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Journal ArticleDOI

Neutron diffraction study of the magnetic ordering in the series R 2 BaNiO 5 (R = Rare Earth)

TL;DR: In this paper, the magnetic structures of R2BaNiO6 octahedra have been determined and refined as a function of temperature, with a magnetic structure characterised by the temperature-independent propagation vector (1/2, 0, 1/2).
Abstract: A neutron diffraction study, as a function of temperature, of the title compounds is presented. The whole family (space group Immm, a ≈ 3.8A, b ≈ 5.8A, c ≈ 11.3A) is structurally characterised by the presence of flattened NiO6 octahedra that form chains along the a-axis, giving rise to a strong Ni-O-Ni antiferromagnetic interaction. Whereas for Y-compound only strong 1D correlations exist above 1.5 K, presenting the Haldane gap characteristic of 1D AF chain with integer spin, 3D AF ordering is established simultaneously for both R and Ni sublattices at temperatures depending on the rare earth size and magnetic moment. The magnetic structures of R2BaNiO5 ( R = Nd, Tb, Dy, Ho, Er and Tm) have been determined and refined as a function of temperature. The whole family orders with a magnetic structure characterised by the temperature-independent propagation vector = (1/2, 0, 1/2). At 1.5 K the directions of the magnetic moments differ because of the different anisotropy of the rare earth ions. Except for Tm and Yb (which does not order above 1.5 K), the magnetic moment of the R3+ cations are close to the free-ion value. The magnetic moment of Ni2+ is around 1.4 , the strong reduction with respect to the free-ion value is probably due to a combination of low-dimensional quantum effects and covalency. The thermal evolution of the magnetic structures from T N down to 1.5 K is studied in detail. A smooth re-orientation, governed by the magnetic anisotropy of R3+, seems to occur below and very close to T N in some of these compounds: the Ni moment rotates from nearly parallel to the a-axis toward the c-axis following the R moments. We demonstrate that for setting up the 3D magnetic ordering the R-R exchange interactions cannot be neglected.
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TL;DR: In this paper, the authors reported the sonochemical synthesis of DBNO NC (dysprosium nickelate nanocomposite) using metal nitrates and core almond as a capping agent.
Abstract: The present work reports the sonochemical synthesis of DBNO NC (dysprosium nickelate nanocomposite) using metal nitrates and core almond as a capping agent. In addition, the effects of the power of ultrasound irradiation were investigated. The BaDy2NiO5/Dy2O3 and BaDy2NiO5/NiO nanocomposites were synthesized with sonication powers of 50 and 30 W, respectively. The agglomerated nanoparticles were obtained using different sonication powers, including 15, 30, and 50 W. The results showed that upon increasing the sonication power, the particle size decreased. After characterization, the optical, electrical, magnetic, and photocatalytic properties of the NC were studied. The nanocomposites showed an antiferromagnetic behavior. In this study, the photocatalytic degradations of two dyes, AR14 and AB92, were investigated in the presence of DBNO NC. Furthermore, the effects of the amount of photocatalyst, the concentration of the dye solution, the type of organic dye, and light irradiation on the photocatalytic activity of the nanocomposite were studied. The results showed that with an increasing amount of catalyst and decreasing concentration of dye, the photocatalytic activity of the nanocomposite was increased. This activity for the degradation of AR14 is higher than that of AB92. Both AR14 and AB92 dyes show higher photocatalytic degradation under UV irradiation than under Vis irradiation.

300 citations

Journal ArticleDOI
TL;DR: In this article, the authors provided support for ferroelectricity of a displacive type possibly involving magnetic ions due to short-range magnetic correlations within a spin-chain, through the demonstration of magnetoelectric coupling in a Haldane spin chain compound Er2BaNiO5 well above its Neel temperature of (TN = ) 32
Abstract: Observation of ferroelectricity among non-d0 systems, which was believed for a long time an unrealistic concept, led to various proposals for the mechanisms to explain the same (i.e. magnetically induced ferroelectricity) during last decade. Here, we provide support for ferroelectricity of a displacive-type possibly involving magnetic ions due to short-range magnetic correlations within a spin-chain, through the demonstration of magnetoelectric coupling in a Haldane spin-chain compound Er2BaNiO5 well above its Neel temperature of (TN = ) 32 K. There is a distinct evidence for electric polarization setting in near 60 K around which there is an evidence for short-range magnetic correlations from other experimental methods. Raman studies also establish a softening of phonon modes in the same temperature (T) range and T-dependent x-ray diffraction (XRD) patterns also reveal lattice parameters anomalies. Density-functional theory based calculations establish a displacive component (similar to d0-ness) as the root-cause of ferroelectricity from (magnetic) NiO6 chain, thereby offering a new route to search for similar materials near room temperature to enable applications.

52 citations

Journal ArticleDOI
TL;DR: In this paper, high-resolution spectroscopy of Nd-nickelate powder samples is used to study crystal-field levels and exchange splittings in these quasi-one-dimensional model compounds.
Abstract: High-resolution spectroscopy of ${\mathrm{Nd}}^{3+}$ in ${\mathrm{Nd}}_{2}\mathrm{Ba}\mathrm{Ni}{\mathrm{O}}_{5}$ and ${\mathrm{Y}}_{2}\mathrm{Ba}\mathrm{Ni}{\mathrm{O}}_{5}:\mathrm{Nd}(5%)$ powder samples is used to study ${\mathrm{Nd}}^{3+}$ crystal-field levels and exchange splittings in these quasi-one-dimensional model compounds. We demonstrate that the ${\mathrm{Nd}}^{3+}$ ground-state splitting in the magnetically ordered state of ${\mathrm{Nd}}_{2}\mathrm{Ba}\mathrm{Ni}{\mathrm{O}}_{5}$ (${T}_{N}=47.5\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, as found from our spectroscopic data) accounts for the low-temperature magnetic properties and for the $4\text{\ensuremath{-}}\mathrm{meV}$ mode observed earlier in inelastic neutron scattering experiments. Crystal-field analysis is performed. Its results show that the directions of ordered magnetic moments in ${\mathrm{Nd}}_{2}\mathrm{Ba}\mathrm{Ni}{\mathrm{O}}_{5}$ are determined by the single-ion anisotropy of ${\mathrm{Nd}}^{3+}$. We argue that the crystal-field parameters obtained for Nd-nickelate (in this work) and Er-nickelate (in our earlier work) can be used to predict the energy-level patterns and magnetic properties of other rare-earth linear-chain nickelates.

35 citations

Journal ArticleDOI
TL;DR: In this article, the interplay between magnetic and dielectric properties of rare earth compounds was studied and it was shown that a linear magnetoelectric effect exists in this compound.
Abstract: The compounds ${R}_{2}\mathrm{Ba}\mathrm{Ni}{\mathrm{O}}_{5}$, with $R$ a rare earth, exhibit low dimensional magnetism including a Haldane gap, originating from ${\mathrm{Ni}}^{2+}$ chains In these compounds, the rare-earth ions give rise to three-dimensional antiferromagnetic ordering which does not eliminate the Haldane-like behavior We study here the interplay between magnetic and dielectric properties of ${\mathrm{Ho}}_{2}\mathrm{Ba}\mathrm{Ni}{\mathrm{O}}_{5}$ on a polycrystalline sample We show that a linear magnetoelectric effect exists in this compound We discuss our results in the light of the rich magnetic phase diagram of ${\mathrm{Ho}}_{2}\mathrm{Ba}\mathrm{Ni}{\mathrm{O}}_{5}$

29 citations

Journal ArticleDOI
TL;DR: It is reported that the spin-chain compound Dy2BaNiO5, recently proven by us to exhibit magnetoelectric coupling below its Néel temperature of 58 K, exhibits strong frequency-dependent behavior in ac magnetic susceptibility and complex dielectric properties at low temperatures, mimicking the 'reentrant' multiglass phenomenon.
Abstract: We report that the spin-chain compound Dy2BaNiO5, recently proven by us to exhibit magnetoelectric coupling below its Neel temperature (TN) of 58 K, exhibits strong frequency-dependent behavior in ac magnetic susceptibility and complex dielectric properties at low temperatures (<10 K), mimicking the 'reentrant' multiglass phenomenon. Such a behavior is not known among undoped compounds. A new finding in the field of multiferroics is that the characteristic magnetic feature at low temperatures moves towards higher temperatures in the presence of a magnetic field (H), whereas the corresponding dielectric feature shifts towards lower temperatures with H, unlike the situation near TN. This observation indicates that the alignment of spins by external magnetic fields tends to inhibit glassy-like slow electric-dipole dynamics, at least in this system, possibly arising from peculiarities in the magnetic structure.

23 citations