QUADRUPOLAR RESPONSE OF MN IONS IN MANGANITES

Mn ions play an important role in the properties of LaMnO3-based syste ms. The Mn ions are in the mixed-valence state of the Mn4+ and Mn3+ co nfigurations. Mn4+ consists of three localized d electrons in t(2g) or bitals with their spins ferromagnetically coupled and is represented b y a spin S=3/2. The Mn3+ configuration has an additional localized d e lectron in one of the e(g), orbitals to form a total spin S+1/2. The e (g) electron hybridizes with conduction electrons and is assumed to fo rm an orbital singlet as in the two-channel Kondo problem. The orbital singlet is partially broken by a small quadrupolar field that lifts t he degeneracy of the e(g) levels. The quadrupolar response is related to the Jahn-Teller effect and determines the local distribution of Mn- O bond lengths. We study the system in the absence of a magnetic held and in the spin-polarized limit. Both limiting cases yield similar res ults, suggesting that the quadrupolar susceptibility does not have a s trong magnetic field dependence.