A crossover with decreasing temperature $T$ from localized moment magnetism to heavy Fermi liquid behavior is reported for the metallic compound ${\mathrm{LiV}}_2{\mathrm{O}}_4$ with the fcc normal-spinel structure. At $T=1\mathrm{}\mathrm{K}$, the electronic heat capacity coefficient $\gamma \approx 0.42\mathrm{J}/\mathrm{mol}{\mathrm{K}}^2$ is exceptionally large for a transition metal compound, the Wilson ratio $\approx 1.7$, and the Korringa ratio $\approx 0.7$. Our sample with the lowest level of paramagnetic defects showed no static magnetic order above 0.02 K. Superconductivity was not observed above 0.01 K.

The nuclear and magnetic structures and properties of ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ with $0.45<~x<~1$ and ${\mathrm{Pr}}_{1-y}{\mathrm{Sr}}_y{\mathrm{MnO}}_3$ $(0.58\mathrm{}<~y<~1)$ were investigated using neutron powder diffraction, resistivity and magnetic measurements. In this paper, we present the full magnetic and structural phase diagram for ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ and a partial phase diagram for ${\mathrm{Pr}}_{1-y}{\mathrm{Sr}}_y{\mathrm{MnO}}_3.$ At low temperatures, we observe a series of structural phase transitions evolving as a function of increasing x as follows: orthorhombic $\mathrm{Pbn}\overrightarrow{m}\mathrm{rhombohedral}$ $R3\mathrm{}¯\overrightarrow{c}\mathrm{orthorhombic}$ $\mathrm{Fmm}\overrightarrow{m}\mathrm{tetragonal}$ $I4/mc\overrightarrow{m}\mathrm{cubic}$ $\mathrm{Pm}3\mathrm{}¯m.\mathrm{}$ At higher temperatures, the orthorhombic Fmmm structural region disappears. We also identify four magnetic states (FM, A, C, and G type) evolving as a function of increasing x. The magnetic and nuclear structural transitions coincide for samples with $0.8<~x<~\mathrm{0.95.}$ In the $0.5<~x<~0.9$ region, resistivity and magnetic measurements show a substantial hysteresis near $T_N.$ This hysteresis of a few K is indicative of a first order antiferromagnetic transition in good agreement with the neutron diffraction results. Our data also suggest the existence of a strong competition between the ferromagnetic and A-type states for $x\sim 0.5,$ and between the C- and G-type states for $x\sim \mathrm{0.95.}$ A similar behavior is observed for ${\mathrm{Pr}}_{1-y}{\mathrm{Sr}}_y{\mathrm{MnO}}_3.$

The crystal and magnetic structures of newly synthesized ${\mathrm{Sr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ $(0\mathrm{}<~x<~1)$ and ${\mathrm{Sr}}_{1-y}{\mathrm{Ba}}_y{\mathrm{MnO}}_3$ $(y<~0.2)$ perovskite materials (of the $\mathrm{AB}{\mathrm{O}}_3$ type) were investigated using neutron and synchrotron x-ray powder diffraction at temperatures between 10 and 530 K. Upon decreasing the size of the A-site ion (or the unit-cell size) a series of structural transitions appears at room temperature from cubic $\mathrm{Pm}3\mathrm{}¯m$ to tetragonal $I4/mcm$ (at $x\sim 0.3)$ to orthorhombic Pbnm at $x\sim \mathrm{0.4.}$ In agreement with neutron-diffraction data, resistive and magnetic measurements show that the samples are antiferromagnetic with Néel temperatures $T_N,$ varying from 233 to ∼125 K and from 233 to 212 K by increasing the Ca and Ba contents, respectively. The observed variation of $T_N$ cannot be solely explained by the changes of the unit-cell size or the average Mn-O-Mn bond angle θ. The behavior of $T_N$ can be satisfactorily described as a function of $〈{\cos }^2\theta 〉$ related to the superexchange interaction integral, and ${\sigma }^2,$ the A-site ionic size variance [L. M. Rodriguez-Martinez and J. P. Attfield, Phys. Rev. B 54, R15 622 (1996)] regardless of the structural symmetry of the perovskite material.

The nuclear and magnetic structures of ${\mathrm{Sr}}_2{\mathrm{FeMoO}}_6$ have been investigated using neutron powder diffraction and Mössbauer spectroscopy at temperatures between 10 and 460 K. Fe and Mo atoms are found to order on alternate sites, as expected, giving rise to a double-perovskite-type unit cell. Upon cooling, a structural phase transition from cubic $\mathrm{Fm}3\mathrm{}¯m$ to tetragonal $I4/m$ occurs at ∼400 K. In the tetragonal $I4/m$ structure as the temperature decreases, the ${\mathrm{FeO}}_6$ and ${\mathrm{MoO}}_6$ octahedra rotate continuously around the c axis by an angle of up to ∼5.6°. In the $I4/m$ phase, the magnetic moments for Fe and Mo order ferrimagnetically. The Fe magnetic spins first align along the c direction and then rotate to an angle of ∼54° with respect to the c axis; the refined Fe magnetic moment saturates at $\sim 4.3{\mu }_B.$ Mössbauer spectroscopy measurements show that the average valence of Fe is intermediate between the high spin configuration values of ${\mathrm{Fe}}^{+2\mathrm{}}$ and ${\mathrm{Fe}}^{+3\mathrm{}}.$ The temperature dependence of the mean hyperfine field is in good agreement with the neutron-diffraction results and gives the same transition temperature.