Origin of magnetic moments and presence of spin-orbit singlets in Ba2YIrO6

Abstract

While it was speculated that 5d 4 systems would possess non-magnetic J = 0 ground state due to strong Spin-Orbit Coupling (SOC), all such systems have invariably shown presence of magnetic moments so far. A puzzling case is that of Ba 2 YIrO 6 , which in spite of having a perfectly cubic structure with largely separated Ir 5+ (d 4 ) ions, has consistently shown presence of weak magnetic moments. Moreover, we clearly show from Muon Spin Relaxation (µSR) measurements that a change in the magnetic environment of the implanted muons in Ba 2 YIrO 6 occurs as temperature is lowered below 10 K. This observation becomes counterintuitive, as the estimated value of SOC obtained by fitting the RIXS spectrum of Ba 2 YIrO 6 with an atomic j − j model is found to be as high as 0.39 eV, meaning that the system within this model is neither expected to possess moments nor exhibit temperature dependent magnetic response. Therefore we argue that the atomic j − j coupling description is not sufficient to explain the ground state of such systems, where despite having strong SOC, presence of hopping triggers delocalisation of holes, resulting in spontaneous generation of magnetic moments. Our theoretical calculations further indicate that these moments favour formation of spin-orbital singlets in the case of Ba 2 YIrO 6 , which is manifested in µSR experiments measured down to 60 mK.

Spin-liquid behavior of the three-dimensional magnetic system Ba3NiIr2O9 with S=1

“…For zero field, the magnitude of coefficient γ is 45 mJ/mol K 2 and the exponent α is 1.0 ± 0.05 within a 0.1 -0.6 K range. The value of γ is very similar to other gapless spin-liquid candidates like Ba 3 CuSb 2 O 9 (43.4 mJ/mol K 2 ) [49], Ba 2 YIrO 6 (44 mJ/mol K 2 ) [50], Ba 3 ZnIr 2 O 9 (25.9 mJ/mol K 2 ) [28], and Sr 2 Cu(Te 0.5 W 0.5 )O 6 (54.2 mJ/mol K 2 ) [51]. Also, the linear T behavior with nonzero γ in an insulator comes due to gapless spinon excitations with a Fermi surface and has been reported in several organic and inorganic spin-liquid candidates [7,49,[51][52][53][54][55].…”

Sr$_3$LiIrO$_6$: a potential quantum spin liquid candidate in the one dimensional $d^4$ iridate family

“…Further, certain ambiguity in the AFM interaction strengths [by means of different values of negative θ CW at the different applied magnetic fields, as revealed by the respective Curie-Weiss fittings, shown in Fig. 5(a)] is also evident in SLIO, likely in consistent with many other existing QSL systems [8,47,48,57].…”

“…The origin of such a large Ir 5+ -moment in SLIO could certainly be attributed to the intersite Ir-Ir hopping via extended Ir-O-O-Ir superexchange pathways within all possible intra and interchain magnetic exchange connectivity (represented by three different exchange interactions in Fig. 1 (b)), causing delocalization of intra-site Ir 5+ holes, and therefore, creating deviation from a perfect atomic J = 0 arrangement [10,47,48]. In addition, the trigonal distortion of the IrO 6 octahedra and the subsequent Ir-t 2g splitting, as well as the hybridization of extended Ir-5d orbitals and the stronger Ir-O covalent interactions together might cause rearrangement in the spin-orbit coupled Ir energy levels in SLIO, and as a result, leading to the possible breakdown of atomic J limit [63][64][65][66].…”

Comparative Study of Potentially Jeff = 0 Ground State Iridium(V) in SrLaNiIrO6, SrLaMgIrO6, and SrLaZnIrO6

“…Concerning the sample quality, it is perhaps more instructive to look at the magnitude of the temperature‐dependent part of the magnetic susceptibility: the smaller the temperature dependence, the less is the amount of magnetic impurities in the supposedly pure J eff = 0 compounds. In the literature we find μ eff ranging from 0.16 to 0.91 μ B for Sr 2 YIrO 6 ,, , and from 0.18 to 1.44 μ B for Ba 2 YIrO 6 , , , . Although these values must be handled with caution since the variations may be caused also by the temperature fitting range, it is nevertheless reasonable to assign the Curie signal to the presence of magnetic impurities.…”