Mössbauer study of the hyperfine interactions and spin dynamics in -iron(II) phthalocyanine

13 pages, 8 figures, 3 tables.-- PACS number(s): 75.50.Xx, 76.80.+y, 75.50.DdThe 57Fe Mössbauer spectroscopy on -iron(II) phthalocyanine (FePc) as a function of temperature (1.3<T<295 K) and applied field (0<B<10 T) has been used to study the peculiar magnetic properties of this ferromagnetic quasilinear chain type compound. One sextet with an internal hyperfine field Bint=66.2 T was observed at 1.3 K, a very large value for a bivalent iron with S=1 pointing to the existence of large positive orbital and dipolar contributions in the investigated FePc. Under an applied field, the experimental spectra exhibited two nonequivalent Fe positions, due to spin canting, with the values for the hyperfine fields of the split sextets increasing with increasing field, an indication that unlike most cases, Bint in -FePc is positive, i.e., parallel to the magnetic moment of iron. Therefore, the origin of the large hyperfine field is the orbital moment rather than the Fermi's contact interaction. This fact is ascribed to the orbital degeneracy of the ground state of Fe(II) in the present configuration, where an unpaired hole occupies the orbital doublet (dxz, dyz). This feature supports and explains the magnetization and susceptibility data as well as the anomalously high hyperfine field observed at 57Fe nucleus. The relaxational behavior in the ac susceptibility and Mössbauer spectra found in the region 5–20 K was ascribed to solitonlike motion of domain walls within the magnetic chains, with a single-kink activation energy of 72 K.This work has been supported by Project No. MAT05/ 1272 of the Spanish Ministry of Education and Science. M. D. Kuz’min acknowledges Grant No. SAB2000-0084. G. F. acknowledges the Royal Society Research Grant at the University of Liverpool and Grant No. SAB2003/0226 from Ministerio de Education, Cultura y Deporte of Spain. The final part of this work was facilitated and supported by EU Network of Excellence MAGMANet.Peer reviewe

Intracluster interactions in butterfly {Fe3 LnO2} molecules with the non-Kramers ions Tb(III) and Ho(III)

The intracluster exchange interactions within the >butterfly> [Fe3Ln(μ3-O)2(CCl3COO)8(H2O)(THF)3] molecules, where Ln(III) represents a lanthanide cation, have been determined by a combination of x-ray magnetic circular dichroism (XMCD) and vibrating sample magnetometry (VSM) along with an interaction model. We have studied the compounds with Ln=Tb and Ho, both non-Kramers lanthanides and with high uniaxial anisotropy, and Ln=Lu(III) and Y(III) as pseudolanthanides, which supply nonmagnetic Ln reference cases. At low temperature, the three Fe atoms can be considered as a self-unit with total spin SFe3=5/2. Using the element selectivity of the XMCD magnetometry, measured at the Ln L2,3 edges, together with the VSM measurements, the local magnetization of the Ln ion and the Fe3 subcluster, as a function of the field and low temperature (T≈2.5K), has been determined separately. These results are described quantitatively in the framework of a theoretical model based on an effective spin Hamiltonian, which considers the competing effects of intracluster interactions and the external applied magnetic field. The Ln-Fe3 exchange interaction within the {Fe3LnO2} cluster has been determined to be antiferromagnetic, in both Tb and Ho compounds, with JFeTb/kB=-0.13(1)K and JFeHo/kB=-0.18(1)K, respectively. In both cases, a field-induced reorientation of the Fe3 and Ln spins from antiparallel to parallel orientation takes place at a threshold field μ0H=1.1 and 2 T, for the {Fe3TbO2} and {Fe3HoO2} compounds, respectively. By comparison with other compounds of the series with uniaxial anisotropy, it is concluded that the polarizability of the Fe3 subcluster magnetic moment decreases in the trend {Fe3YO2}→{Fe3TbO2}→{Fe3HoO2}→{Fe3DyO2}, because of the increasing opposition of the exchange antiferromagnetic field caused by the Ln ion. In the Ln=Tb, Ho, and Dy, the magnetization of the whole molecule is dominated by the anisotropy of the Ln ion. The intracluster Fe3-Ln exchange interactions are very weak compared to the Ln ligand field and Fe-Fe exchange interactions.The projects MINECO (MAT2011/23791, MAT2011/27233-C02-02, and MAT2014/53921-R), DGA IMANA E34, and Alexander Von Humboldt Foundation (D.P.) are acknowledged for financial support.Peer Reviewe

The dynamical association between physical activity and affect in the daily life of individuals with ADHD

Exercise interventions in mental disorders have evidenced a mood-enhancing effect. However, the association between physical activity and affect in everyday life has not been investigated in adult individuals with ADHD, despite being important features of this disorder. As physical activity and affect are dynamic processes in nature, assessing those in everyday life with e- diaries and wearables, has become the gold standard. Thus, we used an mHealth approach to prospectively assess physical activity and affect processes in individuals with ADHD and con- trols aged 14–45 years. Participants wore accelerometers across a four-day period and reported their affect via e-diaries twelve times daily. We used multilevel models to identify the within- subject effects of physical activity on positive and negative affect. We split our sample into three groups: 1. individuals with ADHD who were predominantly inattentive ( n = 48), 2. in- dividuals with ADHD having a combined presentation (i.e., being inattentive and hyperactive; n = 95), and 3. controls ( n = 42). Our analyses revealed a significant cross-level interaction (F(2, 135.072) = 5.733, p = 0.004) of physical activity and group on positive affect. In details, all groups showed a positive association between physical activity and positive affect. Indi- viduals with a combined presentation significantly showed the steepest slope of physical ac- tivity on positive affect (slope_inattentive = 0.005, p < 0.001; slope_combined = 0.009, p < 0.001; slope_controls = 0.004, p = 0.008). Our analyses on negative affect revealed a negative associ- ation only in the individuals with a combined presentation (slope = -0.003; p = 0.001). Whether this specifically pronounced association in individuals being more hyperactive might be a mech- anism reinforcing hyperactivity needs to be empirically clarified in future studies.European Commission 667302ECNP Networ

Intracluster interactions in butterfly {Fe3 LnO2} molecules with the non-Kramers ions Tb(III) and Ho(III)

The intracluster exchange interactions within the "butterfly" Fe3Ln(µ3-O)2(CCl3COO)8(H2O)(THF)3] molecules, where Ln(III) represents a lanthanide cation, have been determined by a combination of x-ray magnetic circular dichroism (XMCD) and vibrating sample magnetometry (VSM) along with an interaction model. We have studied the compounds with Ln=Tb and Ho, both non-Kramers lanthanides and with high uniaxial anisotropy, and Ln=Lu(III) and Y(III) as pseudolanthanides, which supply nonmagnetic Ln reference cases. At low temperature, the three Fe atoms can be considered as a self-unit with total spin SFe3=5/2. Using the element selectivity of the XMCD magnetometry, measured at the Ln L2,3 edges, together with the VSM measurements, the local magnetization of the Ln ion and the Fe3 subcluster, as a function of the field and low temperature (T˜2.5K), has been determined separately. These results are described quantitatively in the framework of a theoretical model based on an effective spin Hamiltonian, which considers the competing effects of intracluster interactions and the external applied magnetic field. The Ln-Fe3 exchange interaction within the {Fe3LnO2} cluster has been determined to be antiferromagnetic, in both Tb and Ho compounds, with JFeTb/kB=-0.13(1)K and JFeHo/kB=-0.18(1)K, respectively. In both cases, a field-induced reorientation of the Fe3 and Ln spins from antiparallel to parallel orientation takes place at a threshold field µ0H=1.1 and 2 T, for the {Fe3TbO2} and {Fe3HoO2} compounds, respectively. By comparison with other compounds of the series with uniaxial anisotropy, it is concluded that the polarizability of the Fe3 subcluster magnetic moment decreases in the trend {Fe3YO2}¿{Fe3TbO2}¿{Fe3HoO2}¿{Fe3DyO2}, because of the increasing opposition of the exchange antiferromagnetic field caused by the Ln ion. In the Ln=Tb, Ho, and Dy, the magnetization of the whole molecule is dominated by the anisotropy of the Ln ion. The intracluster Fe3-Ln exchange interactions are very weak compared to the Ln ligand field and Fe-Fe exchange interactions

Circular economy in the european construction sector: a review of strategies for implementation in building renovation

Building renovation was declared a key point for sustainable development, however, the renovation rate of residential buildings in the European Union is insufficient to meet the climate and energy targets set. This paper analyses the main circular economy models used in the construction sector, as well as the situation of the building renovation market, to set a framework for circular economy models in building renovation. Of all the existing strategies in this sector, design, material recovery, building renovation and end-of-life actions would be the best, respectively. It also includes a market analysis consisting of a literature review covering PEST perspectives (political, economic, social and technical) and a SWOT analysis (strengths, weaknesses, opportunities and threats), concluding with a market gap analysis. The results of these analyses allow the development of a series of suggestions and strategies to be followed in order to solve the main barriers that hinder the implementation of the circular economy in the building´s renovation sector. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Two-dimensional approach to relativistic positioning systems

A relativistic positioning system is a physical realization of a coordinate system consisting in four clocks in arbitrary motion broadcasting their proper times. The basic elements of the relativistic positioning systems are presented in the two-dimensional case. This simplified approach allows to explain and to analyze the properties and interest of these new systems. The positioning system defined by geodesic emitters in flat metric is developed in detail. The information that the data generated by a relativistic positioning system give on the space-time metric interval is analyzed, and the interest of these results in gravimetry is pointed out.Comment: 11 pages, 5 figures. v2: a brief description of the principal bibliography has been adde

Spin glass behavior in an interacting gamma-Fe2O3 nanoparticle system

In this paper we investigate the superspin glass behavior of a concentrated assembly of interacting maghemite nanoparticles and compare it to that of canonical atomic spin glass systems. ac versus temperature and frequency measurements show evidence of a superspin glass transition taking place at low temperature. In order to fully characterize the superspin glass phase, the aging behavior of both the thermo-remanent magnetization (TRM) and ac susceptibility has been investigated. It is shown that the scaling laws obeyed by superspin glasses and atomic spin glasses are essentially the same, after subtraction of a superparamagnetic contribution from the superspin glass response functions. Finally, we discuss a possible origin of this superparamagnetic contribution in terms of dilute spin glass models

Antiferromagnetic single-chain magnet slow relaxation in the {Tb(α-fur)3}n polymer with non-Kramers ions

We report the synthesis, crystal structure and magnetic properties of a new molecular complex based on a Tb(iii) ion supported by 2-furancarboxylic molecules: {Tb(α-fur)(HO)} (α-fur = CHOCOO). Two slightly different Tb sites (A and B) exist depending on the position of one of the dangling ligands. Ab initio calculations predict that, for both sites, the magnetic ground state is highly anisotropic (g∗ = 17.8) and consists of a quasi-doublet with a small gap, well isolated from the next excited state. The α-fur ligand forms 1D polymeric chains of Tb ions of the same type (either A or B) running along the c-axis. The crystal structure is formed by the supramolecular stacking along the a-axis of 2D layers containing parallel chains of the same type. Static magnetization and heat capacity measurements show that, magnetically, the system can be modeled as an ensemble of Ising chains of non-Kramers Tb ions with effective spin S∗ = 1/2, antiferromagnetically (AF) coupled by a weak intrachain interaction (J∗/k = -0.135 K). At very low temperatures, the static susceptibility reflects the presence of a 2-4% concentration of defects in the chains. Ac susceptibility measurements at H = 0 performed down to mK temperatures have enabled us to observe the slow relaxation of magnetization through two different pathways. They are assigned to Single-Chain-Magnet (SCM) behavior in two different types of AF chains (A and B), triggered by the existence of defects breaking the chains into segments with short-range order. At temperatures below 0.1 K this mechanism is replaced by individual relaxation of the ions through direct processes. Under the application of a magnetic field the system slowly relaxes by two distinct direct processes, strongly affected by a phonon bottleneck effect.This work has been financed by MECOM Projects MAT11/23791 and MAT11/27233-C02-02, MAT2015-68204-R, MAT2014-53921-R, DGA IMANA E34 and MOLCHIP E98 Projects. Consolider Nanoselect (CSD2007-00041) and by a grant of the Ministry of National Education, CNCS – UEFISCDI, project number PN-II-ID-PCE-2012-4-0261. D. P. thanks the Alexander von Humboldt (AvH) Foundation for financial support.Peer Reviewe

Heteronuclear {TbxEu1-x} furoate 1D polymers presenting luminescent properties and SMM behavior

We report the synthesis, crystal structure and photo-magnetic properties of novel Tb/Eu polymeric complexes of general formula {TbxEu1-x(a-fur)3(H2O)3}n, supported by 2-furancarboxilic acid: the homonuclear Tb(iii) complex {Tb} (1), four heterodinuclear complexes, {Tb0.8Eu0.2} (2), {Tb0.7Eu0.3} (3), {Tb0.3Eu0.7} (4), and {Tb0.1Eu0.9} (5), and the homonuclear Eu(iii)-only complex {Eu} (6). X-ray diffraction experiments show that the a-furoate ligands, acting in bridging mode, consolidate the 1D polymeric chains along the c-axis. Luminescence studies show the sensitization capability of the furoic acid ligand. Color tuning from green to red can be successfully achieved through the heterodinuclear strategy. We have measured Eu emission by direct excitation at the resonant 7F0 ¿ 5L6 (395 nm), and indirectly, by excitation of the non-resonant wavelength (280 nm) which provokes ligand ¿ Tb ¿ Eu energy transfer. Besides, ac susceptibility measurements under varying frequencies and temperatures reveal that mixed {TbxEu1-x} complexes exhibit field-induced slow relaxation dynamics, with extremely slow relaxation times, owing to direct processes affected by the bottleneck effect. Thus, the {TbxEu1-x} complexes represent interesting low-dimensional multifunctional materials combining both luminescent and SMM magnetic properties