Magnetic properties of undoped Cu2O fine powders with magnetic impurities and/or cation vacancies

TL;DR

This study investigates the magnetic properties of undoped Cu2O powders with different sizes and shapes, revealing defect-induced magnetism likely caused by cation vacancies, with some samples showing weak ferromagnetism at room temperature.

Contribution

It demonstrates that cation vacancies in undoped Cu2O can induce magnetic moments and ferromagnetism, supported by experimental data and density functional theory calculations.

Findings

Octahedral Cu2O is diamagnetic at 5 K.

Nanospheres exhibit paramagnetism at 5 K.

Some polyhedron samples show weak ferromagnetism with T_C = 455 K.

Abstract

Fine powders of micron- and submicron-sized particles of undoped Cu2O semiconductor, with three different sizes and morphologies have been synthesized by different chemical processes. These samples include nanospheres 200 nm in diameter, octahedra of size 1 micron, and polyhedra of size 800 nm. They exhibit a wide spectrum of magnetic properties. At low temperature, T = 5 K, the octahedron sample is diamagnetic. The nanosphere is paramagnetic. The other two polyhedron samples synthesized in different runs by the same process are found to show different magnetic properties. One of them exhibits weak ferromagnetism with T_C = 455 K and saturation magnetization, M_S = 0.19 emu/g at T = 5 K, while the other is paramagnetic. The total magnetic moment estimated from the detected impurity concentration of Fe, Co, and Ni, is too small to account for the observed magnetism by one to two orders of magnitude. Calculations by the density functional theory (DFT) reveal that cation vacancies in the Cu2O lattice are one of the possible causes of induced magnetic moments. The results further predict that the defect-induced magnetic moments favour a ferromagnetically coupled ground state if the local concentration of cation vacancies, n_C, exceeds 12.5%. This offers a possible scenario to explain the observed magnetic properties. The limitations of the investigations in the present work, in particular in the theoretical calculations, are discussed and possible areas for further study are suggested.