Long-range magnetic interaction and frustration in double perovskites Sr₂NiIrO₆ and Sr₂ZnIrO₆

Revealing exchange bias in spin compensated systems for spintronics applications

Antiferromagnetic materials offer potential for spintronic applications due to their resilience to magnetic field perturbations and lack of stray fields. Achieving exchange bias in these materials is crucial for certain applications; however, discovering such materials remains challenging due to their compensated spin structure. The quest for antiferromagnetic materials with exchange bias became a reality through our experimental study and theoretical simulation onSr 2 FeIrO 6 andSr 2 CoIrO 6 . This study also unveils the impact of ionic disorder and lattice distortion on magnetic properties. The presence of exchange bias in both materials, given their antiferromagnetic nature, is intriguing. This study opens up new avenues for achieving exchange bias in spin-compensated systems, offering potential for low power and ultra fast antiferromagnetic spintronic applications in future research endeavors.

High-Pressure Synthesis of Double Perovskite Ba2NiIrO6: In Search of a Ferromagnetic Insulator

Double perovskite oxides with d⁸-d³ electronic configurations are expected to be ferromagnetic from the Goodenough-Kanamori rules, such as ferromagnetic La₂NiMnO₆. In search of new ferromagnetic insulators, double perovskite Ba₂NiIrO₆ was successfully synthesized by high-pressure and high-temperature methods (8 GPa and 1573 K). Ba₂NiIrO₆ crystallizes in a cubic double perovskite structure (space group: Fm3̅m), with an ordered arrangement of NiO₆ and IrO₆ octahedra. X-ray absorption near-edge spectroscopy confirms the nominal Ni(II) and Ir(VI) valence states. Ba₂NiIrO₆ displays an antiferromagnetic order at 51 K. The positive Weiss temperature, however, indicates that ferromagnetic interactions are dominant. Isothermal magnetization curves at low temperatures support a field-induced spin-flop transition.

Observations of ferromagnetic cluster glass and exchange bias behavior in the double perovskite compound La2Cu0.9Cr0.1IrO6

La₂CuIrO₆ is a spin-orbit coupled Mott insulator, and shows a transition to noncollinear antiferromagnetic state from paramagnetic state below 74 K, and further into a weak ferromagnetic state below 54 K. Despite having two different magnetic phases, the La₂CuIrO₆ compound does not exhibit exchange bias phenomenon. In this present work, we report an experimental investigation on the structural and magnetic properties of the double perovskite compound La₂Cu_0.9Cr_0.1IrO₆ through high-resolution synchrotron x-ray diffraction, x-ray absorption near edge structure (XANES), and temperature and field-dependent magnetization measurements. Powder x-ray diffraction analysis reveals that the sample crystallizes in triclinic structure (space group P [Formula: see text]) alike parent La₂CuIrO₆ compound, while XANES measurements rule out the possibility of valence state alteration between constituting elements in this sample. Interestingly, La₂Cu_0.9Cr_0.1IrO₆ compound is found to exhibit ferromagnetic cluster glass behavior, where field-cooled magnetization undergoes two ferromagnetic transitions. A significant enhancement of ferromagnetic component is also evident from hysteresis loop study, which is likely associated with the electron hopping between J _eff = 1/2 pseudospin state of Ir⁴⁺ ions and empty e_g-orbital of Cr³⁺ ions. Exclusively, this Cr-doped compound exhibits exchange bias effect, which is related to the complex interfacial exchange coupling between the ferromagnetic clusters and the host antiferromagnetic matrix.

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.

Unraveling the Nature of Magnetism of the 5d^{4} Double Perovskite Ba_{2}YIrO_{6}

We report electron spin resonance (ESR) spectroscopy results on the double perovskite Ba_{2}YIrO_{6}. On general grounds, this material is expected to be nonmagnetic due to the strong coupling of the spin and orbital momenta of Ir^{5+} (5d^{4}) ions. However, controversial experimental reports on either strong antiferromagnetism with static order at low temperatures or just a weakly paramagnetic behavior have triggered a discussion on the breakdown of the generally accepted scenario of the strongly spin-orbit coupled ground states in the 5d^{4} iridates and the emergence of a novel exotic magnetic state. Our data evidence that the magnetism of the studied material is solely due to a few percent of Ir^{4+} and Ir^{6+} magnetic defects while the regular Ir^{5+} sites remain nonmagnetic. Remarkably, the defect Ir^{6+} species manifest magnetic correlations in the ESR spectra at T≲20  K, suggesting a long-range character of superexchange in the double perovskites as proposed by recent theories.