Structural and Magnetic Properties of the Gd2−x Ho x Ru2O7 Pyrochlore Solid Solution (0≤x≤2)

In this paper, we investigate the structural and magnetic properties of the Gd_2?x Ho _x Ru₂O₇ (0≤x≤2) pyrochlores. X-ray diffractograms of all samples studied presented a cubic pyrochlore type crystal structure with lattice parameters varying linearly in accordance to Vegard’s law. It is shown that by substituting Gd by Ho one can tune the magnetic order of this system moving from antiferromagnetic (in the absence of Ho) to ferromagnetic (in the absence of Gd).     

The Structural and Magnetic Properties of Zn0.8−4x Dy x O y (0.05≤x≤0.10) Compounds Prepared by Solid-State Reactions

In this study, Dy-doped ZnO (Zn_0.8?4x Dy _x O _y (0.05≤x≤0.10)) samples were prepared by the solid-state reaction method, and were characterized by using the XRD, SEM and EDX techniques. The SEM results clearly demonstrate that the grains of the samples are very well connected to each other and tightly packed. From the XRD and EDX spectra, it has been concluded that the substituting of Dy³⁺ for Zn²⁺ in ZnO causes almost no change in the hexagonal wurtzite structure of ZnO. However, the lattice parameters a and c of Dy-doped ZnO are slightly different from those of the pure ZnO. These observations may be due to the slightly different ionic sizes of Zn²⁺ and Dy³⁺ ions. Our magnetization measurements (M–H) and (M–T) show paramagnetic behavior with a negative value of the Curie–Weiss temperature, corresponding to an antiferromagnetic exchange coupling in Dy-doped ZnO. Since, for low magnetic fields the extrapolation of the H/M versus temperature curves cut the T axes at negative values, we believe that the substitution of Dy in ZnO causes an overwhelming antiferromagnetic interaction for x≤0.10.     

Magnetic Phase Diagram of Ca1−x Mn x O

Alternating current susceptibility and direct current magnetization have been studied for polycrystalline Ca_1?x Mn _x O. On increasing the Mn content, magnetic ordering changes from spin glass behavior for 0.25 ≤ x ≤ 0.4 to antiferromagnetic order. The paramagnetic/antiferromagnetic transition is of second order for 0.5 ≤ x ≤ 0.65 and of first order for x ≥ 0.7. For low Mn concentrations, the high-temperature alternating current susceptibility can be described by a diluted Heisenberg magnet model developed for diluted magnetic semiconductors.     

Specific Heat and Magnetocaloric Effect in Ho-Er-Co Solid Solutions

Specific heat measurements have been performed on polycrystalline HoCo₂, ErCo₂ and their solid solutions Ho_1?x Er _x Co₂ (0.1≤x≤0.5). These compounds were synthesized using high-purity rare-earth metals and cobalt. X-ray diffraction patterns taken at room temperature reveal that all compounds have the C15 cubic Laves phase structure. Heat capacity measurements have been performed in the temperature range of 2–300 K without magnetic field and in a magnetic field of 1 and 2 T. The magnetocaloric effect has been estimated in terms of isothermal magnetic entropy change for all solid solutions in magnetic fields up to 2 T. The effect of increasing Er amount in Ho_1?x Er _x Co₂ on the magnetic and magnetocaloric properties will be discussed.     

The Effects of Mn Substitution on Magnetization Reversal Properties in Gd0.7Ca0.3MnO3

Low temperature magnetization in polycrystalline Gd_0.7Ca_0.3Mn_1?x M _x O₃ (M=Cr, Ga, Ru; x=0, 0.2) has been investigated. The samples were prepared via the conventional solid state reaction method. For all the samples, the paramagnetic to ferrimagnetic (PM-FiM) transition temperature (say T _max) can be well defined from the temperature dependent ac susceptibility data. The negative magnetization suppresses due to 20 % Cr or Ga doping at the Mn site. On the other hand, below the compensation temperature (T _comp), the nature of the Ru doping sample is almost similar to that of undoped Gd_0.7Ca_0.3MnO₃. The nonmagnetic Ga doping drastically reduces magnetization and T _max shifts to a lower temperature. However, Ru and Cr doping increase the value of T _max. The network of canted Mn³⁺/Mn⁴⁺ moments changes with the substitution of Cr, Ga, and Ru at the Mn site giving rise to the variation of the internal magnetic moment. Thus, the antiparallel coupling of the Gd moments with Mn/M changes and affects the low temperature magnetization reversal properties.     

Oxide ionic conductivity and crystallographic properties of tetragonal type Bi2O3-based solid electrolyte doped with Ho2O3

Abstract

In the present work, the authors have investigated the binary system of (Bi₂O₃)_1–x(Ho₂O₃)_x. For the stabilisation of the tetragonal type solid solution, small amounts of Ho₂O₃ were doped into the monoclinic Bi₂O₃ via solid state reactions in the stoichiometric range 0·01≤x≤0·1. The crystal formula of the formed solid solution was determined as Bi(III)_4–4xHo(II)_4xO_6–2xVo_(2+2x) (where Vo is the oxide ion vacancy) according to the XRD and SEM microprobe results. In the crystal formula, stoichiometric values of x were 0·04≤x≤0·08, 0·03≤x≤0·09, 0·02≤x≤0·09 and 0·04≤x≤0·09 for annealing temperatures at 750, 800, 805 (quench) and 760°C (quench) respectively. The four probe electrical conductivity measurements showed that the studied system had an oxide ionic type electrical conductivity behaviour, which is increased with increasing dopant concentration and temperature. The obtained solid electrolyte system has an oxygen non-stoichiometry characteristic, and it contains O^2– vacancies, which have disordered arrangements in its tetragonal crystal structure. The increase in the amount of Ho₂O₃ doping and temperature causes an increasing degree of the disordering of oxygen vacancies and a decrease in the activation energy E_a.     

Fish-Tail Effect and Its Evolution Under Neutron Irradiation in Li-Doped YBa2Cu3O7−x

The evolution of the critical current density of Li-doped YBa₂Cu₃O_7?x polycrystalline samples submitted to neutron irradiation is investigated as function of magnetic field (0 ≤ B ≤ 6 T) temperature (5 ≤ T ≤ 85 K) and neutron fluence (0 ≤ Φ ≤ 9.98 × 10¹⁷ cm^?2). At fluences lower than 10¹⁷ cm^?2, a second peak in j _s vs. B dependence is present (fish-tail effect). Its magnitude decreases with increasing the fluence. Above 10¹⁷ cm^?2, the second peak of current density completely disappears; instead, the logarithmic susceptibility shows a second peak at a certain field B _infl. A dependence of B _infl on fluence is proposed.     

The Influence of Vanadium on Magnetism and Magnetocaloric Properties of Fe 8 0 − x V x B12Si8 (x = 8, 10, and 13.7) Amorphous Alloys

Amorphous soft magnetic Fe_80?x V _x B₁₂Si₈ ribbons (0 ≤ x ≤ 14) have been fabricated by melt spinning technique, and their magnetic and magnetocaloric properties have been studied. The value of magnetocaloric effect has been determined from the measurements of magnetization as a function of temperature and an external magnetic field. The addition of vanadium to the ternary Fe₈₀B₁₂Si₈ alloy results in a decrease of the Curie temperature of amorphous alloys, T _C, from 473.5 to 335 K. With an increasing V content, the average magnetic moment of Fe atom and the magnetic entropy change also decrease. Fe_66.3V_13.7B₁₂Si₈ alloy exhibits the highest refrigeration capacity of 93.7 J kg^?1 and moderate peak magnetic entropy of 1.034 J kg^?1 K^?1 (T _C = 335 K) under the maximum applied field of 2 T. The results from this work showed that V containing amorphous alloy 13.7 at. % is an interesting material and potential candidate for magnetic refrigerants working near room temperature. The observed ?ΔS_M ^max values compare favorably with other amorphous Fe-based alloys.     

Investigation of Magnetic Properties of Multilayer Thin Films with Spin-Wave Resonance

A theory has been developed to simulate spin-wave resonance (SWR) modes in the multilayer systems consisting of alternate magnetic and nonmagnetic layers. An equation of motion of magnetization with Gilbert-type damping parameter for simulating SWR modes was used. It has been realized that the theory developed for the magnetic multilayer films is suitable to study the spin dynamics and extract various magnetic parameters. It has been shown that SWR modes strongly depend on an effective magnetic anisotropy constant (K _eff), interlayer exchange coupling constant (A ₁₂) and effective magnetization (M _eff). The nature of the effective magnetic anisotropy and interlayer exchange coupling constants has been investigated by using the developed SWR theory in detail. The separation between optic and acoustic modes strongly depends on the magnitude of the interlayer exchange coupling constant, whereas the relative position of the acoustic and optic modes depends on the sign of \(A_{12}\). With increasing the interlayer exchange coupling constant, the resonance field of the optic mode decreases (increases) for ferromagnetic (antiferromagnetic) coupling. When the effective magnetic anisotropy constant increases, the resonance field of the acoustic and optic modes increases for both the ferromagnetic and antiferromagnetic couplings. The increasing of the effective magnetization results in decreasing of the resonance field of SWR mode at parallel geometry, whereas that of SWR mode increases at the perpendicular geometry. The results are compatible to the other theories and experimental results.     

Spin Gap Characteristic of Y(Ba1−<Emphasis Type="Italic">x</Emphasis>Gd<Emphasis Type="Italic">x</Emphasis>)2Cu3O7−δ

Y(Ba_1?xGd _x )₂Cu₃O_7?δ compounds with x = 0 ～ 0.15 are prepared using the solid reaction technique. With structure analysis by Rietveld refinement of x-ray diffraction, we find that Gd³⁺ ions prefer to occupy Y sites within lighter doping x ≤ 0.08 due to ion size effects, then begin partially to occupy Ba sites with doping content increasing, which gives vital influence on superconductivity and spin-gap properties. The magnetic doping effects of Gd³⁺ ions on spin-gap properties are investigated in detail by contrast of the distinguished behaviors between T* and T_c, indicating that spin-gap temperature is not completely determined by the carrier density, but strongly dependent on the strength of interplane antiferromagnetic coupling. Finally, we propose an expression of in-plane resistivity dependent on the maximal width of spin-gap Δ₀ to derive their values for different samples, which almost keep constant with the increase of Gd doping contents.     

Magnetocaloric Effects in Pr0.6−x Er x Sr0.4MnO3 (0.0≤x≤0.2) Manganese Oxides

The effects of partial substitution of praseodymium by erbium on the structural, magnetic, and magnetocaloric properties of Pr_0.6?x Er _x Sr_0.4MnO₃ (0.0≤x≤0.2) powder samples have been studied. Our polycrystalline compounds were synthesized by the conventional solid state reaction at high temperature. Rietveld refinement of the X-ray diffraction patterns using Fullprof program shows that all our samples are single phase and crystallize in the orthorhombic structure with the Pnma space group. The unit cell volume decreased with increasing the Er amount. Magnetic measurements show that all our samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature T _C shifts to lower values with increasing Er content. From the magnetization isotherms at different temperatures, magnetic entropy changes ΔS _M and relative cooling power RCP have been evaluated. The maximum of the magnetic entropy changes for the Pr_0.45Er_0.15Sr_0.4MnO₃ sample is found to be $| \Delta S_{M}^{\max } | = 2.66~\mathrm{J}\,\mathrm{kg}^{-1}\,\mathrm{K}^{-1}$ under a magnetic applied field change of 2 T.     

Critical current density and flux pinning in Y1−x Ho x Ba2Cu3O7−δ epitaxial films

The critical current densityJ _c of Y_1?x Ho _x Ba₂Cu₃O_7?δ (YHBCO) epitaxial thin films withx=0, 0.2, 0.4, 0.7 at various temperatures and magnetic fields has been measured magnetically. TheJ _c and flux pinning density Fp values are significantly enhanced with the Ho substitute amountx with the optimal effect achieved at Ho concentration around x=0.4 in the entire measured temperature (30–77 K) and magnetic field (0–3 T) ranges. X-ray diffraction patterns have shown that the greater the lattice deformation, the higher theJ _c of the films.     

Cu<Superscript>2+</Superscript> and Al<Superscript>3+</Superscript> co-substituted cobalt ferrite: structural analysis,morphology and magnetic properties

Cu–Al substituted Co ferrite nanopowders, Co_1?x Cu _x Fe_2?x Al _x O₄ (0.0 ≤ x ≤ 0.8) were synthesized by the co-precipitation method. The effect of Cu–Al substitution on the structural and magnetic properties have been investigated. X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) are used for studying the effect of variation in the Cu–Al substitution and its impact on particle size, magnetic properties such as M _s and H _c . Cu–Al substitution occurs and produce a secondary phase, α-Fe ₂ O ₃. The crystallite size of the powder calcined at 800 ^°C was in the range of 19–26 nm. The lattice parameter decreases with increasing Cu–Al content. The nanostructural features were examined by FESEM images. Infrared absorption (IR) spectra shows two vibrational bands; at around 600 (v ₁) and 400 cm ^?1 (v ₂). They are attributed to the tetrahedral and octahedral group complexes of the spinel lattice, respectively. It was found that the physical and magnetic properties have changed with Cu–Al contents. The saturation magnetization decreases with the increase in Cu–Al substitution. The reduction of coercive force, saturation magnetization and magnetic moments are may be due to dilution of the magnetic interaction.     

On the longitudinal static and dynamic susceptibility of spin-1/2 Kondo systems

The impurity spin polarization, static susceptibility, and longitudinal impurity spin relaxation rate are calculated for thes-d model as function of temperature and magnetic field for ferromagnetic and antiferromagnetic exchange coupling. The thermodynamic functions and the dynamical susceptibility are obtained from the impurity relaxation spectrum, which is approximated by taking into account the infrared-like singularities. For antiferromagnetic coupling the zero-field susceptibility obeys a Curie-Weiss law1/χ～4.6(T+θ) for high and intermediate temperatures and it approaches the finite value1/χ～3.8θ for zero temperature. The zero-field relaxation rate is much larger than the Korringa value; it decreases with temperature and approaches the nonzero value1/T ₁～1.2θ for zero temperature. The relaxation rate decreases with increasing field. The results for the spin polarization agree well with the experimental data for the Cu:Fe alloy.     

Structural, magnetic and magnetocaloric properties of Heusler alloys Ni50Mn38Sb12 with boron addition

We report on the structural, magnetic and magnetocaloric properties of the Ni₅₀Mn₃₈Sb₁₂B_x alloys in term of boron addition with x = 1, 3 and 5. We have found that both the paramagnetic-ferromagnetic austenitic transition (T_C) and the ferromagnetic-antiferromagnetic martensitic transition (T_M) are sensitively influenced by the boron addition: T_C tends to increase, while T_M decreases with increasing boron concentration. Temperature dependent X-ray diffraction in the range of 200-500 K clearly shows an evolution of the structural transformation from orthorhombic to cubic structure phase transition on heating for the x = 1 and 3 samples. Strikingly, the addition of boron atoms into the lattice favours the ferromagnetic ordering relatively to the antiferromagnetic arrangement below T_M. This consequently affects on the magneto-structural transition as well as on the size of magnetocaloric effect.     

Correlation Between Charge, Spin and Lattice in La–Eu–Sr Manganites

To understand the structural, electrical, magnetic, elastic and anelastic properties of La_0.67?x Eu _x Sr_0.33MnO₃ (0.30≤x≤0.39) manganites, a series of samples was prepared by citrate gel route. X-ray diffraction studies along with Rietveld analysis indicate the samples crystallize in single phase with Pnma space group. Studies on the variations of magnetization with temperature indicate that the Curie transition temperature (T _C) decreases with increasing Eu content. Furthermore, Eu substitution is found to increase the electrical resistivity and significantly enhances the colossal magnetoresistance effect, while it is found to decrease the characteristic metal–insulator transition temperature (T _P). On analyzing the electrical resistivity data, it has been concluded that the resistivity below T _P can be explained based on electron–electron, electron–phonon and two magnon scattering processes, while that above T _P, the adiabatic small polaron model is found to explain the observed behavior. Finally, the longitudinal modulus (L) and internal friction (Q ^?1) have been measured and a dramatic change in L (T) is observed at T _C, accompanied by a sharp peak in Q ^?1 (T). Simultaneous occurrence of magnetic, transport and lattice anomalous behavior at T _C indicate the presence of strong electron–phonon and spin–phonon interactions in these manganites.     

Magnetic properties of LaInO<Subscript>3</Subscript>-based perovskite-structure photoluminescent materials doped with Nd<Superscript>3+</Superscript>, Cr<Superscript>3+</Superscript>, and Mn<Superscript>3+</Superscript> ions

Single-phase ceramic samples of La_1–xNd_xInO₃ (0.007 ≤ x ≤ 0.05), LaIn_0.99M_0.01O₃, and La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺) solid solutions have been prepared by solid-state reactions, and their crystal structure, magnetic field dependences of their specific magnetization at 5 and 300 K, and temperature dependences of their molar magnetic susceptibility have been studied. It has been shown that the 300-K specific magnetization of the La_1–xNd_xInO₃ (x = 0.02, 0.05), La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺), and LaIn_0.99Mn_0.01O₃ solid solutions increases linearly with increasing magnetic field strength up to 14 T and that the magnitude of the 300-K specific magnetization of the La_0.993Nd_0.007InO₃ and LaIn_0.99Cr_0.01O₃ solid solutions increases linearly, but they have diamagnetic magnetization. At a temperature of 5 K, the magnetization of all the indates studied here increases nonlinearly with increasing magnetic field strength, gradually approaching magnetic saturation, without, however, reaching it in a magnetic field of 14 T. In the temperature range where the Curie–Weiss law is obeyed (5–30 K), the effective magnetic moments obtained for the Nd³⁺ ion (\({\mu _{effN{d^{3 + }}}}\)) in the La_1–xNd_xInO₃ solid solutions with x = 0.007, 0.02, and 0.05 are 2.95μ_B, 3.09μ_B, and 2.75μ_B, respectively, which is well below the theoretical value \({\mu _{effN{d^{3 + }}}}\)= 3.62μ_B. The effective magnetic moments of the Cr³⁺ and Mn³⁺ ions in the LaIn_0.99Cr_0.01O₃ and LaIn_0.99Mn_0.01O₃ solid solutions are 3.87μ^B and 5.11μ^B, respectively, and differ only slightly from the theoretical values \({\mu _{effC{r^{3 + }}}}\)= 3.87μ^B and \({\mu _{effM{n^{3 + }}}}\)= 4.9μ^B.     

Unconventional Magnetic Transition in Na x CoO2 (x>0.7) Single Crystals

Na _x CoO₂ (x>0.7) single crystals with a typical dimension of 0.4×0.4 mm² have been prepared by a “rapid heat-up” technique. By the Benchtop Small Molecule X-ray Crystallography System, the samples have been confirmed to be a single phase of the hexagonal γ-Na _x CoO₂. Magnetic data from the crystal indicate a magnetic phase transition around T=30 K, and the transition is sensitive to the applied magnetic fields. This is most consistent with the formation of an antiferromagnetic spin-density-wave (SDW) with the easy axis for magnetization nearly along the c-axis. Weak and soft ferromagnetism has also been observed from the crystal at low temperature. This unconventional magnetic property may be ascribed to the effect of the small moments of Co^4?x?δ sites at low temperature.     

Effect of Fe Substitution on the Structural,Magnetic and Magnetocaloric Properties of Pr0.6La0.1Mg0.3Mn1−x Fe x O3 (0≤x≤0.3) Perovskite Manganites Prepared by Sol Gel Method

Studies of the structural, magnetic, and magnetocaloric properties of polycrystalline Pr_0.6La_0.1Mg_0.3Mn_1?x Fe _x O₃ (0≤x≤0.3) perovskite manganites were carried out. The compounds were synthesized using the sol–gel method. X-Ray diffraction (XRD) analysis using Rietveld refinement shows that all our compounds crystallize in the orthorhombic structure with the Pnma space group. The surface morphology and elemental analysis of both samples were carried out by scanning electron microscopy (SEM) and the energy dispersive X-ray technique (EDX), respectively. Magnetization measurements versus temperature under magnetic applied field of 0.05 T showed that all our investigated samples display a ferromagnetic-paramagnetic transition. The substitution of Mn by Fe leads to an increase of the Curie temperature T _C from 64 K for x=0 to 380 K for x=0.3. The Arrott plots show that the phase transition is of second order. A large magnetic entropy change |ΔS _M | deduced from isothermal magnetization curves has been recorded in the parent compound Pr_0.6La_0.1Mg_0.3MnO₃ reaching a maximum of 0.79 J/kg K under a magnetic applied field of 2 T close to T _C . Our results on magnetocaloric properties suggest that the Pr_0.6La_0.1Mg_0.3MnO₃ compound is attractive as a possible refrigerant for low temperature magnetic refrigeration.     

Theoretical Work in Magnetocaloric Effect of LaFe13−xSi x Compounds

In this paper, the magnetocaloric effect (MCE) of LaFe_13?xSi _x compounds with 1.2 ≤ x ≤ 2.2 has been investigated. For this purpose, the magnetization dependence on the temperature and magnetic field were measured. Magnetic entropy change (?ΔS_M) allowing estimation of the MCE was determined based on thermodynamic Maxwell’s relation. The experimental results show that T_C increases with the Si content, whereas the magnetic entropy variation decreases. A large magnetic entropy change has been observed. The maximum \((-\Delta \mathrm {S}_{\mathrm {M}}^{\text {max}})\) of LaFe_10.8Si_2.2 occurring close to T_C = 240 K is about 2.3 Jkg^?1 K^?1 for an applied field change of 0–2 T. In addition, a magnetocaloric effect of LaFe_13?xSi _x compounds (x = 1.2 and 1.6) has been also carried out using phenomenological model. Dependence of the magnetization on temperature variation for LaFe_13?xSi _x compounds (x = 1.2 and 1.6) in different applied magnetic fields was simulated. The values of maximum entropy change, full width at half maximum, and relative cooling power (RCP) for the LaFe_11.8Si_1.2 and LaFe_11.4Si_1.6 compounds in different applied magnetic fields were calculated.