Challenge of Magnetism in Strongly Correlated Open-Shell2pSystems

Abstract

We report on theoretical investigations of the exotic magnetism in rubidium sesquioxide Rb4O6, a model correlated system with an open 2p shell. Experimental investigations indicated that Rb4O6 is a magnetically frustrated insulator. The frustration is explained here by electronic structure calculations that incorporate the correlation between the oxygen 2p electrons and deal with the mixed-valent oxygen. This leads to a physical picture where the symmetry is reduced because one third of the oxygen in Rb4O6 is nonmagnetic while the remaining two thirds assemble in antiferromagnetic arrangements. A degenerate, insulating ground state with a large number of frustrated noncollinear magnetic configurations is confidently deduced from the theoretical point of view. These findings demonstrate in general the importance of electron-electron correlations in open-shell p-electron systems.

Verwey-type charge ordering transition in an open-shell p -electron compound

“…Because of on-site electron correlations and weak electronic overlap between neighboring O 2 entities, Cs 4 O 6 adopts an insulating ground state ( 13 ). The Arrhenius plot of conductivity, σ, measured by impedance spectroscopy on a pressed pellet of Cs 4 O 6 (Fig.…”

K2O2: The most stable oxide of K

“…This allows them to exhibit magnetic order, an aspect which was realized in the past 2 as well as motivated recent work. 3 We have recently shown that the orbital degree of freedom could be active in some of the oxides. 4 Taking the example of KO 2 , we have shown that one has interesting orbital ordering physics also.…”

Phonon-Modulated Magnetic Interactions and Spin Tomonaga-Luttinger Liquid in thep-Orbital AntiferromagnetCsO2

“…This is particularly pronounced in systems based on small and light anionic O − 2 molecules: alkali superoxides, AO 2 (A = Na, K, Rb, Cs) [8][9][10][11], and alkali sesquioxides, A 4 O 6 (A = Rb, Cs) [12][13][14][15]. Here, the O − 2 anion carries an S = 1/2 spin in a pair of p-derived degenerate π * orbitals [16].…”

“…Here, the O − 2 anion carries an S = 1/2 spin in a pair of p-derived degenerate π * orbitals [16]. A strong coupling between spin, lattice and orbital degrees of freedom leads to complex physics [12][13][14][15][16][17][18][19][20][21][22], which is nevertheless based on two relatively simple mechanisms characteristic of molecular solids: (i) the O − 2 "dumbbells" can easily reorient, which modulates the overlaps of π * orbitals and thus the exchange coupling between the neighboring spins [11]; (ii) the degeneracy of the π * orbitals is lifted by a structural phase transition involving the tilting of O − 2 dumbbells, which is reminiscent of the Jahn-Teller effect [16]. Calorimetric and magnetic studies indeed revealed several structural phase transitions in AO 2 systems back in the 1970s [9][10][11], but their origin remained largely unexplained.…”