SrCoxZrxFe12−2xO19 and SrNixZrxFe12−2xO19 hexaferrites: A Comparison Study of AC Susceptibility,FC-ZFC and hyperfine interactions

This study compares the AC susceptibility, FC-ZFC and hyperfine interactions of Sr(Co_xZr_x)Fe_12−2xO₁₉ and Sr(Ni_xZr_x)Fe_12−2xO₁₉ hexaferrites (HFs) manufactured via ultrasonic route. The formation of M-type hexaferrites have been confirmed by X-ray powder diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HR-TEM) techniques. Scanning electron microscopy (SEM) presented the hexagonal-platelet morphology of products. The variation in isomer shift, line width, quadrupole splitting and hyperfine magnetic field values of them have been governed by ⁵⁷Fe Mössbauer spectroscopy which showed that Co²⁺ and Zr⁴⁺ ions located at generally octahedral and 2b sites, while Ni²⁺ and Zr⁴⁺ ions located at octahedral 12k and 4f₂ sites. Measurements of magnetization versus temperature (M-T) and AC susceptibility versus temperature were carried out. The various synthesized HFs displayed ferrimagnetic behavior in the temperature interval of 10–325 K. Super-spin glass-like behavior was noticed at lower temperatures. Neel-Arrhenius and Vogel-Fulcher models were used to explore the experimental AC susceptibility. It was showed that a lower Co-Zr substitution content leads to strengthen the magnetic exchange interactions, however even low Ni-Zr substitution content provoke a reduction in magnetic exchange interactions.     

The magnetic susceptibility of hydrogen-doped partially crystalline (Zr76Ni24)1−xHx metallic glasses

The magnetizations of Zr₇₆Ni₂₄ metallic glass and hydrogen-doped partially crystalline (Zr₇₆Ni₂₄)_1−xH_x metallic glasses have been measured in the temperature range 10-300 K and magnetic fields up to 2 T for various dopant concentrations (x=0, 0.024, 0.043, 0.054). It is found that the samples are paramagnetic and magnetic susceptibility at room temperature, χ(300 K), shows a nonmonotonic behaviour upon hydrogenation. The values of χ(300 K) of the hydrogen-doped partially crystalline (Zr₇₆Ni₂₄)_1−xH_x metallic glasses are reduced with increase in hydrogen content up to x=0.043, whereas for x=0.054, an enhancement of χ(300 K) has been revealed. The magnetic susceptibility is weakly temperature dependent down to 110 K, below which an increase is observed. A shallow minimum exists between 90 and 120 K. The form and magnitude of the observed temperature dependence of the magnetic susceptibility are well accounted for by the sum of the quantum corrections to the magnetic susceptibility. Hydrogen reduces the electronic diffusion constant and influences strongly the quantum interference at defects, slowing down the spin diffusion and enhancing the magnetic susceptibility in the temperature range from 110 down to 10 K.     

Universal conductivity variation in glassy Zr-M alloys

Temperature dependence (3–300 K) of the electrical conductivity in a number of amorphous Zr_1?xM_x alloys (M = Cu, Ni, Co and Fe, 0.19 < x < 0.71) has been analysed in some detail. Like in some other alloys with a high electrical resistivity, the conductivity varies as T at lower temperatures (T < 80 K) and √T at higher temperatures. A new feature observed is that the ratio of the coefficients of a low temperature T and a high temperature √T conductivity variation is practically constant for allalloys. Therefore a universal conductivity-temperature curve can be constructed for all amorphous Zr_1?xM_x alloys with the resistivity higher than 150 μohms cm. These results are consistent with the effects of incipient localisation and indicate that the electron-phonon coupling determines the conductivity variation.     

Hyperfine interactions in laves phase intermetallic compounds Zr(Fe1−xMx (M = Al or Co) − A 57Fe Mössbauer study

Recently, results were reported on magnetic hyperfine interactions in context with bulk magnetic properties of Zr- (Fe_1?xA1_x)₂ and Zr(Fe_1?xCo_x)₂. In the present investigation special attention is focussed on the concentra tion dependence of both the isomer shift and the quadrupole interaction and their relation with the lattice dimensions. Moreover the hyperfine parameters are carefully examined in the vicinity of the crystallographic phase transitions occurring in Zr- (Fe_1?xA1_x)₂. Finally the temperature dependence of the internal field, the influence of the local environment upon the hyperfine parameters and the degree of localization of the magnetic moments is examined.     

Quantum corrections to conductivity of glassy Zr100−xCux alloys

The variation of the conductivity of glassy Zr_100?xCu_x alloys (x=50, 58, 67 and 71) in the temperature range 2–300 K is discussed in some detail. It is shown that the conductivity varies as √T for $\text{T}\text{θ}{}_{\mathrm{D}}\text{3}$ and T for the lower temperatures which is consistent with the predictions of a weak localization theory. Another strong temperature variation of the conductivity sets at the lowest temperatures which could be either due to interaction effects or due to electron scattering on the unstable ionic configurations. Some support to the latter effects is presented.     

57Fe,61Ni and91Zr hyperfine field distributions in magnetic Tm-Zr amorphous alloys

Pulsed NMR measurements were performed on [Tm₁ (Tm₂)]_90+x Zr_10?x (Tm=Fe, Co, Ni) amorphous alloys utilizing a newly developed low temperature wide band probehead-preamplifier system. A 11,6 T broad⁵⁷Fe hyperfine field distribution around the average of 23.6 T together with a less intensive peak around 11 T has been found in Fe_90.6Zr_9.4, in excellent agreement with Mössbauer studies. A rather flat distribution around the average value of 14.8 T characterizes the transferred hyperfine field at the Zr sites in the same alloy. Both features provide strong evidence for a broad range of exchange interactions and variations in the spin density at the Fe sites in this material. A much narrower and symmetrical distribution at the Zr sites around 10 T in Co₉₀Zr₁₀ is evidence of the higher magnetic homogeneity of this alloy as compared to Fe₉₀Zr₁₀. In Fe₆₀Ni₃₀Zr₁₀, in addition to the⁵⁷Fe signal, a contribution from⁶¹Ni nuclei could be separated, corresponding to an average hyperfine field value of 15.3 T.     

Sodium nuclear magnetic resonance and dynamic second order quadrupole effects in the superionic conductor nazirpsio

The sodium nuclear magnetic resonance interaction in nazirpsio, Na_1+xZr₂P_3-xSi_xO₁₂ (x = 1.9) is dominated by dynamic second order quadrupole interactions. This has been determined by observing the temperature and frequency dependence of the dipolar-quadrupolar linewidth of the $\text{m=+}\text{1}\text{2}\text{?m=-}\text{1}\text{2}$ transition. This behaviour has been anticipated by Werbelow. The motional narrowing of the quadrupole interaction appears to be thermally activated process and agrees with a model of three dimensional diffusion of the sodium ions. The measured activation energies are consistent with those derived from conductivity measurements.     

Magnetothermopower of nanocomposites in the vicinity of the percolation threshold

The field dependences of the thermopower of composites with Co and Co₄₅Fe₄₅Zr₁₀ nanoparticles in the Al₂O _n insulator matrix are studied in magnetic fields up to 10 kOe at room temperature with compositions up to the percolation threshold (i.e., in the region where tunnel conductivity takes place). In composites obtained in argon, negative magnetothermopower (i.e., a decrease in the thermopower in strong magnetic fields) is observed, while positive magnetothermopower is observed in composites obtained in the atmosphere of argon and oxygen. It is shown that the theory developed for tunnel magnetothermopower in nanocomposites makes it possible to explain the results on a qualitative level in the case when the local density of electron states at the surface of nanoparticles depends on the sputtering conditions. Nanocomposites CoFeZr _x (Al₂O _n )_100?x ) obtained in argon and nitrogen display a strong asymmetry of magnetothermopower relative to the magnetic field direction; this anisotropy is associated with anisotropy of these nanostructures.     

Magnetic and electrical transport properties of amorphous Zr-Fe alloys

Amorphous Zr_1?xFe_x samples were prepared in the composition range 0.2 ? x ? 0.9 either by means of vapour deposition or melt spinning. The electrical resistivity was determined in the range 4.2–300 K. Negative temperature coefficients were observed in the whole concentration range. The extended Ziman theory (diffraction model) was found to be able to explain these results only if the effective valence of the Fe atoms involves not only s electrons but also d electrons. The magnetic properties and the ⁵⁷Fe Mössbauer effect of the Zr_1?xFe_x alloys were studied in the range 4.2–300 K. The Fe-rich alloys are ferromagnetic. The Fe moment vanishes in alloys of an Fe concentration lower than about 50 at%. In most alloys (x ? 0.8) the Curie temperature is below room temperature and continuously decreases with Zr concentration. By means of Mössbauer spectroscopy and magnetic measurements it is shown that compositional short-range order (CSRO) is present to a higher degree in melt-spun alloys than in vapour-deposited alloys. The effect of sign and magnitude of the heat of solution on CSRO and the magnetic properties is discussed.     

Effect of Co or Mn addition on the soft magnetic properties of amorphous Fe89−xZr11Bx (x=5, 10) alloy ribbons

The temperature and field dependent magnetic properties of melt-spun amorphous Fe_89−x−yZr₁₁B_x(Co,Mn)_y (x=5, 10 and 0≤y≤10) alloys in the temperature range 5-1200 K are reported. The Curie temperature and saturation magnetization at room temperature increase (decrease) almost linearly with Co (Mn) addition. With increasing Co concentration, the room temperature coercivity increases at the rate of 2.26 (0.28) A/m per at% for the x=5 (10) samples. The high-field magnetic susceptibility and local magnetic anisotropy decrease (increases) rapidly with increasing Co (Mn) concentration. The thermomagnetic curves show a marked increase in magnetization above 850 K corresponding to the crystallization of α-FeCo (α-Fe) phase in samples containing Co (Mn). The Curie temperature of the crystalline phase increases (remains same) with increasing Co (Mn) concentration with the formation of α-FeCo (α-Fe). Addition of Co up to 10 at% in Fe-Zr-B improves the room temperature saturation magnetization from 0.56 to 1.2 T, and Curie temperature from 315 to 476 K. Also, the coercivity increases with Co addition from 1.27 to 23.88 A/m for x=5 and from 7.64 to 10.35 A/m for x=10 alloy. The non-collinear spin structures that characterize Fe rich Fe-Zr-B amorphous alloys have been used to describe the observed results.     

Curie temperatures and crystallization behavior of amorphous Fe81−xNixZr7B12 (x=10, 20, 30, 40, 50, 60) alloys

Curie temperature, crystal structure and crystallization behavior of amorphous alloys with the stoichiometry Fe_81−xNi_xZr₇B₁₂ (x=10–60) have been studied by X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and AC-magnetization (TMAG) measurements as functions of temperature. The thermal stability of long-range magnetic order, T_C vs. Ni content in as-quenched amorphous alloys exhibits maximum at 352 °C for x=40. The primary crystallization has been detected during annealing at the first crystallization stage of all ribbons investigated.     

Effect of electric field on electrocaloric effect in Pb(Zr1 − xTix)O3 solid solution

A thermodynamic analysis is employed to investigate the intrinsic electrocaloric effect of Pb(Zr_1 − xTi_x)O₃ solid solution system under the different electric field. Theoretical analysis indicates that Pb(Zr_1 − xTi_x)O₃ system has the giant electrocaloric coefficient and the large adiabatic temperature change near its ferroelectric Curie temperature. The applied electric field decreases not only the electrocaloric coefficient but also its temperature dependence. Furthermore, it increases the adiabatic temperature change as well as its dependence of temperature. The temperature corresponding to the maximum of electrocaloric coefficient and adiabatic temperature change increases with the enhancement of electric field because of its first-order phase transition between ferroelectric phase and paraelectric phase.     

Control of the properties of Pb(TixZr1-x )O3 solid solutions by external disturbances

The influence of x-ray irradiation to absorbed radiation doses D = (0.5?12) × 10⁸ rad on the properties of ferroelectric ceramic Pb(Ti_xZr_1?x )O₃ solid solutions with compositions close to the morphotropic phase boundary was studied. The effects of x-ray radiation on the electrical conductivity of ferroelectric ceramics are shown to differ with x ranging from 0.42 to 0.60. Using empirical equations and numerical techniques, quantitative relations are established between the composition, absorbed radiation dose, and electrical conductivity for Pb(Ti_xZr_1?x )O₃.     

Correlation between the magnetic and electrical properties of the (VS)x(Fe2O3)2−x oxysulfide system

The correlation between the magnetic and electrical properties of the (VS)_x(Fe₂O₃)_2?x (0.9<x<1.25) oxysulfide solid solutions has been studied. The crossover of conductivity from the semimetallic to semiconducting type is accompanied by changes in the magnetic susceptibility, which are characteristic of the transition from delocalized to localized electrons. For x=1.25, a region of the ferromagnetic ordering has been established in the temperature range 90–120 K.     

Influence of zirconium doping on structure,microstructure, dielectric and impedance properties of strontium bismuth niobate ceramics

Efforts have been made in this work to enhance the dielectric properties of SrBi₂Nb₂O₉ (SBN) by partial substitution of Zr⁴⁺ for Nb⁵⁺. Systematic investigations on structure, microstructure, dielectric and impedance properties of the SrBi₂(Nb_2−(4/5)xZr_x)O₉ [where, x = 0, 0.1 and 0.2] ceramic samples were carried out to understand the effect of substitution of Zr⁴⁺ for Nb⁵⁺ in SrBi₂Nb₂O₉. The X-ray diffraction (XRD) investigations indicated that the lattice volume of SrBi₂(Nb_{2− (4/5)x}Zr_x)O₉ with x = 0.1 and 0.2 decreases compared to SBN. The SEM investigations revealed an increase in the size of grains and the change on shape of grains to elongated plate shaped structure with the increase of x (x = 0.1 and 0.2) in SrBi₂(Nb_2−(4/5)xZr_x)O₉. Higher Curie temperature and enhanced peak dielectric constant at the Curie temperature were observed for both the SrBi₂(Nb_2−(4/5)xZr_x)O₉ with x = 0.1 and 0.2 ceramic samples compared to SBN. Among the investigated compositions the higher Curie temperature and enhanced peak dielectric constant at the Curie temperature was observed for SrBi₂(Nb_2−(4/5)xZr_x)O₉ with x = 0.1.     

Comparative study of solid-state reaction and sol-gel process for synthesis of Zr-doped Li<Subscript>0.5</Subscript>La<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> solid electrolytes

We investigated the synergistic influences of synthesis methods (solid-state reaction vs. sol-gel process) and Zr⁴⁺ doping on the structure and ionic conductivity of perovskite-structured Li_0.5La_0.5TiO₃ (LLTO) solid electrolytes. The lithium-ion conductivity of Li_0.5La_0.5Ti_1???x Zr _x O₃ ceramic specimens was evaluated as a function of x value and compared carefully between those two synthesis methods. Regarding the conductivity, sol-gel process is better for the synthesis of LLTO than solid-state reaction. As a result, the highest grain conductivity is obtained in the sol-gel-derived pure LLTO sample with x?=?0, reaching 1.10?×?10^?3 S?·?cm^?1. Partial substitution of Zr⁴⁺ enlarges the LLTO’s grain aggregate size and increases the total superficial area of aggregates. Consequently, Zr⁴⁺ substitution not only affects the grain (bulk) conductivity, but more importantly, also improves the grain boundary conductivity and the total conductivity. The highest total conductivity is 5.84?×?10^?5 S?·?cm^?1 with x?=?0.04 by sol-gel process.     

Synthesis and physicochemical properties of Li2 Me x Zr1 − x O3 − δ (Me = Nb,Ti; x = 0.05, 0.1) solid solutions

Complex lithium metallates Li₂ Me _x Zr_{1 ? x} O_{3 ? δ} (Me = Nb, Ti, x = 0.05, 0.1) with iso-and heterovalent substitutions for Zr⁴⁺ ions in lithium zirconate are synthesized for the first time using a citrate technique. The inclusion of Ti⁴⁺ and Nb⁵⁺ ions in the crystal structure of Li₂ZrO₃ is confirmed by means of X-ray diffraction and NMR. It is shown that in the temperature range of 750–820 K, Li₂Ti_0.1Zr_0.9O₃ solid solution has higher conductivity than phases of undoped lithium zirconate.     

Transport properties and magnetoresistance in CoNb1−xMnxSb half-Heusler alloys with a low temperature localization

The transport properties and magnetoresistance of half-Heusler CoNb_1−xMn_xSb (x=0.0-1.0) alloys have been investigated between 2 and 300 K. In this temperature range, a metallic conductivity has been observed for the alloys with higher (x=1.0) and lower (x=0.0-0.2) Mn contents. However, the middle Mn content alloys (x=0.4-0.8) exhibit non-metallic conductive behavior. Their temperature dependence of resistivity undergoes a Mott localization law ρ=ρ₀exp(T₀/T)^p (p=1/4) rather than a thermal excitation regime ρ=ρ₀exp(E_a/kT) at low temperature (). The localization can be attributed to atomic and magnetic disorder. Resistivity peaks from 25 to 300 K were also observed for these alloys. Magnetotransport investigation reveals that these resistivity peaks result from localization effect as well as spin-disorder scattering.     

Ionic conductivity in the system Li9−4xZrx〈PO4〉3

Lithium ion conductors of composition Li_9−4xZr_x〈PO₄〉₃ (0.0 < x < 2.0) have been prepared by the conventional solid state reaction and also by a wet chemical method. X-ray diffraction patterns reveal identical crystallographic morphology for the compounds prepared by the two methods. However, they can be prepared and sintered at much lower temperatures by the wet chemical method. Their conductivities are also higher. Compared to pure Li₃PO₄, one of the end member of the series, the conductivity increases sharply with substitution of lithium by zirconium. The highest conductivity has been obtained in the composition Li_1.8Zr_1.8〈PO₄〉₃ (x = 1.8), prepared by the wet chemical method. The conductivity value of 10⁻³ ω⁻¹ cm⁻¹ is obtained at around 225°C with an activation energy of about 0.5 eV.     

Microstructure and some magnetic properties of bulk amorphous (Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)100−xYx (x=0, 2, 3 or 4) alloys

Microstructure, revealed by X-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy, and magnetic properties such as magnetic susceptibility, its disaccommodation, core losses and approach to magnetic saturation in bulk amorphous (Fe_0.61Co_0.10Zr_0.025Hf_0.025Ti_0.02W_0.02B_0.20)_100−xY_x (x=0, 2, 3 or 4) alloys in the as-cast state and after the annealing in vacuum at 720 K for 15 min. are studied. The investigated alloys are ferromagnetic at room temperature. The average hyperfine field induction decreases with Y concentration. Due to annealing out of free volumes its value increases after the heat treatment of the samples. The magnetic susceptibility and core losses point out that the best thermal stability by the amorphous (Fe_0.61Co_0.10Zr_0.025Hf_0.025Ti_0.02W_0.02B_0.20)₉₇Y₃ alloy is exhibited. Moreover, from Mössbauer spectroscopy investigations it is shown that the mentioned above alloy is the most homogeneous. The atom packing density increases with Y concentration, which is proved by the magnetic susceptibility disaccommodation and approach to magnetic saturation studies.