Effect of substitution Dy by Ho on the magneto-electric behavior of the compound Dy0.8Ho0.2MnO3 was investigated by the different methods of polarized and classical neutron diffraction and macroscopic methods. It is shown that substitution by Ho of 20% on the position of Dy do not change overall crystal symmetry of compound. It remains of Pbnm type down to the very low temperatures. Magnetic ordering, its temperature and field evolution was determined by the use of single crystal neutron diffraction and magnetization measurements. Chiral type of magnetic structure on Mn subsystem is confirmed below Tc & AP;16 K. Using polarized neutron diffraction the 3-component character of rare earth magnetic ordering in Dy0.8Ho0.2MnO3 in contrast to DyMnO3 could be revealed. It was shown that doping by 20% Ho suppresses the spontaneous rare-earth ordering with its own propagation vector and provides the situation when two magnetic subsystems, manganese and rare earth ones have a coherent incommensurate spatial propagation. The influence of the external electric field on the magnetic chirality could be directly evidenced, proving strong magneto-electric coupling in multiferroic phase. The study of the electric polarization under similar temperatures and fields on the same samples provides the direct correlation between the results of the microscopic and macroscopic investigations.

Orthorhombic PbMnBO4 is a rare example of an insulating ferromagnet in which the magnetic properties, in particular the strong magnetic anisotropy, are determined by the Mn3+ Jahn-Teller ion. Here, we report on the detailed investigation of magnetic excitations in the subterahertz and terahertz frequency ranges, as well as lattice excitations in the terahertz range. Using polarized azimuthally resolved Raman spectroscopy, four branches of magnetic excitations were observed and assigned to one acoustic and three optical one-magnon modes. The coupling between ferromagnetic ordering at T-c = 31 K and the Jahn-Teller distortions of [MnO6] octahedra due to the spin-phonon interaction was directly observed for some specific phonon modes involved in these distortions. A spin-wave Hamiltonian was developed that allowed us to determine a unique set of exchange and effective anisotropy parameters. The intensity ratio of the anti-Stokes to Stokes acoustic magnon peaks is found to be anomalous and directly indicates the involvement of the magneto-optical parameters in the magnetic Raman scattering process.

Structural, magnetic and multiferroic properties of single crystals of Dy_1-xHo_xMnO_3 (x = 0, 0.2) were investigated by the different methods of polarized and classical neutron diffraction and macroscopic methods in order to determine the effect of Ho doping on the magneto-electric behavior of the title compounds. It is shown that substitution by Ho of 20 position of Dy do not change overall crystal symmetry of compound. It remains of Pnma type for both compositions down to the very low temperatures. Magnetic ordering do not change the crystal structure. Precise magnetic order and it detailed temperature and field evolution both in the pristine and substituted compounds we determined using single crystal neutron diffraction and magnetization measurements. The results show a complex interplay between transition metal and rear earth magnetic sub lattices leading to so-called "Mn-controlled" and "Dy-controlled" magnetic states. Using polarized neutron diffraction 3D character of rear earth magnetic order in Dy_0.8Ho_0.2MnO_3 in contract to DyMnO_3 and occurrence of the chiral type magnetic structure on Mn subsystem could be revealed. The influence of the external electric field on the magnetic chirality could be directly evidenced, proving strong magneto-electric coupling in multiferroic phase. The study of the electric polarization under similar temperatures and fields on the same samples provides the direct correlation between the results of the microscopic and macroscopic investigations.

In this work, the magnetoelectric response in a series of Dy1-xHoxMnO3 crystals with substitution x from 0 to 0.4 was investigated. The measurement results showed that, as x increases, a decrease in both the polarization Pa and the magnitude of the susceptibility of the inverse magnetoelectric effect αba is observed. In addition, the field Hb increases, at which the P_c-> Pa transition is observed, and the temperature range of the existence of the magnetoelectric response decreases. Thus, an increase in the substitution x suppresses the magnetoelectric effect in this series of compounds. The measurement results also indirectly indicate the prolongation of the Pa state and, consequently, of the magnetic state with a cycloid lying in the ab-plane by an external electric field Ea. The reported study was funded by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science to the research project No.20-42-243008. Keywords: multiferroics, magnetoelectric effect, phase transition, ferroelectricity.

In this work, the magnetodielectric response have been studied in a series of single crystals of Pb 2 Fe 2-x Mn x Ge 2 O 9 with substitution x from 0 to 0.43. The research results showed that an increase in x leads to a change in the orientation of the antiferromagnetism vector in a zero magnetic field. The application of an external magnetic field leads to spin-flop and spin-reorientation magnetic transitions, which are accompanied by anomalies in the behavior of the permittivity.When Fe 3+ ions are replaced by Mn 3+ ions, the response of the magnetic subsystem to an external magnetic field changes, which is naturally reflected in the change in the magnetodielectric response. The permittivity changes stepwise when the magnetic subsystem passes into a state with a nonzero vector of the weakly ferromagnetic moment, or when its magnitude and orientation change due to a spin-flop transition. The latter indicates that a sharp change in polarizability is a consequence of a change in the contribution of the exchange energy, as well as the contribution of the Dzyaloshinskii-Moriya term, due to a change in the skew angle between two interacting magnetic moments. Keywords: magnetodielectric effect, phase transition, week ferromagnetism.

In Dy1-xHoxMnO3 single crystals with the orthorhombic space group Pbnm, ferroelectric hysteresis loops were measured for compositions with x=0 and 0.3. As the content of Ho3+ ions increases, the hysteresis loop narrows and for x=0.3 it no longer manifests itself. An analysis of the signal corresponding to the hysteretic behavior of a ferroelectric showed that even harmonics can be obtained only if the hysteresis loop is not symmetric about the abscissa axis. In view of the latter, the hypothesis that the second harmonic of the magnetoelectric effect is a consequence of the complex dependence of the polarization on time due to its hysteresis becomes doubtful. Measurements of the dependence of the inverse magnetoelectric effect on the amplitude of the applied electric field ΔM(E) showed that the first harmonic remains linear with respect to the electric field even in the electric field strength region where the domain structure of the ferroelectric is rearranged.

Structural and magnetic properties of single crystals of DyMnO3 were investigated by neutron diffraction in order to study the peculiarities of 3d-4f interactions in this compound. Precise magnetic order and its detailed temperature evolution were determined using single crystal neutron diffraction. Elliptical cycloid on manganese subsystem below TCh = 19 K was confirmed, with temperature decrease the elipticity of the Mn magnetic structure reduces significantly, creating almost circular cycloid. Temperature evolution of the magnetic structure demonstrate specific hysteretic behavior. The results show a complex interplay between transition metal and rare earth magnetic sublattices leading to so-called "Mn- controlled" and "Dy- controlled" magnetic states. The strong and complicate 3d-4f interaction leads to the unusual very slow magnetic structure relaxation.

In this work, the magnetodielectric response have been studied in a series of single crystals of Fe2-xMnxGe2Pb2O9 with substitution x from 0 to 0.43. The research results showed that an increase in x leads to a change in the orientation of the antiferromagnetism vector in a zero magnetic field. The application of an external magnetic field leads to spin-flop and spin-reorientation magnetic transitions, which are accompanied by anomalies in the behavior of the permittivity.When Fe3+ ions are replaced by Mn3+ ions, the response of the magnetic subsystem to an external magnetic field changes, which is naturally reflected in the change in the magnetodielectric response. The permittivity changes stepwise when the magnetic subsystem passes into a state with a nonzero vector of the weakly ferromagnetic moment, or when its magnitude and orientation change due to a spin-flop transition. The latter indicates that a sharp change in polarizability is a consequence of a change in the contribution of the exchange energy, as well as the contribution of the Dzyaloshinskii-Moriya term, due to a change in the skew angle between two interacting magnetic moments.

Single crystals of the Pb2Fe2_xMnxGe2O9 (x = 0.16) antiferromagnet have been grown. Using the specific heat measurements, a Ne acute accent el temperature of T-N = (42.0 +/- 0.5) K for the synthesized crystals has been found. It has been shown using the magnetic measurements that, due to the competition between the magnetoanisotropic contributions of the iron and manganese subsystems in the crystals, near a temperature of T-c = 22 K, a spontaneous spin-reorientation transition occurs, the tem-perature of which in an applied magnetic field changes with the field value and orientation relative to the rhombic axes of the crystal. Based on the analysis of the temperature and field dependences of the magnetization obtained at different orientations of the magnetic field, it has been established that, below T-c, an inclined magnetic structure is formed in the crystal. The antiferromagnetic vector of the inclined structure rotates smoothly in the rhombic bc plane with increasing tem-perature from a direction close to the b axis at T = 4.2 K and tends to the rhombic c axis at T = T-c. The rotation of the antiferromagnetic vector occurs also at fixed temperatures T < T-c with increasing magnetic field. In the temperature range of T-c < T < T-N, the antiferromagnetic vector is oriented along the rhombic c axis. Magnetic phase diagrams of states have been built for different magnetic field orientations relative to the rhombic axes of the crystal. The richest phase diagram is shown to correspond to the orientation H||c and contains, along with the above-listed states, one more inclined phase, in which the antiferromagnetic vector rotates toward the rhombic a axis direction with a change in temperature or magnetic field.

In Dy 1-x Ho x MnO 3 single crystals with the orthorhombic space group Pbnm, ferroelectric hysteresis loops were measured for compositions with x=0 and 0.3. As the content of Ho 3+ ions increases, the hysteresis loop narrows and for x=0.3 it no longer manifests itself. An analysis of the signal corresponding to the hysteretic behavior of a ferroelectric showed that even harmonics can be obtained only if the hysteresis loop is not symmetric about the abscissa axis. In view of the latter, the hypothesis that the second harmonic of the magnetoelectric effect is a consequence of the complex dependence of the polarization on time due to its hysteresis becomes doubtful. Measurements of the dependence of the inverse magnetoelectric effect on the amplitude of the applied electric field Delta M(E) showed that the first harmonic remains linear with respect to the electric field even in the electric field strength region where the domain structure of the ferroelectric is rearranged. Keywords: multiferroics, ferroelectricity, hysteresis.

The Pb2Fe2-xMnxGe2O9 (x = 0.43) orthorhombic antiferromagnet single crystals have been synthesized by a modified pseudo-flux technique and their magnetic and magnetodielectric properties have been investigated. It has been established that partial substitution of highly anisotropic Mn3+ ions for iron ones significantly affects the magnetic structure of the crystal. Under magnetization of the crystal along the rhombic b and c axes, magnetization jumps have been detected, which are indicative of the occurrence of orientational transitions identified as first-order ones. No weak ferromagnetism characteristic of the pure crystal in the rhombic a axis direction has been detected. The field dependences of the magnetization for the pure and Mn-doped crystals have been analyzed using the thermodynamic potential that takes into account the crystal symmetry. It has been shown that, in the Mn-substituted crystal, the antiferromagnetic vector in the ground state is parallel to the rhombic b axis; in this state, weak ferromagnetism has not been observed. Under magnetization along the b axis, a conventional spin-flop transition occurs. The orientational transition under magnetization along the c axis has been attributed to the reorientation of the antiferromagnetic vector relative to the a axis with the simultaneous occurrence of a weak ferromagnetic moment along the c axis. Magnetic phase diagrams of the Mn-doped crystal for the magnetic fields H||b and H||c have been built. In the Mn-doped crystal, at E||c and H||c, the orientational transition-induced magnetodielectric response jump has been detected, which is higher than the jumps observed for the undoped crystal by a factor of 3. The magnetodielectric properties of the pure and Mn-doped crystals have been analyzed using their magnetic phase diagrams.

In this work, the magnetoelectric response in a series of Dy1-xHoxMnO3 crystals with substitution x from 0 to 0.4 was investigated. The measurement results showed that, as x increases, a decrease in both the polarization Pa and the magnitude of the susceptibility of the inverse magnetoelectric effect αba is observed. In addition, the field Hb increases, at which the Pc→Pa transition is observed, and the temperature range of the existence of the magnetoelectric response decreases. Thus, an increase in the substitution x suppresses the magnetoelectric effect in this series of compounds. The measurement results also indirectly indicate the prolongation of the Pa state and, consequently, of the magnetic state with a cycloid lying in the ab-plane by an external electric field Ea. The reported study was funded by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science to the research project No.20-42-243008.

Crystals of a diamagnetic PbGaBO4 analog containing a small amount (about 0.5 at %) of Fe3+ ions are grown. The single-ion EPR spectra of Fe3+ in PbGa1 – xFexBO4 single crystals are analyzed with allowance for a crystal structure. The existence of four magnetically nonequivalent positions of Fe3+ ions with different local anisotropy axis directions has been confirmed. The parameters of the spin Hamiltonian written in the approximation of the local orthorhombic symmetry of a paramagnetic center are determined. The values of single-ion anisotropy constants, which are unusually high for S ions, is shown to be caused by a strong distortion of the ligand environment of Fe3+ ions. The single-ion contribution to the energy of the total magnetic anisotropy of a magnetically concentrated PbGaBO4 crystal is estimated. Two-ion mechanisms of the Fe–Fe interaction anisotropy are assumed to play a dominant role in the formation of magnetic anisotropy in a magnetically concentrated crystal.

Correlations between the direct and inverse magnetoelectric effects in orthorhombic DyMnO3 single crystals have been investigated. In the inverse magnetoelectric effect, the magnetic moment of the crystal appears to have a contribution that is sinusoidal oscillating in ac electric fields below the temperature TFE of ferroelectric phase transition. The first and the second harmonics of the inverse magnetoelectric effect are clearly detected. The magnetoelectric susceptibilities α and β, corresponding to first and second harmonics, are found to correlate with the derivative of polarization with respect to the magnetic field. The influence of the magnetic and electric regimes during cooling on magnetoelectric effects has also been studied. The maximum change in the magnetic moment of a sample under the action of electric fields is observed under the same (T, H) conditions as the rotation of the spontaneous polarization vector from the crystallographic c direction to the a axis in the magnetic field H || b.

Near the Curie temperature T-C = 30.3 K, the temperature dependences of the magnetization and heat capacity of a single-crystal ferromagnet PbMnBO4 in the magnetic fields of 1, 3, 10 and 30 kOe are studied. In the strong magnetic fields, both the magnetic contribution to the specific heat and the nonlinearity of the field dependences of the magnetization are maintained up to the temperatures exceeding T-C more than twice. It is assumed that in PbMnBO(4 )the difference between T-C, the paramagnetic Curie temperature theta = 49 K and the broad temperature region above T-C where the magnetic contribution to the specific heat is significant is due to the quasi-one-dimensional character of the magnetic structure of this ferromagnet. Using both the estimation of TC from the Ginzburg-Landau field theory and the theta value, the total exchange interaction parameters 2J approximate to 40.4 K (intrachain) and z'J' approximate to 8.8 K (interchain) are determined, with z' = 4 being the number of neighboring chains. The estimation shows that the Ginzburg-Landau field theory describing the quasi-one-dimensional behavior of PbMnBO4 is well applicable in the temperature range from to T = S(2)J approximate to 80 K. Above this temperature, the mean field approximation with the exchange parameter lambda(theta) based on the paramagnetic Curie temperature theta describes well the experimental temperature dependences of the magnetization in the strong magnetic field and the specific heat is determined by the lattice contribution.

Orthorhombic Pb2Fe2Ge2O9 antiferromagnetic single crystals have been synthesized by a modified pseudo-flux technique and their magnetic, thermodynamic, and magnetodielectric properties have been investigated. It has been found that, below the Ned temperature (45.2 K), iron moments are arranged in a canted antiferromagnetic structure with a weak ferromagnetic moment parallel to the a axis. According to the specific heat measurement data, the T-N value remains invariable in applied magnetic fields of up to 50 kOe within the experimental accuracy. The magnetic entropy in the investigated crystals attains 2Rln(2S + 1) right above T-N, which is indicative of a purely magnetic nature of the transition. It has been shown that the weak ferromagnetic moment is induced by the interplay between the single-ion anisotropy and antisymmetric Dzyaloshinskii-Moriya exchange interaction, with the latter contribution being dominant. It has been established from the angular dependences of the magnetization in three orthorhombic planes that the symmetries of the magnetic and crystal structure are identical. The magnetodielectric properties of the Pb2Fe2Ge2O9 single crystals have been studied at different mutual orientations of the electric and magnetic fields. The most prominent anomalies have been observed in the vicinity of the spin-flop transition in a magnetic field applied along the c axis.

The PbMn1-xFexBO4 (x approximate to 0.1) orthoborate single crystals have been grown for the first time by spontaneous crystallization and their magnetic and resonance properties and specific heat have been examined. It has been established that partial substitution of iron ions for manganese ones leads to an increase in the Curie temperature to 34.2 K from its value of 30.3 K in the unsubstituted crystal, enhances the magnetic anisotropy, and reduces the saturation magnetization. The magnetization drop is explained in the framework of the model of a ferrimagnetic-like structure, in which the magnetic moments of iron and manganese ions form ferromagnetic subsystems coupled by the antiferromagnetic exchange. It has been found that under magnetization along the rhombic b axis the magnetic moments switch stepwise to the magnetic field direction in a certain critical field. The spin-reorientation transition is the first-order one. This feature of the crystal magnetization does not allow the experimental ferromagnetic resonance frequency-field dependence for the rhombic b axis to be described using the calculation for a simple rhombic ferromagnet. It has been established that the increase in the magnetic anisotropy of the crystal upon substitution leads to an increase in the energy gap in the ferromagnetic resonance spectrum to 121.5 GHz at T = 4.2 K.

In this report, we prepared for the first time the orthorhombic Dy1−xHoxMnO3 single crystals with x = 0, 0.1, 0.2, 0.3, and 0.4 using the flux technique. The post-growth processing and chemical and structural characterization of the synthesized samples were performed. Also, we examined the samples obtained by their magnetic properties and the magnetic anisotropy in wide ranges of temperatures and magnetic fields.

The PbMnBO4 orthoborate single crystals were first grown and their magnetic properties and ferromagnetic resonance were studied. It was found that the ferromagnetic state below the Curie temperature TC=31K is characterized by the strong magnetic anisotropy. The significant effective anisotropy fields of PbMnBO4 determine the energy gap in the FMR spectrum, which is extraordinary large for ferromagnets (112GHz at T=4.2K). It was shown that the static Jahn–Teller effect characteristic of the Mn3+ ion leads to both the ferromagnetic ordering and the strong magnetic anisotropy in the crystal. In the strong external magnetic field the induced ferromagnetic ordering is retained in the crystal above the Curie temperature up to the temperatures multiply higher than TC. A weak anomaly of the dielectric permittivity was observed in PbMnBO4 at the Curie temperature at which the long-range ferromagnetic order is established.