Cobalt-(II) metal complexes constitute a versatile platform for investigating how coordination geometry and spin-orbit coupling determine their magnetic properties. Although numerous cobalt-(II) coordination complexes have been reported in recent literature, only a limited number exhibit comprehensive and quantitatively reliable magnetic characterization. In this work, we investigate the magnetic properties of the hexacoordinated cobalt dimer [Co2(μ-L1H)2(μ-H2O)2(H2O)4]-4NO3·2H2O, where L1H denotes the adenine bridging ligand. The hexacoordinated environment stabilizes a high-spin S = 3/2 configuration for both Co-(II) centers, resulting in strong spin-orbit coupling and significant zero-field splitting, described by axial (D) and rhombic (E) anisotropy parameters. Fits to magnetic susceptibility and magnetization data reveal antiferromagnetic coupling between the Co-(II) ions, with a ratio of E/D ≈ 1/4 and D/k B = 89 K, evidencing pronounced magnetic anisotropy in the system. This behavior is further supported by anisotropic Landé factors g x = g y = 2.5 and g z = 2.4, consistent with easy-plane magnetic anisotropy.

Three new coordination polymers, [Ln(3-CCA)3(H2O)2·2H2O]n (Ln = Gd (1), Tb (2), Dy (3)), were synthesized through reaction between the above-mentioned lanthanide ions and coumarin-3-carboxylic acid (3-CCA). Single-crystal and powder X-ray diffraction analyses revealed that complex 1 exhibits a nona-coordination, whereas complexes 2 and 3 adopt an octa-coordinated geometry. The chemical composition of the complexes was confirmed by FTIR and CHN analyses, while their phase purity was verified by powder X-ray diffraction. DC magnetic measurements revealed the presence of weak ferromagnetic interactions between the Ln ions in 1. Moreover, the magnetocaloric properties of this compound were investigated and its performance was evaluated using the Temperature-Averaged Entropy Change (TEC) parameter. Additionally, AC magnetic susceptibility measurements revealed field-induced single-ion magnet (SIM) behavior at low temperatures for complexes 2 and 3.

In this contribution, we report the crystal structure and magnetic properties of a new copper dimer prepared through the reaction of CuCl2 & sdot;6H2O with the pre-ligands H3BTB (1,3,5-tris(4-carboxylphenyl)benzene) and dmdpy (5-5 ' dimethyl-2,2 ' dipyridyl), with the stoichiometric ratio 1:2:1, respectively. The dinuclear complex [Cu2(HBTB)2(dmdpy)2]center dot 2H2O presents two pentacoordinated Cu(II) ions connected by the polycarboxylate HBTB ligand. The study of the magnetic properties revealed no significant magnetic interactions between the Cu (II) ions.

Two 1D coordination polymers, {[Co(H3BTB)2(phen)](NO3)2}n (1) and {[Cu(HBTB)2(phen)] DMF}n (2), were synthesized through a slow diffusion reaction between the metal ions Co2+ or Cu2+, 1,3,5-tris(4-carboxylphenyl)benzene (H3BTB) and 1,10-phenanthroline (phen). Single-crystal X-ray diffraction revealed that both metal centers are involved in a distorted octahedral environment. As expected for a Cu2+ ion with a d9 configuration, a pronounced Jahn-Teller distortion is observed. FTIR, powder XRD, and thermogravimetric analysis were employed for the chemical characterization of the two complexes. CASSCF-NEVPT2 was used to calculate the axial magnetic anisotropy (D) for complex 1, and the results were almost perfectly consistent with the experimental measurements. The AC magnetic susceptibility measurements revealed field-induced single-ion magnet (SIM) behavior at low temperatures for 1. EPR studies of complex 2 indicated that the Cu2+ ions are essentially isolated.

Heusler alloys are widely studied due to their potential for practical applications, making use of their martensitic transformations. However, hysteresis is a long-standing drawback that reduces the chance of transferring these alloys from the laboratory to industry. In this work, we studied a Cr-doped Ni2MnGa-based material designed by integrating data obtained from the previous phase and hysteresis diagrams taken from the literature, reaching Ni2.15Mn0.70Cr0.15Ga. The compound presents a magnetostructural transition at room temperature, with a ferromagnetic martensite phase, and moderate thermal hysteresis of approximately 4 K. The magnetocaloric effect was explored, showing a reversible entropy change higher than 8 Jkg- 1K(-1) under 0-5 T field change, an advance towards high reversibility for this family alloys.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to "Giant Piezomagnetism in Mn3NiN"David Boldrin*David BoldrinMore by David Boldrinhttps://orcid.org/0000-0003-3833-8341, Andrei P. MihaiAndrei P. MihaiMore by Andrei P. Mihaihttps://orcid.org/0000-0002-7204-9087, Bin ZouBin ZouMore by Bin Zou, Jan ZemenJan ZemenMore by Jan Zemen, Ryan ThompsonRyan ThompsonMore by Ryan Thompson, Ecaterina WareEcaterina WareMore by Ecaterina Ware, Bogdan V. NeamtuBogdan V. NeamtuMore by Bogdan V. Neamtu, Luis GhivelderLuis GhivelderMore by Luis Ghivelderhttps://orcid.org/0000-0002-5667-6531, Bryan EsserBryan EsserMore by Bryan Esser, David W. McCombDavid W. McCombMore by David W. McComb, Peter PetrovPeter PetrovMore by Peter Petrovhttps://orcid.org/0000-0003-3643-6685, and Lesley F. CohenLesley F. CohenMore by Lesley F. CohenCite this: ACS Appl. Mater. Interfaces 2024, 16, 2, 2997Publication Date (Web):January 6, 2024Publication History Received5 December 2023Published online6 January 2024Published inissue 17 January 2024https://pubs.acs.org/doi/10.1021/acsami.3c16464https://doi.org/10.1021/acsami.3c16464correctionACS PublicationsCopyright © 2024 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views345Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (1 MB) Get e-Alertsclose Get e-Alerts

Ni-Mn-Ga based alloys are widely studied due to their potential for practical applications, making use of their martensitic transformations. However, hysteresis is a long-standing drawback that reduces the chance of transferring these alloys from the laboratory to industry. In this work, we studied a Cr-doped Ni2.15Mn0.70Cr0.15Ga alloy. We arrived at this composition by integrating data obtained from the previous phase and hysteresis diagrams taken from the literature. The compound presents a magnetostructural transition at room temperature, with a ferromagnetic martensite phase, and moderate thermal hysteresis of approximately 4 K. The magnetocaloric and ferromagnetic shape memory effects were explored, showing a reversible entropy change of approximately 9 Jkg-1K-1 under 0-5 T field change, and a cyclical magnetic -field-induced deformation close to 0.81% under 0-9 T, an advance towards high reversibility for this family alloys.(c) 2022 Elsevier B.V. All rights reserved.

Vortex matter in layered high-[Formula: see text] superconductors, including iron-pnictides, undergo several thermodynamic phase transitions due to the complex interplay of pinning energy, thermal energy and elastic energy. Moreover, the presence of anisotropy makes their vortex physics even more intriguing. Here, we report a detailed vortex dynamics study, using dc magnetization measurements, in a triclinic iron-pnictide superconductor (Ca[Formula: see text]La[Formula: see text])[Formula: see text](Pt[Formula: see text]As[Formula: see text])(Fe[Formula: see text]As[Formula: see text])[Formula: see text], with a superconducting transition temperature, T[Formula: see text] [Formula: see text] 31 K. A second magnetization peak (SMP) feature is observed for magnetic field perpendicular (H[Formula: see text]c) and parallel (H[Formula: see text]ab) to the crystal plane. However, its fundamental origin is quite different in both directions. For H[Formula: see text]c, the SMP can be well explained using an elastic-to-plastic vortex creep crossover, using collective creep theory. In addition, a possible rhombic-to-square vortex lattice phase transition is also observed for fields in between the onset-field and peak-field related to the SMP. On the other hand, for H[Formula: see text]ab, a clear signature of an order-disorder vortex phase transition is observed in the isothermal M(H) measurements at T [Formula: see text] 6 K. The disordered phase exhibits the characteristics of entangled pinned vortex-liquid. We construct a comprehensive vortex phase diagram by displaying characteristic temperatures and magnetic fields for both crystal geometries in this unique superconducting compound. Our study sheds light on the intricate vortex dynamics and pinning in an iron-pnictide superconductor with triclinic symmetry.

Vortex matter in layered high- T_c superconductors, including iron-pnictides, undergo several thermodynamic phase transitions due to the complex interplay of pinning energy, thermal energy and elastic energy. Moreover, the presence of anisotropy makes their vortex physics even more intriguing. Here, we report a detailed vortex dynamics study, using dc magnetization measurements, in a triclinic iron-pnictide superconductor (Ca _0.85 La _0.15 ) _10 (Pt _3 As _8 )(Fe _2 As _2 ) _5 , with a superconducting transition temperature, T _c ∼ 31 K. A second magnetization peak (SMP) feature is observed for magnetic field perpendicular ( H ∥ c ) and parallel ( H ∥ ab ) to the crystal plane. However, its fundamental origin is quite different in both directions. For H ∥ c , the SMP can be well explained using an elastic-to-plastic vortex creep crossover, using collective creep theory. In addition, a possible rhombic-to-square vortex lattice phase transition is also observed for fields in between the onset-field and peak-field related to the SMP. On the other hand, for H ∥ ab , a clear signature of an order-disorder vortex phase transition is observed in the isothermal M ( H ) measurements at T ≥ 6 K. The disordered phase exhibits the characteristics of entangled pinned vortex-liquid. We construct a comprehensive vortex phase diagram by displaying characteristic temperatures and magnetic fields for both crystal geometries in this unique superconducting compound. Our study sheds light on the intricate vortex dynamics and pinning in an iron-pnictide superconductor with triclinic symmetry.

AbstractVortex matter in layered high-$$T_c$$ T c superconductors, including iron-pnictides, undergo several thermodynamic phase transitions due to the complex interplay of pinning energy, thermal energy and elastic energy. Moreover, the presence of anisotropy makes their vortex physics even more intriguing. Here, we report a detailed vortex dynamics study, using dc magnetization measurements, in a triclinic iron-pnictide superconductor (Ca$$_{0.85}$$ 0.85 La$$_{0.15}$$ 0.15 )$$_{10}$$ 10 (Pt$$_3$$ 3 As$$_8$$ 8 )(Fe$$_2$$ 2 As$$_2$$ 2 )$$_5$$ 5 , with a superconducting transition temperature, T$$_c$$ c $$\sim$$ ∼ 31 K. A second magnetization peak (SMP) feature is observed for magnetic field perpendicular (H$$\parallel$$ ‖ c) and parallel (H$$\parallel$$ ‖ ab) to the crystal plane. However, its fundamental origin is quite different in both directions. For H$$\parallel$$ ‖ c, the SMP can be well explained using an elastic-to-plastic vortex creep crossover, using collective creep theory. In addition, a possible rhombic-to-square vortex lattice phase transition is also observed for fields in between the onset-field and peak-field related to the SMP. On the other hand, for H$$\parallel$$ ‖ ab, a clear signature of an order-disorder vortex phase transition is observed in the isothermal M(H) measurements at T$$\ge$$ ≥ 6 K. The disordered phase exhibits the characteristics of entangled pinned vortex-liquid. We construct a comprehensive vortex phase diagram by displaying characteristic temperatures and magnetic fields for both crystal geometries in this unique superconducting compound. Our study sheds light on the intricate vortex dynamics and pinning in an iron-pnictide superconductor with triclinic symmetry.

Below 42 K, the homometallic Co3O2BO3 ludwigite forms magnetic planes separated by nonmagnetic low-spin Co3+ ions. The substitution of Co3+ by other nonmagnetic ions enhances the magnetic interactions, raising the magnetic ordering temperature. However, depending on the nonmagnetic dopant ion, the remaining Co3+ ions could adopt a high-spin state, creating magnetic frustration and lowering the magnetic transition temperature. Doping Co3O2BO3 with nonmagnetic In3+ ions favors the appearance of both high-spin Co2+ and Co3+. The In3+ ions preferentially occupy sites 4 and are randomly distributed in each site. The two-dimensional magnetic character of the parent compound, Co3O2BO3, is preserved, and the magnetic transition temperature increases to 47.8 K. Measurements of magnetization, which show metamagnetic transitions at low temperatures, and specific heat are consistent with ferrimagnetic ordering in this system. Thus, using these results and those reported in the literature, the effects caused by doping of Co3O2BO3 with different nonmagnetic +3 ions are discussed in terms of the presence of high-spin Co2+ and Co3+ in the compounds.

We performed magnetization measurements in a single crystal of the anisotropic bilayer pnictide superconductor KCa2 Fe4As4F2, with Tc similar or equal to 34 K, for H vertical bar vertical bar c-axis and H vertical bar vertical bar ab-planes. A second magnetization peak (SMP) was observed in the isothermal M(H) curves measured below 16 K for H vertical bar vertical bar ab-planes. A peak in the temperature variation of the critical current density, J(c)(T), at 16 K, strongly suggests the emergence of Josephson vortices at lower temperatures, which leads to the SMP in the sample. In addition, it is noticed that the appearance of Josephson vortices below 16 K renders easy magnetic flux penetration. A detailed vortex dynamics study suggests that the SMP can be explained in terms of elastic pinning to plastic pinning crossover. Furthermore, contrary to the common understanding, the temperature variation of the first peak field, H-1, below and above 16 K, behaves non-monotonically. A highly disordered vortex phase, governed by plastic pinning, has been observed between 17 and 23 K, within a field region around an extremely large first peak field. Pinning force scaling suggests that the point defects are the dominant source of pinning for H vertical bar vertical bar ab-planes, whereas, for H vertical bar vertical bar c-axis, point defects in addition to surface defects are at play. Such disorder contributes to the pinning due to the variation in charge carrier mean free path, delta l-pinning. Moreover, the large J(c) observed in our study is consistent with the literature, which advocates this material for high magnetic field applications.

Abstract We performed magnetization measurements in a single crystal of the anisotropic bilayer pnictide superconductor KCa $$_2$$ 2 Fe $$_4$$ 4 As $$_4$$ 4 F $$_2$$ 2 , with $$T_c\;$$ T c $$\simeq$$ ≃ 34 K, for $$H$$ H $$\parallel$$ ‖ $$c$$ c -axis and $$H$$ H $$\parallel$$ ‖ $$ab$$ ab -planes. A second magnetization peak (SMP) was observed in the isothermal M(H) curves measured below 16 K for $$H$$ H $$\parallel$$ ‖ $$ab$$ ab -planes. A peak in the temperature variation of the critical current density, $$J_{c}$$ J c (T), at 16 K, strongly suggests the emergence of Josephson vortices at lower temperatures, which leads to the SMP in the sample. In addition, it is noticed that the appearance of Josephson vortices below 16 K renders easy magnetic flux penetration. A detailed vortex dynamics study suggests that the SMP can be explained in terms of elastic pinning to plastic pinning crossover. Furthermore, contrary to the common understanding, the temperature variation of the first peak field, $$H_1$$ H 1 , below and above 16 K, behaves non-monotonically. A highly disordered vortex phase, governed by plastic pinning, has been observed between 17 and 23 K, within a field region around an extremely large first peak field. Pinning force scaling suggests that the point defects are the dominant source of pinning for H $$\parallel$$ ‖ $$ab$$ ab -planes, whereas, for H $$\parallel$$ ‖ $$c$$ c -axis, point defects in addition to surface defects are at play. Such disorder contributes to the pinning due to the variation in charge carrier mean free path, $$\delta l$$ δ l -pinning. Moreover, the large $$J_c$$ J c observed in our study is consistent with the literature, which advocates this material for high magnetic field applications.

Due to their large surface-volume ratio, thin films are good candidates for magnetocaloric effect applications in refrigeration devices. With this aim, we studied the magnetic and magnetocaloric properties of the bilayers manganite thin films, La0.88Sr0.12MnO3/La0.75Sr0.25MnO3 and La0. 75Sr0.25MnO3/La0.88Sr0.12MnO3, and their control single layer films, La0.75Sr0.25MnO3 and La0.88Sr0.12MnO3. These films were grown by pulsed laser deposition on silicon substrates, resulting in polycrystalline films with average grain size of 35 nm. We found that, for the bilayers, the temperature range of the magnetocaloric effect can be broadened without reducing the refrigerant capacity. Therefore, it is possible to combine the magnetocaloric effect qualities of nanocomposites and thin films in order to improve the performance and expand their potential use in refrigeration devices.

The novel A-doped Co3O2BO3 (A(4+)=Zr, Hf) ludwigites have been synthetized by the first time and investigated by X-ray diffraction, magnetization and specific heat experiments. The non-magnetic ions place mainly at sites 4 of the structure. This doping strengthens the magnetic interactions rising the magnetic transition temperatures from 42 K, for the undoped compound, to 71 K and 72 K for Zr and Hf, respectively. These magnetic transition temperature are 10 K below that shown by the Sn4+-doped Co3O2BO3. As expected, all these isostructural and isovalent compounds exhibit the same magnetic features. However, low temperature specific heat experiments and magnetization curves with typical metamagnetic behavior revealed that doping with the non-magnetic open-shell ions d(0) Zr and Hf preserves the two-dimensional antiferromagnetic character of the parent ludwigite Co3O2BO3 while the closed-shell d(10 )Sn leads to a three-dimensional magnetism. The experimental results are compatible with an antiferromagnetic structure with a ferromagnetic component for these two compounds. The difference in T-N and dimensionality of these compounds are related to super-superexchange (SSE) interaction between two Co2+ mediated by the nonmagnetic ion A(4+). The non-magnetic closed-shell d(10) ion turned out to be more effective in mediating SSE interactions between 1-2-3 magnetic layers. (C) 2021 Elsevier B.V. All rights reserved.

We performed magnetization measurements in a single crystal of the anisotropic bilayer pnictide superconductor KCa[Formula: see text]Fe[Formula: see text]As[Formula: see text]F[Formula: see text], with [Formula: see text] [Formula: see text] 34 K, for [Formula: see text] [Formula: see text] [Formula: see text]-axis and [Formula: see text] [Formula: see text] [Formula: see text]-planes. A second magnetization peak (SMP) was observed in the isothermal M(H) curves measured below 16 K for [Formula: see text] [Formula: see text] [Formula: see text]-planes. A peak in the temperature variation of the critical current density, [Formula: see text](T), at 16 K, strongly suggests the emergence of Josephson vortices at lower temperatures, which leads to the SMP in the sample. In addition, it is noticed that the appearance of Josephson vortices below 16 K renders easy magnetic flux penetration. A detailed vortex dynamics study suggests that the SMP can be explained in terms of elastic pinning to plastic pinning crossover. Furthermore, contrary to the common understanding, the temperature variation of the first peak field, [Formula: see text], below and above 16 K, behaves non-monotonically. A highly disordered vortex phase, governed by plastic pinning, has been observed between 17 and 23 K, within a field region around an extremely large first peak field. Pinning force scaling suggests that the point defects are the dominant source of pinning for H [Formula: see text] [Formula: see text]-planes, whereas, for H [Formula: see text] [Formula: see text]-axis, point defects in addition to surface defects are at play. Such disorder contributes to the pinning due to the variation in charge carrier mean free path, [Formula: see text] -pinning. Moreover, the large [Formula: see text] observed in our study is consistent with the literature, which advocates this material for high magnetic field applications.

In this work, we investigate the representative case of the homometallic Co ludwigite Co$^{2+}_2$Co$^{3+}$O$_2$BO$_3$ ($Pbam$ space group) with four distinct Co crystallographic sites [$M1$-$M4$] surrounded by oxygen octahedra. The mixed-valent character of the Co ions up to at least $T=873$ K is verified through x-ray absorption near-edge structure (XANES) experiments. Single crystal x-ray diffraction (XRD) and neutron powder diffraction (NPD) confirm that the Co ions at the $M4$ site are much smaller than the others at low temperatures, consistent with a Co$^{3+}$ oxidation state at $M4$ and Co$^{2+}$ at the remaining sites. The size difference between the Co ions in the $M4$ and $M2$ sites is continuously reduced upon warming above $\approx 370$ K, indicating a gradual charge redistribution within the $M4$-$M2$-$M4$ (424) ladder in the average structure. An increasing structural disorder, is noted above $\approx 370$ K, The local Co-O distance distribution, revealed by Co $K$-edge Extended X-Ray Absorption Fine Structure (EXAFS) data and analyzed with an evolutionary algorithm method, is similar to that inferred from the XRD crystal structure below $\approx 370$ K. At higher temperatures, the local Co-O distance distribution remains similar to that found at low temperatures, at variance with the average crystal structure obtained with XRD. We conclude that the oxidation states Co$^{2+}$ and Co$^{3+}$ are instantaneously well defined in a local atomic level at all temperatures, however the thermal energy promotes local defects in the charge-ordered configuration of the 424 ladders upon warming. These defects coalesce into a phase-segregated state within a narrow temperature interval ($475< T < 495$ K). Finally, a transition at $\approx 500$ K revealed by differential scanning calorimetry (DSC) in the iron ludwigite Fe$_3$O$_2$BO$_3$ is discussed.

Ferromagnetic Ni2MnGa based materials have been subject of intense study due to the strong coupling of structural and magnetic transitions, named a magnetostructural transformation, present in some off stoichiometry compounds. This property is promising for numerous applications, such as solid state cooling and energy harvesting. In this work the magnetic and thermal properties of the polycrystalline Heusler compounds Ni2Mn0.75Cu0.25Ga0.84Al0.16 with martensitic transition and Ni2Mn0.70Cu0.30Ga0.84Al0.16 with magnetostructural transformation were investigated by magnetization and heat flow measurements, both as a function of temperature and magnetic field. It is found that these materials present high values of entropy change around room temperature under 0 to 1 T magnetic field change.

In this work we investigate the critical behavior of two manganite compounds, Pr0.5Sr0.5MnO3 (PSMO) and Pr0.5Sr0.41Ca0.09MnO3 (PSCMO). These are complex magnetic systems, which undergo a paramagnetic to ferromagnetic phase transition on cooling, followed by a first order magnetic transition to a charge ordered antiferromagnetic states at lower temperatures. Magnetization measurements and magnetocaloric calculations were performed in order to determine their critical behavior. As a main result we show that the scaling of the entropy change - Delta SM with magnetization M, instead of the usual scaling with magnetic field H, is a powerful tool to study the critical behavior through magnetocaloric analysis. We use this property, in conjunction with Modified Arrot Plot technique, to determine the basic critical exponents beta and gamma for each sample. The exponents values indicate that the samples are near to universality class models based in nearest neighbor interactions. Besides intrinsic differences between the Ca-doped and the undoped sample, we confirm the applicability of the magnetocaloric analysis in order to determine critical behavior in complex magnetic systems.