Covalency and vibronic couplings make a nonmagnetic j=3/2 ion magnetic

Abstract

For 4d1 and 5d 1 spin-orbit-coupled electron configurations, the notion of nonmagnetic j = 3/2 quartet ground state discussed in classical textbooks is at odds with the observed variety of magnetic properties. Here we throw fresh light on the electronic structure of 4d 1 and 5d 1 ions in molybdenum-and osmium-based doubleperovskite systems and reveal different kinds of on-site many-body physics in the two families of compounds: while the sizable magnetic moments and g factors measured experimentally are due to both metal d -ligand p hybridization and dynamic Jahn-Teller interactions for 4d electrons, it is essentially d -p covalency for the 5d 1 configuration. These results highlight the subtle interplay of spin-orbit interactions, covalency and electronlattice couplings as the major factor in deciding the nature of the magnetic ground states of 4d and 5d quantum materials. Cation charge imbalance in the double-perovskite structure is further shown to allow a fine tuning of the gap between the t2g and eg levels, an effect of much potential in the context of orbital engineering in oxide electronics.

Spin-orbital-lattice entangled states in cubic d1 double perovskites

“…The present DFT value of l for Ba 2 NaOsO 6 is close to the previous calculation, 0.536 [17]. The spinorbit coupling parameters λ SO from the ab initio calculations are also in good agreement with previous calculations [16]. However, as in the case of l , λ SO may be overestimated by post HF calculations.…”

Magnetic order and multipoles in the 5d2 rhenium double perovskite Ba2YReO6Thompson1, Marjerisson2, Badrtdinov3 et al. 2021Phys. Rev. B7180View full textAdd to dashboardCite

“…We will return to the possibility of multipolar moments later. Third, some of the shortfall could be the result of assuming a free-ion form factor, which is insufficient to describe 5d ions with extended d orbitals and strong covalency [28]. This is illustrated by the example of K 2 IrCl 6 , where the space group and Wyckoff site of the magnetic Ir 4+ (d 4 ) ions are the same as in Ba 2 YReO 6 , and which shows drastic (up to 50%) departures from the dipolar approximation even at κ ∼ 1 Å −1 [29].…”

Interplay between multipolar spin interactions, Jahn-Teller effect, and electronic correlation in a Jeff=32 insulator

“…1). This apparent violation of the JT theorem [23,24] has been explained by the entanglement of vibronic dynamics with SOC, suggesting the presence of a dynamical Jahn-Teller effect with small static component [3,10] and orbital selective quadrupolar charge ordering [25]. This explains the breaking of local point symmetry and suggests that the canted magnetic ground state of BNOO should be described in terms of the spin-orbital-lattice entangled states involving high-rank spin interactions.…”

“…Double perovskites with strong spin-orbit coupling (SOC) represent a unique playground for the emergence of exotic spin-orbital-lattice entangled phases [1][2][3][4][5]. Structural and orbital frustrations [6], SOC-induced formation of effective J manifolds [7] and relatively strong electronic correlation give rise to a wide range of unusual electronic and magnetic phases including so-called Dirac-Mott insulating states [8,9], multipolar spin interactions [1,2,8] and entangled SOC-Jahn-Teller effects [3,10].…”