Diffusion doping of cobalt in rod-shape anatase TiO₂ nanocrystals leads to antiferromagnetism†

Authors

Shahzahan Mia, University of South Dakota
Shelton J.P. Varapragasam, University of South Dakota
Aravind Baride, University of South Dakota
Choumini Balasanthiran, The Pennsylvania State University
Balamurugan Balasubramanian, University of Nebraska-LincolnFollow
Robert M. Rioux, The Pennsylvania State University
James D. Hoefelmeyer, University of South DakotaFollow

ORCID IDs

Shahzahan Mia http://orcid.org/0000-0003-0109-9447

Shelton J. P. Varapragasam http://orcid.org/0000-0002-6857-6837

Aravind Baride http://orcid.org/0000-0001-7582-1522

Choumini Balasanthiran http://orcid.org/0000-0003-0450-7370

Balamurugan Balasubramanian http://orcid.org/0000-0001-6136-3778

Robert M. Rioux http://orcid.org/0000-0002-6019-0032

James D. Hoefelmeyer http://orcid.org/0000-0002-5955-8557

Date of this Version

2020

Citation

Nanoscale Adv., 2020, 2, 4853

DOI: 10.1039/d0na00640h

Comments

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.

Abstract

Cobalt(II) ions were adsorbed to the surface of rod-shape anatase TiO2 nanocrystals and subsequently heated to promote ion diffusion into the nanocrystal. After removal of any remaining surface bound cobalt, a sample consisting of strictly cobalt-doped TiO2 was obtained and characterized with powder Xray diffraction, transmission electron microscopy, UV-visible spectroscopy, fluorescence spectroscopy, X-ray photoelectron spectroscopy, SQUID magnetometry, and inductively-coupled plasma atomic emission spectroscopy. The nanocrystal morphology was unchanged in the process and no new crystal phases were detected. The concentration of cobalt in the doped samples linearly correlates with the initial loading of cobalt(II) ions on the nanocrystal surface. Thin films of the cobalt doped TiO2 nanocrystals were prepared on indium-tin oxide coated glass substrate, and the electrical conductivity increased with the concentration of doped cobalt. Magnetic measurements of the cobalt-doped TiO2 nanocrystals reveal paramagnetic behavior at room temperature, and antiferromagnetic interactions between Co ions at low temperatures. Antiferromagnetism is atypical for cobalt-doped TiO2 nanocrystals, and is proposed to arise from interstitial doping that may be favored by the diffusional doping mechanism.