Influence of manganese ions environment in octahedral sublattice of La0.7Sr0.3Mn0.9Fe0.1 – xMgxO3 + γ manganites on their properties

Structural, magnetic, and electrical characteristics of manganites in the system La3+0.7Sr2+0.3Mn3+0.6–x-2γMn4+0.3+x+2γFe3+0.1–x Mg2+xO2-3+γ (0 ≤ x ≤ 0.1) synthesized by solid-state reactions are presented. Sintering was performed in air at 1423 K. Samples with stoichiometric oxygen content (γ = 0) were obtained by annealing at 1223 K and a partial oxygen pressure of 0.1 Pa. All studied manganites have a rhombohedral structure. With an increase in the magnesium content, the volume of the unit cell decreases, and annealed samples have a larger cell volume than the initial, sintered manganites containing over-stoichiometric oxygen. The ratio c/a of lattice parameters is practically unchanged. Curie point of manganites decreases in general with an increase in the magnesium content, showing a weakly expressed plateau in the region of 0.025 < x < 0.075. Magnetization and “metal-semiconductor” transition temperature have maximum values at x = 0, then change non-monotonically, and at x > 0.075 fall sharply. Manganite, which contains the largest amount of magnesium, has the highest resistance at temperatures below 180 K and is characterized by the largest width of the temperature interval of “ferromagnetic-paramagnetic” transition, which indicates the existence of magnetic inhomogeneities. The electromagnetic parameters of the initial and annealed samples differ slightly. A number of effects and competing factors that determine complicated dependencies of electromagnetic characteristics of the manganites of this system on the composition are considered.

Identification of spatial magnetic inhomogeneities by nuclear forward scattering of synchrotron radiation

Spatially confined magnetic inhomogeneities were revealed by measuring nuclear forward scattering time spectra on the same sample in two different geometric arrangements. They differ by 180° rotation of the sample around one of the polarization axes. A basic theoretical description of this phenomenon and its relation to a spatial distribution of nuclei featuring different magnetic moments is provided. From an experimental point of view, the violation of rotational invariance was observed for an inhomogeneous Fe81Mo8Cu1B10 metallic glass. The development of magnetic inhomogeneities and their relation to the evolution of time spectra was studied during thermal annealing.

Микромагнитные структуры, индуцированные неоднородным электрическим полем, в магнитодноосных пленках с флексомагнитоэлектрическим эффектом

The features of the manifestation of the flexo-magnetoelectric effect in magnetically uniaxial films under the local influence of an electric field on their surface are investigated. It is shown that with its increasing influence, there is a gradual transformation of the structure of the 180° domain boundary from the Bloch to the quasi-Bloch, and at a certain field value to the Néel boundary. It was revealed that in large fields it is possible to nucleate a 0° domain boundary with a non-Bloch structure, the laws of which have analogies with the formation of magnetic inhomogeneities on defects of the “potential well” type. The contribution of the partial parts of the inhomogeneous magnetoelectric interaction due to the presence of div m and curl m in the phenomena under consideration is also determined.

Магнитные фазы и неоднородные микромагнитные структуры в феррит-гранатовой пленке с ориентацией (210)

Possible magnetic states of a cubic ferromagnet with a uniaxial anisotropy induced along the [210] direction are theoretically investigated. It is demonstrated that the orientation phase diagram of a magnet is nontrivial and admits the existence of three types of magnetic phases that differ in transformational properties and the presence of quintuple points, isostructural phase transitions, etc. It is found that magnetic inhomogeneities, regardless of the values of parameters of the matter, have a common structure: they correspond to 180-degree domain boundaries with a noncircular trajectory of the magnetization vector. The features of homogeneous and inhomogeneous magnetic states, found in these materials, make it possible to explain the manifestation of a flexomagnetoelectric effect in them.