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An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022340045

The anisotropic magnetoelectric properties of an ytterbium aluminum borate YbAl (BO single crystal having noncentrosymmetric crystal structure (space group R32) are studied, including the orientational, field, and temperature dependences of the polarization in magnetic fields up to 5 T in the temperature range of 2–300 K. It has been shown experimentally for the first time that the symmetry of the observed magnetoelectric effects exactly corresponds to the trigonal structure of the crystal and is characterized by two quadratic magnetoelectric constants. The polarization in the basal plane P a, b is a quadratic function of the field at low fields and reaches 250–300 μC/m2 in a field of 5 T at a temperature of 2 K, almost an order of magnitude exceeding the previously reported values. A theoretical model based on the spin Hamiltonian of the ground Kramers doublet of Yb3+ ions in the crystal field is proposed including magnetoelectric interactions allowed by the symmetry. This model makes it possible to quantitatively describe all observed magnetic and magnetoelectric properties of YbAl3(BO3)4.

We experimentally investigated the role of background signal in time resolved photoluminescence experiments with single quantum dots on substrates. We show that the background fluorescence signal from thin gold films fabricated by electron-beam evaporation and from Al2O3 layers fabricated by atomic layer deposition have to be taken into consideration in experiments on the single photon level. Though all investigated components can be distinguished by their photoluminescence decay rates, the presence of the background signal prevents the observation of photon antibunching from single quantum dots. Moreover, a single quantum dot acts as a hot spot enabling the plasmon supported fluorescence enhancement of gold.

Single crystals of M-type substitution hexaferrites BaSc x Fe12 − x O19 and SrSc x Fe12 − x O19 (x = 1.3–1.7) have been grown. Their anisotropic magnetic and magnetoelectric properties have been studied at temperatures of 2–360 K in magnetic fields up to 200 kOe. In all compounds under study, a spontaneous transition from the collinear ferrimagnetic uniaxial phase to a conical structure has been detected with a decrease in the temperature at a temperature increasing with the concentration of Sc up to room temperature. In magnetic fields both parallel and perpendicular to the c axis, the conical phase is suppressed and the transition to the collinear ferrimagnetic structure occurs. Phase diagrams have been plotted in H-T coordinates. In conical magnetic structures, a magnetic-field-induced electric polarization (higher than 40 μC/m2 at 4 K) has been detected in the geometry corresponding to the inverse Dzyaloshinskii-Moriya interaction mechanism (spin current). A higher stability of the polar state with respect to magnetic fields (higher than 50 kOe) and temperatures (up to 100 K) has been revealed as compared to previous studies of the Ba system. Various possibilities of controlling the chirality of the conical structure determining the sign of the polarization, which is important for applications, have been demonstrated.

We study, both experimentally and theoretically, the scattering of electromagnetic waves by a subwavelength hole fabricated in a thin metallic film. We employ the scanning near-field optical microscopy in order to reconstruct experimentally the full three-dimensional structure of the electromagnetic fields in the vicinity of the hole. We observe an interference of all excited waves with an incident laser beam which allows us to gain the information about the wave phases. Along with the well-known surface plasmon polaritons propagating primarily in the direction of the incident beam polarization, we observe the free-space radiation diffracted by the hole. We compare the experimental results with the fields of pure electric and pure magnetic dipoles as well as with direct numerical simulations. We confirm that a single hole in a thin metallic film excited at the normal incidence manifests itself as an effective magnetic dipole in the visible spectral range.

Critical lateral pressure for a pore formation and phase diagram of porous membrane are derived analytically as functions of the microscopic parameters of the lipid chains. The derivation exploits path-integral calculation of the free energy of the ensembles of semi-flexible strings and rigid rods that mimic the hydrophobic tails of lipids in the lipid bilayers and bolalipid membranes respectively. Analytical expressions for the area stretch/compressibility moduli of the membranes are derived in both models., 4 pages, 2 figures, submitted to JETP Letters

The magnetic, dielectric, and ferroelectric properties of Eu1 − x Ho x MnO3 single crystals (0 < x ≤ 0.5), where magnetic ordering can be varied from the canted antiferromagnetic phase to modulated spin structures, have been studied. It has been found that a ferroelectric state appears at x ≥ 0.2 and low temperatures. As the temperature decreases and the holmium content increases, the electric polarization in this state is reoriented from the a axis to the c axis. It has been shown that the polarization is reoriented owing to a change in the spin rotation plane in the cycloidal phase from the ab to cb plane because of the stabilization of the latter upon an increase in the rare-earth contribution to the anisotropy energy. The T-x phase diagram of magnetic and ferroelectric states has been constructed.

Resonance modes that are due to magnetic excitations in the exchange-coupled subsystems of rare-earth ions (R = Nd3+, Sm3+, and Gd3+) and Fe3+ ions have been detected in submillimeter transmission spectra (0.1–0.6 THz) of RFe3(BO3)4 iron borate-multiferroic single crystals. The strong interaction between spin oscillations of the Fe and R subsystems has been revealed, which determines the behavior of the modes depending on the anisotropy of the exchange splitting of the ground doublet of the R ion. It has been shown that the intensities of coupled modes (contributions to the magnetic permeability) depend strongly on the difference between the g factors of Fe and R ions. This dependence makes it possible to determine the sign of the latter g factor. In particular, a noticeable intensity of exchange Nd modes in NdFe3(BO3)4 is due to an increase in their contribution at g ⊥, ‖ Nd < 0, while in GdFe3(BO3)4 with g Gd ≈ g Fe ≈ 2, the Fe and Gd contributions compensate each other and the exchange (Gd) mode is not observed. In spite of the weak interaction of Sm ions with the magnetic field, SmFe3(BO3)4 exhibits resonance modes, which are attributed to the excitation of Sm ions through the Fe subsystem.

The colossal (more than threefold) decrease in the dielectric constant ɛ in the easy-plane SmFe3(BO3)4 ferroborate in a magnetic field of ∼5 kOe applied in the basal ab plane of the crystal has been found. A close relation of this effect to anomalies in the field dependence of the electric polarization has been established. It has been shown that this magnetodielectric effect is due to the contribution to ɛ from the electric susceptibility, which is related to the rotation of spins in the ab plane, arises in the region of the antiferromagnetic ordering T < TN = 33 K, and is suppressed by the magnetic field. A theoretical model describing the main features of the behavior of ɛ and electric polarization in the magnetic field has been proposed, taking into account the additional anisotropy in the basal plane induced by the magnetoelastic stresses.

The transition from a stable orthorhombic structure to a hexagonal structure has been revealed in Tb1−xYxMnO3 multiferroics at x = 0.2–0.4. It has been shown that almost single-phase crystals with an orthorhombic or hexagonal structure can be obtained by choosing the growth conditions. It has been found that the magnetic and dielectric properties of orthorhombic single crystals with x = 0.2–0.3 are similar to the properties of pure TbMnO3 and are characterized by a strong anisotropy of the magnetic susceptibility at low temperatures and by the presence of a number of magnetic phase transitions, including those to the ferroelectric state. New spontaneous (T ≤ 15 K) and magnetic-field induced (H | C6) phase transitions accompanied by the appearance of an uncompensated rare-earth magnetic moment ∼1 μB/mole have been observed in hexagonal single crystals with x = 0.3–0.5.

The effect of the substitution of Co2+, Mn2+, and Zn2+ ions for Ni2+ ions on the magnetic, dielectric, and ferroelectric properties of vanadate single crystals (Ni1 − x T x )3V2O8 has been analyzed. It has been found that the low-level (x ≤ 0.1) substitution of both magnetic and nonmagnetic ions stabilizes the ferroelectric state with a cycloidal magnetic structure. The existence region of this state is expanded to low temperatures down to 3 K for Zn2+ and below 1.8 K for Co2+ and Mn2+ owing to the suppression of a low-temperature weak ferromagnetic phase. At the same time, the ferroelectric phase disappears completely at large concentrations of Co and Mn. The effect of magnetic fields on the magnetic and ferroelectric states has been analyzed. It has been shown that the magnetic field along the c axis suppresses the ferroelectric state, whereas the magnetization along the antiferromagnetism axis (a axis) induces the reentrant phase transition from a paraelectric weak ferromagnetic structure to a ferroelectric structure. The corresponding H-T phase diagrams have been drawn.

The features of the magnon spectrum in easy-plane multiferroics (such as BiFeO3), which allow inhomogeneous magnetoelectric (flexomagnetoelectric) interaction P[(L∇)L − LdivL], where L and P are the antiferromagnetic moment and electric polarization, respectively, have been theoretically analyzed. It has been shown that, in contrast to the magnon spectrum of a usual easy-plane antiferromagnet, a multiferroic with this magnetic structure is characterized by, first, the interaction between magnons of both branches propagating along the weak ferromagnetic moment and the appearance of a minimum (or zero) of the frequency of one of the branches, which reflects the instability of the system with respect to the transition to an inhomogeneous state with increasing flexomagnetoelectric interaction and, second, the nonequivalence (nonreciprocity) of the propagation of spin waves along and against the antiferromagnetism vector, which coincides with the toroidal moment in this system.

The magnetic, magnetoelectric, and magnetoelastic properties of DyFe3(BO3)4 single crystals and the Nd0.75Dy0.25Fe3(BO3)4 substituted compound with the competitive Nd-Fe and Dy-Fe exchange interactions have been investigated in magnetic fields up to 210 kOe. It has been shown that the antiferromagnetic state in Nd0.75Dy0.25Fe3(BO3)4 below the Neel temperature is easy-plane and a spontaneous spin-reorientation transition to a uniaxial state occurs near 25 K. Anomalies are observed in various physical characteristics in a spin-flop transition induced by the magnetic field along the trigonal axis. The H-T phase diagrams are constructed; they are in good agreement with a simple model taking into account the anisotropy of the exchange splitting and g factors of the ground doublets of the Dy3+ and Nd3+ ions. The features of the magnetoelectric effect in various magnetic phases have been studied. Spontaneous electric polarization has been revealed in the region of the existence of an easy-plane antiferromagnetic state in the substituted compound. A qualitative theoretical justification of the possibility of the appearance of the spontaneous spin-reorientation transition in the Nd0.75Dy0.25Fe3(BO3)4 substituted compound is given.

Symmetry analysis of magnetoelectric interactions in rare-earth orthoferrites and orthochromites has been performed. It has been shown that symmetry allows the appearance of spontaneous electric polarization or the magnetic-field-induced polarization in the region of antiferromagnetic (centro-asymmetric) ordering of the rare-earth ions. The analysis reveals a number of pronounced anomalies in the behavior of the electric polarization at the metamagnetic and spin-reorientation transitions in DyCrO3 and TbFeO3. This behavior points to a strong sensitivity of the magnetoelectric properties of such magnets to the antiferromagnetic state of the rareearth subsystem and the spin orientation of the d ions.

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.