The complex impedance of a ${\mathrm{Pr}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ crystal has been measured. The frequency dependence is studied for a wide range of temperatures (50–403 K) and is found to be characteristic of relaxation process with a single Debye time relaxation constant, which is interpreted as a dielectric constant of the material. A strong peak is observed in this dielectric constant (up to ${10}^6)$ at the charge ordering transition suggesting an interpretation in terms of ordering electric dipoles at $T_{\mathrm{CO}}$ or in term of phase separation. Comparison with ${\mathrm{Pr}}_{0.63}{\mathrm{Ca}}_{0.37}{\mathrm{MnO}}_3$—in which the phase separation is much smaller and the peak in the dielectric constant is absent—suggests an interpretation in term of phase separation between insulating and metallic states.

Up to now, electric-field-induced nonlinear conduction in the ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ system (PCMO) has been ascribed to a current-induced destabilization of the charge ordered phase. However, for $x<~0.25,$ a ferromagnetic insulator state is observed, and charge ordering (CO) is absent whatever the temperature. A systematic investigation of nonlinear transport in the ferromagnetic insulator ${\mathrm{Pr}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_3$ shows rather similar results to those obtained in charge-ordered systems. However, the experimental features observed in ${\mathrm{Pr}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_3$ are distinct in that the collapse of the CO energy gap cannot be invoked as is usually done in the other members of the PCMO system. We propose interpretations in which the effectiveness of the double exchange is restored upon application of an electric field.

The resistivity of thin ${\mathrm{La}}_{0.7}{A}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ films $(A=\mathrm{Ca},\mathrm{Sr})$ is investigated in a wide temperature range. The comparison of the resistivities is made among films grown by different techniques and on several substrates allowing to analyze samples with different amounts of disorder. In the low-temperature nearly half-metallic ferromagnetic state the prominent contribution to the resistivity scales as $T^{\alpha }$ with $\alpha \simeq 2.5$ for intermediate strengths of disorder supporting the theoretical proposal of single magnon scattering in presence of minority spin states localized by the disorder. For large values of disorder the low-temperature behavior of the resistivity is well described by the law $T^3$ characteristic of anomalous single magnon scattering processes, while in the regime of low disorder the $\alpha$ exponent tends to a value near 2. In the high temperature insulating paramagnetic phase the resistivity shows the activated behavior characteristic of polaronic carriers. Finally in the whole range of temperatures the experimental data are found to be consistent with a phase separation scenario also in films doped with strontium $(A=\mathrm{Sr})$.

Bending effect on the magnetic anisotropy in 20 nm Co₂FeAl Heusler thin film grown on Kapton^® has been studied by ferromagnetic resonance and glued on curved sample carrier with various radii. The results reported in this Letter show that the magnetic anisotropy is drastically changed in this system by bending the thin films. This effect is attributed to the interfacial strain transmission from the substrate to the film and to the magnetoelastic behavior of the Co₂FeAl film. Moreover, two approaches to determine the in-plane magnetostriction coefficient of the film, leading to a value that is close to λ^CFA= 14 × 10⁻⁶, have been proposed.

We study the influence of the Joule effect on the nonlinear behavior of the transport $I\text{-}V$ curves in polycrystalline samples of the manganite ${\mathrm{Pr}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_3$ by using the crystalline unit-cell parameters as an internal thermometer in x-ray and neutron diffractions. We develop a simple analytical model to estimate the temperature profile in the samples. Under the actual experimental conditions we show that the internal temperature gradient or the difference between the temperature of the sample and that of the thermal bath is at the origin of the nonlinearity observed in the $I\text{-}V$ curves. Consequences on other compounds with colossal magnetoresistance are also discussed.