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A comprehensive study is made of the properties of samples of BiFe1−xMnxO3 (0.05 ≤ x ≤ 0.15) solid solutions synthesized using the sol-gel technique. Stabilization of the main phase, a reduction in the average granule size, and an increase in the dielectric constant are observed upon an increase in concentration x. The presence of Mn ions in BiFe1−xMnxO3 solid solutions results in semiconductor-type conductivity and the emergence of magnetic ordering at 605 K (х = 0.05) and 550 K (х = 0.15).

A slowly decaying anomaly of magnetic susceptibility (characteristic time τ ~ 103 s) is revealed in studying the ferromagnetic–paramagnetic phase transition in polycrystalline cobaltite GdBaCo2O5.53 that occurs due to the remaining short-range magnetic order at temperatures above the Curie point (TC = 275 K). High hydrostatic pressures (up to 1.48 GPa) are found to have a weak effect on TC with baric coefficient dTC/dP = 2.1 K/GPa.

Complex magnetic, resistive, and dielectric studies of Pr1–xCaxMnO3 (х = 0.15–0.30) manganites reveal multiferroic properties at T≫TC in these solid solutions. States with local magnetization in the form of ferromagnetic clusters (nucleation temperature T* ≈ 700 K) and high dielectric constants coexist in the temperature window TC ≤ T ≤ T*. There is a correlation between the temperature dependences of specific resistance and specific magnetization.

Structural, magnetic, and resonance studies of BixLa1–xMnO3 are performed. Nanopowders of weakly doped compounds (x = 0.0–0.1) with particle sizes of ≤40 nm are prepared using the sol–gel technique. Nanopowder sintering under the same conditions leads to a sharp increase in the mean granule size with increasing Bi concentration. The 55Mn NMR signal of manganites prepared via solid synthesis corresponds to rapid exchange Mn4+ ↔ Mn3+. Measurements of the magnetic susceptibility reveal an inhomogeneity in the ferromagnetic state of the BixLa1–xMnO3 system.