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Póster presentado a la XXXVII Reunión Bienal de la Real Sociedad Española de Física celebrada en Zaragoza del 15 al 19 de julio de 2019., The self-assembly of magnetic molecules on supporting surfaces provides potentially very interesting magnetic nano-devices in the fields of high-density information storage, information processing and spintronics. We have previously evaporated wheel molecules of formula {Cr10(OMe)20(O2CCMe3)10}, ({Cr10} from now-on) by direct sublimation in UHV on a Ag(110) single-crystal. In powder form, these molecules show ferromagnetic interactions, therefore, they are good candidates as magnetic molecules in a 2D array. In this work, the molecules are deposited onto the Au(111) surface. The STM image in Fig. 1 shows a monolayer of {Cr10} molecules, self-organized in a quasi-hexagonal 2D network. We have studied three samples: a monolayer (1ML) and a multilayer (14 ML) of {Cr10} on Au(111) as well as the {Cr10} molecular material in bulk, powder form. XMCD measurements were performed at the L2,3 edges of Cr at T=2 K and magnetic field up to B=6T. Magnetization and susceptibility were measured by SQUID magnetometry on the multilayer and the powder sample up to B=14 T. We have measured magnetization of the three samples. Both M(H) and X(T) for the powder sample resemble the curves reported earlier, where the {Cr10} wheels were described in terms of a total molecule spin S=9 ground state, with overall ferromagnetic coupling (XT>0). The overall ferromagnetic coupling is lost by depositing the molecules onto the Au(111) surface on the 14 ML sample (XT< 0). Monte Carlo simulations considering the Cr(III) as Heisenberg S=3/2 spin entities describing the M(H) curves yield quantitative results consistent with this behavior: the evaporation of the molecules into 2D regular arrays on Au(111) weakens the Cr-Cr intramolecular exchange pathways, although maintaining the ground state S=9 found for the randomly oriented powder. The M(H) XMCD determination of the {Cr10} 1ML is coincident with that of the 14 ML, within experimental error.

Resumen del trabajo presentado a la XXXVII Reunión Bienal de la Real Sociedad Española de Física celebrada en Zaragoza, del 15 al 21 de julio de 2019.

Resumen del póster presentado a la XXXVII Reunión Bienal de la Real Sociedad Española de Física celebrada en Zaragoza del 15 al 19 de julio de 2019., Single molecule magnet (SMM) behaviour can be observed in molecules with clusters formed by transition metals M and rare earths. While M provides most of the cluster magnetization, Ln metals generate an enhanced magnetic anisotropy via the intracluster M-Ln interactions. The possible interactions between the transition metals. can be explored using yttrium as a non-magnetic substitution for Ln in isostructural compounds. The "butterfly" molecule Fe3Y(μ3-O)2(CCl3COO)8(H2 O)(THF)3 ({Fe3YO2}) includes 3 close Fe3+ ions which build an Fe3 cluster with a strong intracluster antiferromagnetic exchange J = -50 K and a total spin S=5/2. We present heat capacity and DC susceptibility measurements below 2 K, which show the cluster anisotropy and inter-cluster interactions. No phase transition to a long-range magnetically ordered phase is observed down to 20 mK. The intercluster interaction is analysed in the framework of the one-dimensional Blume-Capel model with an antiferromagnetic chain exchange constant J \' = -40 mK, and a uniaxial anisotropy with parameter D = -0.56 K. The chains are formed by Fe3 clusters along the shortest intercluster distances in {Fe3YO2} and the anisotropy axes lie on the Fe3 cluster’s plane (fig. 1). AC susceptibility measurements reveal magnetic relaxation below 5 K with quantum tunnelling of the magnetization below 0.2 K, and a thermally activated process for higher temperature (fig. 2).

Resumen del póster presentado a la 7th European Conference on Molecular Magnetism (ECMM), celebrada en Florencia (Italia) del 15 al 18 de septiembre de 2019., Lanthanide based single-ion magnets (SIMs) have received increasing attention in the field of molecular magnetism because of their large magnetic moment and strong anisotropy. Research has been strongly focused in heavy Ln(III) ions, mainly Dy3+ and Tb3+, whereas the number of works dedicated to SIMs based on light lanthanide ions remains low. However, light Ln(III) ions such as Nd3+ are less critical and cheaper than heavy Ln(III) ions based on European Union and U.S. DOE assessments. Here we present the study of two novel Neodymium based molecular magnets of formula {[Nd(α-fur)3(H2O)2]·DMF}n (1) and {[Nd0.065La0.935(α-fur)3(H2O)3]}n (2), α-fur=C4H3OCOO. In (1) the furoate ligands, in bidentate bridging mode, consolidate zig-zag chains running along the a-direction. Compound (2) is a magnetically diluted complex of a bidentate polymeric chain along the b-axis. Ab initio calculations yielded the gyromagnetic factors gx*=0.52, gy*=1.03, gz*=4.41 for (1) and gx*=1.35, gy*=1.98, gz*=3.88 for (2), and predicted energy gaps of Δ/kB=125.5 K (1) and Δ/kB=58.8 K (2), showing that Nd(III) holds significant anisotropy in both compounds. Heat capacity, dc magnetization and ac susceptibility measurements agree with these predictions. Absence of slow relaxation at H=0 is attributed to the sizable transverse anisotropy component. It can also be attributed to either dipolar or exchange interactions, which would enhance quantum tunnelling probability. Under small external applied field of 80 Oe, two slow relaxation processes appear. A relaxation mechanism above 3 K is associated to a combination of Orbach process, with activation energy U/kB=121 K at 1.2 kOe for 1, Raman and direct processes. For complex 2 a smaller U/kB=61 K at 1.2 kOe is found, and the low-frequency process is quenched. The absence of Nd-Nd interaction in the magnetically diluted compound 2 reduces the direct process contribution to the relaxation time, resulting in longer times at low temperatures. The two new furoate-based complexes enlarge the still scarce family of Nd(III) based compounds. The energy barrier of compound 1 is the highest ever reported for a Nd complex.

Resumen del trabajo presentado a la 64th Annual Conference on Magnetism and Magnetic Materials (MMM), celebrada en Las Vegas (USA) del 4 al 8 de noviembre de 2019.

Trabajo presentado a la 7th European Conference on Molecular Magnetism (ECMM), celebrada en Florencia (Italia) del 15 al 18 de septiembre de 2019.

Resumen del trabajo presentado al 9th Joint European Magnetic Symposia (JEMS), celebrado en Mainz (Alemania) del 3 al 7 de septiembre de 2018., Clusters in molecules with transition metals M and rare earths Ln can show single molecule magnet (SMM) behaviour. While M provides most of the cluster magnetization, Ln metals generate an enhanced magnetic anisotropy via the intracluster M-Ln interactions. The use of Y as a non-magnetic substitution for Ln in isostructural compounds provides a way to explore possible interactions between the transition metals. The >butterfly> molecule Fe3Y(μ3−O)2(CCl3COO)8(H2O)(THF)3 (in brief {Fe3YO2}) includes three close Fe3+ ions which build a robust Fe3 cluster with a strong intracluster antiferromagnetic exchange J = −50 K and a total spin S=5/2. We present heat capacity and DC susceptibility measurements below 2 K, which show the cluster anisotropy and intercluster interactions. However, no phase transition to a long-range magnetically ordered phase is observed down to 20 mK. The intercluster interaction is analysed in the framework of the one-dimensional Blume-Capel model with an antiferromagnetic chain exchange constant J '≈ −0.04 K, and a uniaxial anisotropy with parameter D ≈ −0.56 K. This is proposed to be associated to chains of Fe3 clusters oriented along the shortest intercluster distances displayed by the crystal structure of {Fe3YO2}. AC susceptibility measurements reveal magnetic relaxation below 5 K with quantum tunnelling of the magnetization below 0.2 K, and a thermally activated process for higher temperature.

The 4′-alkoxy-tetrafluorophenyl dithiadiazolyls, ROC6F4CNSSN [R = Me (1), Et (2), nPr (3), nBu(4)] all adopt cis-oid dimers in the solid state. The methoxy derivative 1 adopts a π-stacked AA’AA’ motif, whereas propoxy (3) and butoxy (4) derivatives exhibit an AA’BB’ stacking. The ethoxy derivative (2) is polymorphic. The α-phase (2α) adopts an AA’BB’ motif comparable with 3 and 4, whereas 2β and 2γ are reminiscent of 1 but combine a mixture of both monomers and dimers in the solid state. The structure of 2β exhibits Z’ = 6 with two dimers and two monomers in the asymmetric unit but undergoes a thermally induced phase transition upon cooling below −25 °C to form 2γ (Z’ = 14) with six dimers and two monomers in the asymmetric unit. The transition is associated with both rotation and translation of the dithiadiazolyl ring. Detailed differential scanning calorimetry and variable temperature powder X-ray diffraction studies coupled with SQUID magnetometry have been used to show that 2α converts irreversibly to 2β upon heating and that 2β and 2γ interconvert through a reversible phase transition with a small thermal hysteresis in its magnetic response., We would like to thank the Canada Research Chairs Program for financial support (J.M.R.), the University of Windsor for a scholarship (Y.B.) and C.F.I./O.R.F. support for infrastructure. We thank the Inorganic Chemistry Exchange (I.C.E.) Program for the opportunity for R.S. to visit U. Windsor. We also acknowledge support from the Ministerio de Economia y Competividad of Spain (Grant No. MAT2015-68200-C2-2-P). Additional support from Diputacion General de Aragon (DGA-M4) is also acknowledged. (J.C. and A.A.)

Trabajo presentado al X Meeting de GEFES (División de Física de la Materia Condensada de la Real Sociedad Española de Física), celebrado en Valencia del 24 al 26 de enero de 2018, We report on the magnetic properties of {Cr10} wheels (Cr10(OMe)20(O2CCMe)10) UHVsublimated on Cu(111) and Au(111) single-crystals investigated by means of by XAS & XMCD, SQUID magnetometry and STM. We discuss the magnetic anisotropy and magnetic moment field-dependence of the grafted {Cr10} molecules, as a function of the metallic substrate and layer thickness, and compare it with bulk material. Our results demonstrate that evaporated molecules show negligible anisotropy and weak dependence with the substrate. A combination of XMCD and SQUID magnetometry show that Mono- and Multilayer {Cr10} samples exhibit a magnetic behavior stemming from a S = 9 ground state, ruling out some previous results. Montecarlo simulations show that the magnetic evolution can be explained by {Cr10} molecules magneticaly consisting of two semi-crowns containing 4 Cr ions interacting ferromagnetically, separated by 2 Cr ions with antiferromagnetic interactions, giving rise to the ground S = 9 state, in agreement with previous EPR data in literature. Evaporation of {Cr10} onto a substrate producing subtle structural changes induce strong changes in the Cr-Cr interactions and distinct magnetic behavior from the bulk.

Five-coordinate oxo-derivatives [NBu 4 ][MO(C 6 F 5 ) 4 ] (1) have been prepared for the heavier Group 6 elements: 1-Mo and 1-W. The magnetic properties of that salts have been studied by a combination of Electron paramagnetic resonance (EPR), calorimetric and magnetochemical techniques, pointing out the existence of weak ferromagnetic interactions. These have been correlated with the arrangement of the magnetic units in the crystal.

Correction for 'Magnetic properties of the seven-coordinated nanoporous framework material Co(bpy)1.5(NO3)2 (bpy = 4,4'-bipyridine)' by Elena Bartolomé et al., Dalton Trans., 2012, 41, 10382-10389.