Spin-polarized oxygen hole states in cation deficient La(1-x)CaxMnO(3+delta)

TL;DR

This study reveals the presence of spin-polarized oxygen hole states in cation-deficient La(1-x)CaxMnO(3+delta), evidenced by NMR and x-ray absorption, indicating a novel electronic state in doped manganites.

Contribution

It provides experimental evidence for spin-polarized oxygen hole states in cation-deficient La(1-x)CaxMnO(3+delta), a phenomenon not previously reported in these materials.

Findings

Strong hyperfine fields at La sites in low Ca-doped samples

Formation of spin-polarized holes on oxygen orbitals

Correlation with x-ray absorption data

Abstract

When holes are doped into a Mott-Hubbard type insulator, like lightly doped manganites of the La(1-x)CaxMnO3 family, the cooperative Jahn-Teller distortions and the appearance of orbital ordering require an arrangement of Mn(3+)/Mn(4+) for the establishment of the insulating canted antiferromagnetic (for x<=0.1), or of the insulating ferromagnetic (for 0.1<x<= 0.2) ground state. In the present work we provide NMR evidence about a novel and at the same time puzzling effect in La(1-x)CaxMnO(3+delta) systems with cation deficience. We show that in the low Ca-doping regime, these systems exhibit a very strong hyperfine field at certain La nuclear sites, which is not present in the stoichiometric compounds. Comparison of our NMR results with recent x-ray absorption data at the Mn K edge, suggests the formation of a spin-polarized hole arrangement on the 2p oxygen orbitals as the origin of this effect.