Comment on "Theoretical design of molecular nanomagnets for magnetic refrigeration" [Appl. Phys. Lett. 103, 202410 (2013)]

Garlatti et al. [Appl. Phys. Lett. 103, 202410 (2013)] report theoretical simulations aimed at showing that the best molecular nanomagnets for magnetic refrigeration between T = 10 K and sub-Kelvin region are those made of strongly ferromagnetically-coupled magnetic ions. This Comment revises such conclusion based on results that, apparently, contrast with the established belief in this research field.Comment: 3 pages, 2 figure

Magnetocaloric effect in hexacyanochromate Prussian blue analogs

We report on the magnetocaloric properties of two molecule-based hexacyanochromate Prussian blue analogs, nominally CsNi[Cr(CN)_6](H_2O) and Cr_3[Cr(CN)_6]_2x12(H_2O). The former orders ferromagnetically below Tc=90 K, whereas the latter is a ferrimagnet below Tc=230 K. For both, we find significantly large magnetic entropy changes DSm associated to the magnetic phase transitions. Notably, our studies represent the first attempt to look at molecule-based materials in terms of the magnetocaloric effect for temperatures well above the liquid helium range.Comment: 4 pages, 6 figure

A spin crossover ferrous complex with ordered magnetic ferric anions

El pdf del artículo es la versión post-print.The first tetrahaloferrate spin crossover compound, [Fe(Metz) 6](FeBr 4) 2 (Metz = 1-methyltetrazole), is reported. The FeBr 4 - ions form ferromagnetically coupled 1D stacks and exhibit an antiferromagnetic order at 2.2 K, which coexists with the gradual spin crossover centred at 165 K. © 2012 The Royal Society of Chemistry.We are grateful to Spanish MINECO (contracts MAT2009-13977-C03 and MAT2011-24284) for funding.Peer Reviewe

Magnetic "Molecular Oligomers" based on decametallic supertetrahedra: A giant Mn49 cuboctahedron and its Mn25Na4 fragment

et al.Two nanosized Mn and MnNa clusters based on analogues of the high-spin (S=22) [Mn Mn (μ-O)] supertetrahedral core are reported. Mn and MnNa complexes consist of eight and four decametallic supertetrahedral subunits, respectively, display high virtual symmetry (O), and are unique examples of clusters based on a large number of tightly linked high nuclearity magnetic units. The complexes also have large spin ground-state values (Mn: S=61/2; MnNa: S=51/2) with the Mn cluster displaying single-molecule magnet (SMM) behavior and being the second largest reported homometallic SMM.This work was supported by the Cyprus Research Promotion Foundation grant ANABAVMISH/PAGIO/0308/12 which is co-funded by the Republic of Cyprus and the European Regional Development Fund, the US National Science Foundation (Grant DMR-1213030 to G.C.), and the Spanish MINECO (Project FEDER-MAT2012-38318-C03-01).Peer Reviewe

Building 1D lanthanide chains and non-symmetrical [Ln2] “triple-decker” clusters using salen-type ligands: magnetic cooling and relaxation phenomena

et al.A solvothermal reaction between Ln(NO)·6HO (Ln: Gd, Tb and Dy), 2-hydroxy-1-naphthaldehyde, 2-OH-naphth, and ethylenediamine, en, in MeOH in the presence of a base, NEt, led to the formation of the 1D coordination polymers [Ln(L)(MeO)(MeOH)]·MeOH (Ln = Gd (1·MeOH), Tb(2), Dy (3·MeOH); HL = 1,1′-((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen-2-ol), the Schiff-base ligand derived from the condensation of 2-OH-naphth and en), while a similar reaction in an excess of NaN yielded 1D coordination polymers [Ln(L)(N)(MeO)(MeOH)] (Ln = Gd (4), Tb (5), Dy (6)). Finally, upon replacing ethylenediamine with o-phenylenediamine, o-phen, we managed to isolate the discrete dimers [Dy(L′)(MeOH)]·2MeOH (7·2MeOH) and [Gd(L′)(MeOH)]·2MeOH (8·2MeOH) (HL′ = 1,1′-((1E,1′E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene))bis (naphthalen-2-ol), the Schiff-base ligand from the condensation of 2-OH-naphth and o-phen). Polymers 1-3 describe one-dimensional chains, containing alternating seven- and eight-coordinate Ln metal centers, polymers 4-6 contain eight-coordinate lanthanide ions, while in both 7 and 8 the two Ln centers are eight- and seven-coordinate, adopting square antiprismatic and “piano-stool” geometry, respectively. The magnetocaloric properties of the three Gd analogues were determined from magnetic measurements, yielding the magnetic entropy change-ΔS = 21.8, 23.0 and 16.0 J kg K at T = 3.0 K on demagnetization of 7 T to 0, for 1, 4 and 8, respectively. The study of the magnetic properties also revealed that all three Dy analogues (3, 6 and 7) display out-of-phase signals, therefore suggesting slow magnetic relaxation, while such behaviour was not established in the Tb analogues.The research fund for CJM and ABC has been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF) – Research Funding Program: THALES. Investing in knowledge society through the European Social Fund. GL and ME thank Spanish MINECO (MAT2015-68204-R). MS, MO and TL: “Project partially supported by Wroclaw Centre of Biotechnology, programme The Leading National Research Centre (KNOW) for years 2014–2018”Peer Reviewe

The importance of being exchanged: [Gd III 4M II 8(OH) 8(L) 8(O 2CR) 8] 4+ clusters for magnetic refrigeration

El pdf del artículo es la versión post-print.-- et al.Playing it cool: Almost all of the constituent parts of the complex [Ln III 4M II 8(OH) 8(L) 8(O 2CR) 8]X 4, namely the lanthanide ions Ln 3+, the transition-metal ions M 2+, the bridging ligand L, the carboxylates, and the counterions X can be exchanged, thus allowing a thorough understanding of the individual contributions to the magnetocaloric effect. Example in picture: Gd purple, Cu green, O red, N blue. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.E.K.B. wishes to thank the EPSRC for funding. M.E. acknowledges contracts MAT2009-13977-C03 and CSD2007-00010. S.P. thanks the Danish Natural Science Research Council for a Sapere Aude Fellowship (10-081659).Peer Reviewe

Cryogenic magnetocaloric effect in the Fe17 molecular nanomagnet

Trabajo presentado al "The 23rd IIR International Congress of Refrigeration" celebrado del 21 al 26 de Agosto del 2011 en Praga.-- Dedicated to Alfred Werner on the 100th Anniversary of his Nobel prize in Chemistry in 1913.We study the magnetothermal properties of magnetically isotropic high-spin molecular nanomagnets containing 17 Fe3+ ions per molecule linked via oxide and hydroxide ions, packed in a crystallographic cubic symmetry. Low-temperature magnetization and heat capacity experiments reveal that each molecular unit carries a net spin ground state as large as S = 35/2 and a magnetic anisotropy as small as D = −0.023 K, while no magnetic order, purely driven by dipolar interactions, is to be expected down to very-low temperatures. These characteristics suggest that the Fe17 molecular nanomagnet can potentially be employed as a sub-Kelvin magnetic refrigerant.This work has been partially supported by Spanish MINECO through grants MAT2009-13977-C03 and PIE201060I012, the EPSRC and The Leverhulme Trust (UK).Peer Reviewe

Large adiabatic temperature and magnetic entropy changes in EuTiO3

Under the terms of the Creative Commons Attribution license.-- et al.We have investigated the magnetocaloric effect in single and polycrystalline samples of quantum paraelectric EuTiO3 by magnetization and heat capacity measurements. Single crystalline EuTiO3 shows antiferromagnetic ordering due to Eu2+ magnetic moments below TN=5.6K. This compound shows a giant magnetocaloric effect around its Néel temperature. The isothermal magnetic entropy change is 49Jkg-1K-1, the adiabatic temperature change is 21 K, and the refrigeration capacity is 500Jkg-1 for a field change of 7 T at TN. The single crystal and polycrystalline samples show similar values of the magnetic entropy and adiabatic temperature changes. The large magnetocaloric effect is due to suppression of the spin entropy associated with the localized 4f moment of Eu2+ ions. The giant magnetocaloric effect, together with negligible hysteresis, suggest that EuTiO3 could be a potential material for magnetic refrigeration below 40 K.R.M. acknowledges the support of MOE Tier 1 Grant No. R144-000-308-112. J.-S.W. acknowledges the support of MOE Tier 2 Grant No. R144-000-349-112. M.E. acknowledges financial support from MINECO through Grant No. FEDER-MAT2012-38318-C03-01.Peer Reviewe

A ferromagnetically coupled diphenoxo-bridged Gd3+-Mn2+ dinuclear complex with a large magneto-caloric effect

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.A novel diphenoxo-bridged Gd3+-Mn2+ dimer is proposed as a good candidate for cryogenic magnetic refrigeration. The large MCE is enhanced by the ferromagnetic interaction between the two metal ions. © 2013 The Royal Society of Chemistry.We are grateful to MINECO (contracts MAT2012-38318-C03 and CTQ2011-24478), EC for a Marie Curie-IEF (PIEF-GA-2011-299356 to GL). EKB thanks the EPSRC and Leverhulme Trust.The authors also thank the Unit of Information Resources for Research (URICI-CSIC) for the co-financing of this publication in Open Access.Peer Reviewe