Slow magnetic dynamics in the K3M3IIM2IIIF15 multiferroic system

K3Fe5F15 is a multiferroic material belonging to the K3M3IIM2IIIF15 family. Zero-field cooled and field cooled magnetization measured as a function of temperature demonstrate magnetic transition in K3Fe5F15, K3Fe3Cr2F15, and K3Cu3Fe2F15. Complementary to this, the magnetic behavior below the magnetic transition was studied via magnetic relaxation at different temperatures after switching magnetic field from H to −H. A slow change of magnetization on the hours time scale was observed and it was best described by a logarithmic time dependence for all three compounds over a broad temperature and field range. It follows that a distribution of magnetic moments over anisotropy barriers, which block the magnetic moments against reorientation, is present. We introduced a model of thermal activation of the magnetic moments of regions distributed over the barriers to describe the temperature and field dependence of the relaxation parameters. The dimensions of these magnetic regions were estimated to be of nanometer size

Magnetic memory effect in multiferroic K3Fe5F15 and K3Cr2Fe3F15

The fluorides K3Fe5F15 and K3Cr2Fe3F15 are known as multiferroic materials. Here we report the detection of a magnetic memory effect in these materials and its dependence on temperature and aging time. We succeeded in writing, reading, and deleting 3-bits digital information in these systems. These results show that in addition to their already known magneto-electric multiferroic properties, K3Fe5F15 and K3Cr2Fe3F15 also possess a new functionality: they can be used as materials for a thermal memory cell

The Influence of Thermal Treatment on Magnetic Moments in i-Al-Pd-Mn Quasicrystals

The influence of cooling rate on thermal strains in the quasicrystalline icosahedral Al-Pd-Mn complex metallic alloy was investigated. In general, measurements of the electronic magnetization can be used as an indirect method for determining the short-scale disorder in the crystal structure as the magnetic moments at the Mn sites are highly dependent on their local environment. Excluding the contributions of thermal vacancies and second phase precipitates by proper selection of preannealing temperatures and durations, the changes in magnetization can be ascribed to the appearance or disappearance of thermal strains in the crystal structure. It was found that water-quenching increases thermal strains irrespective of previous thermal history.</p

Influence of bridging and chelating co-ligands on the distinct single-molecule magnetic behaviours in ZnDy complexes

Four new heterometallic ZnDy complexes, [ZnDy(L)(NO3) 3(py)] CH2 Cl2 (1) (py stands for pyridine), [ZnDy(L)(m-OAc)(OAc)2] 3H2 O (2), [ZnDy(L)(m-OAc)(OAc)(NO 3)] (3), and [ZnDy(L)(m-piv)(piv)2][ZnDy(L) (m-piv)(piv)(OAc)] 1.5H2O (4), have been synthesized from a methyl substituted o-vanillin based compartmental Schiff base ligand, N,N0-bis(3-methoxy-5-methylsalicylidene)-1,2-phenylenediamine (H2L), in association with various secondary co-ligands like acetate (OAc), nitrate and pivalate (piv), and magneto-structurally characterised. They possess a nearly identical [Zn(II)–Dy(III)] core, bridged by the phenoxo-O atoms of the compartmental Schiff base ligand. Magnetic studies revealed the distinct single- molecule magnetic (SMM) behaviours through single to multiple relaxation channels, in which 1, 2 and 4 can display slow relaxation of magnetisation at a zero dc field, the performance of which can be further improved by applying a magnetic field at the expense of the reduction of under barrier relaxation processes, while 3 shows only field-induced weaker slow magnetic relaxation behaviours. Ab initio calculations were performed for the in-depth understanding of the magnetic dynamics in these complexes. The difference in the magnetic behaviours of the four complexes can be ascribed to the effect of bridging/chelating co-ligands in these complexes. Therefore, the present report highlights that the magnetic anisotropy is sensitive to the bridging/chelating co-ligands used, leading to the distinct magnetic dynamics in these systems.publishe

Magnetic properties of nickel manganite obtained by a complex polymerization method

Spinel materials based on Mn and Ni has been intensively studied over the past years due to their excellent semiconductor properties. Nickel manganite as NTC thermistor is widely used today in different industrial sectors. Here we report the complex polymerization method (CPM) for producing nickel manganite fine particles with a homogeneous distribution of constituent cations in the crystal lattice that ensures formation of dense monophased ceramic with the novel magnetic properties after been sintered in oxygen and air atmosphere. Phase composition of the synthesized materials was examined by XRPD, while the morphology of the powder and microstructure of ceramic were investigated using FESEM and SEM analyses, respectively. The magnetic properties of the samples have been studied by measuring the temperature and field dependence of magnetization. Magnetic measurements of M(T) reveal rather complex magnetic properties and multiple magnetic phase transitions. In the case of air atmosphere we found three magnetic phase transitions with transition temperatures at TM1=35 K, TM2=101 K and TM3=120 K. TM1 maximum is strongly dependent on the strength of the applied magnetic field (TM1 decreases with increasing applied field) whereas the TM3 is field independent The values of the coercivity, remanent magnetization and saturation magnetization at 100 K are: HC = 184 Oe, Mr = 1.92 emu/g and MS = 7.88 emu/g, respectively. The measured values at 5 K are HC = 1035 Oe, Mr = 7.70 emu/g and MS = 14.47 emu/g. Moreover, hysteresis properties measured after cooling of the sample in magnetic field show exchange bias effect with an exchange bias field |HEB=196 Oe. For the sample synthetized in oxygen atmosphere, the magnetization dependence of temperature M(T) and AC susceptibility data obtained from SQUID measurements clearly demonstrates that quadruple magnetic phase transitions can be readily detected at TM1~115 K, TM2~105 K, TM3~38 K and TM4~7 K. These findings suggest the novel magnetic transition for nickel manganite at low temperature TM4. The temperatures of observed maximums in χ’(T) and χ’’(T) parts of susceptibility are frequency independent, whereas the height of the peaks decreases with increasing frequency. The fact that TM4 does not shift with the increase of the frequency led us to the conclusion that there are no spin-glass/surface effect and/or blocking temperature/finite size effect connected to the NiMn2O4 ceramic. Therefore, the low-temperature peak TM4 in AC susceptibility is associated with ferromagnetic-like and antiferromagnetic-like magnetic transition in the interfacial FM/AFM internal structure. The exchange bias effect was found in a field cooled hysteresis loops at 5 K. The field cooling of the sample was under a magnetic field of 100 Oe and 10 kOe whereas the determined exchange bias fields were |HEB|=129 Oe and 182 Oe, respectively. The analysis of the results and comparison with literature data allowed us to conjecture that the mixed oxidation states of Mn ions and ferromagnetic and antiferromagnetic sublattice orders tailor these interesting magnetic properties

Hall Effect of the Triclinic Al73Mn27 and T-Al73Mn27–xPdx (0 ≤ x ≤ 6) Complex Metallic Alloys

The Hall coefficient, RH, of the triclinic Al73Mn27 and Taylor-phase Al73Mn27xPdx (x = 0, 2, 4 and 6) complex metallic alloys has been measured from 90 to 400 K. The Hall coefficients of all the samples are positive and they decrease strongly with the increase of temperature, T. For the separation of the normal, R0, and anomalous, RS, Hall coefficient the results for the paramagnetic susceptibility,χ(T), and electrical resistivity, ρ(T), have been used. The well defined linearity of the RH vs. χ(T)·ρ2(T) plots confirms the assumption that in these materials RH is dominated by spin-orbit interaction. The values deduced from the RH vs. χ and RH vs. χ·ρ2 plots in T­AlMnPd phases, fall between –2 × 10–10 m3 C–1 and 0 for R0, and are about 5 × 10–7 m3 C–1 for RS. The values deduced from the RH vs. χ·ρ2 plots in the triclinic Al73Mn27 alloy are about –15 × 10–10 m3 C–1 for R0, and about 1.5 × 10–5 m3 C–1 for RS.</p

Strong Antiferromagnetism in Isolated Anionic Dicopper(II) Methanoato Paddle-wheel Complex

A new ionic compound (C5H6NO)2[Cu2(μ-O2CH)4(O2CH)2], 1 formed of 4-hydroxy-pyridinium cations and a complex anion was synthesized. The anion is a paddle-wheel dicopper carboxy-late complex with four syn,syn-bridging and two axial anionic methanoato ligands. The XRD structure de-termination of 1 reveals that the molecular structure is stabilized by two H-bonds between the cations and the axial paddle-wheel anions (N–H···O 2.755(3), O–H···O 2.489(2) Å). The compound exhibits a very strong (2J = 500 cm–1) intra-binuclear antiferromagnetic interaction noticed already at room temperature attributed to the methanoato intra-binuclear bridges. The typical EPR S = 1 spin system signals of the dicopper paddle-wheel complexes at 90 and 450–700 mT are found in the room temperature spectrum, but they are poorly seen in the 110 K spectrum. These signals are of very low intensity and are accompanied by a dominant signal at 320 mT, all closely related to a very strong antiferromagnetic interaction present in 1

Unconventional photo-induced charge-density-wave dynamics in 2H-NbSe2_{2}

We investigated temperature ($T$) dependent ultrafast near-infrared (NIR) transient reflectivity dynamics in coexisting superconducting (SC) and charge density wave (CDW) phases of two-dimensional 2H-NbSe$_{2}$ using NIR and visible excitations. With visible pump-photon excitation (400 nm) we find a slow high-energy quasiparticle relaxation channel which is present in all phases. In the CDW phase, we observe a distinctive transient response component, irrespective of the pump-photon energy. The component is marked by the absence of coherent amplitude mode oscillations and a relatively slow, picosecond rise time, which is different than in most of the typical CDW materials. In the SC phase, another tiny component emerges that is associated with optical suppression of the SC phase. The transient reflectivity relaxation in the CDW phase is dominated by phonon diffusive processes with an estimated low-$T$ heat diffusion constant anisotropy of $\sim30$. Strong excitation of the CDW phase reveals a weakly non-thermal CDW order parameter (OP) suppression. Unlike CDW systems with a larger gap, where the optical OP suppression involves only a small fraction of phonon degrees of freedom, the OP suppression in 2H-NbSe$_{2}$ is characterised by the excitation of a large amount of phonon degrees of freedom and significantly slower dynamics

Synthesis, structural and magnetic properties of Y1-xYbxF3 solid solution

Many works devoted to obtaining nanodispersed BaTiO3 powder modified with different dopants for suitable properties providing. In particular, recently considerable attention has been given to obtaining modified nanopowders BaTiO3 possessing relaxor behavior order to ensure reliable work of dielectrics. Generally, Ca,Zr,Mn, ,Pb and rare earth elements such as Nb,Y adds order to provide stress, inhibit grain growth and provide Pinching effect, and hence to increase dielectrics relaxor behavior. However, there is still an issue associated with obtaining satisfactory stoichiometry of the obtained powder. From this viewpoint Ca,Zr-doped BaTiO3 were prepared with co-precipitation method via multiligand complexes formation and influence of the precursor type on Ca,Zr-doped BaTiO3 stoichiometry were investigated. Their stoichiometry, crystal structure was examined in order to determine preferential solubility site of Ca,Zr ions in perovskite structure. Stoichiometry Ca,Zr-modified BaTiO3 will be evaluated considering different precursor type. X-ray, IR spectroscopy and X-ray fluorescence analysis were carried out to obtain the knowledge on the occupation site in the Ba1-xСaxTi1-yZryO3 perovskite structure. These results proved influence complex formation on Ca,Zr-modified BaTiO3 stoichiometry

Interplay between the structural and magnetic probes in the elucidation of the structure of a novel 2D layered V_4O_4(OH)_2(O_2CC_6H_4CO_2)_4·DMF

The title compound has been synthesized under solvothermal conditions by reacting vanadium(V) oxytriisopropoxide with terephthalic acid in N,N-dimethylformamide. A combination of synchrotron powder diffraction, infrared spectroscopy, scanning and transmission electron microscopy, thermal and chemical analysis elucidated the chemical, structural and microstructural features of new 2D layered inorganic-organic framework. Due to the low-crystallinity of the final material, its crystal structure has been solved from synchrotron X-ray powder diffraction data using a direct space global optimization technique and subsequent constraint Rietveld refinement. [V_4O_4(OH)_2(O_2CC_6H_4CO_2)_4•DMF] crystallizes in the monoclinic system (space group P2/m (No. 10)); cell parameters: a = 20.923(4), b = 5.963(4), c = 20.425(1)Å, β = 123.70(6)º, V = 2120.1(9)Å^3, Z = 2. The overall structure can be described as an array of parallel 2D layers running along [-101] direction, consisting of two types of vanadium oxidation states and coordination polyhedra: face-shared trigonal prisms (V^4+) and distorted corner-shared square pyramids (V^5+). Both configurations form independent parallel chains oriented along the 2-fold symmetry crystallographic b-axis mutually interlinked with terephthalate ligands in a monodentate mode perpendicular to it. The morphology of the compound exhibits long nanofibers, with the growth direction along the layered [-101] axis. The magnetic susceptibility measurements show that the magnetic properties of V_4O_4(OH)_2(O_2CC_6H_4CO_2)_4•DMF can be described by a linear antiferromagnetic chain model, with the isotropic exchange interaction of J = −75 K between the nearest V^4+ neighbours of S = 1/2