Multiferroic behavior in the new double-perovskite Lu2_2MnCoO6_6

We present a new member of the multiferroic oxides, Lu$_2$MnCoO$_6$, which we have investigated using X-ray diffraction, neutron diffraction, specific heat, magnetization, electric polarization, and dielectric constant measurements. This material possesses an electric polarization strongly coupled to a net magnetization below 35 K, despite the antiferromagnetic ordering of the $S = 3/2$ Mn$^{4+}$ and Co$^{2+}$ spins in an $\uparrow \uparrow \downarrow \downarrow$ configuration along the c-direction. We discuss the magnetic order in terms of a condensation of domain boundaries between $\uparrow \uparrow$ and $\downarrow \downarrow$ ferromagnetic domains, with each domain boundary producing a net electric polarization due to spatial inversion symmetry breaking. In an applied magnetic field the domain boundaries slide, controlling the size of the net magnetization, electric polarization, and magnetoelectric coupling

Síntesis hidrotermal de monocristales LnMn₂O₅ (Ln= Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho y Er)

Ten single crystals of the series LnMn₂O₅ (Ln= Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er) were synthesized by hydrothermal synthesis in a single step and without subsequent thermal treatments from aqueous solutions of metals salts at 240 ^ºC. The obtained single crystals have a size of various micrometers and their morphology changes throughout the serie: they are polygonal in the case of the compounds with Ln= Pr, Nd, Sm, Eu and Gd and needle-like in the case of the compounds with Ln= Y, Tb, Dy, Ho and Er. After the analysis of the obtained products employing different conditions of synthesis we attributed the different morphology to a greater growth rate along the c axis when the smaller ions (Y, Tb, Dy, Ho y Er) are involved, due to their better adaptation to the compound’s crystal structure.<br><br>Se han conseguido preparar monocristales de 10 óxidos mixtos de la serie LnMn₂O₅ (Ln= Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho y Er) mediante síntesis hidrotermal optimizada, en un único paso y sin tratamientos térmicos posteriores partiendo de las correspondientes sales metálicas en disolución acuosa a 240 ^ºC. Los monocristales obtenidos son relativamente grandes, de varias micras y su morfología varía a lo largo de la serie: es poligonal en el caso de los compuestos de los lantánidos del inicio de la serie (Ln= Pr, Nd, Sm, Eu y Gd) y acicular en el caso de los compuestos de Y y de los lantánidos del final de la serie (Ln= Tb, Dy, Ho y Er). Tras el análisis de los productos obtenidos empleando distintas condiciones de síntesis atribuimos la diferente morfología a una mayor velocidad de crecimiento cristalino a lo largo del eje c cuando intervienen los iones más pequeños (Y, Tb, Dy, Ho y Er) debido a la mejor adaptación de éstos últimos a la estructura cristalina del compuesto

Giant barocaloric tunability in [(CH<inf>3</inf>CH<inf>2</inf>CH<inf>2</inf>)<inf>4</inf>N]Cd[N(CN)<inf>2</inf>]<inf>3</inf> hybrid perovskite

We report the barocaloric performance of cadmium-dicyanamide perovskite [(CH3CH2CH2)4N]Cd[N(CN)2]3 ([TPrA]Cd[dca]3). The introduction of Cd, a large second-row post-transition metal, into this hybrid organic-inorganic perovskite structure leads to three separate thermally driven phase transitions and four polymorphs, which we characterize in full using temperature-dependent X-ray diffraction and temperature-dependent calorimetry. Amongst these transitions, the non-isochoric orthorhombic to tetragonal phase transition at high temperatures, with a large volume change of ∼0.4%, leads to a large reversible pressure-driven isothermal change in entropy of ∼11.5 J K-1 kg-1, and a giant barocaloric tunability of the transition temperature with pressure of ∼38.2 K kbar-1, which are both desirable for future low-pressure barocaloric cooling applications.The authors are grateful for financial support from Ministerio de Economía y Competitividad MINECO and EU-FEDER (project MAT2017-86453-R), and ERC Starting Grant no 680032. J. M. B. G. acknowledges Xunta de Galicia for a Postdoctoral Fellowship. X. M. is grateful for support from the Royal Society

Near room temperature dielectric transition in the perovskite formate framework [(CH(3))(2)NH(2)][Mg(HCOO)(3)].

We report that the hybrid organic-inorganic compound [(CH(3))(2)NH(2)][Mg(HCOO)(3)] shows a marked dielectric transition around T(t) ∼ 270 K, associated to a structural phase transition from SG R3[combining macron]c (centrosymmetric) to Cc (non-centrosymmetric). This is the highest T(t) reported so far for a perovskite-like formate that is thus a promising candidate to display electric order very close to room temperature

A simple in situ synthesis of magnetic M@CNTs by thermolysis of the hybrid perovskite = TPrA[M(dca)3

In this work, the incorporation of dicyanamide building blocks in organic–inorganic hybrid compounds is found to be a promising strategy for the synthesis of multiwalled carbon nanotubes embedded with magnetic nanoparticles (M@CNTs). Following a novel one-step, scalable and fast synthetic route, M@CNTs are obtained by simple calcination of the organic–inorganic hybrid perovskite [TPrA][M(dca)3] (TPrA = tetrapropylammonium, M = Ni2+ and Co2+, dca = dicyanamide). The resulting M@CNTs (M = Ni and Co) display a regular morphology and an essentially mesoporous network of ∼250 m2 g−1, whereas the Co@CNT composite displays a broad pore size distribution (PSD) up to 6 nm, Ni@CNTs show a strictly controlled unimodal PSD, centered at around 5 nm. Monitoring of their thermal decomposition by X-ray diffraction, electron microscopy, thermogravimetric and spectroscopic analyses allows proposing a calcination mechanism and establishing the conditions to obtain optimal materials. Moreover, magnetization studies reveal a ferromagnetic behaviour of the obtained M@CNTs, with small coercive fields due to the size of the magnetic nanoparticles. In addition, preliminary assays of oil adsorption–desorption capacity reveal a promising potential for spilled oil recovery using this easily-synthesized materials. All these physicochemical properties make these composites good candidates for other nitrogen-rich CNT common applications.The authors are grateful for the financial support from Ministerio de Economía y Competitividad MINECO and EU‐FEDER under project ENE2014‐56237‐C4‐4‐R and Xunta de Galicia under project GRC2014/042. J. M. B.‐G. wants to thanks Barrié Foundation for a predoctoral fellowship and S. Y.‐V. to the Xunta de Galicia for a postdoctoral fellowshipPeer reviewe