Increase Of Dy Concentration Research Articles

Rare earth substituted lithium ferrite/carbon black ceramic composites for shielding electromagnetic radiation

The requirement for electromagnetic interference (EMI) shielding materials have been increased in the last few years due to the extensive usage of portable communication/wireless devices. These devices radiate harmful electromagnetic waves; hence it is imperative to explore suitable materials to protect human health from the radiation. In this study, Dy substituted lithium ferrite/carbon black (LiFe5-xDyxO8/CB) composites have been developed for better shielding efficiency. The effect of Dy on structural, microstructural, and magnetic responses is studied systematically. The fluctuations in the lattice constant are attributed to the differences in the ionic radius of Dy and Fe. The addition of Dy caused the inhibition of grain growth and the formation of irregular grains. The saturation magnetization is also enhanced with an increase in Dy concentration up to x = 0.1 (LD10FO/CB) and then decreased after that Neels’ sublattice model interprets the variation in magnetization and the effective magneto crystalline anisotropy is analyzed. The EMI shielding effectiveness (SE) due to absorption and the reflection is enhanced by incorporating Dy (in the X- and Ku- bands). A maximum SE of 26 dB is observed for x = 0.1 compositions. It is noticed that absorption is the dominant mechanism rather than reflection. The highest absorption coefficient (Aeff) of 99.6% is achieved for LD10FO/CB in the range of 17–18 GHz. The values of complex permittivity and permeability for LD10FO/CB are in the range of (20–40) and (2–6), respectively. The incorporation of Dy (rare earth ion) in spinel ferrite led to promote 4f − 3d coupling along with 3d − 3d, which helped to enhance the magnetic and electrical properties. The results demonstrate that such ceramics can be used as a commercial microwave absorber.

Study of structural, electrical and hyperfine properties of Dy doped YFeO3

Investigations on effect of Dysprosium (Dy) on structural and electrical properties of polycrystalline Yttrium Iron Oxide (YFeO3) are presented in this paper. Y1xDyxFeO3(x = 0,0.2,0.4,0.6,0.8) samples are prepared through sol-gel process. Rietveld refined XRD plots confirms formation of mono phase orthorhombic structures. From the Rietveld data, lattice parameter values are found to increase with increase in Dy concentration. Raman spectroscopic study enables us to understand the subtle changes occurring in crystal structure due to Dy doping and also confirms the pure phase of samples. When Dy+3 is doped in place of Y+3, Raman bands are seen to be shifted to lower frequencies, which indicates an increase in lattice constants in the samples. SEM morphology investigations demonstrate that grains are not homogeneous in size and are irregular in shape. Up to x = 0.4, J-E graphs indicate a rise in leakage current density but however on further substitution of Dy, leakage current is found to decrease. From ln J vs ln E plots, it is observed that Ohmic conduction dominates the whole electric field range. Room temperature 57Fe Mössbauer studies dismiss any existence of magnetic impurities and confirm that samples have magnetic ordering.

Enhanced refrigeration capacity in Ho1-xDyxB2 compounds around liquid hydrogen temperature

In this study, the crystal structure, magnetic properties, and magnetocaloric effect of Ho1-xDyxB2 compounds were investigated. It was found that nearly single-phase (Ho,Dy)B2 compounds with the AlB2-type structure directly form in the as-arc melted alloys and have two successive magnetic transitions. With the increase of Dy concentration x from 0 to 0.8, the spin reorientation transition temperature remains at about 13 K, while the Curie temperature significantly increases from 16 to 43 K. As a result, the full-width at half-maximum of the magnetic entropy change versus temperature curve increases from 19.9 to 48.2 K. Also, these Ho1-xDyxB2 compounds exhibit a large refrigeration capacity of 523–635 J kg−1 under a magnetic field change of 5 T, although the maximum magnetic entropy change decreases from 34.3 to 17.2 J kg−1 K−1. In addition, Dy-containing compounds exhibit a table-like magnetocaloric effect compared with the HoB2 compound. Our results indicate that Ho1-xDyxB2 compounds are a promising candidate for cryogenic magnetic refrigeration around liquid hydrogen temperature.

Heat Stagnation of Dy-Doped La2/3Ca1/3MnO3 Manganese Oxides in the Measurement Process of Warming and Cooling.

(La1–xDyx)2/3Ca1/3MnO3 samples with the perovskite structure were prepared by the sol–gel method, and the R–T curves of the samples in 0–3000 Gs magnetic field during warming and cooling processes were compared. It is found that the transition temperature (Tc) of the samples decreases and peak resistance (RP) of the samples increases with the increase of Dy concentration in the same magnetic field. In addition, for the samples with the same Dy concentration, Tc of the samples increases and magnetoresistance (MR) of the samples decreases with the increase of the magnetic field, and the increase of Tc as well as the decrease of resistance is more obvious during the cooling process than those during the warming one. Besides, the variation of MR during the cooling process is also larger than that during the warming one.

Effect of Dy on electrochemical supercapacitive behaviour of α-MnO2 nanorods

α-MnO2 nanorods doped with different molar concentrations of Dysprosium (Dy) have been successfully synthesised via hydrothermal method as an electrode material. The electrochemical properties are evaluated using cyclic voltammetry, Galvanostatic charge discharge studies where we demonstrate an increase in capacitance with increase in Dy concentration. For α-MnO2: Dy (15 mol %), capacitance enhances by twice than that of bare α-MnO2. XRD (X-Ray diffraction) and FE-SEM (Field Emission- Scanning Electron Microscopy) measurements show that although the structure of Dy doped α-MnO2 remains tetragonal, the crystallinity degrades along with the reduction in aspect ratio of nanorods. In addition, BET (Brunauer-Emmett-Teller) measurement shows that the surface area and size of the pores increase with increase in Dy concentration. Poor crystallinity, large surface area and smaller nanorods are an evidence of high capacitance observed in α-MnO2: Dy (15 mol %). The effect of Dy concentration on structure, morphology, surface area and electrochemical properties are discussed in detail for the application of supercapacitor.

Effect of Dy-substitution on structural and magnetic properties of Mn[sbnd]Zn ferrite nanoparticles

This paper describes the structural and magnetic properties of Dy-substituted MnZn ferrite nanoparticles. MnZnDy ferrite nanoparticles of the composition Mn0.5Zn0.5DyxFe2-xO4 (x=0.05, 0.1, 0.15 and 0.2) were synthesized by a facile chemical co-precipitation method. The samples were characterized through X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM) and Curie temperature. The XRD patterns confirm the synthesis of single crystalline phase of MnZnDy ferrite nanoparticles. Lattice parameter increases with increase in Dy-substitution which confirms the replacement of Fe3+ ions by Dy3+ ions. Crystallite size is of the order of 6–8 nm for all these samples. The particle sizes observed from TEM analysis are in good agreement with the XRD values. The magnetic measurements show superparamagnetic nature of the samples. The saturation magnetization decreases with increase in Dy-concentration and can be correlated to modifications in the A-B exchange interactions as a result of the structural modifications due to Dy-substitution. The Curie temperature for Mn0.5Zn0.5Fe2O4 nanoparticles is 124 °C and decreases up to 84 °C with the increase in the Dy-concentration. The decrease in Curie temperature can be attributed to the weakening of the superexchange interaction between A-site and B-site as a result of Dy-substitution. The low value of Curie temperature and higher value of thermomagnetic coefficient kT shown by these samples makes them suitable for the preparation of temperature sensitive ferrofluid for heat transfer applications.

Synthesis and magnetostrictive properties of Pr1−xDyx(Fe0.8Co0.2)1.93 cubic Laves compounds

The structure, magnetic properties and magnetostriction of high-pressure synthesized Pr1−xDyx(Fe0.8Co0.2)1.93 compounds were investigated. These compounds, which could not be readily synthesized under ambient pressure, exhibit single cubic Laves phase owing to the effects of high-pressure annealing. The Curie temperature increases with increasing x, indicating that 3d-4f coupling becomes stronger with the increase of Dy concentration. The saturation magnetization decreases with increasing x, which can be ascribed to the competition of sublattice magnetization. The easy magnetization direction of the compound lies along <111 > with x ≤ 0.05 while lies along <100 > when x ≥ 0.10. Meanwhile, the low-field magnetostriction λ∥ − λ⊥ of the compound system peaks at x = 0.05 and then decreases with increasing x, which reveals that the composition anisotropy compensation between Pr3+ and Dy3+ might be realized in Pr1−xDyx(Fe0.8Co0.2)1.93 system. Pr0.95Dy0.05(Fe0.8Co0.2)1.93 compound combines a large low-field magnetostriction (648 ppm at 3 kOe) and the merits of low-cost raw materials, which may make it a potential material for magnetostrictive application.

Quantum corrections to low temperature electrical conductivity in Dy doped ZnO thin films

We have grown thin films of Dy doped ZnO (Dy:ZnO) on sapphire substrate using pulsed laser deposition with Dy concentration varying from 0.05at.% to 1.8at.%. These as grown Dy:ZnO thin films were characterized using low temperature four probe electrical measurements (in the range ~300K to 4K). All the Dy:ZnO thin films showed metal like behavior with a transition from positive to negative temperature coefficient of resistivity (TCR) and again to positive TCR with an increase of Dy concentration. This anomaly in conduction mechanism was investigated by considering quantum corrections to classical Boltzmann conductivity. All the Dy:ZnO thin films also exhibited negative magneto-resistance that supported for a significant contribution of weak localization in quantum corrections to conductivity.

Effect of Dy-substitution on the structural, vibrational, and multiferroic properties of BiFeO3 nanoparticles

Dysprosium (Dy) modified BiFeO3 [Bi1−xDyxFeO3 (x = 0.05, 0.10, and 0.15)] nanoparticles have been synthesized by a low temperature co-precipitation method. Rietveld analysis of X-ray diffraction data reveals a transformation from rhombohedral structure to orthorhombic structure with increase in the Dy concentration. From the transmission electron microscopy analysis, it is observed that the particle sizes of Bi1−xDyxFeO3 (x = 0.05, 0.10, and 0.15) nanoparticles range between 50–70, 40–50, and 30–50 nm, respectively. Raman spectra of Bi1−xDyxFeO3 (x = 0.05) belonging to rhombohedral (R3c) structure show 4A1 and 7E fundamental Raman modes in the range of 100–650 cm−1 and two-phonon scattering modes such as 2A4 (longitudinal optical), 2E8 (transverse optical (TO)), and 2E9 (TO) in the range of 950–1270 cm−1. Suppression, broadening, and shifting of Raman modes have been observed with further increase in Dy concentration. The fundamental Raman modes of Bi1−xDyxFeO3 (x = 0.15) are assigned under orthorhombic (pnma) rather than rhombohedral (R3c) as the Rietveld analysis of X-ray diffraction data predicts a structural transformation for this particular composition. A complete suppression of two phonon modes has been noticed for this composition. An anomaly in the temperature dependent dielectric studies has been observed in all the samples at the vicinity of Neel temperature indicating a magnetic ordering, and an increase in magnetization with increase of Dy concentration in BiFeO3 is noticed from the room temperature magnetic studies. P–E hysteresis loop studies show a decrease of remnant polarization (Pr) with the increase in Dy concentration and disappearance of hysteresis loop occurs for Bi1−xDyxFeO3 (x = 0.15) depicting a transformation from non-centrosymmetric (R3c) to centrosymmetric (Pnma) system.

Synthesis, structural and electrical properties of Bi1−xDyxFeO3 multiferroic ceramics

Abstract Polycrystalline ceramic samples of dysprosium (Dy 3+ ) doped bismuth ferrite of general formula Bi 1− x Dy x FeO 3 ( x =0.00, 0.01, 0.05 and 0.1) have been prepared by standard solid state reaction method. Powder X-ray diffraction (XRD) analysis reveals that all the samples crystallize in the rhombohedral structure with noncentrosymmetric R 3 c space group. The refined lattice parameters decrease with the increase of Dy concentration within the same structure symmetry. The bond lengths among atoms for all the compounds were calculated by the Rietveld analysis. The frequency and temperature dependent dielectric constants (real and imaginary parts) have been measured. The real part of dielectric constant reveals that the Neel temperature decreases with the increase of Dy-substitution down to ∼200 °C for 10% substitution to the Bi site.

Structural, electrical and optical properties of Dy doped ZnO thin films grown by buffer assisted pulsed laser deposition

Abstract Transparent conductive dysprosium doped ZnO (Dy:ZnO) thin films with preferential orientation in the (0 0 0 2) direction were deposited on (0 0 0 1) sapphire substrate by buffer assisted pulsed laser deposition. The experimental results show that the resistivity of Dy:ZnO thin films decreased to a minimum value of ∼7.6×10−4 Ω cm with increasing Dy concentration up to ∼0.45 at%, then increased with the further increase of Dy concentration. On the contrary, the band gap and carrier concentration of Dy:ZnO thin films initially increased, then decreased with increase of Dy concentration. The blue shift of band gap of Dy:ZnO thin films with increasing carrier concentration was attributed to the competing effects of Burstein-Moss shift and band gap narrowing. A bright room temperature photoluminescence observed at ∼575 nm in all the Dy:ZnO thin films, with maximum intensity at ∼0.45 at% of Dy doping, was attributed to be due to intra-band transitions of Dy3+ in ZnO. Near band edge photoluminescence of ZnO was observed at ∼380 nm with photoluminescence intensity decreasing with increase of Dy concentration. Such Dy:ZnO thin films are found to be suitable candidate for luminescent device applications.

Structural and optical properties of Dy doped ZnO thin films prepared by pyrolysis technique

Structural, optical and Raman scattering studies have been performed on the Dy substituted zinc oxide (ZnO) thin films (1, 3 & 5 wt%) fabricated through a sol gel based spray pyrolysis technique on preheated glass substrates. The hexagonal crystal structure with (002) preferred orientation was confirmed from the X-ray diffraction analysis for the undoped and Dy doped ZnO films. The crystallinity of the films decreased with increasing Dy content with a corresponding decease in the intensity of (002) orientations. Reduction in grain size with increase in Dy content was observed. The shift of E2 (high) mode observed in the Raman spectra towards the lower wave numbers with increase in Dy concentration was correlated with the increase in stress on the ZnO matrix upon Dy substitution. The optical band gap was found to increase from 3.17 eV to 3.27 eV with a transparency of 80% for higher Dy concentrations. A blue shift in the NBE emission was also observed for Dy doping.

Magnetic properties of Er1−xDyxTiCo11

The structural and magnetic properties of Er1−xDyxTiCo11 compounds with 0⩽x⩽1 have been studied to find out their suitability as permanent magnet materials. Crystal structure was analyzed using the Rietveld refinement of the powder x-ray diffractograms. Thermomagnetic analysis showed that the spin reorientation transitions shift to lower temperatures with increase in Dy concentration, which has been attributed to the increase in the axial anisotropy of these compounds. The magnetic properties have been explained by taking into account the structural details.

Magnetic and electrical properties of(La1−xDyx)0.7Ca0.3MnO3perovskites

The effect of substituting La with Dy in the ferromagnetic perovskite La 0 . 7 Ca 0 . 3 MnO 3 has been studied in the series (La( 1 - x )Dy x ) 0 . 7 Ca 0 . 3 MnO 3 (x= 0, 0.114, 0.243, and 0.347). Magnetic and transport properties have been measured using ac susceptibility, dc magnetization, neutron-depolarization, neutron-diffraction, and resistivity techniques. These studies show that an increase in Dy concentration suppresses the low-temperature ferromagnetic ground state, driving the system (for x=0.114 and 0.243) first into a randomly canted ferromagnetic state with a reduced metal-insulator transition temperature and then (for x = 0.347) to an ''insulating cluster-spin-glass state. Such deterioration of ferromagnetism and metallic conduction with Dy substitution is explained on the basis of a decrease in the transfer integral, t o (describing the hopping of e g electrons between Mn 3 + and Mn 4 + , known as ferromagnetic double-exchange interaction), resulting from an increase in the structural distortion. The randomly canted ferromagnetic state and the cluster-spin-glass state for x = 0.243 and 0.347 compounds, respectively, have been confirmed by neutron-depolarization measurements. These observed features have been attributed to a competition between the coexisting ferromagnetic double-exchange and the antiferromagnetic superexchange interactions in the distorted structures with reduced geometrical tolerance factor t and the randomness resulting from the random substitutions of La 3 + with Dy 3 + .

Magnetic phase transition and 3d susceptibility in Laves phase Gd 1− xDy xCo 2 compounds

Magnetization and AC susceptibility measurements have been carried out to investigate the magnetic phase transition of Gd 1− x Dy x Co 2 compounds. It is revealed that the type of the magnetic phase transition changes from second order to first order around x c=0.8 with the increase of Dy concentration. A satisfactory explanation is offered in terms of the Inoue-Shimizu model. The exchange-enhanced susceptibility of the compounds within the exchange-enhanced paramagnetism model is in good agreement with the 3d-electrons susceptibility deduced by Inoue–Shimizu model.

Thermal behaviour and magnetic properties of B-rich NdFeB nanocomposite hard magnetic alloys with partial substitution of Dy for Nd

B-rich NdFeB base alloys with partial substitutions of Dy for Nd ((Nd1-xDyx)4.5Fe77B18.5 (x = 0-0.4)) were chosen to study the influence of Dy on thermal behaviour and magnetic properties. It was found that partial substitution of Dy for Nd results in a dramatic enhancement of coercivity jHc from 183 to 261 kA m-1 and of maximum magnetic product (BH)max from 110.6 to 133.7 kJ m-3. However, the saturation magnetization Ms only decreases about 22.8 kA m-1 for every 0.1 increment of Dy content x. Differential thermal analysis traces show that the crystallization process of the initial amorphous ribbons is a three-peak process. X-ray diffraction and differential thermal analysis indicate that the three peaks correspond to the formation of crystalline Fe3B, Nd2Fe14B, and α-Fe, respectively. With increase of Dy concentration, jHc increases to a maximum value at about x = 0.1, and then reduces gradually. The enhancement of coercivity arises from the increase of the anisotropy field for the hard magnetic phase. The reduction of intrinsic coercivity jHc is attributed to the emergence of α-Fe after annealing at the third peak and the reduction of the fraction of hard magnetic phase due to the Dy addition. In order to obtain the optimum magnetic properties, a special annealing method was used.