59Co-NMR Probe for Stepwise Magnetization and Magnetotransport in SrCo6O11 with Metallic Kagome Layer and Triangular Lattice with Local Moments

TL;DR

This study uses 59Co-NMR to uncover the magnetic and electronic properties of SrCo6O11, revealing stepwise magnetization, field-induced magnetic transitions, and the role of different Co sites in its metallic and magnetic behavior.

Contribution

It provides a microscopic understanding of the magnetic transitions and magnetotransport phenomena in SrCo6O11 through site-selective NMR analysis, highlighting the distinct roles of Co sites.

Findings

Local moments at Co(3) sites are magnetically ordered without bulk magnetization at zero field.

Field-induced ferrimagnetic to ferromagnetic transition at Co(3) sites explains magnetization steps.

Magnetotransport is dominated by nonmagnetic Co(1) and Co(2) sites with metallic conductivity.

Abstract

We report on novel magnetic and electronic properties of SrCo6O11 that exhibits a unique stepwise magnetization and its relevant magnetotransport phenomena investigated by the site-selective 59Co nuclear magnetic resonance (NMR) at zero and applied magnetic fields. This compound is composed of three Co sites in the unit cell, i.e., Co(1) in the metallic Kagome layer, a Co(2) dimerized pillar between the layers and Co(3) in the triangular lattice. Zero-field NMR spectra have revealed that large local moments at the Co(3) sites are magnetically ordered without any trace of bulk magnetization M at zero field. The field-swept NMR spectra show that the internal hyperfine field at the Co(1) site is derived from fully polarized moments Ms at the Co(3) sites in the "1"-plateau state at fields higher than 2.5 T, whereas it is partially cancelled out in the "1/3"-plateau state in which one-third of Ms is induced at intermediate fields once a small field is applied. It has been clarified from a microscopic point of view that the local moments at Co(3) site undergo a field-induced ferrimagnetic (up-up-down)-to-ferromagnetic (up-up-up) transition, which is consistent with the evidence obtained from the recent neutron diffraction experiment. The Co(1) Kagome layer and the dimerized pillar Co(2) site between the layers are of nonmagnetic origin, suggesting that the nearly quasi-2D metallic conductivity is dominated by nonmagnetic Co(1) and Co(2) sites. Consequently, unique magneto-transport phenomena observed in SrCo6O11 are demonstrated owing to the interaction between the conduction electrons at the Co(1) and Co(2) sites and the local moments at Co(3) sites.