Investigation of Magnetic,Magnetocaloric, and Critical Properties of La<Subscript>0.5</Subscript>Ba<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> Manganite

We present an extensive study of the magnetic properties of a novel La_0.5Ba_0.5MnO₃ perovskite material prepared by the hydrothermal method. The explored sample was structurally studied by the x-ray diffraction (XRD) method which confirms the formation of a pure cubic phase of a perovskite structure with Pm3m space group. The magnetic properties were probed by employing temperature M (T) and external magnetic field M (μ_oH) dependence of magnetization measurements. A magnetic phase transition from ferromagnetic to paramagnetic phase occurs at 339 K in this sample. The maximum magnetic entropy change (\(\left | {{\Delta } S}_{M}^{\max } \right |\)) took a value of 1.4 J kg^??1 K^??1 at the applied magnetic field of 4.0 T for the explored sample and has also been found to occur at Curie temperature (T_C). This large entropy change might be instigated from the abrupt reduction of magnetization at T_C. The magnetocaloric effect (MCE) is maximum at T_C as represented by M (μ_oH) isotherms. The relative cooling power (RCP) is 243.2 J kg^??1 at μ_oH =?4.0 T. Moreover, the critical properties near T_C have been probed from magnetic data. The critical exponents δ, β, and γ with values 3.82, 0.42, and 1.2 are close to the values predicted by the 3D Ising model. Additionally, the authenticity of the critical exponents has been confirmed by the scaling equation of state and all data fall on two separate branches, one for T < T_C and the other for T > T_C, signifying that the critical exponents obtained in this work are accurate.     

Biocompatible nanoclusters of <Emphasis Type="Italic">O</Emphasis>-carboxymethyl chitosan-coated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles: synthesis,characterization and magnetic heating efficiency

In this work, we developed a polymer encapsulation of Fe₃O₄ nanoparticles as a core–shell nanocluster with different sizes to investigate the cluster structure effect on their magnetic properties and magnetic heating behavior. Well-dispersed nanoclusters of O-carboxymethyl chitosan-coated Fe₃O₄ nanoparticles were synthesized by microwave-assisted co-precipitation. The cluster sizes were tunable by varying the concentration of polymers used during synthesis. Nanoclusters present superparamagnetic behavior at room temperature with a reduction in saturation magnetization as a consequence of coating layer. The shift of blocking temperature to the higher value with increasing clusters size shows the stronger magnetic interaction in larger magnetic clusters. In a low alternating magnetic field with frequency of 178 Hz and amplitude of 103 Oe, nanoclusters offer a high heating efficiency. A maximum specific absorption rate of 204 W/g is observed in the sample with hydrodynamic size of 53 nm. In vitro cytotoxicity analysis performed on HeLa cells verified that nanoclusters show a good biocompatibility and can be an excellent candidate for applications in hyperthermia cancer treatment.     

Structural,Magnetic, and Transport Properties of NiTiIr Shape Memory Alloy

The structural, magnetic, and transport properties of the Ni_49.5Ti₄₈Ir_2.5 alloy have been presented. The alloy is formed in the B2-type phase with a small amount of Ti₂NiIr as an additional phase. In the DSC curve, two distinct peaks are observed on heating and cooling. These peaks correspond to the martensitic transformations from the B2 to the R phase and from the R to the B19 ′ phase on cooling and a reverse transformation from the B19 ′ to the R to the B2 phase on heating, respectively. From the resistivity curve, the martensitic start (M _S), martensitic finish (M _f), austenite start (A _S), and austenite finish (A _f) temperatures are found to be 211, 170, 273, and 298 K, respectively. In the magnetization-versus-temperature (M–T) curve, no evidence of the ferromagnetic ordering temperature is observed. However, the magnetization-versus-field (M–H) curves at 5 and 300 K show existence of ferromagnetic order in the alloy.     

Study of Magnetic Entropy Change in Nd<Subscript>0.67</Subscript>Ba<Subscript>0.33</Subscript>Mn<Subscript>0.98</Subscript>Fe<Subscript>0.02</Subscript>O<Subscript>3</Subscript> by Means of Theoretical Models

Magnetic entropy change (?ΔS _M ) of Nd_0.67 Ba_0.33Mn_0.98Fe_0.02O₃ perovskite have been analyzed by means of theoretical models. An excellent agreement has been found between the (ΔS_M) values estimated by Landau theory and those obtained using the classical Maxwell relation. In order to estimate the spontaneous magnetization M _{s pont}(T), we used the mean-field theory to analyses the (ΔS_M) vs. M ² data. The obtained M _{s pont}(T) values are in good agreement with those found from the classical extrapolation from the Arrott plots(H/M vs. M ²), confirming that the magnetic entropy is a valid approach to estimate the spontaneous magnetization in our system. At a relatively low magnetic field, a phenomenological model has been used to estimate the values of the magnetic entropy change. The results are in good agreement with those obtained from the experimental data using Maxwell relation.     

Nanomagnetics with lasers

Both liquid and vapour phase pulsed laser deposition (PLD) techniques have been used to synthesize nanophase magnetic alloys of CoPt. While the liquid route results in soft phase (disordered fcc) nanoparticles of CoPt near equiatomic composition dispersed in a surfactant-polymer matrix, the conventional vapour phase PLD allows growth of high coercivity nanoscale structures of CoPt on (001) SrTiO₃. The magnetization, M(T), dynamics of the colloidal particles is examined. Two distinct particle distributions are established from analysis of M(T) data, in conformity with results of electron microscopy. In vapour deposited films at low growth rate (～0.4 Å/s), morphology changes from a self-similar fractal to nanodots as the deposition temperature is raised from 700–800°C. The large lattice mismatch between (001) SrTiO₃ and the ac/bc plane of L1₀ ordered phase imparts tensile strain to the films whose morphological manifestations can be suppressed at high growth rates.     

The H-T and P-T Phase Diagram of the Superconducting Phase in Pd:Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>

We study the magnetic field vs. temperature (H – T) and pressure vs. temperature (P – T) phase diagrams of the T _c ≈ 5.5 K superconducting phase in Pd _x Bi₂Te₃ (x ≈ 1) using electrical resistivity versus temperature measurements at various applied magnetic fields (H) and magnetic susceptibility versus temperature measurements at various applied magnetic fields (H) and pressure (P). The H – T phase diagram has an initial upward curvature as observed in some unconventional superconductors. The critical field extrapolated to T = 0 K is H _c (0) ≈ 6–10 kOe. The T _c is suppressed approximately linearly with pressure at a rate d T _c /d P ≈ ?0.28 K/GPa.     

The Effect of Annealing on Phase Stability and Magnetic Properties of Hexaferrite BaFe<Subscript>12</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>19</Subscript>

The hexaferrite BaFe₁₂ O ₁₉ phase was synthesized through the mechanical alloying process followed by subsequent annealing. Rietveld refinements of as-milled powder annealed at 700 ^°C confirm the formation of the BaFe₁₂ O ₁₉ phase with the presence of an important amount of the α-Fe₂ O ₃ phase. Thus, prior mechanical milling shows much lower reaction temperature and less reaction time compared to conventional methods. Further annealing up to 900 and 1100 ^°C could not enable the formation of a single BaFe₁₂ O ₁₉ phase, reaching an optimum phase composition ratio close to BaFe₁₂ O ₁₉/ α-Fe₂ O ₃ 70/30. The crystallite size was found to be in the nanoscale level but increases with increasing temperature (BaFe₁₂ O ₁₉ = 20–62 nm; α-Fe₂ O ₃ = 31–74 nm). SEM micrographs show that as the annealing temperature rises, the particles become more regular with sharp edges and hexagonal-like shapes. Magnetic measurements reveal that both M _s and M _r increase with annealing temperature to reach maximum values at 900 ^°C then remain unchanged, associated with phase composition. The coercivity H _c increases upon annealing up to 700 ^°C to a much higher value, from 1.7 kOe for as-milled powder to 4.8 kOe. Its value then decreases, attributed to grain (particle) growth (formation of larger particles) due to high annealing temperatures: 900–1100 ^°C. The obtained composites show very interesting magnetic properties and can be considered for potential applications, such as hyperthermia, heavy metal and dye removal, and hard/soft magnetic composites.     

Multifunctional lymph-targeted platform based on Mn@mSiO<Subscript>2</Subscript> nanocomposites: Combining PFOB for dual-mode imaging and DOX for cancer diagnose and treatment

A universal platform with Mn doping and hyaluronic acid (HA) modification, based on mesoporous silica (mSiO₂), was designed and used as a basic multifunctional material with magnetic resonance (MR) imaging. Furthermore, we added flexible functions through the addition of functional molecules. Specially, two typical compounds, hydrophobic perfluorooctyl bromide (PFOB) and hydrophilic doxorubicin (DOX), were loaded into the channels to obtain PFOB@Mn@mSiO₂@HA (PMMH) or DOX@Mn@mSiO₂@HA (DMMH) nanoparticles for dual-mode imaging or imaging and therapy, respectively. The PMMH and DMMH nanoparticles were highly targeted to the lymph system in vitro and in vivo. MR and ultrasound imaging of PMMH nanoparticles were performed in the lymph system, while MR imaging and chemotherapy of DMMH nanoparticles was used to detect cancer. These results showed that both PMMH and DMMH nanoparticles can be designed with high lymph targeting efficiency. PMMH nanoparticles are a dual-mode contrast agent for both ultrasound and MR imaging for the lymph system and DMMH nanoparticles are powerful agents for the combined diagnosis and therapy of cancer in vivo.

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The influence of the formation and storage conditions of silicon nanoparticles obtained by laser-induced pyrolysis of monosilane on the nature and properties of defects

A detailed study of the paramagnetic properties of silicon nanoparticles obtained by laser-induced pyrolysis of monosilane is carried out by the method of electron-paramagnetic-resonance spectroscopy as dependent on the conditions of subsequent processing and storage. Defects of the P _b0-, P _b1-, and D-center types are detected, and their parameters and concentration values are determined. It is established that the defects in the studied structures are centers of nonradiative recombination. It is shown that, to obtain samples with low concentrations of paramagnetic centers and stable luminescence, the procedure of etching the original silicon nanoparticles in an aqueous solution of HF and HNO₃ acid followed by natural oxidation under normal conditions can be used.     

Grain Boundary Shortening in CuTl-1234 Superconductor by the Addition of ZnO Nanoparticles

The superconducting properties of Cu_0.5Tl_0.5 Ba₂Ca₃Cu₄O_12?x are studied after the inclusion of ZnO nanoparticles. The ZnO nanoparticles prepared by a sol-gel method were incorporated during the second stage of the synthesis of Cu_0.5Tl_0.5Ba₂Ca₃Cu₄O_12?x phase in y =?0, 3.0, 5.0, and 7.0 wt%. It is observed that the structure, the morphology, and the superconductivity properties are greatly influenced by the inclusion of ZnO nanoparticles. The lattice parameters of the orthorhombic phase of Cu_0.5Tl_0.5Ba₂Ca₃Cu₄O_12?x superconductor are decreased with the increase of x. Similarly, the grain morphology has been changed from needle-like to spherical grains. One of the major benefits of the inclusion of ZnO nanoparticles is the increase in critical temperature, critical magnetic fields, and critical current density as observed from the theoretical calculations of fluctuation-induced conductivity analysis.     

Monte Carlo Study of Magnetic and Thermal Phase Transitions of a Diluted Magnetic Nanosystem

Monte Carlo (MC) simulation method with the Metropolis algorithm is used to study the magnetic and thermal phase transition properties of a spherical nanoparticle. The system consists of two concentric spheres of rays R _C and R _S, respectively (R _c < R _s). For r < R _c, the spin is σ = ±3 /2 and ±1 /2, and for R _C < r ≤ R _S, the spin is S = ±7 /2, + 5/2, ±3 /2, and ±1 /2 with antiferromagnetic interface coupling. Between R _C and R _S, the sites are populated with the probability (p). We present a detailed discussion on the magnetic and thermal phase transition characteristics of the system under consideration. Our investigations show that this system can be used as a magnetic nanostructure possessing potential applications in magnetism.     

Critical Behavior of La<Subscript>0.67</Subscript>Ba<Subscript>0.33</Subscript>Mn<Subscript>0.95</Subscript>Fe<Subscript>0.05</Subscript>O<Subscript>3</Subscript> Manganite

The critical behavior of perovskite manganite La_0.67Ba_0.33Mn_0.95Fe_0.05O₃ at the ferromagnetic–paramagnetic has been analyzed. The results show that the sample exhibited the second-order magnetic phase transition. The estimated critical exponents derived from the magnetic data using various such as modified d’Arrott plot Kouvel–Fisher method and critical magnetization M(T _C, H). The critical exponents values for the La_0.67Ba_0.33Mn_0.95Fe_0.05O₃ are close to those expected from the mean field model β = 0.504 ± 0.01 with T _C = 275661 ± 0.447 (from the temperature dependence of the spontaneous magnetization below T _C ), γ = 1.013 ± 0.017 with T _C = 276132 ± 0.452 (from the temperature dependence of the inverse initial susceptibility above T _C ), and δ = 3.0403 ± 0.0003. Moreover, the critical exponents also obey the single scaling equation of M(H, ε) = |ε| ^β f _±(H/|ε| ^β+γ ).     

Impact of High Pressure and High Temperature on Annealed Oxygen-deficient CoSrO<Subscript>3−<Emphasis Type="Italic">δ</Emphasis></Subscript> Perovskites: Structural and Magnetization Studies

In this brief article, structural, magnetization studies of oxygen deficient perovskite cobalt oxides CoSrO_3?δ synthesized in two different ways are reported. The structural refinements (JANA2006) of X-ray powder diffraction data indicate that the sample prepared under ambient pressure (stage-1) shows a hexagonal structure with P6₃/mmc (194) as a possible space group. The stage-1 sample subsequently sintered at 1450?°C for 1–2 h under high-pressure 6 GPa conditions (stage-2) crystallizes in tetragonal symmetry with I4/mcm (140) space group having a=5.444(7) Å and c=7.68(2) Å. While the stage-1 sample exhibits a paramagnetic nature in the magnetic susceptibility, M(T), measurements, interestingly the sample annealed under high-pressure conditions shows ferromagnetism in the magnetic susceptibility, M(T) and field dependence magnetization, M(H) measurements. The high-pressure annealed sample shows hysteresis opening with a quite large coercive field of 7.3 kOe at 1.8 K. The temperature dependence of the inverse molar susceptibility curves exhibits linear behavior in the high-temperature regime and could be fitted to the Curie–Weiss expression, χ(T)=C/(T?θ _W). The experimental values of θ _W and p _eff obtained from the linear region of the inverse molar magnetic susceptibility curves are found to be: ?210.7(5) K and 2.38(2) μ _B/Co for stage-1 and 260.2(7) K and 1.87(3) μ _B/Co for stage-2 samples, respectively. A negative sign of θ _W indicates rather strong antiferromagnetic correlations in the stage-1 sample. Apart from these results, the structural parameters reported by various groups for the strontium-based perovskite cobalt oxides are also presented in the form of literature collections.     

Oriented In<Subscript>3–<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>4</Subscript> films on the (100) surface of Si,GaAs, and InP single crystals

Spray pyrolysis of aqueous solutions, with thiourea as a sulfurizing agent, has been used to grow cubic indium sulfide films on single-crystal substrates: In_3–x S₄(111)/Si(100), In_3–x S₄(111)/GaAs(100), and In_3–x S₄(111)/InP(100). The lattice parameter a of the sulfide has been shown to increase with an increase in the lattice parameter of the substrate, whereas the film grown on GaAs has the highest lattice strain (as assessed from X-ray diffraction line broadening). The films have a constant phase composition and (111) texture, in contrast to films grown on glassy substrates by the same method.     

Hexagonal-Type Ising Nanowire with Core/Shell Structure Designed with Half-Integer Spins: Compensation Behaviors and Phase Diagrams in the Temperature and Interaction Planes

The effective field theory with correlation is used to investigate the magnetic behaviors of the mixed spin-1/2 and spin-3/2 hexagonal Ising nanowire (HIN) with core/shell in the crystal field. The total magnetization as a function of the temperature is used to describe the compensation behaviors of the system, and the N-, Q-, P-, R-, and S-type compensation types are given. The dependence of the phase diagrams on interaction parameters is studied in detail and presented the phase diagrams in the six different planes, namely (J ₁, Δ, T), (J _C, Δ, T), (J _S, Δ, T), (J ₁, J _C, T), (J ₁, J _S, T) and (J _C, J _S, T).Besides, the system exhibit second-order phase transition and first-order phase transitions, which can be found via the variations of the total magnetization with the crystal field in the mixed spin-1/2 and spin-3/2 HIN.     

Characterization of the structural,magnetic and magnetocaloric properties of double perovskite La<Subscript>1.95</Subscript>Sr<Subscript>0.05</Subscript>BMnO<Subscript>6</Subscript> (B = Ni and Co)

An exhaustive study of structural, magnetic and magnetocaloric properties on La_1.95Sr_0.05BMnO₆ (B?=?Ni and Co) double perovskite were performed. The samples were prepared by the sol–gel method. The crystallographic structure was studied by the X-ray diffraction patterns and Rietveld refinement which revealed that all samples crystallize in a monoclinic structure with P2₁/n space group. The magnetic behaviors of these double perovskite have been studied in detail. For La_1.95Sr_0.05NiMnO₆, the M(T) curves exhibit double magnetization transition temperature at 68 K and 266 K which can be ascribed to Ni³⁺–O–Mn³⁺ and Ni²⁺–O–Mn⁴⁺ superexchange interaction, respectively. However, unique magnetic transition has been observed for the La_1.95Sr_0.05CoMnO₆ double perovskite at 210 K due to Co²⁺–O–Mn⁴⁺ superexchange interaction. A deep investigation based on the Landau Theory and Arrot analysis confirmed a second order ferromagnetic phase transition for both samples. Besides, the magnetocaloric behaviors of these new samples have been studied by analysis the magnetic entropy change. This latter reached maximum values of 1.01 and 1.35 J/kg/K for La_1.95Sr_0.05NiMnO₆ and La_1.95Sr_0.05CoMnO₆, respectively, under µ₀H?=?5 T. Moreover, the relative cooling power values for La_1.95Sr_0.05NiMnO₆ and La_1.95Sr_0.05CoMnO₆ are found to be 94 J/kg and 116 J/kg, respectively, under µ₀H?=?5 T. Based on the obtained ΔS_M data, we have also described the universal master curve for (ΔS_M/\(\Delta S_{M}^{{\hbox{max} }}\)) versus rescaled temperature to confirm the order magnetic phase transition. Interestingly, all the ΔS_M(T, H) data points are collapsed into a universal curve in the whole temperature range. The significant values of relative cooling power for both samples suggest that they might be an interesting candidate for exploring a new kind of magnetic refrigerants.     

Synthesis,structure, and properties of solid solutions based on bismuth ferrite

Solid solutions of Bi_{1 ? x} Pb _x Fe_{1 ? x} Zr _x O₃ (x = 0.1?0.2) are synthesized by the methods of liquid-phase and modified solid-phase synthesis. Also, solid solutions of [Bi_0.9(Pb_0.9Ln_0.1)_0.1][Fe_0.9(Zr_0.65Ti_0.35)_0.1]O₃, and [Bi_0.9(Pb_0.9Ln_0.1)_0.1][Fe_0.9(Zr_0.53Ti_0.47)_0.1]O₃ (Ln - La, Pr, Gd, Yb) are made, including synthesis of their precursors with organic ligands. Comprehensive investigations involving thermal analysis, IR spectroscopy, X-ray powder diffraction, atomic force microscopy, dielectric and magnetic measurements, and neutron powder diffraction are performed. The full-profile analysis of X-ray and neutron diffraction patterns by the Rietveld method shows that, over the whole temperature interval of 10–700 K under study, the Bi_0.9Pb_0.1Fe_0.9Zr_0.1O₃ and Bi_0.8Pb_0.2Fe_0.8Zr_0.2O₃ compounds are characterized by the perovskite structure (space group R3c). The magnetic measurements reveal an antiferromagnetic phase transition in the Bi_0.9Pb_0.1Fe_0.9Zr_0.1O₃ and Bi_0.8Pb_0.2Fe_0.8Zr_0.2O₃ solid solutions. The Néel temperature (T _N ) decreases considerably with growing PbZrO₃ concentration as compared to the Néel point in pure BiFeO₃ (T _N = 633 K). The perovskite structure with a hexagonal distortion is found in lanthanide-substituted solid solutions and specific features of the surface morphology of the ceramics are analyzed. The magnetic measurements suggest the presence of an antiferromagnetic phase transition in the solid solutions under study, with a considerable drop of T _N in the Ln-alloyed compound as compared to the T _N value in pure BiFeO₃     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> addition on the microstructure and electrical properties of LaMnO<Subscript>3</Subscript>-based NTC thermistors

A study to develop a new system of negative temperature coefficient thermistors for wide temperature range, A series of Mn-based perovskite-structured ceramics of composition (LaMn_1?x Al _x O₃)_0.9(Al₂O₃)_0.1 has been synthesized by conventional solid state reaction at 1350?°C. The X-ray diffraction patterns showed that for all the samples, the substitution of manganese by aluminum up to x?=?0.1 preserved the rhombohedral perovskite LaMnO₃-like phase. For x?=?0.2, apart from the LaMnO₃-like structure, a second perovskite phase based on the cubic LaAlO₃ structure was formed. For x?=?0.3 and 0.4, the phase present was LaAlO₃ -type structure. The grain sizes of the sintered body detected by scanning electron microscope were decreased with increasing Al₂O₃ content. The resistivity increases with increasing the Al content. The obtained values of ρ _25?°C and B _25/50 and E _a are in the range of 10–13103 Ω cm, 1813–2794 K, 0.156–0.241 eV, respectively. The resistance variation (ΔR/R) was <0.241% and the minimum value (0.0483%) was obtained for aging at 125?°C at 500 h. The aim of this work was explored new composite ceramics materials, which could be used as potential candidates for wide temperature range from ?100 to 500?°C thermistors applications.     

Crystal structure and phase transitions of Sr<Subscript>2</Subscript>Ni<Subscript>1–<Emphasis Type="Italic">y</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>MoO<Subscript>6</Subscript> solid solutions

Sr₂Ni_1–yMg _y MoO₆ mixed oxides with a double perovskite structure have been synthesized via the pyrolysis of glycerol–salt mixtures. The phase composition and structure of the samples have been determined using X-ray diffraction and Raman spectroscopy. The temperatures of phase transitions in Sr₂Ni_1–yMg _y MoO₆ with y = 0.25, 0.5, and 0.75 have been determined by high-temperature X-ray diffraction and dilatometry.     

Ab Initio Study of the Electronic Structure,Elastic Properties,Magnetic Feature and Thermodynamic Properties of the Ba<Subscript>2</Subscript>NiMoO<Subscript>6</Subscript> Material

We report first-principles calculations of the elastic properties, electronic structure and magnetic behavior performed over the Ba₂NiMoO₆ double perovskite. Calculations are carried out through the full-potential linear augmented plane-wave method within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient and Local Density Approximations, including spin polarization. The elastic properties calculated are bulk modulus (B), the elastic constants (C₁₁, C₁₂ and C₄₄), the Zener anisotropy factor (A), the isotropic shear modulus (G), the Young modulus (Y) and the Poisson ratio (υ). Structural parameters, total energies and cohesive properties of the perovskite are studied by means of minimization of internal parameters with the Murnaghan equation, where the structural parameters are in good agreement with experimental data. Furthermore, we have explored different antiferromagnetic configurations in order to describe the magnetic ground state of this compound. The pressure and temperature dependence of specific heat, thermal expansion coefficient, Debye temperature and Grüneisen parameter were calculated by DFT from the state equation using the quasi-harmonic model of Debye. A specific heat behavior C_V?≈?C_P was found at temperatures below T = 400 K, with Dulong–Petit limit values, which is higher than those, reported for simple perovskites.