We investigated the influence of 10% substitution of rare-earth (RE) elements on the crystallographic, transport, and magnetic properties of La_0.67–x RE _x Ca_0.33MnO₃(RE = Nd, Sm, and Gd, x = 0.0, 0.1) manganite perovskite compounds. The bulk polycrystalline samples were synthesized using solid-state reaction method. The phase purity and crystal structure of studied samples were confirmed by room temperature X-ray diffraction followed by the Rietveld refinement analysis. A high temperature insulator to low temperature metal phase transition is observed in electrical transport measurement. We observed an enhancement in the temperature coefficient of resistance (TCR) and magnetoresistance (MR) by partially substituting La with RE ions. The maximum TCR ≈ 22% and MR ≈ 96% are observed in Gd doped sample. The magnetic transition temperature, T _c , decreases from ∼254 K for the pristine sample to about ∼165 K for the Gd-doped sample. Our analysis of electrical and thermal transport data shows that the Small Polaron Hopping (SPH) is predominant at high temperatures conduction mechanism, whereas at low temperatures mechanism is dominated by electron-magnon scattering. The high temperature insulator paramagnetic phase to low temperature metallic ferromagnetic phase transitions are also observed in thermal conductivity and specific heat.

We report a detailed investigation of $R$CoPO ($R$ $=$ La, Pr) and LaCoAsO materials performed by means of muon spin spectroscopy. Zero-field measurements show that the electrons localized on the Pr${}^{3+}$ ions do not play any role in the static magnetic properties of the compounds. Magnetism at the local level is indeed fully dominated by the weakly itinerant ferromagnetism from the Co sublattice only. The increase of the chemical pressure triggered by the different ionic radii of La${}^{3+}$ and Pr${}^{3+}$, on the other hand, plays a crucial role in enhancing the value of the magnetic critical temperature and can be mimicked by the application of external hydrostatic pressure up to 24 kbar. A sharp discontinuity in the local magnetic field at the muon site in LaCoPO at around 5 kbar suggests a sizable modification in the band structure of the material upon increasing pressure. This scenario is qualitatively supported by ab initio density-functional-theory calculations. DOI: http://dx.doi.org/10.1103/PhysRevB.87.064401 ©2013 American Physical Society

Magnetization, x-ray diffraction, and specific-heat measurements reveal that SmCoAsO undergoes three magnetic phase transitions. A ferromagnetic transition attributed to the Co ions, emerges at $T_C=57\text{K}$ with a small saturation moment of $\sim 0.15{\mu }_B/\text{Co}$. Reorientation of the Co moment to an antiferromagnetic state is obtained at $T_{N2}=45\text{K}$. The relative high paramagnetic effective moment $P_{\text{eff}}=1.57{\mu }_B/\text{Co}$ indicates an itinerant ferromagnetic state of the Co sublattice. The third magnetic transition at $T_{N1}=5\text{K}$ is observed clearly in the specific-heat study only. Both magnetic and ${}^{57}\text{F}\text{e}$ Mossbauer studies show that substitution of small quantities of Fe for Co was unsuccessful.