Mixed orbital states and modulated crystal structures in La1−x Ca x MnO3 deduced from synchrotron X-ray diffraction

Abstract In the model manganese perovskites La1−x Ca x MnO3, several important phenomena have been observed, including ferromagnetic metallic/insulating states, colossal magnetoresistance effects, and charge- and orbital-ordered states. In the past, only compounds with x = 1/2, 2/3 and 3/4 and an insulating ground/antiferromagnetic state have been studied. To fully understand the crystal and electronic structures of these materials, it is important to study compounds with doping levels in the range of 0.5 < x < 2/3. Here we study the crystal structure in a series of compounds with 0.5 < x ≤ 0.6 using ultrahigh-resolution synchrotron X-ray diffraction. The experimental results reveal that all compounds undergo a structural transition at T < T CO(x) ≈ 200 − 220 K with the concomitant emergence of superlattice Bragg peaks, which can be indexed assuming a superstructure with a modulation propagation vector, τ. At the base temperature of 5 K, the modulation vector of the superstructure τ = [τ a , 0, 0] is parallel to the a-axis, with τ a varying linearly with x, as τ a  ≈ 1 − x. Our results may aid attempts to understand more deeply phenomena related to spin, charge, and orbital ordering, as well as colossal magnetoresistance and symmetry breaking and emergent order in quantum states

Control of Both Superconducting Critical Temperature and Critical Current by Means of Electric-Field-Induced Reconfigurable Strain

The controlled modification of superconductivity by any means is a long-standing issue in low-temperature physics. In this work, we present data on the control of the superconducting properties of conventional low critical-temperature (T C ) Nb thin films with thickness (d Nb ) = 15 and 20 nm under application of reconfigurable strain, S induced by an external electric field, and E ex to a piezoelectric (PE) single crystal, namely (1 − x)Pb(Mg 1/3 Nb 2/3 )O 3 − x PbTiO 3 (PMN-PT) with x = 0.30-0.31. The experimental results (reduction of T C and critical current (J C ) on the order of 6% and 90-100%, respectively) are nicely reproduced with a phenomenological model that incorporates the constitutive relation S(E ex ) that describes the electro-mechanical response of the PE crystal to well-established formulas that describe T C and J C of the SC thin films

Electric-field control of the remanent-magnetic-state relaxation in a piezoelectric-ferromagnetic PZT-5%Fe3O4 composite

Magnetoelectric (ME) composites that exhibit both ferroelectric and ferromagnetic properties have attracted significant attention, thanks to their potential applications, e.g., low-energy-consumption storage devices. Here, we study bulk composites based on Pb(Zr0.52Ti0.48)O3 (PZT) as a piezoelectric (PE) matrix and Fe3O4 nanoparticles (NPs) as soft ferromagnetic (FM) and magnetostrictive additives, in the form PZT-xFe3O4 with 0% ≤ x ≤ 50 wt. %, all sintered at T = 1000 °C for 2 h in air. We focus our study on a completely insulating sample x = 5% and measure its properties at room temperature upon an out-of-plane external electric field, Eex: namely, piezoelectric response [in-plane strain, S(Eex)], polarization [P(Eex)], and relaxation of the remanent magnetization, [mrem(t,Eex)], prepared upon application and removal of an external magnetic field. The peaks observed in the butterflylike S(Eex) curves at E±peak= ±6 kV/cm and the nucleation field recorded in the P(Eex) loops at the same range around E±nuc= ±6 kV/cm (both referring to the PZT PE matrix) are clearly imprinted on the relaxation behavior of the mrem(t,Eex) data (referring to the Fe3O4 FM NPs). This experimental fact proves the ME coupling between the PZT matrix and the embedded Fe3O4 NPs. We ascribe this feature to the comparable piezoelectricity of the PZT matrix and the magnetostriction of the Fe3O4 NPs that probably motivate and/or promote a strain transfer mechanism occurring at the PZT matrix-Fe3O4 NP interfaces. Our work proves that the low cost PZT-xFe3O4 composite is a promising candidate ME material for future studies, aiming to potential applications

Trinuclear NiII-LnIII-NiII Complexes with Schiff Base Ligands: Synthesis, Structure, and Magnetic Properties

The reaction of the Schiff base ligand o-OH-C6H4-CH=N-C(CH2OH)3, H4L, with Ni(O2CMe)2&middot;4H2O and lanthanide nitrate salts in a 4:2:1 ratio lead to the formation of the trinuclear complexes [Ni2Ln(H3L)4(O2CMe)2](NO3) (Ln = Sm (1), Eu (2), Gd (3), Tb (4)). The complex cations contain the strictly linear NiII-LnIII-NiII moiety. The central LnIII ion is bridged to each of the terminal NiII ions through two deprotonated phenolato groups from two different ligands. Each terminal NiII ion is bound to two ligands in distorted octahedral N2O4 environment. The central lanthanide ion is coordinated to four phenolato oxygen atoms from the four ligands, and four carboxylato oxygen atoms from two acetates which are bound in the bidentate chelate mode. The lattice structure of complex 4 consists of two interpenetrating, supramolecular diamond like lattices formed through hydrogen bonds among neighboring trinuclear clusters. The magnetic properties of 1&ndash;4 were studied. For 3 the best fit of the magnetic susceptibility and isothermal M(H) data gave JNiGd = +0.42 cm&minus;1, D = +2.95 cm&minus;1 with gNi = gGd = 1.98. The ferromagnetic nature of the intramolecular Ni&middot;&middot;&middot;Gd interaction revealed ground state of total spin S = 11/2. The magnetocaloric effect (MCE) parameters for 3 show that the change of the magnetic entropy (&minus;&Delta;Sm) reaches a maximum of 14.2 J kg&minus;1 K&minus;1 at 2 K. A brief literature survey of complexes containing the NiII-LnIII-NiII moiety is discussed in terms of their structural properties

Synthesis, Crystal Structures and Magnetic Properties of Trinuclear {Ni2Ln} (LnIII = Dy, Ho) and {Ni2Y} Complexes with Schiff Base Ligands

The reaction of the Schiff base ligand o-OH-C6H4-CH=N-C(CH2OH)3, H4L, with Ni(O2CMe)2&#8729;4H2O and lanthanide nitrate salts in a 4:2:1 ratio lead to the formation of the trinuclear complexes [Ni2Ln(H3L)4(O2CMe)2](NO3) (Ln = Dy (1), Ho (2), and Y (3)) which crystallize in the non-centrosymmetric space group Pna21. The complex cation consists of the three metal ions in an almost linear arrangement. The {Ni2Ln} moieties are bridged through two deprotonated Ophenolato groups from two different ligands. Each terminal NiII ion is bound to two ligands through their Ophenolato, the Nimino atoms and one of the protonated Oalkoxo groups in a distorted octahedral. The central lanthanide ion is coordinated to four Ophenolato oxygen from the four ligands, and four Ocarboxylato atoms from two acetates which are bound in the bidentate chelate mode, and the coordination polyhedron is biaugmented trigonal prism, which probably results in a non-centrosymmetric arrangement of the complexes in the lattice. The magnetic properties of 1&ndash;3 were studied and showed that 1 exhibits field induced slow magnetic relaxation

Synthesis, Crystal Structures and Magnetic Properties of Trinuclear {Ni₂Ln} (Ln^III = Dy, Ho) and {Ni₂Y} Complexes with Schiff Base Ligands

The reaction of the Schiff base ligand o-OH-C6H4-CH=N-C(CH2OH)3, H4L, with Ni(O2CMe)2∙4H2O and lanthanide nitrate salts in a 4:2:1 ratio lead to the formation of the trinuclear complexes [Ni2Ln(H3L)4(O2CMe)2](NO3) (Ln = Dy (1), Ho (2), and Y (3)) which crystallize in the non-centrosymmetric space group Pna21. The complex cation consists of the three metal ions in an almost linear arrangement. The {Ni2Ln} moieties are bridged through two deprotonated Ophenolato groups from two different ligands. Each terminal NiII ion is bound to two ligands through their Ophenolato, the Nimino atoms and one of the protonated Oalkoxo groups in a distorted octahedral. The central lanthanide ion is coordinated to four Ophenolato oxygen from the four ligands, and four Ocarboxylato atoms from two acetates which are bound in the bidentate chelate mode, and the coordination polyhedron is biaugmented trigonal prism, which probably results in a non-centrosymmetric arrangement of the complexes in the lattice. The magnetic properties of 1–3 were studied and showed that 1 exhibits field induced slow magnetic relaxation

Simulation of magnetic relaxation measurements of tetragonal Bi2Sr2CaCu2O8+x and Bi2Sr2Ca2Cu3O10+y thin films

Magnetic relaxation data at various temperatures and magnetic fields are taken from high-quality, epitaxial thin films of and and are simulated using a method developed by Brandt and coworkers. Assuming thermally activated resistivity and logarithmic activation energy we obtain good simulations of the experimental data. The critical current resulting from the simulation is evaluated as a function of the temperature and is found to decrease linearly with it and the current-voltage characteristics are extracted and are linear on a scale at all temperatures. The activation energy is calculated as a function of the current and it is shown to be a decreasing function of the magnetic field following a power law . The critical current is also shown to decrease with the magnetic field and can be described well by the exponential form . Comparison between the two phases and indicates that pinning in the film is stronger due to the lower anisotropy of this phase and probably because of the existence of more defects. Finally, the distribution of the local magnetic moment and the magnetic induction on the surface of the film at different times during the relaxation procedure is nicely depicted with surface and contour plots

Exploring the Magnetic and Electrocatalytic Properties of Amorphous MnB Nanoflakes

Two-dimensional (2D) metal borides are a class of ceramic materials with diverse structural and topological properties. These diverse material properties of metal borides are what forms the basis of their interdisciplinarity and their applicability in various research fields. In this study, we highlight which fundamental and practical parameters need to be taken into consideration when designing nanomaterials for specific applications. A simple one-pot chemical reduction method was applied for the synthesis of manganese mono-boride nanoflakes at room temperature. How the specific surface area and boron-content of the as-synthesized manganese mono-boride nanoflakes influence their magnetic and electrocatalytic properties is reported. The sample with the highest specific surface area and boron content demonstrated the best magnetic and electrocatalytic properties in the HER. Whereas the sample with the lowest specific surface area and boron content exhibited the best electric conductivity and electrocatalytic properties in the OER

Interactions between H-bonded [Cu II3(μ3-OH)] triangles; a combined magnetic susceptibility and EPR study

International audienceThe X-ray crystal structure of the CuII complex [Cu3(μ3-OH)(μ-pz)3(PhCOO)3]− (pz− = pyrazolato anion) shows an isosceles triangular core, further forming a hexanuclear H-bonded aggregate. Cleavage of the H-bonds in solution results in isolated trinuclear species. Analysis of variable temperature magnetic susceptibility data of a powder sample shows an antiferromagnetically-coupled Cu3-core with a doublet ground state and isotropic exchange parameters (Jave = −355 cm−1, Hiso = −JijSiSj). The fitting of magnetic data requires the inclusion of antisymmetric exchange, AE (HAE = Gij·Si × Sj) with Gz = 31.2 cm−1 and no detectable inter-Cu3 isotropic exchange. X-band EPR spectroscopy in a frozen tetrahydrofuran solution of the compound indicates isolated Cu3-species with g‖,eff = 2.25, g⊥,eff = 1.67. The small value of g⊥,eff (≪2.0) is consistent with the presence of AE in agreement with the analysis of the magnetic measurements. The parallel component exhibits a hyperfine pattern corresponding to one I = 3/2 nucleus with A‖ = 425 MHz. This implies a specific exchange coupling scheme obeying the order |J12| = |J13| < |J23| consistent with the crystallographically determined two long and one short Cu⋯Cu distances. The role of AE in modulating the hyperfine parameters in antiferromagnetic Cu3 clusters is studied. EPR spectra at X- and Q-band were performed with powder samples of the cluster at liquid helium temperatures. The spectra in both bands are consistent with two interacting Sa,b = 1/2 species in the point dipolar approximation. Fitting of the spectra reveals that each spin is characterized by g‖ = 2.24, g⊥ = 1.65 which is in agreement with an isolated Cu3 cluster in the ground state. The determined inter-spin distance of 4.4–4.5 Å is very close to the distance between the Cu(1) and Cu(1)′ sites of the two trimeric units as imposed crystallographically (4.3 Å). This constitutes further verification of the specific exchange coupling scheme within each trimer. Magnetostructural correlations previously adopted for antiferromagnetically coupled Cu3 clusters are discussed in the light of the combined magnetic measurements and EPR spectroscop