We performed zero and transverse field µSR experiments on a large number of YBa2Cu3O6+x samples. We detect coexistence of antiferro-type (AF) short range magnetism with superconductivity below T f 10 K in compositions 0.37 x 0.39. Most muons experience local AF fields, even when SQUID detects a full superconducting volume fraction, which points to a local minimal interference organization of short AF stripes embedded in the superconductor. A detailed phase diagram is produced and the consequences of the minimal interference are discussed. Neutron scattering also detects magnetic correlations, notably [10] in YBa 2 Cu 3 O 6.35 , exclusively dynamic in nature, although their static counterpart could be elusive due to a very short correlation length. The doubled magnetic unit cell indicates an antiferromagnetic (AF) structure, with a suggested stripe-like character.In all the samples explored so far by µSR [5,6,7,8,9] it has been hinted that the cluster spin glass nature of magnetism (low spin freezing temperature, T f , large distributions of B i and absence of long range order as from neutron diffraction [11,12]) might be favored by the disorder inherent in cation substituted perovskites, which directly influences the CuO 2 layers. Conversely in YBa 2 Cu 3 O 6+x (123, hereafter) the source of disorder, namely the basal CuO x layers, are farther removed from the CuO 2 layers, but systematic µSR data were lacking, prior to the present work. Our aim is to clarify whether the appearance of coexisting superconducting and magnetic properties is indeed intrinsic to the unperturbed underdoped CuO 2 layers and whether the two properties cooperate or interfere.We performed µSR measurements on twenty-four polycrystalline 123 samples (Y 1−24 ) prepared by the topotactic technique, which consists of oxygen equilibration of stoichiometric quantities of the two end member specimens, tightly packed in sealed vessels [13]. Low temperature annealing yields high quality homogeneous samples with an absolute error of δx=±0.02 in oxygen content per formula unit and a much smaller relative error between samples of the same batch. The width of the interval were the resistance drops from 90% to 10% of the onset value is 0.5 K at optimal doping and 6-7K at x 0.4 (vs. e.g. 10K in Ref.10). The hole content h was determined from the resistive T c for the superconducting samples [14], and from the Seebeck coefficient S at 290 K for the non-superconducting ones, using the exponential dependence [14] of S on h, with fit parameters determined from our series of samples [15]. Samples Y 1−8 , with oxygen content 0.20≤x≤0.32 and hole content per planar Cu atom 0.033≤h≤0.055, never superconduct, and their AF properties were reported previously [16]. Samples Y 9−24 , with 0.32≤x≤0.42 and 0.055≤h≤0.08, are superconductors and are the subject of the present work.The µSR experiment were performed on the MUSR spectrometer of the ISIS pulsed muon facility, where the external magnetic field H may be applied either parallel to the initial muon spin S µ , in...

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An Fe2O3−SiO2 composite was prepared by a gelation method that adopts tetraethoxysilane and iron(III) nitrate as starting materials. The dried gel was treated at increasing temperatures, and the samples were characterized by XRD, TEM, magnetic susceptibility measurements, and EPR and Mössbauer spectroscopies. Nanometer size (3−4 nm) X-ray-amorphous iron(III) oxide particles are observed in the samples treated at low temperature. These particles display superparamagnetic behavior in the Mössbauer spectra and susceptibility measurements, and their magnetic moments indicate antiferromagnetic clustering. The occurrence of two sites for iron ions, one in the bulk and one on the surface of nanoparticles, is suggested by EPR and Mössbauer spectroscopies. Heating of the samples to higher temperatures (T > 700 °C) gives rise to a small increase of the particle size. Simultaneously XRD and TEM exhibit the formation of γ-Fe2O3 crystalline particles, Mössbauer spectra reveal a large change in the magnetization, magnetic measurements show the transition from antiferro- to ferrimagnetic behavior, and the signals of ferrimagnetic resonance appear in the EPR spectra. Superparamagnetic relaxation in these particles was investigated by ac susceptibility measurements and paramagnetic resonance experiments at variable temperatures. Further increase in temperature gives rise to the formation of α-Fe2O3. Atomic reorganization processes taking place during these transitions are discussed.

This paper focuses on the magnetic properties of CoFe 2 O 4 nanoparticles, discussing the influence of nanoparticles arrangements obtained by different synthesis methods. Using high thermal decomposition (HTD) and direct micellar (DM) routes, three samples of CoFe 2 O 4 nanoparticles with equal primary particle size (∼5 nm) were prepared. The HTD method allows one to obtain highly crystalline primary nanoparticles coated by oleic acid organized in a self-assembling arrangement (ACoFe HTD ). The DM method results to be appropriate to prepare either irregular arrangements (IACoFe DM ) or spherical iso-oriented nanoporous assemblies (SACoFe DM ) of primary CoFe 2 O 4 nanocrystals. Despite the same particle size, magnetization measurements of the HTD sample show a tendency toward cubic anisotropy (M r / M s ≈ 0.7), while in DM samples, a uniaxial anisotropy (M r /M s ≈ 0.4) is observed. The comparison between IACoFe DM and SACoFe DM samples indicates that the ordering of nanocrystals at the mesoscopic scale induces an increase of the coercive field (μ 0 H c ≈ 1.17 T → μ 0 H c ≈ 1.45 T) and of the reduced remanent magnetization (M r /M s ≈ 0.4 → M r /M s ≈ 0.5). The reason for these differences is discussed. In particular, a detailed study on interparticle interactions is carried out, highlighting the influence of the molecular coating and the formation of spherical iso-oriented assemblies.

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Here we report on new tris(haloanilato)metallate(III) complexes with general formula [A]3[M(X2An)3] (A = (n-Bu)4N(+), (Ph)4P(+); M = Cr(III), Fe(III); X2An = 3,6-dihalo derivatives of 2,5-dihydroxybenzoquinone (H4C6O4), chloranilate (Cl2An(2-)), bromanilate (Br2An(2-)) and iodanilate (I2An(2-))), obtained by a general synthetic strategy, and their full characterization. The crystal structures of these Fe(III) and Cr(III) haloanilate complexes consist of anions formed by homoleptic complexes formulated as [M(X2An)3](3-) and (Et)3NH(+), (n-Bu)4N(+), or (Ph4)P(+) cations. All complexes exhibit octahedral coordination geometry with metal ions surrounded by six oxygen atoms from three chelate ligands. These complexes are chiral according to the metal coordination of three bidentate ligands, and both Λ and Δ enantiomers are present in their crystal lattice. The packing of [(n-Bu)4N]3[Cr(I2An)3] (5a) shows that the complexes form supramolecular dimers that are held together by two symmetry related I···O interactions (3.092(8) Å), considerably shorter than the sum of iodine and oxygen van der Waals radii (3.50 Å). The I···O interaction can be regarded as a halogen bond (XB), where the iodine behaves as the XB donor and the oxygen atom as the XB acceptor. This is in agreement with the properties of the electrostatic potential for [Cr(I2An)3](3-) that predicts a negative charge accumulation on the peripheral oxygen atoms and a positive charge accumulation on the iodine. The magnetic behaviour of all complexes, except 5a, may be explained by considering a set of paramagnetic non-interacting Fe(III) or Cr(III) ions, taking into account the zero-field splitting effect. The presence of strong XB interactions in 5a are able, instead, to promote antiferromagnetic interactions among paramagnetic centers at low temperature, as shown by the fit with the Curie-Weiss law, in agreement with the formation of halogen-bonded supramolecular dimers.

Abstract:The aim of the present work is to highlight the unique role of anilato-ligands, derivatives of the 2,5-dioxy-1,4-benzoquinone framework containing various substituents at the 3 and 6 positions (X = H, Cl, Br, I, CN, etc.), in engineering a great variety of new materials showing peculiar magnetic and/or conducting properties. Homoleptic anilato-based molecular building blocks and related materials will be discussed. Selected examples of such materials, spanning from graphene-related layered magnetic materials to intercalated supramolecular arrays, ferromagnetic 3D monometallic lanthanoid assemblies, multifunctional materials with coexistence of magnetic/conducting properties and/or chirality and multifunctional metal-organic frameworks (MOFs) will be discussed herein. The influence of (i) the electronic nature of the X substituents and (ii) intermolecular interactions i.e., H-Bonding, Halogen-Bonding, π-π stacking and dipolar interactions, on the physical properties of the resulting material will be also highlighted. A combined structural/physical properties analysis will be reported to provide an effective tool for designing novel anilate-based supramolecular architectures showing improved and/or novel physical properties. The role of the molecular approach in this context is pointed out as well, since it enables the chemical design of the molecular building blocks being suitable for self-assembly to form supramolecular structures with the desired interactions and physical properties.Keywords: benzoquinone derivatives; molecular magnetism; multifunctional molecular materials; spin-crossover materials; metal-organic frameworks General IntroductionThe aim of the present work is to highlight the key role of anilates in engineering new materials with new or improved magnetic and/or conducting properties and new technological applications. Only homoleptic anilato-based molecular building blocks and related materials will be discussed. Selected examples of para-/ferri-/ferro-magnetic, spin-crossover and conducting/magnetic multifunctional materials and MOFs based on transition metal complexes of anilato-derivatives, on varying the substituents at the 3,6 positions of the anilato moiety, will be discussed herein, whose structural features or physical properties are peculiar and/or unusual with respect to analogous compounds reported in the literature up to now. Their most appealing technological applications will be also reported.

Abstract-This paper presents an agent-based artificial cryptocurrency market in which heterogeneous agents buy or sell cryptocurrencies, in particular Bitcoins. In this market, there are two typologies of agents, Random Traders and Chartists, which interact with each other by trading Bitcoins. Each agent is initially endowed with a finite amount of crypto and/or fiat cash and issues buy and sell orders, according to her strategy and resources. The number of Bitcoins increases over time with a rate proportional to the real one, even if the mining process is not explicitly modelled.The model proposed is able to reproduce some of the real statistical properties of the price absolute returns observed in the Bitcoin real market. In particular, it is able to reproduce the autocorrelation of the absolute returns, and their cumulative distribution function. The simulator has been implemented using object-oriented technology, and could be considered a valid starting point to study and analyse the cryptocurrency market and its future evolutions.