Jul 12, 2018
Research: Unraveling the nature of magnetism of the pentavalent iridium double perovskite Ba2YIrO6
Typical ESR spectra of Ba2YIrO6 at a frequency of 9.56 GHz. Different contributions to the total magnetic response are clearly spectroscopically resolved. The triplet structure at the high-field side, labelled gright, corresponds to the Ir6+ (S = 3/2) species, the gmid signal corresponds to the Ir4+ (jeff = 3/2) defect sites, and the leftmost gleft signal is due to the radical centers localized at the structural imperfections.
Our multifrequency electron spin resonance (ESR) experiments on the pentavalent iridium double perovskite Ba2YIrO6 reveal presence of different paramagnetic centers with the total concentration of ∼4%. Their origin can be unambiguously assigned to defect Ir4+ (jeff = 1/2) and Ir6+ (S = 3/2) sites. Hence, our data evidence that the magnetism of the studied material is solely due to these magnetic defects while the regular Ir5+ sites remain nonmagnetic. These clear–cut experimental results question, in general, the recently proposed scenario of the breakdown of the spin-orbit coupled jeff states in the 5d4 double perovskite iridates and the occurrence of a weak magnetic moment on every Ir5+ (5d4) site. Remarkably, the defect Ir6+ species which give the major contribution to the total magnetic response manifest magnetic correlations in the ESR spectra at T≲20 K highlighting the relevance of long-range magnetic interactions in 5d double perovskites proposed in recent theoretical models. In fact, they might be even responsible for the magnetic order of defect Ir-based spin centers in Ba2YIrO6 if their concentration exceeds a certain threshold value.
S. Fuchs, T. Dey, G. Aslan-Cansever, A. Maljuk, S. Wurmehl, B. Büchner, V. Kataev,
Unraveling the nature of magnetism of the 5d4 double perovskite Ba2YIrO6,
Phys. Rev. Lett. 120, 237204 (2018) (arXiv)