© 2020 Wiley-VCH GmbH.)