Robust half-metallicity and magnetic phase transition in Sr2CrReO6 via strain engineering

The Magnetism of Nonstoichiometric Sr2Cr1+xRe1-xO6 (0 < x < 0.5) Double Perovskites

The effect of nonstoichiometry on the cation distribution, crystal structure, and magnetic properties of a series of Cr-rich Sr2Cr1+xRe1-xO6 samples has been investigated. The double perovskite structure is maintained over a wide solid solution range that extends from x = 0 to approximately x = 0.5. For most of the solid solution range, the Cr-rich octahedral site maintains a nearly constant occupancy, 87% Cr and 13% Re, that is comparable to prior studies of Sr2CrReO6, while Cr steadily replaces Re on the other octahedral site. As x approaches 0.5, long-range Cr/Re ordering drops precipitously. Analysis of X-ray powder diffraction peak shapes reveals antiphase boundaries, associated with Cr/Re ordering, the concentration of which increases steadily with increasing x. Neutron powder diffraction studies confirm antiferromagnetic coupling between antisite Cr3+ ions and Cr3+ ions that occupy the normal sites, leading to site-dependent ferrimagnetic ordering. Density functional theory calculations indicate that chromium maintains a +3 oxidation state across the series, while the oxidation state of rhenium increases with increasing x. Calculations are also used to explore the energies of competing magnetic ground states. Except for the most chromium-rich compositions (x ≈ 0.5), site-dependent ferrimagnetism is retained with only a modest reduction in TC. The saturation magnetization steadily decreases as the chromium content increases due to a combination of Cr/Re antisite disorder and antiphase boundaries.

Crystallography at non-ambient conditions and physical properties of the synthesized double perovskites, Sr2(Co1-xFex)TeO6

Polycrystalline double perovskite-type Sr₂(Co_1-xFe_x)TeO₆ with various stoichiometric compositions (x = 0, 0.25, 0.5, 0.75, and 1) were synthesized by solid-state reactions in air. The crystal structures and phase transitions of this series at different temperature intervals were determined by X-ray powder diffraction, and from the obtained data the crystal structures were refined. It has been proven that for the compositions x = 0.25, 0.50, and 0.75, the phases crystallize at room temperature in the monoclinic space group I2/m. Down to 100 K, depending on the composition, these structures experience a phase transition from I2/m to P2₁/n. At high temperatures up to 1100 K their crystal structures show two further phase transitions. The first one is a first-order phase transition, from monoclinic I2/m to tetragonal I4/m, followed by a second-order phase transition to cubic Fm3̄m. Therefore, the phase transition sequence of this series detected at temperatures ranging from 100 K to 1100 K is P2₁/n → I2/m → I4/m → Fm3̄m. The temperature-dependent vibrational features of the octahedral sites were investigated by Raman spectroscopy, which furthermore complements the XRD results. A decrease in the phase-transition temperature with increasing iron content has been observed for these compounds. This fact is explained by the progressive diminishing of the distortion of the double-perovskite structure in this series. Using room-temperature Mössbauer spectroscopy, the presence of two iron sites is confirmed. The two different transition metal cations Co and Fe at the B sites allow exploring their effect on the optical band-gap.

Large-scale synthesis of mixed valence K3[Fe2S4] with high dielectric and ferrimagnetic characteristics

Large scale, high purity synthesis of K3[Fe2S4] which indicates soft ferrimagnetic, high dielectric and semiconductive characteristics.

Interplay between Spin-Orbital Coupling and Electron-Correlation: Induction of Phase Transitions and Giant Magnetic Anisotropy in Strained LaSr_{1−x}Ca_xNiReO_6

In recent decades, 3d-5d based double perovskite oxides (DPO) have received considerable attention due to the existence of the Mott-insulating (MI) state, which is owing to the spin-orbit coupling (SOC)...