New heat generation material in AC magnetic field for Y3Fe5O12-based powder material synthesized by reverse coprecipitation method

We found the most promising powder material for the application of the thermal coagulation therapy for the treatment of cancerous tissues. The maximum heat generation ability (ΔT = 40-77 °C, 370 kHz, 1.77 kA·m^− 1) was obtained for the powder materials by the calcination at 1100 °C for the Y_3 − XGd_XFe₅O₁₂ system. This ΔT value is higher than ca. ΔT = 30 °C in same magnetic field for fine FeFe₂O₄ particles as the candidate material for this type of therapy. The particle growth with the formation of the cubic single phase might influence to the high heat generation. As an unexpected result, the Gd₃Fe₅O₁₂ (X = 3) has no heat generation ability in an AC magnetic field.     

Large magnetocaloric effect in Ti-modified La0.70Sr0.30MnO3 perovskite

The effect of Ti substitution on the magnetocaloric effect of the La_0.70Sr_0.30MnO₃ perovskite was investigated. The magnetic entropy change (− ΔS_M) was deduced by two methods: a Maxwell relation and the Landau theory. The magnetocaloric data displays a large value of the magnetic entropy change (− ΔS_M) near the Curie temperature (T_C = 210 K), which increases when increasing the applied magnetic field. A good agreement is found between the experimental (− ΔS_M) and the one estimated by Landau theory. The relative cooling power values vary from 49 to 288 J kg^− 1 upon variation of the applied magnetic field at 1 and 5 T. Under 5 T, the relative cooling power value for La_0.70Sr_0.30Mn_0.90Ti_0.10O₃ is about 70% of the conventional refrigerant Gd material. As a result, the herein reported compound can be considered as a promising material in magnetic refrigeration technology.     

Synthesis of fine magnetite powder using reverse coprecipitation method and its heating properties by applying AC magnetic field

Nano-sized FeFe₂O₄ ferrite powder for local thermal coagulation therapy was synthesized by a reverse coprecipitation method. The crystal diameter for the samples from the reverse coprecipitation method was smaller than that from a normal coprecipitation method. The crystal diameter increased with an increase in the synthesized temperature for both methods. The maximum increasing temperature under the AC magnetic field was at around a 12 nm crystal diameter. The FeFe₂O₄ powder was oxidized to Fe₂O₃ by calcination at 600 °C in ambient air. The heating ability almost depended on the hysteresis loss value. Although the increased temperature under the AC magnetic field for the fresh FeFe₂O₄ sample was very close to that for the commercialized MgFe₂O₄ powder, it was gradually decreased for FeFe₂O₄ with time in ambient air.     

Magnetic and structural properties of Fe65Co35 alloys obtained by melting,high-energy milling and heat treatment

The influence of milling and annealing conditions on the structural and magnetic behaviour of mechanically milled Fe₆₅Co₃₅ alloys has been studied. By differential scanning calorimetry measurements we determined the internal stress relaxation temperature, recrystallisation temperature and structural order/disorder transition temperature of bulk and mechanical milled Fe₆₅Co₃₅. The width of the X-ray diffraction peaks was found to increase with the milling time. Two types of annealing were performed: a conventional heat treatment at 500, 550 and 600 °C for 2 h and a rapid annealing for a maximum of 2 min at 700, 750 or 800 °C followed by quenching. Crystallite size increases with increasing heat treatment temperature and time, as both are parameters that influence the magnetic properties of the sample. Magnetic permeability variations result from internal stress evolution, changes in crystallite size, supposing that the crystallite size of the annealed samples is at the border between viability of the Herzer model and the classical behaviour of the permeability vs. crystallite size.     

Magnetocaloric properties in Ln0.67Ba0.33Mn1 − xFexO3 (Ln = La or Pr) manganites

We have investigated the magnetocaloric properties of Ln_0.67Ba_0.33Mn_1 − xFe_xO₃ (Ln = La or Pr) manganites with x = 0 and 0.05. All compounds present a maximum and large magnetocaloric effect near the Curie temperature (T_C). The associated maximum value of the magnetic entropy change, at 5 T applied change in the magnetic field, is 4.37 J.kg^− 1.K^− 1 for Pr_0.67Ba_0.33MnO₃ manganite with a T_C value of 205 K. The corresponding relative cooling power (RCP) reaches 230 J.kg^− 1. All the samples present similar RCP values that are relatively high and are promising materials to be used in ecologically friendly magnetic refrigeration technology. Iron doping reduces both T_C and ΔS_M^max and spreads the temperature working range with an almost constant RCP and can then be used to tune the working conditions of a refrigerator device.     

Synthesis of nanocrystalline xCuFe2O4-(1 − x)BiFeO3 magnetoelectric composite by chemical method

xCuFe₂O₄-(1 − x)BiFeO₃ spinel-perovskite nanocomposites with x = 0.1, 0.2, 0.3 and 0.4 were prepared using citrate precursor method. X-ray diffraction (XRD) analysis showed phase formation of xCuFe₂O₄-(1 − x)BiFeO₃ calcined at 500 °C. Transmission electron microscopy (TEM) shows formation of nanocrystallites of xCuFe₂O₄-(1 − x)BiFeO₃ with an average particle size of 40 nm. Variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Coercivity, saturation magnetization and squareness have been found to vary with concentration of ferrite phase and annealing temperature due to the increase in crystallite size. Squareness and coercivity increased with an increase in annealing temperature up to 500 °C and then decreased with a further increase in temperature to 600 °C. Magnetoelectric effect of the nanocomposites was found to be strongly depending on the magnetic bias and magnetic field frequency.     

Crystal structure and magnetic properties of the compound FeDy6Sb2

The crystal structure of a compound FeDy₆Sb₂ was determined by X-ray powder diffraction using the Rietveld method. The compound crystallizes in the hexagonal, space group P6¯2m (No. 189) with the Fe₂P structure type and lattice parameters a = 0.81449(5) nm, c = 0.41641(3) nm, z = 1 and D_calc = 8.842 g/cm³. The maximum magnetic entropy change ΔS_M for the compound is 3.41 J kg^− 1 K^− 1 near its Curie temperature (143.4 K) on the magnetic field changes of 0-2.0 T.     

Structural and magnetic properties of CoFe2O4 thin films deposited by laser ablation on Si (001) substrates

Cobalt ferrite (CoFe₂O₄) thin films have been deposited on Si (001) substrates, with different substrate temperatures (T_dep = 25 °C − 600 °C). The films were prepared by pulsed laser ablation with a KrF excimer laser (wavelength λ = 248 nm). The oxygen pressure during deposition was 2 × 10⁻² mbar. The films structure was studied by X-ray diffraction (XRD) and their surface was examined by scanning electron microscopy (SEM). The magnetic properties were measured with a vibrating sample magnetometer (VSM). For low deposition temperatures, the films presented a mixture of a CoFe₂O₄ phase, with the cubic spinel structure, and cobalt and iron antiferromagnet oxides with CoO and FeO stoichiometries. As the deposition temperature increased, the CoO and FeO relative content strongly decreased, so that for T_dep = 600 °C the films were composed mainly by polycrystalline CoFe₂O₄. The magnetic hysteresis cycles measured in the films were horizontally shifted due to an exchange coupling field (H_exch) originated by the presence of the antiferromagnetic phases. The exchange field decreased with increasing deposition temperature, and was accompanied by a corresponding increase of the coercivity and remanence ratio of the cycles. This behavior was due to the strong reduction of the CoO and FeO content, and to the corresponding dominance of the CoFe₂O₄ phase on the magnetic properties of the thin films.     

Physicochemical properties of solid-solid interactions in nanosized NiO-substituted Fe2O3/TiO2 system at 1200 °C

The solid-solid interactions between nanosized pure and NiO-substituted ferric and titanium(IV) oxides have been investigated using XRD technique and microstructure studies, also magnetic properties were studied using vibrating samples magnetometer (VSM). The amounts of substituting Ni²⁺ were x = 0, 0.2, 0.4, 0.6, 0.8 and 1 mole. A mixture equimolar proportions of finely powdered Fe₂O₃ and TiO₂ were mixed with NiO, ball milled, compressed at 250 kg/cm² and fired at 1200 °C for 4 h.The obtained results showed that with substituting Ni²⁺ concentration x = 0 only Fe₂TiO₅ phase is present (∼80 nm) which showed a very small saturation magnetic flux density (B_s), remnant magnetic flux density (B_r) and the maximum energy product (BH)_max. By the addition of x = 0.2 NiO, new phases were observed NiTiO₃ and NiFe₂O₄ of crystallite sizes 160 and 110 nm, respectively. By the increase of substituting Ni²⁺ concentration the NiTiO₃ and NiFe₂O₄ phases increased on the expense of Fe₂TiO₅ up to x = 0.4, then the increase in substituting Ni²⁺ concentration led to a decrease in Fe₂TiO₅ and NiTiO₃ while NiFe₂O₄ increases which results in a great improvement of magnetic properties.All samples exhibit a catalytic activity towards H₂O₂ decomposition and the values of rate constant increase with increasing amount of Ni²⁺ substituting. The most acidic active sites are shown by specimens substituted with x = 0 this concludes that H₂O₂ decomposition is not favored on acidic active sites.     

High frequency properties of Ni75Fe25-SiO2 granular thin films with very high resistivity

Excellent soft magnetic properties have been achieved in low metal volume fraction(x ∼ 0.52) of (Ni₇₅Fe₂₅)_x(SiO₂)_1−x granular film fabricated by magnetron sputtering. The coercivity of 247 A m^− 1 with very high resistivity ρ over 1.18 × 10⁴ μΩ cm has been obtained. At the frequency lower than 1 GHz, the real part μ′ of the complex permeability keeps about 55 and the imaginary part μ? is less than 2. A combined study of TEM and XRD indicates that the sample consists of Ni₇₅Fe₂₅ particles uniformly embedded in insulating SiO₂ matrix. The excellent soft magnetic properties are ascribed to the magnetic dipole interaction between particles. The investigations of field cooled and zero field cooled curves as well as Henkle Plot prove the existence of this intergranular interaction.     

Fine Fe16N2 powder prepared by low-temperature nitridation

α-Fe was prepared by reduction of a fine γ-Fe₂O₃ powder under hydrogen at 500 °C for 8 h. The α-Fe fine powder, about 100 nm in crystallite size, was then nitrided under an ammonia flow at 130 °C for 100 h. X-ray single-phase Fe₁₆N₂ was obtained with a magnetization value of 225 emu/g at room temperature under a magnetic field of 15 kOe. The Mössbauer spectrum at room temperature could be resolved into three sets of hyperfine fields with an average magnetic moment of 2.52 μ_B. An additional paramagnetic component was present in the spectrum with an area ratio of 19%.     

Properties of TiO2 prepared by acid treatment of BaTiO3

TiO₃ powders were prepared by acid treatment of BaTiO₃ and their properties were investigated. The BaTiO₃ powder was subjected to HNO₃ in concentrations ranging from 10⁻³ to 8 M at 90 °C for 0.5-6 h. Dissolution of BaTiO₃ and precipitation of TiO₂ occurred at acid concentrations of 2-5 M. BaTiO₃ dissolves completely to form a clear solution at reaction times of 0.5-1 h, but a rutile precipitate is formed after 2 h of acid treatment. By contrast, anatase is precipitated by adjusting the pH of the clear solution to 2-3 using NaOH or NH₄OH solution. The rutile crystals were small and rod-shaped, consisting of many small coherent domains connected by grain boundaries with small inclination angles and edge dislocations, giving them a high specific surface area (S_BET). With increasing HNO₃ concentration, the S_BET value increased from 100 to 170 m²/g while the crystallite size decreased from 25 to 11 nm. The anatase crystals obtained here were very small equi-axial particles with a smaller crystallite size than the rutile and S_BET values of about 270 m²/g (higher than the rutile samples). The photocatalytic activity of these TiO₂ was determined from the decomposition rate of Methylene Blue under ultraviolet irradiation. Higher decomposition rates were obtained with larger crystallite sizes resulting from heat treatment. The maximum decomposition rates were obtained in samples heated at 500-600 °C. The photocatalytic activity of the TiO₂ was found to depend more strongly on the sample crystallite size than on S_BET.     

Study on properties of CaO-SiO2-B2O3 system glass-ceramic

Low temperature co-fired ceramic (LTCC) is prepared by sintering a glass selected from CaO-SiO₂-B₂O₃ system, and its sintered bodies are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that the optimal sintering temperature for this glass-ceramic is 820 °C for 15 min, and the major phases of this material are CaSiO₃, CaB₂O₄ and SiO₂. The glass-ceramic possesses excellent dielectric properties: ?_r = 6.5, tan δ < 2 × 10⁻³ at 10 MHz, temperature coefficient of dielectric constant about −51 × 10⁻⁶ °C⁻¹ and coefficient of thermal expansion about 8 × 10⁻⁶ °C⁻¹ at 20-400 °C. Thus, this material is supposed to be suitable for the tape casting process and be compatible with Ag electrode, which could be used as the LTCC materials for the application in wireless communications.     

Growth and properties of Ca0.28Ba0.72Nb2O6 single crystals

Calcium barium niobate Ca_0.28Ba_0.72Nb₂O₆ (CBN-28) crystals were successfully grown by the Czochralski method. X-ray powder diffraction experiments indicated that CBN single crystals are tetragonal with a = 12.432(±0.002) Å and c = 3.957(±0.001) Å, which have almost the same structure as the Sr_0.50Ba_0.50Nb₂O₆ (SBN-50) crystal. The thermal expansion coefficient perpendicular to Z-direction had been measured to be 1.25 × 10⁻⁵ K⁻¹ between 293.15 and 572.15 K, and along Z-axis was negative between 298.15 and 543.15 K. The specific heat of the crystal had been measured by the differential scanning calorimetric experiments. The transmittance spectra from 200 to 3200 nm were also measured. The measured temperature dependence of dielectric constants showed that the Curie temperature of the CBN-28 crystals is 260 °C, which is about 200 °C higher than that of the (SBN) crystal.     

Synthesis of (1 − x)Ca2/5Sm2/5TiO3-xLi1/2Nd1/2TiO3 ceramic powder via ethylenediaminetetraacetic acid precursor

(1 − x)Ca_2/5Sm_2/5TiO₃-xLi_1/2Nd_1/2TiO₃ (CSLNT) ceramic powder was prepared by a liquid mixing method using ethylenediaminetetraacetic acid (EDTA) as the chelating agent. TG, DTA, XRD and TEM characterized the precursors and derived oxide powders. When x = 0.3, perovskite CSLNT was synthesized at 1000 °C for 3 h in air. The CSLNT (x = 0.3) ceramics sintered at 1200 °C for 3 h show excellent microwave dielectric properties of ?_r = 99, Q_f = 6200 GHz and τ_f = 9 × 10⁻⁶ °C⁻¹.     

Novel multiferroic La0.95Sb0.05FeO3 orthoferrite

A series of La_1−xSb_xFeO₃ was prepared using the conventional solid state method. XRD revealed the formation of the orthorhombic structure with space group Pbnm. The data showed that, the molar magnetic susceptibility and coercive field H_C were increased from 9.16 × 10⁻³ to 26.9 × 10⁻³ emu g⁻¹ mol and 1196 to 5465 Oe from for LaFeO₃ to La_0.95Sb_0.05FeO₃, respectively. The coercive field (H_C) of the sample with x = 0.05 increased 6 times than that of the parent LaFeO₃ and the saturation magnetization (M_s) was increased from 0.1614 emu g⁻¹ for the parent LaFeO₃ to 0.2654 emu g⁻¹ for the doped sample_. The dielectric constant (?′) was increased with increasing the Sb³⁺ content. The ac conductivity (σ) increases from 2.36 × 10⁻³ Ω⁻¹ m⁻¹ for the LaFeO₃ to 30 × 10⁻³ Ω⁻¹ m⁻¹ for the sample La_0.95Sb_0.05FeO₃ at T = 553 K and frequency 1 MHz. The sample La_0.95Sb_0.05FeO₃ is concluded to be a novel single phase multiferroic material.     

Ferromagnetism and high magnetic moments induced by Ba substitution for Ca in charge ordered Nd0.5Ca0.5MnO3

The magnetic properties of the Nd_0.5Ca_0.5−xBa_xMnO₃ series have been investigated. Similar to the Pr_0.5Ca_0.5−xBa_xMnO₃ series (Raveau et al., J. Phys.: Condens. Matter 15 (2003) 7055), the substitution of Ba for Ca can also induce a ferromagnetic (FM) ground state and sharp magnetization steps at low temperature (2.5 K) in the Nd ones. The FM fraction first quickly increases with x due to the local ‘counter-distortion’ effect introduced by barium cations, reaches a maximum value of 26% for x = 0.03, and then slowly decreases as more Ba is introduced where the A-site size mismatch has increased dramatically. In comparison with the Pr series, the Nd series exhibit a greater ability to induce ferromagnetism. When the magnetic field is increased, for low substitution levels (x < 0.06) the latter series show higher magnetizations and lower critical fields where the magnetization steps appear. A possible interpretation for this behavior is that the Nd-Mn magnetic interactions can destabilize the antiferromagnetic structure and favour the development of FM domains.     

Crystal structure and ionic conductivity of ruthenium diphosphate ARu2(P2O7)2, A=Li, Na, and Ag, with a tunnel structure

Crystal structure and ionic conductivity of ruthenium diphosphates, ARu₂(P₂O₇)₂ A=Li, Na, and Ag, were investigated. The structure of the Ag compound was determined by single crystal X-ray diffraction techniques. It crystallized in the triclinic space group P−1 with a=4.759(2) Å, b=6.843(2) Å, c=8.063(1) Å, α=90.44(2)°, β=92.80(2)°, γ=104.88(2)°, V=253.4(1) Å³. The host structure of it was composed of RuO₆ and P₂O₇ groups and formed tunnels running along the a-axis, in which Ag⁺ ions were situated. The ionic conductivities have been measured on pellets of the polycrystalline powders. The Li and Ag compounds showed the conductivities of 1.0×10⁻⁴ and 3.5×10⁻⁵ S cm⁻¹ at 150 °C, respectively. Magnetic susceptibility measurement of the Ag compound showed that it did not obey the Curie-Weiss law and the effective magnetic moment decreased as temperature decreased due to the large spin-orbital coupling effect of Ru⁴⁺ ions.     

Rietveld refinement and switching properties of Cr substituted NiFe2O4 ferrites

A series of ferrite samples of the chemical formula NiCr_xFe_2 − xO₄ (x = 0.0 to x = 1.0) were prepared by a wet chemical co-precipitation method and annealed at 600 °C for 4 h. The prepared samples were shown to have the cubic spinel structure by applying the full pattern fitting of the Rietveld method using the Full Prof program. The unit cell dimension, discrepancy factor and interatomic distance have been determined. It was observed that the unit cell dimensions decrease with an increase in Cr³⁺ content x. The grain size of the synthesized powder has been determined from XRD data and strain graph. The grain size of all samples is in the range of 26 to 40 nm. The IR spectra show three absorption bands in the wave number range of 200 to 800 cm^− 1. All samples were studied for electrical switching. Current controlled negative resistance type switching was observed for all samples.     

Synthesis and ferromagnetic property of new binary copper iron pyrophosphate CuFeP2O7

The pyrophosphate of CuFeP₂O₇ was synthesized through one step-thermal synthesis at 500 °C using the mixing of copper carbonate, iron metals and phosphoric acid. FTIR and XRD results indicate the dominant feature of pyrophosphate (P₂O₇⁴⁻) anion and a pure monoclinic phase with space group C_2h⁶ (Z = 4), respectively. The crystallite size of 25 ± 9 nm for the CuFeP₂O₇ was estimated by X-ray line broadening. Room temperature magnetization result shows ferromagnetic behavior of the CuFeP₂O₇ powder, having hysteresis loop in the range of ± 10,000 Oe with the specific magnetization value of 1.57 emu g^− 1. This property is important for specific application and is presented for the first time.