Recent EPR and susceptibility measurements in ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ support the existence of a bottleneck EPR regime up to 1000 K quantitatively. The EPR linewidth and electrical conductivity follow the same temperature dependence in the range of 250 to 650 K predicted by the small polaron hopping model. This indicates that spin-lattice relaxation in manganates is due to the relaxation of spins of $e_g$ Jahn-Teller polarons to the lattice.

Electron-paramagnetic resonance (EPR) measurements on ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ provide experimental evidence of a three-spin polaron, consisting of two ${\mathrm{Cu}}^{2+}$ ions and one $p$ hole. The symmetry properties and the peculiar temperature dependence of the $g$ values of the EPR line indicate the presence of dynamical Jahn-Teller distortions and formation of a collective mode of polarons and surrounding strongly correlated Cu ions (bottlenecked regime).

The ESR, magnetic susceptibility, and resistivity measurements of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_{4+\mathrm{\delta }}$ doped with Mn are performed in the broad regions of temperature, Mn and Sr concentrations, respectively. The temperature and Mn concentration dependence of the ESR signal can be understood according to a model of the collective motion of the magnetic moments of Mn and Cu ions with the ESR linewidth determined mainly by the spin relaxation ${\mathrm{\Gamma }}_{\mathrm{\sigma }\mathit{L}}$ of the total magnetic moment of Cu ions to the lattice and by their susceptibilities (bottleneck effect). We found that ${\mathrm{\Gamma }}_{\mathrm{\sigma }\mathit{L}}$ is proportional to temperature ${\mathrm{\Gamma }}_{\mathrm{\sigma }\mathit{L}}$≊BT in a broad region of temperatures with B increasing with Sr doping. At low temperatures T<${\mathit{T}}_{\min }$, with ${\mathit{T}}_{\min }$∼20–110 K depending both on Mn and Sr concentration, the ESR line experiences a sharp broadening which we attribute to the partial opening of the bottleneck. It reveals an inhomogeneous contribution to the Mn ESR linewidth and the relaxation rate ${\mathrm{\Gamma }}_{\mathit{s}\mathrm{\sigma }}$ of the Mn ions to the antiferromagnetic fluctuations in the ${\mathrm{CuO}}_2$ layers, which were hidden in the bottleneck regime. We found ${\mathrm{\Gamma }}_{\mathit{s}\mathrm{\sigma }}$∼${\mathrm{\Gamma }}^{\mathrm{\alpha }}$, with α≊2 for T<${\mathit{T}}_{\min }$, and give some speculations on the origin of this broadening.

A detailed electron-spin-resonance (ESR) investigation is performed in the one-dimensional magnet ${\mathrm{CuSb}}_2{\mathrm{O}}_6$ on both single crystals and polycrystals. Angular-dependent ESR data on the single crystal are interpreted in terms of the anisotropic Zeeman interaction due to the Jahn-Teller distortion of the two inequivalent ${\mathrm{CuO}}_6$ octahedra. The very strong increase of the ESR linewidth with increasing temperature on approaching the monoclinic-to-tetragonal phase transition at about 400 K indicates the thermal activation of a dynamic Jahn-Teller process. Utilizing temperature-dependent x-ray diffraction experiments we propose the monoclinic angle $\beta$ as the order parameter of this phase transition.

In the low doping range of $x$ from 0.01 to 0.06 in ${\mathrm{L}\mathrm{a}}_{2-x}{\mathrm{S}\mathrm{r}}_x{\mathrm{C}\mathrm{u}\mathrm{O}}_4$, a narrow electron paramagnetic resonance (EPR) line has been investigated. This line is distinct from the known broad line and both lines are due to probing ${\mathrm{M}\mathrm{n}}^{2+}$ ions. The narrow line is ascribed to metallic regions in the material, and its intensity increases exponentially upon cooling below $\sim 150\mathrm{K}$. The activation energy deduced $\Delta =460\left(50\right)\mathrm{K}$ is nearly the same as that found in the doped superconducting regime by Raman and neutron scattering. The intensity of the narrow EPR line follows the same temperature dependence as the in-plane resistivity anisotropy in lightly doped ${\mathrm{L}\mathrm{a}}_{2-x}{\mathrm{S}\mathrm{r}}_x{\mathrm{C}\mathrm{u}\mathrm{O}}_4$ single crystals.