Interplay between itinerant and localized states in CaMn1-xRuxO3 (x =0 - 0.5) manganites

TL;DR

This study investigates how pressure and Ru doping influence magnetic and transport properties in CaMn1-xRuxO3 manganites, revealing complex interactions between itinerant and localized states and their dependence on composition.

Contribution

It introduces a comprehensive energy-level diagram model that explains pressure and doping effects on magnetic interactions and conductivity in CaMn1-xRuxO3.

Findings

Pressure suppresses ferromagnetic correlations for x ≤ 0.4 but enhances them at x=0.5.

The pressure coefficient of spontaneous magnetization decreases linearly with increasing x.

Disorder from Ru-doping affects magnetic interactions and energy states.

Abstract

Magnetic properties of polycrystalline CaMn1-xRuxO3 (x = 0 - 0.5) samples were investigated in the temperature range 4.2 - 250 K, under external magnetic field up to 15 kOe and under hydrostatic pressure up to 12 kbar. Transport properties of the samples with x = 0.1, 0.2, 0.4, 0.5 were also investigated under pressure up to 10 kbar. For x up to 0.4, the pressure was found to suppress ferromagnetic correlations and to increase the resistivity, while for x = 0.5 to act in the opposite way. While long ferromagnetic order is completely suppressed, in small clusters ferromagnetic correlations probably survive under pressure, as was revealed for CaMn0.9Ru0.1O3. The pressure effect on the magnetic interactions and on the volume of ferromagnetic phase was found to depend strongly on the Ru-content, and absolute value of the pressure coefficient of spontaneous magnetization was found to decrease practically linearly with increasing x in the range 0.1 < x < 0.5. The experimental data are discussed in the frame of proposed energy-level diagram, which includes magneto-impurity states at low and moderate Ru-doping and mixed-valence states of Ru presented by a strongly-correlated t2g-like band at heavy Ru-doping. An impact of disorder introduced by Ru-doping on the energy diagram and on derived magnetic interactions is discussed. Predictions of the model regarding the pressure effects on conductivity and temperature scales characteristic for magnetic interactions are in reasonable agreement with experiment.