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

Abstract

In this work we study the complex entanglement between spin interactions, electron correlation and Janh-Teller structural instabilities in the 5d 1 J ef f = 3 2 spin-orbit coupled double perovskite Ba2NaOsO6 using first principles approaches. By combining non-collinear magnetic calculations with multipolar pseudospin Hamiltonian analysis and many-body techniques we elucidate the origin of the observed quadrupolar canted antifferomagnetic. We show that the non-collinear magnetic order originates from Jahn-Teller distortions due to the cooperation of Heisenberg exchange, quadrupolar spin-spin terms and both dipolar and multipolar Dzyaloshinskii-Moriya interactions. We find a strong competition between ferromagnetic and antiferromagnetic canted and collinear quadrupolar magnetic phases: the transition from one magnetic order to another can be controlled by the strength of the electronic correlation (U ) and by the degree of Jahn-Teller distortions.

Spin-orbital Jahn-Teller bipolarons

“…The non-polaronic d 1 sites (gray isosurfaces in Fig. 1(a)) preserves a J eff = 3/2 ground state, as in the pristine material [31]. Regardless the speciőc type of coupling, jj or LS, both DFT and DMFT predict spin-orbital J eff states, clearly indicating that the polaron is integrated into the SO-Mott background, it exhibits an individual spin-orbital state, and does not break the preexisting J eff = 3/2 state at the other Os sites.…”

“…With a SO coupling strength λ of 0.3 eV, a large on-site Hubbard U of 3.4 eV and sizable JT vibration modes [28ś31], BNOO represents the ideal candidate for questing 5d spin-orbital polarons. BNOO is a Mott insulator with a low temperature canted antiferromagnetic (cAFM) ordered phase below 7 K, where SO splits the effective l = 1 t 2g levels on the Os 7+ d 1 ion into a lower J eff = 3/2 ground state and a doublet J eff = 1/2 [27,31,32] (see Fig. 1(a)).…”

Ferro-octupolar order and low-energy excitations in d$^2$ double perovskites of Osmium

“…We start with the general formula for the magnetic neutron-scattering cross-section 10,11 from a lattice of atoms:…”

“…Since Q is a time-odd operator, only multipoles for odd K contribute into (10). By inserting (10) into (8) and then the resulting expression for Q⊥ t (q) into ( 7), one obtains an expression for the magnetic INS cross-section through the form-factors and matrix elements of the multipole operators: (11) where F µ is the 3D vector of form-factors for the multipole µ. Finally, using the same steps as in the standard derivation of the cross-section within the dipole approximation 10 we obtain the following expression for the magnetic INS cross-section of non-polarized neutrons:…”

“…The Jahn-Teller (JT) active 5d 1 DP are described by an effective J ef f = 3 2 model [3]. The unusual canted antiferromagnetic GS with small ordered moment in d 1 Ba 2 NaOsO 6 (and related DP) attracted a lot of attention [3,[6][7][8][9][10][11][12][13][14] and has been shown to arise through a complex interplay of dipolar and quadrupolar interactions between Kramers ions coupled with JT distortions [14][15][16]. Conversely, the nature of ordered phases in the comparatively less studied 5d 2 version Ba 2 M OsO 6 (M =Ca, Mg, Zn) is still debated [1,5,[17][18][19][20].…”