Evaluation of Neel Temperatures from Fully Self-Consistent Broken-Symmetry GW and High-Temperature Expansion: Application to Cubic Transition-Metal Oxides

Abstract

Using fully self-consistent thermal broken-symmetry GW, we construct effective magnetic Heisenberg Hamiltonians for a series of transition metal oxides (NiO, CoO, FeO, and MnO), capturing a rigorous but condensed description of the magnetic states. Then applying high-temperature expansion, we find the decomposition coefficients for spin susceptibility and specific heat. The radius of convergence of the found series determines the Neel temperature. The NiO, CoO, and FeO contain a small ferromagnetic interaction between the nearest neighbors (NNs) and the dominant antiferromagnetic interaction between the next-nearest neighbors (NNNs). For them, the derived Neel temperatures are in good agreement with experiment. The case of MnO is different because both NN and NNN couplings are antiferromagnetic and comparable in magnitude, for which the error in the estimated Neel temperature is larger, which is a signature of additional effects not captured by electronic structure calculations.

Enhancement of Magnetic Stability in Antiferromagnetic CoO Films by Adsorption of Organic Molecules

“…The AF order is indeed due to a superexchange interaction between Co spins with coupling parameter J , mediated by oxygen atoms. This one represents the strongest among the Co–Co interactions, being the one not mediated by oxygen almost negligible. , The value of J is derived from a system of equations E k = ∑ < i , j > J i , j S k , i S k , j in which the sum on indexes < i , j > is done on unique next nearest neighbor Co pairs, E k is the total energy of the spin configuration k (with arbitrary reference) and S k , i , S k , j are the spin directions associated with Co atoms and they are set equal to +1 or −1. To set a system of equations from which to extract J , we consider different spin configurations in which the spin of a single Co atom on the surface is flipped.…”

Natural orbitals and two-particle correlators as tools for the analysis of effective exchange couplings in solids

“…In the compounds considered, the effective magnetic Hamiltonian 27,30,63,146 has only non-zero couplings between the nearest neighbors J 1 and between the next-nearest neighbors J 2 , and is expressed asSemiempirical Goodenough–Kanamori (GK) rules 147–149 are commonly used to explain the magnetic origin of effective interactions in transition-metal oxides and related compounds. They are based on simplistic models and assume localized interactions between the orbitals and their overlaps.…”

“…This theoretical framework has been used within a number of methods 57,58 both for derivation purposes as well as constructing new approximations based on the physics of the effective Hamiltonians. 59–63 Another but related strategy utilizes finite-order perturbative expansions of effective Hamiltonians and investigates configurations that contribute to the effective exchange coupling. For example, Kramers 64 and Anderson 65 used the latter strategy, and classified various terms into direct exchange, kinetic exchange, and spin-polarisation terms.…”