Magnetic properties of multiferroics-semiconductors Eu(1-x)Ce(x)Mn2O5

Landau Diamagnetism and de Haas-van Alphen Oscillations, Formed in Single Crystals of Y3Fe5O12, in Local Nanodimensional-Sized 2D Phase Separation Regions, Located inside Layered Domain Walls at Room Temperature and T = 77 K

This paper presents results of the magnetic dynamics study (the microwave power absorptions at the fixed frequencies during magnetic field sweeping) in samples of Y₃Fe₅O₁₂ single crystals in the form of plates and spheres of various sizes, at frequencies exceeding 30 GHz, in magnetic fields up to 18 kOe, at room temperature, and T = 77 K. It was found that in this case, the inhomogeneity's of the magnetic state manifested itself in the Y₃Fe₅O₁₂ samples as 2D local phase separation regions. Such 2D phase separation regions formed inside layered domain walls representing superlattices with sizes of 700-900 Å. Depending on the shape and size of the studied plates and spheres, Landau diamagnetism or de Haas-van Alphen oscillations were observed in the 2D phase separation regions at room temperature and T = 77 K.

Optical Control of Superlattices States Formed Due to Electronic Phase Separation in Multiferroic Eu0.8Ce0.2Mn2O5

The effect of optical pumping and magnetic field on properties of the electronic phase separation regions, which are the multiferroic semiconductor heterostructures in the form of superlattices, have been studied in Eu_0.8Ce_0.2Mn₂O₅. These superlattices are formed due to self-organization in a dielectric crystal matrix as a result of the competing internal interactions balance and occupy a small crystal volume. The dynamical equilibrium states of superlattices are initially formed during cycling of as-grown samples in a magnetic field. The superlattices in such states are ferromagnetic and electrically neutral. Sets of ferromagnetic resonances were observed from individual layers of superlattices. Their features give rise information on properties of these layers and of a superlattice as a whole. The differences in the parameters of these resonances were due to different distributions of Mn³⁺ and Mn⁴⁺ ions in individual superlattices layers. It has been found that optical pumping having different powers allows us to control of multiferroic properties of superlattices layers by changing their magnetic and electric properties. It is shown that, under certain conditions, it is possible to significantly increase the temperatures at which multiferroic heterostructures exist.

Common features of low-temperature spin-charge separation and superlattice formation in multiferroic manganites and antiferromagnetic cuprates

The paper reports on new results obtained for tetragonal quasi-2D antiferromagnetic Eu2CuO4 at temperatures below 30-40 K. A set of ferromagnetic resonance lines similar to ones obtained earlier for a number of multiferroic manganites (Sanina et al 2012 J. Phys.: Condens. Matter 24 346002), with similar electric polarization and local conductivity, were measured, i.e., a multiferroic behavior was revealed in Eu2CuO4 at low temperatures. We attribute these observations to the 1D superlattices that are formed due to phase separation and self-organization of charge carriers and occupy a small crystal volume, as in the multiferroic manganites studied earlier. Characteristic features of these superlattices include a spin-charge separation and conductivity in their ferromagnetic layers. It is supposed that superlattices are domain walls separating the volume antiferromagnetic domains. A similarity between the superlattices in a number of crystals having different symmetries and bulk properties suggests that a topological order similar to that of the topological insulator exists in them at low temperatures.

High pressure iso-structural phase transition in BiMn2O5

The high pressure behavior of multiferroic BiMn2O5 has been investigated using powder x-ray diffraction and Raman scattering techniques as well as density functional theory based first principles calculations. Our investigations show a reversible iso-structural phase transition in BiMn2O5 above 10 GPa. The compressibility along the c axis, i.e. along the edge-shared distorted Mn(4+) octahedral chains, has been found to be significantly reduced above this phase transition, suggesting a dominant role of the relatively rigid Mn-O framework in the high pressure phase rather than that of the coordination sphere around the Bi atom. Bader charge analysis of the charge densities obtained from first principles calculations shows partial atomic charge redistribution among Bi(3+) and Mn(3+) atoms across the phase transition which could be the probable cause of this phase transition.

Spin-wave excitations in superlattices self-assembled in multiferroic single crystals

Spin-wave excitations revealed in the dynamically equilibrated one-dimensional superlattices formed due to phase separation and charge carrier self-organization in doped single crystals of Eu(0.8)Ce(0.2)Mn(2)O(5) and Tb(0.95)Bi(0.05)MnO(3) multiferroics are discussed. Similar excitations, but having lower intensities, were also observed in undoped RMn(2)O(5) (R=Eu, Er, Tb, Bi). This suggests that a charge transfer between manganese ions with different valences, which give rise to the superlattice formation, occurs in undoped multiferroics as well. The spin excitations observed in the native superlattices represent a set of homogeneous spin-wave resonances excited in individual superlattice layers. The positions of these resonances depend on the relation between the numbers of Mn(3+) and Mn(4+) ions, charge carrier concentrations, and barrier depths in the superlattice layers. It has been found that the spin-wave excitations observed in the frequency interval studied (30-50 GHz) form two spin-wave minibands with a gap between them.