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The field induced transition from the space modulated spin structures to the homogeneous antiferro-magnetic state in magnetic ferroelectrics R x Bi1–x FeO3 (R = La3+, Nd3+, Dy3+) was investigated. It has been established that space modulated spin structures (SMSS) exists in compounds: with La up to concentration x = 0.6; with Nd up to x = 0,1 and Dy up to x = 0.1. For all investigated compounds the polarization curves have linear dependence upon the field above Hcr . The critical field decreases with increase of concentration x and magnetic moment of the R ions. Coexistence of weak ferromagnetic moment and SMSS was observed on the compound La x Bi1–x FeO3 at x ⩾ 0,1.

An investigation was done of the field induced phase transition from the spatially modulated spin structures to the homogeneous antiferromagnetic state in magnetic ferroelectrics R x Bi 1− x FeO 3 (R = La, Nd) and magnetoelectrics Fe x Cr 2− x O 3 in pulsed magnetic field up to 30 T. It has been found that this transition is accompanied by a large change in the magnitude of the magnetoelectric effect. In contrast to the R x Bi 1− x FeO 3 , where the linear magnetoelectric effect appears in strong magnetic fields ( H > H c ) in Fe x Cr 2− x O 3 such effect exists in the low-field phase ( H H c ). This is associated with the different character of the spatially modulated spin structure in these materials (cycloid structure in R x Bi 1− x FeO 3 and cone spiral in Fe x Cr 2− x O 3 ).

We have studied various spontaneous and magnetic-field-induced phase transitions in single crystals of multiferroic Mn${}_{0.9}$Co${}_{0.1}$WO${}_{4}$ using magnetic and magnetoelectric measurements and neutron diffraction. Compared to pure MnWO${}_{4}$, our data consistently confirm that the anisotropic Co${}^{2+}$ ions induce reorientation of the spin cycloid structure to the $ac$ plane and reveal ${P}_{a}$ and ${P}_{c}$ components of spontaneous electric polarization. Field-induced phase transitions accompanied by anomalies of magnetic susceptibility and suppression of both ${P}_{a}$ and ${P}_{c}$ polarizations have been observed for $H$$\ensuremath{\parallel}$$c$ ($\ensuremath{\sim}$3 T) and $H$$\ensuremath{\parallel}$$a$ ($\ensuremath{\sim}$8.5 T). Neutron diffraction has revealed that in both cases the spin cycloid plane flops in direction almost perpendicular to $H$, i.e., close to the $ab$ and $bc$ planes, respectively. Parameters describing the magnetic structures including wave vectors, orientations of the main elliptical axes, etc., have been determined in all spontaneous and field-induced states.

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 spin reorientations in HoFeO3 were studied. It was found that above 34 K the Fe3+ magnetic moments leave the (ac) plane of the orthorhombic lattice by a continuous rotation toward a finite angle, probably in the (bc) plane:GzFx−GzyFx. Then above 45 K they start returning to the (ac) plane in a jumpwise manner to go on with the well known continuous reorientationGzxFxz−GxFz towards thea-axis.

Magnetostriction λ∥(H) and field-induced phase transitions were studied in the single crystal of La1−xSrxMnO3 (x=0, 0.05, 0.1, and 0.175) in the pulsed magnetic fields up to 230 kOe. Anomalies in the λ∥(H) curves were revealed at 200 kOe in the LaMnO3, which were identified with the spin-reorientation AyFz→AzFy in the magnetic field H∥b axis. A complicated magnetostriction behavior was observed in La0.875Sr0.175MnO3, related to the field-induced transition between orthorhombic and rhombohedral crystal structures.

Submillimeter dynamic properties (dielectric permittivity e′(ν,T), dynamic conductivity σ′(ν,T)) at frequencies ν=3–20 cm−1 as well as static ones (magnetization, AC magnetic susceptibility, resistance and magnetoresistance) of the La1−xSrxMnO3 (x=0.1, 0.175, 0.2 and 0.3) ferromagnets have been studied at temperatures between 5 K and 400 K. A sharp increase of σ′(ν,T) was observed near the Curie temperature at a metal–semiconductor transition in La0.825Sr0.175MnO3. σ′(ν,T) was described by the Drude model and was equal or slightly greater than its static value. In La0.9Sr0.1MnO3 σ′(ν,T) was considerably greater than the static value, because not only the Drude-like charge carriers contribute to the dynamic conductivity σ′(ν,T) but also the crystal lattice. A significant anisotropy of e′(T) was observed for different crystallographic directions. A jump of e′(T) as well as anomalies in the AC magnetic susceptibility were found at T=100–120 K in La0.9Sr0.1MnO3 which indicate the existence of an additional phase transition (polaron ordering) besides the magnetic transition at 160 K.

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.

In ferroelectric YMn2O5 weak ferromagnetism was found along a-axis of rhombic crystal. It was shown that the nature of ferromagnetic sublattices cant is determined by magnetoelectric ordering. Reorientation of magnetic moment was observed under strong magnetic field applied along b-axis of crystal, that was accompanied by sharp increase of magnetostriction and jumps of electric polarization. In EuMn2O5, as in YMn2O5, spontaneous and magnetic field induced phase transitions from incommensurate to commensurate phase were observed, accompanied by cardinal changing of magnetoelectrical properties.

Magnetic, anisotropic, and magnetoelastic properties have been investigated for Nd1−xCaxMnO3 monocrystals (x=0; 0.25; 0.05; 0.3) in pulsed magnetic fields up to 250 kOe in temperature range 10– 100 K . Jumps of magnetization and magnetostriction induced by the strong magnetic field H||b have been observed at H>100 kOe in the x=0, 0.25, 0.05 compounds. We attribute this phenomena to a reorientation of the weak ferromagnetic moment from c- to b-axis. Corresponding H–T phase diagrams were obtained.

The magnetostriction, magnetoelectric effect and phase transitions induced by a strong magnetic field in EuMn 2 O 5 single crystal have been investigated. It is known that EuMn 2 O 5 compounds show structural and magnetic phase transitions and incommensurate magnetic structure around 40 K. New phase transitions from a modulated spin structure to a homogeneous structure in EuMn 2 O 5 at 26 K accompanied by a significant change of electrical polarization induced by a high magnetic field have been studied.

Thermal expansion Δl/l(T) and longitudinal and transverse magnetostriction λ||,⊥(H,T) in pulsed magnetic fields H up to 250 kOe were studied in single La1−xSrxMnO3 crystals ( x=0.1, 0.125 and 0.15). A strong increase of the field-induced magnetostriction λ||,⊥(H) (from 10−4 up to 7×10−4) was observed in the Jahn–Teller distorted O′ phase as compared to the charge-ordered and pseudocubic ones, which was accompanied by additional features in the vicinity of the spontaneous transitions. The results may be related to a suppression of the O′ phase and field-induced transitions to a new orbital-ordered ferromagnetic state.

Anomalon in temperature dependence of the magnetic moment (FexCr1−x)2O3 single crystal has been observed which can be explained by antiparallel orientation of the mean weakly-ferromagnetic moments of the d subsystems (weak ferromagnetism). The disappearance of the linear magneto-electric effect for x=0.1 below 45 K is explained by a spontaneous phase transition from a conical spiral to a cycloidal spin structure, which is found to agree with a thermodynamic treatment.

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.

This review treats the little-studied magnetic phase transitions of the order-order, spin-reorientation type, in which a rotation of the magnetization vector (or of die antiferromagnetism vector) with respect to the crystallographic axes occurs upon change of temperature, magnetic field, or external pressure. It presents theoretical ideas about magnetic phase transitions of the spin-reorientation type; it considers the effect of domain structure on spin-reorientation phase transitions, aad critical fluctuations during such transitions. Taking as an example rare-earth magnets (orthoferrites, iron-garnets, and rare-earth metals and intermetallic compounds), it considers the experimental data on various types of spin-reorientation transitions and on the anomalies of physical properties at such transitions.

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.

CONTENTS Introduction 154 1. Spin reorientation in rare-earth orthoferrites 154 2. Elastic properties of orthoferrites and features of their behavior near the spin-orientation temperature 156 3. Influence of pressure on the spin-reorientation temperature 160 Cited literature 161

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.

The magnetostriction (MS) of the high-temperature superconductors HoBa2Cu3O7−δ (HoBaCuO) and YBa2Cu3O7−δ (YBaCuO) is investigated in order to clarify a contribution of the Ho 3+ ions into the magnetoelastic (ME) properties and to describe the ME interactions in the framework of the crystal field theory.