Ordered vs. disordered perovskites; structural studies of Fe-doped SrIrO3 and SrRuO3

Structural, magnetic and dielectric properties in 3d-5dbased Sr2FeIrO6thin films

The structural, magnetic and dielectric properties have been investigated in 3d-5dbased double perovskite Sr₂FeIrO₆thin films deposited by pulse laser deposition technique. To understand the effect of strain, epitaxial films are grown with varying thickness as well as on different substrates i.e., SrTiO₃(100) and LaAlO₃(100). The films with highest thickness are found to be more relaxed. Atomic force microscope images indicate all films are of good quality where grain sizes increase with increase in film thickness. X-ray absorption (XAS) spectroscopy measurements indicate a Ir⁵⁺charge state in present films while providing a detailed picture of hybridization between Fe/Ir-dand O-porbitals. The bulk antiferromagnetic transition is retained in films though the transition temperature shifts to higher temperature. Both dielectric constant (ϵ_r) and loss (tan δ) show change around the magnetic ordering temperatures of bulk Sr₂FeIrO₆indicating a close relation between dielectric and magnetic behaviors. A Maxwell-Wagner type relaxation is found to follow over whole frequency range down to low temperature in present film. On changing the substrate i.e., LaAlO₃(100), theϵ_r(T) and (tan δ(T)) show almost similar behavior butϵ_rshows a higher value which is due to an increased strain coming from high mismatch of lattice parameters.

Unusual exchange bias in Sr2FeIrO6/La0.67Sr0.33MnO3 multilayer

Here, we study interface induced magnetic properties in a 3d-5d based multilayer made of La_0.67Sr_0.33MnO₃ and double perovskite Sr₂FeIrO₆, respectively. Bulk La_0.67Sr_0.33MnO₃ is metallic and shows ferromagnetic (FM) ordering above room temperature. In contrast, bulk Sr₂FeIrO₆, is an antiferromagnet (AFM) with a Néel temperature around 45 K ([Formula: see text]) and exhibits an insulating behavior. Two set of multilayers have been grown on SrTiO₃ (1 0 0) crystal with varying thickness of FM layer. A multilayer with equal thickness of La_0.67Sr_0.33MnO₃ and Sr₂FeIrO₆ (∼10 nm) shows exchange bias (EB) effect both in conventionally field cooled (FC) as well as in zero field cooled (ZFC) magnetic hysteresis measurements which is rather unusual. The ZFC EB effect is weakened both with increasing maximum field during initial magnetization process at low temperature and with increasing temperature. Interestingly, a multilayer with reduced thickness of La_0.67Sr_0.33MnO₃ (∼5 nm) does not exhibit ZFC EB phenomenon, however, the FC EB effect is strengthened showing much higher value. We believe that an AFM type exchange coupling at the interface and its evolution during initial application of magnetic field causes this unusual EB in present multilayers.

Doped Sr2FeIrO6-Phase Separation and a Jeff ≠ 0 State for Ir5

High-resolution synchrotron X-ray and neutron powder diffraction data demonstrate that, in contrast to recent reports, Sr₂FeIrO₆ adopts an I1̅ symmetry double perovskite structure with an a^-b^-c^- tilting distortion. This distorted structure does not tolerate cation substitution, with low levels of A-site (Ca, Ba, La) or Fe-site (Ga) substitution leading to separation into two phases: a stoichiometric I1̅ phase and a cation-substituted, P2₁/ n symmetry, a^-a^-c⁺ distorted double perovskite phase. Magnetization, neutron diffraction, and ⁵⁷Fe Mössbauer data show that, in common with Sr₂FeIrO₆, the cation substituted Sr_{2- x}A _xFe_{1- y}Ga _yIrO₆ phases undergo transitions to type-II antiferromagnetically ordered states at T_N ∼ 120 K. However, in contrast to stoichiometric Sr₂FeIrO₆, cation substituted samples exhibit a further magnetic transition at T_A ∼ 220 K, which corresponds to the ordering of J_eff ≠ 0 Ir⁵⁺ centers in the cation-substituted, P2₁/ n symmetry, double perovskite phases.

Structure, magnetism and electronic properties in 3d-5d based double perovskite ([Formula: see text]Y x )2FeIrO6

The 3d-5d based double perovskites are of current interest as they provide model systems to study the interplay between electronic correlation (U) and spin-orbit coupling (SOC). Here, we report detailed structural, magnetic and transport properties of doped double perovskite material ([Formula: see text]Y _x )₂FeIrO₆ with [Formula: see text]. With substitution of Y, the system retains its original crystal structure but structural parameters change with x in nonmonotonic fashion. The magnetization data for Sr₂FeIrO₆ show antiferromagnetic type magnetic transition around 45 K; however, a close inspection of the data indicates a weak magnetic phase transition around 120 K. No change of structural symmetry has been observed down to low temperature, although the lattice parameters show sudden changes around the magnetic transitions. Sr₂FeIrO₆ shows an insulating behavior over the whole temperature range, which nevertheless does not change with Y substitution. The nature of charge conduction is found to follow thermally activated Mott's variable range hopping and power law behavior for parent and doped samples, respectively. Interestingly, evolution of structural, magnetic and transport behavior in ([Formula: see text]Y _x )₂FeIrO₆ is observed to reverse with [Formula: see text], which is believed to arise due to a change in the transition metal ionic state.

Contrasting Magnetic Behaviors in Rhodium- and Ruthenium-Doped Cubic Perovskite SrFeO3 : Nearly Ferromagnetic Metal versus Spin-Glass Insulator

The effects of Rh and Ru doping for SrFeO₃ , a helimagnetic metal with a cubic perovskite structure, are studied by magnetic and resistivity measurements. Although SrRhO₃ is a paramagnetic metal and SrRuO₃ is a ferromagnetic one, the Rh doping induces a nearly ferromagnetic metallic state, whereas the Ru doping induces a spin-glass insulating state. Mössbauer measurements evidence a marked difference between SrFe_0.8 Rh_0.2 O₃ and SrFe_0.8 Ru_0.2 O₃ in the formal valences of Fe, which are estimated to be 4+ and 3.75+, respectively. The contrasting magnetic behaviors of Rh- and Ru-doped SrFeO₃ are discussed in terms of the subtle balance between the double-exchange ferromagnetism and the superexchange antiferromagnetism.