Investigation of the ferromagnetic transition in the correlated 4d perovskites SrRu1−x_{1-x}Rhx_xO3_3

The solid-solution SrRu$_{1-x}$Rh$_x$O$_3$ ($0\le x \le1$) is a variable-electron-configuration system forming in the nearly-cubic-perovskite basis, ranging from the ferromagnetic 4$d^4$ to the enhanced paramagnetic 4$d^5$. Polycrystalline single-phase samples were obtained over the whole composition range by a high-pressure-heating technique, followed by measurements of magnetic susceptibility, magnetization, specific heat, thermopower, and electrical resistivity. The ferromagnetic order in long range is gradually suppressed by the Rh substitution and vanishes at $x \sim 0.6$. The electronic term of specific-heat shows unusual behavior near the critical Rh concentration; the feature does not match even qualitatively with what was reported for the related perovskites (Sr,Ca)RuO$_3$. Furthermore, another anomaly in the specific heat was observed at $x \sim 0.9$.Comment: Accepted for publication in PR

Competing ground states in transition metal oxides: Behavior of itinerant Sr

The ferromagnetic (FM) phase transition of the itinerant electron-system Sr1−xCaxRuO3 can be tuned by chemical composition resulting in a quantum critical point (QCP) at the critical concentration xc ≈ 0.7. Applying epitaxial pressure at constant x leads to a reduction of the Curie temperature TC which is found to be proportional to the shrinkage of the unit-cell volume Vuc, shifting xc to higher values for tensile strained films. Surprisingly, the tetragonal distortion seems to play here only a minor role. With increasing x the critical scaling of the order parameter shows unusual behavior. The magnetic critical exponents β, γ, and δ change systematically from typical mean-field values at x = 0 with increasing x towards β = 1, γ = 0.9 and δ = 1.6 at x = 0.7. The results are discussed with respect to a crossover from mean-field-like behavior at x = 0 to a line of fixed points that might emerge in the strong-disorder limit as the system approaches the QCP at or near xc. Magnetic inhomogeneities are indeed suggested by a non-vanishing magnetic moment at xc and the evidence of a Griffiths phase as well as glass-like behavior close to xc. Although spin fluctuations certainly play an important role around xc as proposed previously, our highly accurate data of the magnetization M(T,B) and specific heat C(T,B) for x = 0.7 suggest dynamic scaling with an unusual dynamic exponent z = 1.8, incompatible with standard spin-fluctuation theories at a ferromagnetic QCP

REXS contribution to electronic ordering investigation in solids

Resonant Elastic X-Ray Scattering (REXS) has played a fundamental role in understanding electronic properties and in revealing hidden order, local symmetries and exotic states realized in correlated solids. This article reports on some of the relevant scientific contributions and technical advances over the last 20 years, by providing a list of related publications produced by various groups all around the world. The given perspective is that of a group of young scientists involved at various times in the investigation of the beauty of electronic ordering by the REXS technique. © 2012 EDP Sciences, Springer-Verlag