Híbridos orgánico-inorgánicos con propiedades dieléctricas, magnéticas y multiferroicas, y precursores de óxidos nanoestructurados

[Resumen] Los materiales con orden magnético, dieléctrico, elástico, y aquellos que combinan al menos dos de estas propiedades (multiferroicos), son fundamentales en el desarrollo de nuevas tecnologías. Tradicionalmente estas propiedades se han estudiado en óxidos metálicos con muy buenos resultados, sin embargo, la aparición de nuevos materiales híbridos, que combinan componentes orgánicos e inorgánicos en una misma estructura, ha abierto un nuevo campo de posibilidades. En esta tesis se han preparado y caracterizado híbridos porosos [M2(NH2- bdc)2(dabco)][G], y densos con estructura perovskita: [CH3NH3]M(HCOO)3, [NH4]Cd(HCOO)3 y [(CH3)4N]Mn(N3)3. Los híbridos porosos [M2(NH2-bdc)2(dabco)][G] presentan dos anomalías dieléctricas debidas a la rotación del ligando NH2-bdc y al movimiento de las moléculas de disolvente ocluidas. Estos híbridos se emplearon como precursores de los óxidos ZnO y Co3O4 nanoestructurados. Los fomiatos [CH3NH3]M(HCOO)3 con M= Mn+2, Co+2, Ni+2 y Cu+2 presentan ferromagnetismo débil a baja temperatura. Además, [NH3CH3]Co(HCOO)3 es uno de los pocos materiales híbridos con acoplamiento magnetoeléctrico. El compuesto [NH4]Cd(HCOO)3 presenta polarización eléctrica neta en condiciones ambientales y ésta se puede incrementar al aplicar altas presiones. El híbrido [(CH3)4N]Mn(N3)3 presenta una transición estructural antiferroeléctrica y ferroelástica a 310 K junto con biestabilidad magnética, siendo uno de los pocos materiales que muestra simultáneamente orden magnético, dieléctrico y elástico.[Resumo] Os materiais con orde magnética, dieléctrica, elástica e aqueles que combinen polo menos dúas destas propiedades (multiferroicos), son fundamentais no desenrolo de novas tecnoloxías. Tradicionalmente estas propiedades téñense estudado nos óxidos metálicos con moi bos resultados, sen embargo, a aparición de novos materiais híbridos, que combinan compoñentes orgánicos e inorgánicos nunha mesma estrutura, abriu un novo campo de posibilidades. Nesta tese preparáronse e caracterizáronse híbridos porosos [M2(NH2- bdc)2(dabco)][G], e densos con estrutura perovskita: [CH3NH3]M(HCOO)3, [NH4]Cd(HCOO)3 e [(CH3)4N]Mn(N3)3. Os híbridos porosos [M2(NH2-bdc)2(dabco)][G] presentan dúas anomalías dieléctricas debidas á rotación do ligando NH2-bdc e ao movemento das moléculas de disolvente ocluídas. Estes híbridos empregáronse coma precursores dos óxidos ZnO y Co3O4 nanoestruturados. Os formiatos [CH3NH3]M(HCOO)3 con M= Mn+2, Co+2, Ni+2 e Cu+2 presentan ferromagnetismo débil a baixa temperatura. Ademais, [NH3CH3]Co(HCOO)3 é un dos poucos materiais híbridos con acoplamento magnetoeléctrico. O composto [NH4]Cd(HCOO)3 presenta polarización eléctrica neta en condicións ambientais que se pode incrementar ao aplicar altas presións. O híbrido [(CH3)4N]Mn(N3)3 presenta unha transición estrutural antiferroeléctrica e ferroelástica a 310 K xunto con biestabilidade magnética, sendo un dos poucos materiais que mostra simultaneamente orde magnético, dieléctrico e elástico.[Abstract] Materials which exhibits magnetic, dielectric or elastic ordering, and those that combine two of these properties (multiferroics) are fundamentals for the developing of new technologies. These properties were traditionally searched and successfully found in metal oxides. However, the occurrence of new hybrid materials that combine organic and inorganic components in the same structure have opened a new field of possibilities. In the present thesis it has been synthesized and characterized several hybrid materials: porous [M2(NH2-bdc)2(dabco)][G], and dense with perovskite architecture: [CH3NH3]M(HCOO)3, [NH4]Cd(HCOO)3 and [(CH3)4N]Mn(N3)3. The porous hybrids [M2(NH2-bdc)2(dabco)][G] present two dielectric anomalies due to the rotation of the NH2-bdc ligand and the movement of the solvent molecules occluded. These hybrids were employed as precursors of the nanostructured oxides ZnO and Co3O4. The [CH3NH3]M(HCOO)3 formates where M= Mn+2, Co+2, Ni+2 and Cu+2, show weak ferromagnetism at low temperature. Furthermore, [NH3CH3]Co(HCOO)3 is one of the few examples of hybrid materials with magnetoelectric coupling. The [NH4]Cd(HCOO)3 compound displays electric polarization at ambient conditions which can be increased by the application of high pressures. The [(CH3)4N]Mn(N3)3 hybrid shows an structural, antiferroelectric and ferroelastic transition at 310 K, together with magnetic bistability. This is one of the few examples of material which shows simultaneous magnetic, dielectric and elastic ordering

A simple solvothermal synthesis of MFe2O4 (M=Mn, Co and Ni) nanoparticles

This is the accepted manuscript of the following article: Yáñez-Vilar, S., Sánchez-Andújar, M., Gómez-Aguirre, C., Mira, J., Señarís-Rodríguez, M., & Castro-García, S. (2009). A simple solvothermal synthesis of MFe2O4 (M=Mn, Co and Ni) nanoparticles. Journal Of Solid State Chemistry, 182(10), 2685-2690. doi: 10.1016/j.jssc.2009.07.028Nanoparticles of MFe2O4 (M=Mn, Co and Ni), with diameters ranging from 5 to 10 nm, have been obtained through a solvothermal method. In this synthesis, an alcohol (benzyl alcohol or hexanol) is used as both a solvent and a ligand; it is not necessary, therefore, to add a surfactant, simplifying the preparation of the dispersed particles. We have studied the influence of the synthetic conditions (temperature, time of synthesis and nature of solvent) on the quality of the obtained ferrites and on their particle size. In this last aspect, we have to highlight that the solvent plays an important role on the particle size, obtaining the smallest diameters when hexanol was used as a solvent. In addition, the magnetic properties of the obtained compounds have been studied at room temperature (RT). These compounds show a superparamagnetic behaviour, as was expected for single domain nanoparticles, and good magnetization values. The maxima magnetization values of the MFe2O4 samples are quite high for such small nanoparticles; this is closely related to the high crystallinity of the particles obtained by the solvothermal methodThe authors are grateful for financial support from the MEC of Spain (Project CSD2006-00012 of Consolider-Ingenio 2010 Programme and FPI fellowship to S. Yáñez-Vilar), from the Xunta de Galicia (Project PGIDIT06PXIB103298PR, Rede Galega de Nanomedicina and Parga Pondal Programme) and from the EU (FEDER)S

Atypical Magnetic Behavior in the Incommensurate (CH3NH3)[Ni(HCOO)3] Hybrid Perovskite

A plethora of temperature-induced phase transitions have been observed in (CH3NH3)[M(HCOO)3] compounds, where M is Co(II) or Ni(II). Among them, the nickel compound exhibits a combination of magnetic and nuclear incommensurability below Néel temperature. Despite the fact that the zero-field behavior has been previously addressed, here we study in depth the macroscopic magnetic behavior of this compound to unveil the origin of the atypical magnetic response found in it and in its parent family of formate perovskites. In particular, they show a puzzling magnetization reversal in the curves measured starting from low temperatures, after cooling under zero field. The first atypical phenomenon is the impossibility of reaching zero magnetization, even by nullifying the applied external field and even compensating it for the influence of the Earth’s magnetic field. Relatively large magnetic fields are needed to switch the magnetization from negative to positive values or vice versa, which is compatible with a soft ferromagnetic system. The atypical path found in its first magnetization curve and hysteresis loop at low temperatures is the most noticeable feature. The magnetization curve switches from more than 1200 Oe from the first magnetization loop to the subsequent magnetization loops. A feature that cannot be explained using a model based on unbalanced pair of domains. As a result, we decipher this behavior in light of the incommensurate structure of this material. We propose, in particular, that the applied magnetic field induces a magnetic phase transition from a magnetically incommensurate structure to a magnetically modulated collinear structureThe authors thank financial support from the Ministerio de Economía y Competitividad MINECO and EU-FEDER (projects MAT2017-86453-R and PDC 2021-121076-I00). The authors are grateful to Dra. Ana Arauzo at Servicio de Medidas Físicas of the Universidad de Zaragoza for heat capacity data. O.F. acknowledges the Spanish Ministry of Universities (UNI/551/2021) and the European Union through the Funds Next GenerationS

Coexistence of magnetic and electrical order in the new perovskite-like (C3N2H5)[Mn(HCOO)3] formate

This is the accepted manuscript of the following article: Pato-Doldán, B., Gómez-Aguirre, L., Bermúdez-García, J., Sánchez-Andújar, M., Fondado, A., & Mira, J. et al. (2013). Coexistence of magnetic and electrical order in the new perovskite-like (C3N2H5)[Mn(HCOO)3] formate. RSC Advances, 3(44), 22404. doi: 10.1039/c3ra43165gIn this work we further the structural characterization of the recently discovered (C3N2H5)[Mn(HCOO)3] metal–organic framework with perovskite-like structure, and we present its magnetic and dielectric properties up to 350 K. At low temperature, the C3N2H5+ imidazolium cations, that sit oblique within the cavities of the [Mn(HCOO)3]− framework structure, show a cooperative order resulting in an antiparallel arrangement of their electrical dipole moments. Very interestingly, it is only above 220 K that thermal energy seems to be able to break this antiferroelectric order, resulting in a linear increase of its dielectric constant with temperature. In addition, this Mn(II) compound is antiferromagnetic below TN = 9 K, with a slightly non-collinear arrangement of its magnetic moments, yielding to a weak ferromagnetism. Therefore, this is a new multiferroic material which exhibits coexistence of magnetic and electric orderingThe authors are grateful for financial support from Ministerio de Economía y Competitividad MINECO (Spain) under project FEDER MAT2010-21342-C02-01 and from Xunta de Galicia under project PGIDIT10PXB103272PR. B.P.-D. also wants to thank MICINN for a FPI fellowshipS

Magnetic transitions and isotropic versus anisotropic magnetic behaviour of [CH3NH3][M(HCOO)3] M = Mn2+, Co2+, Ni2+, Cu2+ metal–organic perovskites

Here we present an in-depth study of the magnetic properties of a family of metal–organic perovskites ABX3, [CH3NH3][M(HCOO)3] in which A = CH3NH3+ is the methylammonium cation, B = M is a divalent metal cation (Mn2+, Co2+, Ni2+ or Cu2+), and X is the formate anion (HCOO−). The magnetic properties have been measured on powdered samples and along the different orientations of mm-sized single crystals. They display spin-canted weak ferromagnetism with Néel temperatures of 8.0 K (Mn2+), 15.7 K (Co2+) and 34 K (Ni2+), which are inversely proportional to the ionic radii of the metal cations. The Cu2+ member displays low-dimensional magnetism as a result of orbital ordering of the Cu2+ d orbitals originating from a Jahn–Teller distortion. Pulsed-field magnetization experiments (fields of up to 60 T at temperatures down to 0.6 K) show that Mn2+, Co2+ and Ni2+ formates display cation-characteristic spin flop transitions. A saturation magnetization value of 5 μB (at 12.5 T) was observed for Mn2+, meanwhile the Co2+ formate shows an orientation dependent quasi saturation (5.1 μB at 21 T along [101] vs. 5.8 μB at 26 T along [010]). The different isotropic/anisotropic behaviour can be explained by the orbital contribution to the magnetic responseThe Spanish authors are grateful for financial support from Ministerio de Economía y Competitividad (MINECO) (Spain) and EU under the project ENE2014-56237-C4-4-R, and Xunta de Galicia under the project GRC2014/042. L. C. G.-A. acknowledges UDC for a predoctoral fellowship and Fundación Barrié for the research stay grant at LANL. Work at LANL, A. P. H. and B. P.-D.'s visit to LANL were funded by the Laboratory Directed Research and Development program at LANL. The NHMFL pulsed-field facility is funded by the U.S. National Science Foundation through Cooperative Grant No. DMR-1157490, the State of Florida, and the U.S. Department of EnergyS