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The magnetic, magnetoelectric, and magnetoelastic properties of RFe3(BO3)4 ferroborates are studied. The measurement of the field dependences of the magnetoelectric polarization along the a axis in holmium ferroborate and in the mixed composition Ho0.5Sm0.5Fe3(BO3)4 revealed the following dependences for easy-plane ferroborates: (a) the longitudinal and transverse magnetoelectric effects have the opposite signs and (b) magnetically induced polarization changes its sign in a field close to the field of exchange between rare-earth and iron ions. These dependences agree well with theoretical predictions based on the symmetry of the compounds. The relatively low f-d exchange field in holmium ferroborate (about 20 kOe), which magnetizes the rare-earth subsystem, causes smaller polarization jumps (about 30 μC/m2) in fields lower than 10 kOe as compared to the jumps in other easy-plane ferroborates (R = Sm, Nd). The increase in the electric polarization induced in HoFe3(BO3)4 in magnetic fields higher than 100 kOe (200–300 μC/m2) is found to be significantly smaller than in neodymium ferroborate, which indicates a substantial dependence of the magnetoelectric effects on the electronic structure of a rare-earth ion.

The magnetic and magnetoelectric properties of terbium aluminum borate are studied. It is established that temperature dependences of the magnetoelectric effects of terbium aluminum borate are analogous to those of terbium ferroborate, despite the difference in effective magnetic fields acting on rare-earth ions in these compounds. This confirms the general assumption on the decisive role of the rare-earth element in the magnetoelectric properties of borates.

Results of a complex investigation of the magnetic, magnetoelectric, and magnetoelastic properties of a SmFe3(BO3)4 single crystal are presented. Samarium iron borate is similar to another easy-plane iron borate, NdFe3(BO3)4, in that it possesses a large value of the magnetic-field-induced polarization (about 500 μC/m2), the sign of which changes when the field direction is changed between axes a and b of the crystal. However, the temperature dependence of the magnetic susceptibility and the field dependence of polarization and magnetostriction of the two compounds are significantly different, which is explained by the weak effect of external magnetic field on the ground-state multiplet of samarium ion, which is characterized by an extremely small value of its g-factor.

The magnetic, magnetoelectric, and magnetoelastic properties of a PrFe 3 (BO 3 ) 4 single crystal and the phase transitions induced in this crystal by the magnetic field are studied both experimentally and theoretically. Unlike the previously investigated ferroborates, this material is characterized by a singlet ground state of the rare-earth ion. It is found that, below T N = 32 K, the magnetic structure of the crystal in the absence of the magnetic field is uniaxial ( l || c ), while, in a strong magnetic field H || c ( H cr ~ 43 kOe at T = 4.2 K), a Fe 3+ spin reorientation to the basal plane takes place. The reorientation is accompanied by anomalies in magnetization, magnetostric- tion, and electric polarization. The threshold field values determined in the temperature interval 2-32 K are used to plot an H - T phase diagram. The contribution of the Pr 3+ ion ground state to the parameters under study is revealed, and the influence of the praseodymium ion on the magnetic and magnetoelectric properties of praseodymium ferroborate is analyzed.

Magnetic phase transitions in multiferroic bismuth ferrite (BiFeO3) induced by magnetic field, epitaxial strain, and composition modification are considered. These transitions from a spatially modulated spin spiral state to a homogenous antiferromagnetic one are accompanied by the release of latent magnetization and a linear magnetoelectric effect that makes BiFeO3-based materials efficient room-temperature single phase multiferroics., Comment: In this version Figure 7 is replaced to more informative one. The footnotes are added to reflect the up-to-date situation in the area

Complex experimental and theoretical investigations of the magnetic, magnetoelectric, and magnetoelastic properties of neodymium iron borate NdFe3(BO3)4 along various crystallographic directions have been carried out in strong pulsed magnetic fields up to 230 kOe in a temperature range of 4.2–50 K. It has been found that neodymium iron borate, as well as gadolinium iron borate, is a multiferroic. It has a much larger (above 300 μC/m2) electric polarization controlled by the magnetic field and giant quadratic magnetoelectric effect. The exchange field between the rare-earth and iron subsystems (∼50 kOe) has been determined for the first time from experimental data. The theoretical analysis based on the magnetic symmetry and quantum properties of the Nd ion in the crystal provides an explanation of the unusual behavior of the magnetoelectric and magnetoelastic properties of neodymium iron borate in strong magnetic fields and correlation observed between them.

Our experimental and theoretical investigation was aimed at the study of different gadolinium ferroborate single-crystal properties both at spontaneous and high magnetic field-induced phase transitions.

A tendency to form multiferroic states with a spatially modulated antiferromagnetic structure and electric polarization in pure orthorhombic manganites RMnO 3 upon decreasing of the rare-earth ionic radii has been realized in single crystals of substituted compounds Eu 1x- Y x MnO 3 (0.2 ≤ x ≤ 0.5) and Gd 1-y Y y MnO 3 (0 < y ≤ 0.2). While the parent pure and slightly substituted (x ≤ 0,1) compounds exhibited a spontaneous transition from the incommensurate (IC) to the canted antiferromagnetic (CAF) state at T CA < T N = 45-50 K, the transitions from IC to commensurate ferroelectric (C/FE) phase were observed at T lock < T N for x ≥ 0.3 and y ≥ 0.05 accompanied by dielectric anomalies. Various phase transitions were observed in magnetic fields up to 250 kOe along the a-, b-, c-axes by magnetization, magnetostriction and electric polarization measurements. The latter indicate the existence of a spontaneous electric polarization below T lock .

Magnetoelectric interactions have been investigated in a single crystal of gadolinium iron borate GdFe3(BO3)4, whose macroscopic symmetry is characterized by the crystal class 32. Using the results of this study, the interplay of magnetic and electric orderings occurring in the system has been experimentally revealed and theoretically substantiated. The electric polarization and magnetostriction of this material that arise in spin-reorientation transitions induced by a magnetic field have been investigated experimentally. For H ‖ c and H ⊥ c, H-T phase diagrams have been constructed, and a strict correlation between the changes in the magnetoelectric and magnetoelastic properties in the observed phase transitions has been ascertained. A mechanism of specific noncollinear antiferroelectric ordering at the structural phase transition point was proposed to interpret the magnetoelectric behavior of the system within the framework of the symmetry approach in the entire temperature range. This ordering provides the conservation of the crystal class of the system when the temperature decreases to the antiferroelectric ordering point. The expressions that have been obtained for the magnetoelectric and magnetoelastic energy describe reasonably well the behavior of gadolinium iron borate observed experimentally.

The magnetic, magnetoelectric, and magnetoelastic properties of ErMn2O5 single crystals have been studied at low temperatures and strong magnetic fields (up to 250 kOe) and compared to the analogous results obtained previously for YMn2O5. Based on these data, the possible mechanisms of various spontaneous and magnetic-field-induced phase transitions in these compounds are considered within the framework of the theory of representations of the Pbam-D 2 9 space group. It is shown that a biquadratic exchange plays an important role in the formation (and mutual transformation) of magnetic structures revealed by neutron diffraction in the RMn2O5 oxide family.

Complex studies of the magnetic, magnetoelectric, and magnetoelastic properties of GdMn2O5 single crystals in strong pulsed magnetic fields are carried out in order to obtain additional indirect information on the character of the rare-earth and manganese spin ordering. It is shown that magnetic ordering of Gd3+ spins affects the manganese sublattice spin orientation and initiates new magnetic phase transitions. The observed magnetoelectric properties of the GdMn2O5 system are interpreted in terms of the theory of phase transitions.

The magnetic and magnetoelastic properties of single crystals of electron-doped rare-earth manganites La1−x Sr x MnO3 are studied. Phase transitions from the A-type antiferromagnetic phase to the C-type anti-ferromagnetic phase in a strong magnetic field are revealed in La1−x Sr x MnO3 manganites with a strontium content x = 0.65. A similar phase transition is observed in manganites with a strontium content x = 0.8, at which the La0.2Sr0.8MnO3 manganite is assumed to transform from the C-type antiferromagnetic phase to the G-type antiferromagnetic phase.

Recently discovered magnetoelectricity in the rare-earth aluminum borates RAl${}_{3}$(BO${}_{3}$)${}_{4}$ has attracted attention due to the large values of magnetoinduced electric polarization. We have observed for the first time the magnetoelectric polarization in TbAl${}_{3}$(BO${}_{3}$)${}_{4}$ exhibiting anomalous temperature dependence: an electric polarization induced by in-plane magnetic field ($P||a,H\ensuremath{\perp}c$ axis) which is small at low temperatures ($4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), remarkably increases by almost an order of magnitude at high temperatures ($150--300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$). The observed nonmonotonic temperature behavior of the field-induced polarization, including a change of sign at $\ensuremath{\sim}65--70\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, is attributed to the competition of the ground and excited crystal-field states of Tb${}^{3+}$ ions. Quantum theory analysis, involving the combination of analytical and numerical methods, has enabled us to quantitatively describe the observed magnetic and magnetoelectric properties of TbAl${}_{3}$(BO${}_{3}$)${}_{4}$.

The discovery of a new magnetic field induced phase transition between the space-modulated spin structure (SMSS) and the homogeneous antiferromagnetic state (HAFS) is reported. This phase transition is accompanied by large magnetoelectric (ME) anomalies. It is well known that BiFeO, shows the ferroelectric ordering (T c = 1083 K) and antiferromagnetic ordering (T N = 673 K). ME properties of BiFeO3 so far remain a challenging experimental and theoretical problem. While the crystal symmetry of BiFeO3 allows a linear ME effect, it cannot be observed because the antiferromagnetic order of BiFeO3 is SMSS (cycloid). We show that there is a Lifshits invariant, which decreases the ground state energy and induces the SMSS. In a high magnetic field the energy of the HAFS decreases more rapidly than the energy of the SMSS. Hence the field induced phase transition between SMSS and HAFS is possible. We stress that a large variation of the ME effect is expected at the transition due to a rising linear ME cont...

The properties of antiferromagnetic materials with violated space-time parity are considered. Particular attention is given to the bismuth ferrite BiFeO3 ferroelectric magnet. This material is distinguished from other antiferromagnets in that the inversion center is absent in its crystal and magnetic structures. This circumstance gives rise to the diversified and unusual properties, namely, to the appearance of a spatially modulated spin structure and to the unique possibility of the linear magnetoelectric effect coexisting with a weak ferromagnetic moment. The magnetic-induced phase transitions accompanied by the suppression of the modulated spin structure and appearance of a number of new and unusual effects are considered. These are the linear magnetoelectric effect and the appearance of a toroidal moment and a weak ferromagnetic moment of the magnetoelectric nature., 11 pages, 11 figures

In this paper the results of experimental and theoretical researches of bismuth ferrite in high magnetic fields that were conducted by the authors in the last decade are considered. The rise of several new effects at the destruction of the space modulated spin structure such as magnetoelectric effect, weak ferromagnetism and toroidal moment were theoretically predicted and proved experimentally. The explanation of the origin of these effects is given. The unique possibility of coexistence of linear magnetoelectrical effect and weak ferromagnetic moment in BiFeO3 at the phase transition to homogenous state is shown. Noteworthy that such a coexistence is not possible for ordinary antiferromagnetics.

Using magnetization and magnetostriction measurements we have investigated various field-induced and spontaneous spin-reorientation phase transitions (SRPT) in pure NdCrO 3 and Nd 1- x Eu x CrO 3 ( x = 0, 0.3, 0.5, 0.9) single crystals. Analysis of these data gives evidence that spontaneous Morin type Γ 2 ( G z F x ) − Γ 1 ( G y ) SRPT in Nd 1- x Eu x CrO 3 is determined by a competition between two contributions (Zeeman-like and Van Vleck) in the bc -plane anisotropy energy resulting from an anisotropic Nd-Cr exchange.

It is theoretically shown and experimentally found that in the TbFe1−xAlxO3 system the presence of non-magnetic ions Al3+ (magnetic vacancies) results in a considerable increase of anisotropy energy in the ac-plane and suppresses the spontaneous orientational transition Γ42 Γ2, observed in pure TbFeO3. The character of the orientational transition Γ42 Γ2 induced by the applied field H along the a-axis is studied. The Hx−T phase diagram contains a tricritical point. A qualitative change of the temperature dependence of magnetization and susceptibility along the c-axis is found in TbFe1−xAlxO3 as compared to TbFeO3. This is explained by the deviation of the Ising axes of Tb3+ ions from the ab-plane of the crystal. It is experimentally shown that the magnetic vacancies suppress the antiferromagnetic ordering of the terbium ions. [Russian Text Ignored].

An investigation is made of magnetic, magnetoelastic, and elastic properties of erbium orthoferrite in the region of the phase transitions. The first and the second magnetoelastic constants of this orthoferrite, and the first and the second anisotropy constants of the iron sublattice are determined. It is shown that the compensation point in the field H ‖ σ0 is the first-order phase transition. On the basis of magnetization and Young's modulus measurements, and also from symmetry considerations it is concluded that in the temperature range 2 to 4 K Γ12 is the magnetic structure of ErFeO3. [Russian Text Ignored]

Magnetic and neutron diffraction investigations on polycrystalline samples of TmFe1−xMnxO3 compounds (x = 0.1 and x = 0.3) reveal some interesting features of the Mn3+-ion influence on the thulium orthoferrite magnetic properties. Preliminary X-ray diffraction data indicate an increase of the unit cell distortion with growing content of Mn3+ ions. A decrease of the Neel temperature with higher Mn3+ amount is observed. For the compound with x = 0.1 a reorientation transition from GxFz to GzFx (Γ4 − Γ2) spin configuration is observed, whereas in the case of the compound with x = 0.3 a phase transition to antiferromagnetic phase (Γ1) is established. The neutron diffraction results point out to the occurrence of a complicated transitions sequence in the last case. [Russian Text Ignored].

Magnetic measurements and Mossbauer spectroscopy revealed two types of spin reorientation in DyFe0.9975Co0.0025O3 in the temperature range 77–300 K. The higher temperature transition was a continuous rotation of Fe3+ spins from the a to the c axes of the single crystal in the region 260-145 K. The lower temperature transition was from a weakly ferromagnetic to the purely antiferromagnetic state. A peculiarity was observed with both methods. When the Fe3+ spins, turning from the a towards the c axis, form an angle of about 20° with the latter, they do not proceed to reach c, but jump to the b axis and the crystal becomes a pure antiferromagnet. An external magnetic field of 10 kOe, Hext  c, does not change this reorientation pattern, but a smaller field along a completes the reorientation along the c axis. Mossbauer spectra indicate two hyperfine fields during the continuous spin reorientation.

We report the experimental and theoretical study of the magnetostriction (MS) in orthoaluminates with Ising rare earth (RE) ions, TbAlO 3 , DyAlO 3 and also with an S-ion, GdAlO 3 . The field and the temperature dependence of the MS is found to depend strongly on the nature of the RE ion ground state. In the case of GdAlO 3 , with L = 0 for the Gd 3+ ion ground state, the MS behaviour is basically described well by the formulae of the phenomenological even effects theory. A microscopic theory predicts a specific dependence of the MS on H and T for the orthoaluminates TbAlO 3 and DyAlO 3 , in which the RE ions Tb 3+ and Dy 3+ can be treated as Ising ions. The MS of the crystals with Tb 3+ and Dy 3+ exhibits a strong field dependence in the magnetization saturation region. Generally speaking, these crystals do not obey the phenomenological theory of even effects. Experiments on TbAlO 3 and DyAlO 3 confirm fully these conclusions.

The influence of diamagnetic Ga 3+ substitution for Fe 3+ ions in dysprosium orthoferrite was investigated. Samples of different gallium contents were studied by magnetic techniques and Mossbauer spectroscopy. It was found that in DyFe 1- x Ga x O 3 the Morin transition temperature is shifted upwards by ≈ 30 K for the case of x = 0.05, and ≈ 70 K, when x = 0.18, compared to pure DyFeO 3 . Reasons are discussed and the “magnetic vacancy” contribution to the magnetic anisotropy in DyFeO 3 with Ga 3+ substitution for Fe 3+ is evaluated from the point of view of the magnetic vacancy model. Mossbauer data indicate that the spin reorientation in the case of 5% Ga substitution may not be of the same type as in pure DyFeO 3 .

Results of magnetic measurements carried out on single crystals of TmFe1-xMnxO3 (x=0, 0.12, 0.21 and 0.33) at temperatures in the region 2-700K and neutron diffraction investigations performed on powder samples at temperatures 80-650K are presented. The compounds are weak ferromagnets at room temperature. For compounds with a lower amount of manganese (x=0.12 and x=0.21) the spin reorientation phase transition GxFz-GzFx is observed as was already reported for pure TmFeO3(x=0). For the compound with x=0.33 a phase transitions sequence unusual for the pure orthoferrites is established. On the temperature dependence of the spontaneous magnetisation along the crystal a axis a compensation point was observed in the case of all compounds investigated. A qualitative explanation of the experimental results is given on the basis of recent theoretical considerations about the influence of Mn3+ doping ions on rare earth orthoferrite properties.

The uptake of Mn2+ by Saccharomyces cerevisiae at the expense of endogenous sources of energy depends on the stage of culture development and is maximum in the middle of the exponential phase. The ability of cells to take up Mn+ is related to the content of intracellular potassium at all stages of growth, to the content of ATP during the exponential phase and it is not related to the content of inorganic polyphosphates. The uptake is inhibited by oligomycin (25 microgram/ml) by 50-85% and under anaerobic conditions by 10-50%, depending on the stage of growth, indicating the role of aerobic phosphorylation in the process. The uptake of Mn+ is apparently associated with a hydrolysis of low-molecular weight polyphosphates and ATP, as well as with the exit of K+ from cells.

The content of total, bound and osmotically free magnesium was estimated in various fungi and in the yeast Saccharomyces cerevisiae. Total magnesium increases at lower growth rates of Endomyces magnusii and Penicillium chrysogenum 140A as well as during the logarithmic stage of growth of Penicillium chrysogenum Q-176. The binding of magnesium requires orthophosphate, decreasing during lack of external phosphate when the intracellular concentration of free magnesium rises. The fungi were found to contain a novel form of bound magnesium, a polymeric magnesium orthophosphate (PO Mg), which appears to take part in the control of free magnesium level in Penicillium chrysogenum Q-176. The level of free magnesium is proportional to the growth rate of Endomyces magnusii and Penicillium chrysogenum Q-176 and 140A. Total, as well as free, magnesium changes less than three-fold as external Mg concentration is changed 13,000-fold. The magnesium is taken up against concentration gradients of 1 : 25 to 1 : 1300, the metal being distributed non-uniformly in the cells of Saccharomyces cerevisiae.

Manganese transport into yeast cells is energy-dependent. It is dependent on endogenous sources of energy and is inhibited by olygomycin (12.5-25 microgramg/ml), 2,4-dinitrophenol (1 mM), 2-deoxyglucose (1-50 mM) and sodium azide (1-10 mM), but is stimulated by cyanide and glucose. The stimulating effect of glucose is eliminated by N-ethylmaleimide and iodoacetate, which apparently inhibit the transport of glucose itself. About 75% of the manganese accumulated in the presence of glucose is found in yeast protoplasts and nearly 25% in the cell walls. A major portion of the accumulated manganese is found in vacuoles. The concentration of osmotically free manganese in the cytosol did not exceed 2 mM, but the concentration in vacuoles was up to 14 mM. The tonoplast is assumed to have a transport system for divalent cations, thereby regulating their concentration in the cytosol.