The article presents a comprehensive investigation of the crystal structure, impedance spectra, magnetic, magnetodielectric, and magnetoresistive properties of (1-x)CoFe2O4-xPbTiO3 composites with varying concentrations (& khcy; = 0, 0.2, 0.4, and 0.6). The study also examines the effects of applying a uniaxial pressure of 1 GPa to the synthesized powders using Bridgman anvils. Our findings reveal that the synthesis of these composites results in the formation of an additional phase, lead hexaferrite PbFe12O19, which exhibits multiferroic properties. Additionally, the coherent scattering region of the components is significantly reduced after mechanical activation. Notably, the real part of the resistivity rho '(omega) of nanostructured CoFe2O4 ceramics increases eightfold at T = 240 degrees C. The composites demonstrate significant magnetoresistance at room temperature, reaching up to 250 %. The study also reveals that the signs of the magnetodielectric MD(B) and magnetoresistive coefficient MR(B) vary with the frequency of the measuring field for certain concentrations. Using the first-order reversal curve (FORC) method, it was observed that after nanostructuring CoFe2O4 through mechanical activation, the interaction field Hu shifts from +/- 0.6 kOe to +/- 0.8 kOe, while the coercive field Hc increases from 1.05 kOe to 5 kOe. Moreover, the two-dimensional FORC maps of the composites show increased complexity, due to the formation of additional magnetic phases.

In this work, the concentration dependencies of unit cell parameters, microstructure, dielectric, impedance spectra, and magnetic properties of (1 – x)SmFeO3–xNaNbO3 were studied for the first time. It was found that at a concentration x = 0.7, the unit cell parameter a, the tilt angles θ and rotation angles φ of oxygen octahedra and the bond lengths Fe-O1 and Fe-O3 of samarium ferrite SmFeO3 (SFO) have a maximum, and Fe-O2 has a minimum value. The tilt angle θ, rotation angle φ of the octahedral, and the bond lengths of sodium niobate NaNbO3 (NNbO) change nonmonotonically. For x = 0.9, the unit cell parameters b and c, as well as all bond lengths in the NaO9 tetradecahedra, reach their minimum values. Anomalies corresponding to the spin-reorientation transition temperatures TSR1 and TSR2 were detected in the dielectric spectra of SFO at temperatures of 200 and 309 °C. The jump in the real part of the dielectric constant ε′(T), starting before – 100 °C, is attributed to the response of the dipole moments to the magnetic moment jump and spin switching (TSSW). Anomalies corresponding to transitions between different phases in this antiferroelectric were found in the temperature dependences of ε′(T) and dielectric loss tangent tgδ(T) of NNbO at temperatures of – 75, 23, 160, 278, 379, and 433 °C. From magnetic measurements, it was found that the composition with x = 0.8 has a minimum size of coherent scattering regions of D = 94 nm, representing the second critical size at which the coercive field Hc reaches its maximum value.

Nanocomposite films of BiFeO3-Bi2Fe4O9 were fabricated on a sapphire substrate Al2O3 using the method of gas discharge high-frequency cathodic sputtering of a ceramic target with a stoichiometric composition in an oxygen atmosphere. The results of the film analysis using X-ray structural analysis, Raman scattering, XPS, and atomic force microscopy are presented. The lattice parameters, surface topography, chemical composition of the films, concentration, and average sizes of the crystallites for each phase were determined. It was shown that the ratio of the BiFeO3 to Bi2Fe4O9 phases in the obtained film is approximately 1:2. The sizes of the crystallites range from 15 to 17 nm. The optical and magnetic properties of the nanocomposite layers were studied, and the band gap width and magnetization hysteresis characteristic of ferromagnetic behavior were observed. The band gap width was found to be 1.9 eV for the indirect and 2.6 eV for the direct interband transitions. The magnetic properties are characterized by a hysteresis loop resembling a “wasp-waist” shape, indicating the presence of magnetic anisotropy.

Проведены исследования теплоемкости микро-и нанокристаллической керамики Er 3 Fe 5 O 12 (ErF) в области высоких температур и фазовых переходов.Установлено, что структурные дефекты, возникающие в процессе механоактивации, играют существенную роль в формировании теплофизических свойств керамики.Показано, что механическая активация приводит к значительному размытию антиферромагнитного перехода и сдвигу температуры фазового перехода в низкотемпературную область.

In this work, the structure and physical properties of (1 − x)(CoFe2O4) − x(PbTiO3) compositions, synthesized by the solid-phase method, were studied for the first time using complex methods. It was found that the solid-phase sintering of the inverse spinel CoFe2O4 (CFO) and the ferroelectric PbTiO3 (PTO) is frequently accompanied by the formation of additional phases—hexaferrite PbFe12O19 (PFO) and solid solutions, which were identified by X-ray diffraction, energy-dispersive X-ray analysis, and Raman spectroscopy. The dependencies of the unit cell parameters of the main components and additional phases on the concentration of PTO were studied at room temperature. The concentration interval (x = 0.3–0.7) with extreme values of structural parameters and non-monotonic changes of the physical properties was discovered. Complex quantities such as dielectric permittivity ɛ*(ω) and electric modulus M*(ω) were studied over a wide range of frequencies and temperatures using dielectric spectroscopy. The polarization switching kinetics of (1 − x)(CFO) − x(PTO) compositions were studied, and the saturated ferroelectric hysteresis loops P(E) with maximum spontaneous polarization Ps equal to 132 μC/cm2 were obtained for the first time. The bandgap Eg was determined by optical absorption spectroscopy at room temperature; Eg varies depending on the PTO concentration in the range 2.11–2.57 eV. The dynamic properties of the compositions were studied by Fourier transform infrared spectrometer (FTIR) and Raman spectroscopy. The Raman modes corresponding to PFO are well detected starting from compositions 0.3(CFO)–0.7(PTO).

The pure-phase BiFeO3 was obtained in one stage by solution combustion synthesis. The influence of the heat treatment process on the phase composition, magnetic, and optical properties was studied. The calcination of the powder led to a decrease in the fraction of the impurity phase from 7 to 1% and an increase in the crystallite size. X-ray diffraction revealed the formation of a pure phase upon heat treatment at 600 °C. The band gap of the samples increases from 1.91 to 2.06 eV with an increase in the crystallite size. M–H loops measured at room temperature showed a strong ferromagnetic character. For the initial powder, Ms was ~ 1.9 emu/g. The dependence of the magnetic properties on the crystallite size has been established.

In this paper, we present the synthesis and studies of physical properties of the ferroelectromagnetic composites (1–x)PbMn1/3Ta2/3O3–xPbTiO3 [(1–x)PMnT–xPT], which exhibit a relaxor behavior. Using a synergistic application of scanning electron microscopy (SEM), X-ray structure analysis, and energy-dispersive X-ray analysis (EDX), we revealed that two phases always coexist in the synthesis of the composition PbMn1/3Ta2/3O3 (PMnT), one phase of which has a pyrochlore structure, and the other has a pseudo-cubic cell of the perovskite structure. We further demonstrated that doping with lead titanate PbTiO3 (PT) suppresses the dielectric polarization’s relaxor behavior. Using X-ray diffraction techniques at room temperature, we studied the dependencies of the structural parameters of each phase on the mole fractions of PT. The dielectric characteristics were studied at various frequencies by the dielectric spectroscopy method, and the dependency of the bandgap Eg on the dopant’s mole fractions was determined by the optical absorption method. The dopant’s influence on the IR Fourier spectra and magnetic hysteresis loops was analyzed. The magnetodielectric and magnetoresistive effects in these composites were studied.

The specific heat and the dielectric permittivity of Bi 0.8 Ho 0.2 FeO 3 multiferroics have been studied in the wide temperature range 300–750 K. The doping with rare-earth element holmium is found to lead to substantial changes in the temperature dependences of specific heat C p and dielectric permittivity ε' at high temperatures. The additional contribution to the specific heat is shown can be interpreted as a Schottky anomaly for three-level states which form due to a distortion of the lattice parameters as a result of doping. Additional anomaly characteristic of a phase transition is observed in temperature dependences of C p and ε'. The results are discussed in combination with the data of structural studies.

The heat capacity and permittivity of Bi0.8Ho0.2FeO3 multiferroics were studied in a wide temperature range of 300--750 K. It was found that doping with holmium with rare-earth element leads to significant changes in the temperature dependences of the specific heat Cp and permittivity ε 'at high temperatures. It is shown that an additional contribution to the specific heat can be interpreted as a Schottky anomaly for three-level states arising due to distortion of the lattice parameters upon doping. An additional anomaly characteristic of the phase transition was found in the temperature dependences of Cp and ε '. Research results are discussed in conjunction with structural studies.

Wereport on structural, dielectric and vibrational properties of the relaxor-ferroelectric system (1-x).Pb(Mn1/3Nb2/3)O-3 - x.(PbTiO3) in the concentration range of 0.15 <= x <= 0.25. The range corresponds to a morphotropic (MPT) phase boundary between the rhombohedral R3mand tetragonal P4 mm phases of the solid solution. The non-doped Pb(Mn1/3Nb2/3)O-3 was of the R3m space group, demonstrating smeared phase transitions and relaxor behavior. Increasing concentration of the dopant led to a gradual suppression of the relaxor behavior with occurrence of a sharp firstorder phase transition.

The heat capacity and dielectric properties of microcrystalline and nanostructured SmFeO 3 ceramics obtained by solid phase synthesis are studied. The ceramics is synthesized by the treatment of the batch at room temperature in Bridgman anvils by forceful action combined with shear deformation followed by sintering. It is established that the mechanoactivation results in noticeable broadening antiferromagnetic–ferroelectric transition and shifting the temperature of phase transition in the low-temperature area. The phase transition having typical for relaxation oscillator frequency dependent character is found at 558 K. It is shown that the defect structure can take a dominant place in the formation of the physical properties of ceramics.

The heat capacity and thermal conductivity of multiferroics Bi1-xPrxFeO3 (0 <= x <= 0.50) has been studied in the temperature range of 130-800 K. A slight substitution of praseodymium for bismuth is found to lead to a noticeable shift of the antiferromagnetic phase transition temperature whilst the heat capacity increases. The temperature dependences of the heat capacity and thermal conductivity exhibit additional anomalies during phase transitions. The experimental results suggest that the excess heat capacity can be attributed to the Schottky effect for three-level states. The basic mechanisms of the heat transfer of phonons are highlighted and the dependence of the mean free path on temperature is determined.

Structure and dielectric properties of polycrystalline multiferroics of Bi1 – xSmxFeO3 (x = 0–0.2) system are studied. Using X-ray diffraction, two coexisting phases (rhombohedral R3c and orthorhombic Pbam) are found in the nanostructured sample with x = 0.1. Four anomalies characteristic for phase transitions are found near temperatures of ~180, 250, 300°C and TN at ~350°C on temperature dependences of permittivity ε'(T). It is shown that when samarium content is increased, the permittivity ε' grows and tanδ decreases.

The structure and dielectric properties of polycrystalline multiferroics of the Bi1-xSmxFeO3 system (x = 0-0.2) are investigated. X-ray diffraction revealed that two phases coexist in the x = 0.1 nanostructured sample: rhombohedral R3c and orthorhombic Pbam. On the temperature dependences of the dielectric constant ε'(T), four anomalies characteristic of phase transformations were found in the temperature range of ~ 180°С, ~ 250°С, ~ 300°С and TN ~ 350°С. It is shown that with increasing samarium concentration, the dielectric constant ε' increases, and tgδ decreases

Dielectric permittivity, dielectric losses and ac-conductivity of polycrystalline Bi1-xSmxFeO3 (x = 0; 0.05; 0.1; 0.15; 0.2) are measured in the frequency range 1 kHz-10 MHz and in the temperature range 25-600 degrees C. Anomalies have been observed at the 200 degrees C, 300 degrees C and at the Neel temperature. It has been demonstrated that doping with Sm has enhanced the dielectric properties and increased conduction in the frequency region <1 MHz. At high frequency (>1 MHz) and at a certain temperature T-m, depending on the composition Bi1-xSmxFeO3, the conductivity reaches a maximum. The results are discussed with reference to the model of correlated barrier hopping.

AbstractThe heat capacity and dielectric properties of microcrystalline and nanostructured SmFeO_3 ceramics obtained by solid phase synthesis are studied. The ceramics is synthesized by the treatment of the batch at room temperature in Bridgman anvils by forceful action combined with shear deformation followed by sintering. It is established that the mechanoactivation results in noticeable broadening antiferromagnetic–ferroelectric transition and shifting the temperature of phase transition in the low-temperature area. The phase transition having typical for relaxation oscillator frequency dependent character is found at 558 K. It is shown that the defect structure can take a dominant place in the formation of the physical properties of ceramics.

4 Федеральный исследовательский центр Южный научный центр РАН; Россия, 344006, г.Ростов-на-Дону