Cation spin and superexchange interaction in oxide materials below and above spin crossover under high pressure

Abstract

We derived simple rules for the sign of superexchange interaction based on the multielectron calculations of the superexchange interaction in the transition metal oxides that are valid both below and above spin crossover under high pressure. The superexchange interaction between two cations in d n configurations is given by a sum of individual contributions related to the electron-hole virtual excitations to the different states of the d n+1 and d n−1 configurations. Using these rules, we have analyzed the sign of the superexchange interaction of a number of oxides with magnetic cations in electron configurations from d 2 till d 8 : the iron, cobalt, chromium, nickel, copper and manganese oxides with increasing pressure. The most interesting result concerns the magnetic state of cobalt and nickel oxides CoO, Ni2O3 and also La2CoO4, LaNiO3 isostructural to well-known high-TC and colossal magnetoresistance materials. These oxides have a spin 1 2 at the high pressure. Change of the interaction from antiferromagnetic below spin crossover to ferromagnetic above spin crossover is predicted for oxide materials with cations in d 5 (FeBO3) and d 7 (CoO) configurations, while for materials with the other d n configurations spin crossover under high pressure does not change the sign of the superexchange interaction.

Resonant Pumping of d−d Crystal Field Electronic Transitions as a Mechanism of Ultrafast Optical Control of the Exchange Interactions in Iron Oxides

“…The virtual hopping of the spin-up electron from the left cation in the ground state to oxygen and back is the same as it was before the laser excitation, while for the right excited cation the virtual hopping of the second oxygen spin-down electron and back is possible for the spin-up cation, where four electrons of the excited 4 T2 term remain parallel to the spin of the left cation, so their interaction becomes ferromagnetic (FM). We should remark that this picture is just a cartoon of the complicated calculation [43,46] where the effective spin Hamiltonian including both ions in the ground and excited states is obtained by means of a perturbation theory.…”

Magnetic Interaction in Doped 2D Perovskite Cuprates with Nanoscale Inhomogeneity: Lattice Nonlocal Effects vs Superexchange

“…If Ŝh = Ŝe ± 1 it's FM contribution. Other terms are missing, and all electronhole wave functions |h and |e in the hopping integral [50][51][52] in the superexchange…”

Обменное взаимодействие в LaCoO-=SUB=-3-=/SUB=- между ионами кобальта Co-=SUP=-3+-=/SUP=- в различных спиновых состояниях

“…где J tot i j -полный обмен пары узлов, Ŝin 0 -оператор спина на i-м узле, n(h,e) in 0 -операторы числа квазичастиц для дырочного (h) и электронного (e) термов, представляет собой сумму вкладов от всех основных и возбужденных состояний, каждый из которых можно графически представить в виде виртуальной электроннодырочной пары или так называемой обменной петли [38]. Знак каждого вклада определяется соотношением спинов S(d n+1 ) и S(d n−1 ) электронного и дырочного термов, если S(d n−1 ) = S(d n+1 ), то взаимодействие антиферромагнитно.…”