We report on structural, magnetic, and electrical properties of Sr-doped ${\mathrm{LaMnO}}_3$ single crystals for doping levels $0.4<~x<~\mathrm{0.85.}$ The complex structural and magnetic phase diagram can only be explained assuming significant contributions from the orbital degrees of freedom. Close to $x=0.6\mathrm{}$ a ferromagnetic metal is followed by an antiferromagnetic metallic phase below 200 K. This antiferromagnetic metallic phase exists in a monoclinic crystallographic structure. Following theoretical predictions this metallic antiferromagnet is expected to reveal an ${(x}^2-y^2)$-type orbital order. For higher Sr concentrations an antiferromagnetic insulator is established below room temperature.

The temperature-dependent Raman spectra of orthorhombic $R\mathrm{Mn}{\mathrm{O}}_3$ $(R=\mathrm{Pr},\mathrm{Nd},\mathrm{Sm},\mathrm{Eu},\mathrm{Gd},\mathrm{Tb},\mathrm{Dy},\mathrm{Ho},\mathrm{Y})$ were studied in the $5–300\mathrm{K}$ temperature range. It was established that while the materials with large $R^{3+}$ ionic radius $r_R$ and $A$-type antiferromagnetic order $(R=\mathrm{Pr},\mathrm{Nd},\mathrm{Sm})$ exhibit significant phonon softening and other anomalies with decreasing temperature near and below $T_N$, the effect of magnetic ordering is much weaker or negligible in compounds with $R=\mathrm{Eu}$, Gd, Tb, Dy, Ho, and Y, characterized by small $r_R$ and incommensurate magnetic structure. The results are discussed accounting for the variations with $r_R$ of the type of magnetic ordering and related spin-phonon interaction.

We report on structural, magnetic, dielectric, and thermodynamic properties of ${\mathrm{Eu}}_{1-x}{\mathrm{Y}}_x\mathrm{Mn}{\mathrm{O}}_3$ for Y doping levels $0⩽x<1$. This system resembles the multiferroic perovskite manganites $R\mathrm{Mn}{\mathrm{O}}_3$ (with $R=\mathrm{Gd},\mathrm{Dy},\mathrm{Tb}$) but without the interference of magnetic contributions of the $4f$ ions. In addition, it offers the possibility to continuously tune the influence of the $A$-site ionic radii. For small concentrations $x⩽0.1$ we find a canted antiferromagnetic and paraelectric ground state. For higher concentrations $x⩾0.3$ ferroelectric polarization coexists with the features of a presumably spiral magnetic phase analogous to the observations in $\mathrm{Tb}\mathrm{Mn}{\mathrm{O}}_3$. In the intermediate concentration range around $x\approx 0.2$ a multiferroic scenario is realized combining weak ferroelectricity and weak ferromagnetism, presumably due to a conelike magnetic structure.

The magnetic, electric, magnetoelectric, and magnetoelastic properties of rare-earth ferroborates $\mathrm{R}{\mathrm{Fe}}_3{\left(\mathrm{B}{\mathrm{O}}_3\right)}_4$ ($\mathrm{R}=\mathrm{Pr}$ , Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) as well as yttrium ferroborate $\mathrm{Y}{\mathrm{Fe}}_3{\left(\mathrm{B}{\mathrm{O}}_3\right)}_4$ have been studied comprehensively. A strong dependence not only of the magnetic but also magnetoelectric properties on the type of rare-earth ion, specifically, on its anisotropy, which determines the magnetic structure and the large contribution to the electric polarization, has been found. This is manifested in the strong temperature dependence of the polarization below the Néel point $T_N$ and its specific field dependence, which is determined by the competition between the external and exchange $f\text{-}d$ fields. A close correlation has been found between the magnetoelastic properties of ferroborates and the magnetoelastic and magnetic anomalies at magnetic-field induced phase transitions. It is found that in easy-plane ferroborates, together with magnetic-field induced electric polarization spontaneous polarization also arises below the Néel point. The ferroelectric ordering in ferroborates is of extrinsic character, giving rise to strong magnetoelectric coupling below $T_N$ . Aside from the antiferromagnetic phase transition, the particulars of the structural phase transition accompanied by anomalies of the dielectric and magnetoelectric properties are examined for the first time. The character of the dielectric anomalies at a structural transition is analyzed for the first time on the basis of Landau’s approach.