Abstract
In this paper, a temperature-induced valence-state transition is studied in a narrow composition range 0.2⩽x⩽ 0.375 of Ba2−xSrxTbIrO6 by means of x-ray and neutron powder diffraction, resonant inelastic x-ray scattering, magnetic susceptibility, electrical resistivity, and specific heat measurements. The valence-state transition involves an electron transfer between Tb and Ir leading to the valence-state change between Tb3+/Ir5+ and Tb4+/Ir4+ phases. This first-order transition has a dramatic effect on the lattice, transport properties, and the long-range magnetic order at low temperatures for both Tb and Ir ions. Ir5+ ion has an electronic configuration of 5d4 (Jeff=0), which is expected to be nonmagnetic. In contrast, Ir4+ ion with a configuration of 5d5(Jeff = 1/2) favors a long-range magnetic order. For x=0.1 with Tb3+/Ir5+ configuration to the lowest temperature (2 K) investigated in this paper, a spin-glass behavior is observed around 5 K indicating Ir5+ (Jeff=0) ions act as a spacer reducing the magnetic interactions between Tb3+ ions. For x=0.5 with Tb4+/Ir4+ configuration below the highest temperature 400 K of this paper, a long-range antiferromagnetic order at TN = 40 K is observed highlighting the importance of Ir4+ (Jeff = 1/2) ions in promoting the long-range magnetic order of both Tb and Ir ions. For 0.2 ⩽x⩽ 0.375, a temperature-induced valence-state transition from high-temperature Tb3+/Ir5+ phase to low-temperature Tb4+/Ir4+ phase occurs in the temperature range 180 K ⩽T⩽ 325 K and the transition temperature increases with x. The compositional dependence demonstrates the ability to tune the the valence state for a critical region of x that leads to a concurrent change in magnetism and structure. This tuning ability could be employed with suitable strain in thin films to act as a switch as the magnetism is manipulated.
