Quadrupolar response of Mn ions in manganites

Mn ions play an important role in the properties of LaMnO-based systems. The Mn ions are in the mixed-valence state of the Mn4+ and Mn3+ configurations. Mn4+ consists of three localized d electrons in t orbitals with 2g their spins ferromagnetically coupled and is represented by a spin S = The Mn3+ configuration has an additional localized d electron in one of the e g orbitals to form a total spin S + 1. The e electron hybridizes with conduction g electrons and is assumed to form an orbital singlet as in the two-channel Kondo problem. The orbital singlet is partially broken by a small quadrupolar field that lifts the degeneracy of the e levels. The quadrupolar response is related to the g Jahn-Teller effect and determines the local distribution of Mn-O bond lengths. We study the system in the absence of a magnetic field and in the spin-polarized limit. Both limiting cases yield similar results, suggesting that the quadrupolar susceptibility does not have a strong magnetic field dependence.