Analytical expressions for contributions to crystal fields on rare-earth ions due to the spatial distribution of electron densities of f-electrons and ligands have been derived. Numerical calculations of intrinsic parameters a(2)((2)), a(2)((4)), and a(2)((6)) have been carried out on the Hartree-Fock wave functions of Nd3+-O2- and of Er3+-O2- pairs. The dependencies of the extended charge contribution to intrinsic parameters on the distance between ions are compared with those which are expected in the semiempirical model of exchange charges on the rare-earth ion-ligand bond.

Some layered phyllosilicates are characterized by spontaneous scrolling due to size mismatch between sublayers. The doping of layers by transition metal ions allows nanoscrolls to acquire magnetic properties. The magnetic behavior of synthetic (Mg1 – xCox)3Si2O5(OH)4 (x = 0.2, 0.4, 0.6, 0.8, 1) phyllosilicates with the chrysotile structure before and after partial hydrogen-induced reduction is studied. The dominant ferromagnetic behavior has been revealed in all studied phyllosilicates. Ensembles of cobalt metal nanoparticles in a silicate matrix have demonstrated a collective magnetic response at room temperature with a narrow hysteresis loop and fast saturation.

A layered perovskite-like oxides LaxSr2−xTi1−x/2Cux/2O4 (x = 0.2, 0.3, 0.5) with a K2NiF4-type structure were obtained. The introduction of copper into the titanium sublattice reduces the band gap. Copper in these materials serve as a photoactivity regulator and is presented in two oxidation states in accordance with optical, voltammetric and EPR data. LaxSr2−xTi1−x/2Cux/2O4 (x = 0.2) exhibits the greatest photoactivity in the oxidation of phenolic compounds and As(III) under the influence of UV and blue light; with increasing degree of substitution x, the photoactivity of LaxSr2−xTi1−x/2Cux/2O4 decreases. This is explained by the formation of a magnetic polaron, which is observed in LaxSr2−xTi1−x/2Cux/2O4 (x = 0.5) in the temperature range from 50 to 200 K and is proven by ESR method. The expansion of the spectral range of LaxSr2−xTi1−x/2Cux/2O4 to the visible region is explained by the formation of acceptor levels ( Cu^2 + + e^ - →Cu^ + / Cu^ + + h^ + →Cu^2 + ) in the band gap of Sr2TiO4, which increases the efficiency of separation of photogenerated electron–hole pairs. The presence of Cu (I) в LaxSr2−xTi1−x/2Cux/2O4 enhance photoactivity through the formation of active superoxygen radical on its surface ( Cu^ + + O_2( ad)→Cu^2 + +·O_2^ - ).

Mn1.17Co1.83BO5 and Mn1.39Co1.61BO5 ludwigites were synthesized by the flux technique and investigated by means of X-ray diffraction, X-ray fluorescence, DC and AC magnetic susceptibility, and specific heat analysis. The crystal structure of both ludwigites belongs to the Pbam space group with a = 9.25 angstrom, b = 12.41 angstrom, and c = 3.05 angstrom for Mn1.17Co1.83BO5 and a = 9.27 angstrom, b = 12.45 angstrom, and c = 3.05 angstrom for Mn1.39Co1.61BO5. The simultaneously observed negative values of the Curie-Weiss temperatures and ferromagnetic-type hysteresis loops allow us to assume that the ferrimagnetic ordering is realized in Mn1.39Co1.61BO5 below TF = 60.8 K, while in Mn1.17Co1.83BO5 in addition to the above mentioned experimental facts the frequency dependencies of the real and imaginary parts of the AC magnetization were observed assuming the presence of the canonical spin-glass state below TSG = 44.5 K. The observed difference in coercive forces of M-H curves at low temperatures can be associated with presence of two spin subsystems for Mn1.17Co1.83BO5.

Temperature-dependence measurements specific heat, thermoelectric power, conductivity, and electron paramagnetic resonance measurements were performed on Mn 0 . 75 Co 2 . 25 BO 5 powder at temperatures above 290 K. Single crystals of Mn 0 . 75 Co 2 . 25 BO 5 were grown by the flux method using Bi2Mo3O12-based solvent diluted with Na2CO3. To investigate EPR and specific heat capacity, the single crystals were ground to powder. The temperature dependencies of the resistance, specific heat, Seebeck constant, and EPR spectra in the range from 290 K to 700 K were obtained. The transition from the dielectric state to the semiconductor state was detected at 348 K, consistent with the change in the fine structure of the EPR spectrum associated with S = 5/2 for the manganese ion Mn2+.

In the spiral conical phase of manganese monosilicide, MnSi, the EPR spectra are studied at a frequency of 9.3 GHz in the temperature range of 5-30 K for an external magnetic field oriented along the crystallographic direction [100]. It is found that in the temperature range T < T* = 25 K, located 4 K below the paramagnetic phase-conical phase transition temperature T-C = 29 K, a complex EPR spectrum consisting of several lines appears. A procedure is proposed for decomposing experimental spectra into components, which makes it possible to find for each spectral line the temperature dependences of the resonance magnetic field, line width, and integrated intensity. At T-f similar to 16 K, one of the main lines in the EPR spectrum with the highest integrated intensity demonstrates a maximum in the temperature dependence of the line width W(T), corresponding to a change in W by a factor of similar to 2.8. We argue that this unusual behavior appears as a consequence of a spin fluctuation transition in the conical spiral magnetic phase with long range magnetic order.

Double perovskite Ba2CoNbO6, obtained by pyrolysis of nitrate-organic mixtures, was studied by XRD, XRF, DFT, AC/DC-magnetization, specific-heat, thermoelectric, and ESR methods. The sample has cubic symmetry space group Pm3m with a = b = c = 4.0074(11) & Aring;. Deficiency in oxygen ions shows the presence of Co ions in both 3+ and 2+ valency. According to AC-magnetization and specific-heat data, Ba2CoNbO6 demonstrates spin-glass ordering at TSG = 30 K at external field value of 0.1 kOe. This temperature of spin glass transition drops with field power increase down to complete suppression at 10 kOe. The effective magnetic moment determined using the Curie-Weiss approximation is 4.29 mu B, which is consistent with the theoretical estimation for Co ions in the intermediate-spin state. The peak at T = 90 K, observed in the temperature dependence of the specific heat and accompanied by a peak in the ESR linewidth, is possibly due to the structural transition at this temperature. The Seebeck coefficient of the compound is S = 4-6.5 mu V/K and the band gap obtained within the small-polaron-jump conductivity model is Delta E = 0.284 eV in the temperature range of 350-550 K connected with DFT calculation. An intensity ESR line, related to Co2+ ions, was observed in ESR spectra.

Results are presented from investigating the structure of Mn2.25Co0.75BO5 via powder neutron diffraction. Crystals of ludwigite Mn2.25Co0.75BO5 are grown by flux method using a Bi2Mo3O12-based solvent diluted with Na2CO3 carbonate. Boric acid H_3^11BO_3 is used as the boron-containing reagent. Powder neutron diffraction measurements are made at a temperature of 100 K on powder prepared by grinding grown single crystals. Rietveld studies show that the grown Mn2.25Co0.75BO5 crystals belong to Pbam space group. Crystallographic sites occupied by cobalt and manganese ions are identified by analyzing powder neutron diffractograms. A bottleneck regime is observed in the temperature dependence of the EPR spectra.

By pyrolysis of nitrate-organic mixtures, we synthesized double perovskite Sr2Fe0.6NbO5.4. We performed the study of the temperature dependencies of the EPR spectra, DC and AC magnetization, and magnetization isotherms in a wide temperature range of 4–300K. The EPR spectrum is described by the sum of two contributions below 125 K and indicates phase separation of the sample. The paramagnetic part of the inverse magnetic susceptibility is well approximated by the Curie–Weiss law with ΘCW≈−60 K. The exchange integrals between iron spins, calculated from the temperature dependence of the ESR integral intensity and the Curie–Weiss temperature, coincide and are equal to J/kB≈10 K. The negative sign of the Curie–Weiss temperature and the hysteresis loops indicate the antiferromagnetic canted nature of exchange interactions, which is further confirmed by the presence of a peak in the real part of the AC magnetization and its absence in the imaginary part.

layered perovskite-like oxides La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 ( x = 0.2, 0.3, 0.5) with a K 2 NiF 4 -type structure were obtained. The introduction of copper into the titanium sublattice reduces the band gap. Copper in these materials serve as a photoactivity regulator and is presented in two oxidation states in accordance with optical, voltammetric and EPR data. La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 ( x = 0.2) exhibits the greatest photoactivity in the oxidation of phenolic compounds and As(III) under the influence of UV and blue light; with increasing degree of substitution x , the photoactivity of La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 decreases. This is explained by the formation of a magnetic polaron, which is observed in La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 ( x = 0.5) in the temperature range from 50 to 200 K and is proven by ESR method. The expansion of the spectral range of La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 to the visible region is explained by the formation of acceptor levels ( Cu^2 + + e^ - →Cu^ + / Cu^ + + h^ + →Cu^2 + ) in the band gap of Sr 2 TiO 4 , which increases the efficiency of separation of photogenerated electron–hole pairs. The presence of Cu (I) в La x Sr 2− x Ti 1− x /2 Cu x /2 O 4 enhance photoactivity through the formation of active superoxygen radical on its surface ( Cu^ + + O_2( ad)→Cu^2 + +·O_2^ - ).

The rare-earth manganites of Eu, La0.7−xEuxSr0.3MnO3 (x = 0.0–0.7) were investigated by the technique of electron paramagnetic resonance (EPR) in the temperature range from 30 to 500 K. They revealed the coexistence of two to three magnetic phases in the samples with different Eu concentrations. The corresponding Curie temperatures were estimated from the characteristics of the variable-temperature EPR spectra for the various samples. The EPR data indicated the presence of Griffiths phases for the samples La0.7−xEuxSr0.3MnO3, from which the respective Griffiths temperatures were determined. It was found that the structural disorder (σ2), caused by the presence of different sets of atoms in crystal cells, characterized by the distribution of the cation radius, increased as x increased from 0.1 to 0.3 and decreased as x increased from 0.3 to 0.7. This, in turn, resulted in the sample with the maximum structural disorder, i.e. the sample with x = 0.3, being characterized by the maximum activation temperature. The activation energies are estimated here from the EPR data using the hopping model. The EPR linewidth behavior is found to be consistent with that predicted by the bottlenecked spin relaxation model. The perovskite La0.5Eu0.2Sr0.3MnO3 is found to be potentially useful in the design of magnetocaloric refrigeration units as a working fluid, since its Curie temperature (TC) is close to the room temperature/ The different ferromagnetic components in the samples studied here have been resolved by the technique of EPR, not possible by other techniques.

The Europium rare-earth manganites, La0.7−xEuxSr0.3MnO3 (x = 0.0–0.7), were investigated by the technique of X-band electron paramagnetic resonance (EPR) in the temperature range from 30 to 500 K. As the temperature was lowered, the various samples made transitions from paramagnetic to ferromagnetic phases. Furthermore, coexistence of anywhere from two to three ferromagnetic phases in the various samples was found. The third ferromagnetic phase was observed only in the samples with x = 0.1, 0.2, 0.3. The Curie temperatures for the various samples were estimated from the characteristics of the variable-temperature EPR spectra. The EPR data indicated the presence of Griffiths phases in the samples with x = 0.2, 0.3, 0.4, 0.5, 0.6, from which the respective Griffiths temperatures were determined. The activation energies were estimated here from the EPR data using the hopping model. The EPR linewidth behavior is found to be consistent with that predicted by the bottlenecked spin-relaxation model. The perovskite La0.5Eu0.2Sr0.3MnO3 is potentially useful in the design of magnetocaloric refrigeration units as a working fluid, since its Curie temperature TC is found to be close to the room temperature. The various ferromagnetic components in the samples observed here have been resolved only by the technique of EPR, not possible by other techniques.

The authors study the formation of crystals of Fe-Ga oxides and Fe–Ga–Cu borates in a multicomponent flux system based on Bi2Mo3O12–Na2B4O7. The Curie–Weiss temperature (θCW = 289 K) and the temperature of the ferrimagnet–paramagnet phase transition (TC = 288 K) are determined from the electron spin resonance (ESR) spectrum and the magnetization of an Fe1.1Ga0.9O3 single crystal, depending on temperature. Lines of spin-wave resonance are observed in the spectrum of magnetic resonance in the ordered phase.

Magnetic and dielectric properties of Sr2MnTiO5.87 double perovskite have been studied. Magnetic phase transitions were observed at 12 and 43 K in the FC and ZFC curves of magnetization and magnetic heat capacity, the nature of which is being discussed. From the analysis of the lattice contribution to the specific heat, the Debye and Einstein temperatures were determined, which were θD = 217 К, θЕ1 = 275 К, θЕ2 = 615 К, θЕ3 = 2000 К.

The scandium orthosilicate monocrystal Sc228SiO5 (SSO) doped with 51V isotope in small concentrations (0.005% at.) was studied. We used continuous wave (CW) and pulsed electron spin resonance (ESR) methods with frequencies in the X-band range (9.3–9.8 GHz). From the orientational dependencies of the CW ESR spectra we found the following: the hyperfine interaction of the vanadium ions is very anisotropic and the Zeeman interaction is almost isotropic with principal values of the g – tensor near electron g – factor. In addition to that, we found that the charge state of vanadium ions is V4+. The directions of the principal axes of the A and g tensors were determined. The phase memory and spin–lattice relaxation were measured. It was found that the temperature dependence of the spin–lattice relaxation time can be approximated by the sum of direct and Aminov–Orbach processes with decent accuracy. The phase memory time stays in the microseconds range even at the temperature T = 30 K.

The double perovskite Sr2TiMnO5.87 was synthesized via the solution combustion precursor method using Sr(NO3)2, MnO2, i-Ti(OC3H7)4, and disubstituted ammonium citrate as a complexing agent. The crystal structure and unit cell parameters are refined by the Rietveld method using powder X-ray diffraction. The magnetic properties of double perovskites Sr2TiMnO5.87 were studied using the ESR spectroscopy, specific heat measurements in the temperature range ~ 5–300 K, and magnetometry under cooling in zero- (ZFC) and nonzero-fields (FC). The four ESR line were observed in ESR spectra, three ESR lines with g ~ 2 and fourth ESR at Bres = 50 mT in both X-and Q-bands measurements in the temperature range 37.5–42 K in Sr2TiMnO5.87. The peaks obtained in real and imaginary parts of AC magnetization measurements confirm phase separation at the same temperatures. The antiferromagnetic ordering was found out below the temperature TN ≈ 12 K. The fitting Debye and Einstein temperatures, obtained from the specific heat measurements, are equal to θD = 217 K, θE1 = 275 K, θE2 = 615 K, and θE3 = 2000 K.

A double perovskite Sr 2 CrNbO 6 powder compound was studied by using X-ray diffraction, AC and DC magnetization, and ESR measurements. Two transitions in antiferromagnetically ordered regimes were observed through magnetization measurements at T = 5 and 2 K and were confirmed by the linear dependence of the magnetization on the applied magnetic field at these temperatures, approximations of the temperature dependence of the ESR linewidth, and AC magnetization. The zero field cooling curve was approximated by Bonner–Fisher law for quasi one dimensional chain with the exchange integral J / k B = 1 K between chromium spins. An approximation of linear part of magnetic susceptibility temperature dependence was performed using Curie–Weiss law. To describe the obtained effective moment μ eff = 3.577μ B , the presence Cr 3+ and Cr 4+ ions is estimated at a respective ratio about 0.8 : 0.2.