Organometallic-like localization of 4d-derived spins in an inorganic conducting niobium suboxide

TL;DR

This paper reveals a novel class of transition metal oxide, orthorhombic Nb12O29, with organometallic-like localized 4d spins forming one-dimensional spin chains within a conducting nanowire network.

Contribution

It introduces a new transition metal oxide with localized Nb dimer orbitals and a unique 1D spin chain structure, modeled by an anisotropic Heisenberg-Kondo lattice.

Findings

Discovery of organometallic-like localized 4d spins in Nb12O29

Formation of one-dimensional spin chains in the crystal structure

Proposal of a 2D anisotropic Heisenberg-Kondo lattice model

Abstract

Based on the refined crystal structure comprised of columns of 3*4 planar blocks of NbO6 octahedra and first principles electronic structure methods, we find that orthorhombic (o)-Nb$_{12}$O$_{29}$ introduces a new class of transition metal oxide. The electronic system consists of a large Nb dimer-based localized orbital comparable in size to those in organometallic compounds, yet is tightly bound and weakly interacting with itinerant electronic bands. These local moments, a rare occurrence for Nb, form one-dimensional spin chains that criss-cross perpendicularly oriented conducting nanowires. The local moment bandwidth is comparable to what is seen in rare earth compounds with extremely localized orbitals. The microscopic origin is traced to the local structure of the NbO6 octahedra and associated orbital+spin ordering. The resulting 1D$_s$*1D$_c$ anisotropic two dimensional Heisenberg-Kondo lattice model (s=spin, c=charge) provides a strongly anisotropic spin-fermion lattice system for further study.