Temperature-induced valence-state transition in double perovskite Ba2-xSrxTbIrO6

Abstract

In this work, a temperature-induced valence-state transition is studied in a narrow composition range of Ba${}_{2-x}$Sr${}_x$TbIrO${}_6$. The valence-state transition involves an electron transfer between Tb and Ir leading to the valence-state change between Tb${}^{3+}$/Ir${}^{5+}$ and Tb${}^{4+}$/Ir${}^{4+}$ 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. Ir${}^{5+}$ ion has an electronic configuration of 5$d^4$ ($J{}_{\mathrm{eff}}$ = 0) which is expected to be nonmagnetic. In contrast, Ir${}^{4+}$ ion with a configuration of 5$d^5$($J{}_{\mathrm{eff}}$ = 1/2) favors a long-range magnetic order. For $x$ = 0.1 with Tb${}^{3+}$/Ir${}^{5+}$ configuration to the lowest temperature (2 K) investigated in this work, a spin-glass behavior is observed around 5 K indicating Ir${}^{5+}$ ($J{}_{\mathrm{eff}}$ = 0) ions act as a spacer reducing the magnetic interactions between Tb${}^{3+}$ ions. For $x$ = 0.5 with Tb${}^{4+}$/Ir${}^{4+}$ configuration below the highest temperature 400 K of this work, a long-range antiferromagnetic order at $T{}_{\mathrm{N}}$ = 40 K is observed highlighting the importance of Ir${}^{4+}$ ($J{}_{\mathrm{eff}}$ = 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 Tb${}^{3+}$/Ir${}^{5+}$ phase to low-temperature Tb${}^{4+}$/Ir${}^{4+}$ 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.

10 pages, 8 figures