The effects of size and orientation on magnetic properties and exchange bias in Co3O4 mesoporous nanowires

Abstract

Co 3 O 4 mesoporous nanowires with average single crystalline grain sizes of about 8 nm, 12nm, 25 nm, and 45 nm were synthesized by sintering of microwave-assisted hydrothermal processed belt-Co(OH) 2 precursors at 300-500 C for 2 h. Microstructure analysis was conducted by x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), field emission SEM (FESEM), transmission electron microscopy (TEM), and high resolution TEM (HRTEM) to confirm the composition, structure, and orientation in the nanowires. Systematic magnetic measurements have also been conducted on the nanowires. It was found that the size and orientation have significant effects on the magnetic and exchange bias properties. The interesting finding was made that room temperature ferromagnetism appeared at 350 C in the high orientation samples. Systematic comparison and analysis of the relationships among the grain size, microstructure, orientation (texture), surface electric structure (O vacancies), and defects with magnetic properties (ferromagnetism, coercive field, exchange bias, etc.) are presented in this work.

Role of cobalt cations in short range antiferromagnetic Co3O4 nanoparticles: a thermal treatment approach to affecting phonon and magnetic properties

“…Moreover, many metal oxides show lattice expansion with a reduction of particle size which could be either because of the finite size effect, cation/anion vacancies, lattice stress etc . However, in general, Co 3 O 4 nanoparticles synthesized by using different methods exhibit the common trend of lattice expansion with an increase of particle size 33–35 . For charge neutrality, some of the Co 3+ vacancies could be substituted by Co 2+ ions, which resulted in the contraction of the Co 2+ –O 2− bond length.…”

“…Zeng et al . 35 reported the observation of a CEB field of −600 Oe from 25 nm Co 3 O 4 nanoparticles using a cooling field of 50 kOe arising from the intercoupling between a spin-glass-like shell and an uncompensated AFM core. Wang et al .…”

Crystal Facet Effects on Nanomagnetism of Co3O4

“…Zeng et al found the size and orientation dependence of the room-temperature ferromagnetic performance of antiferromagnetic Co 3 O 4 nanowires. 26 Karthik et al demonstrated the possible asperomagnetism and/or spin glass behavior of the NiO nanoparticles with a size of 16 nm. 9 The ferromagnetic Fe 3 O 4 nanoparticles show superparamagnetic properties when the particle size is less than ∼30 nm.…”

Fabrication of Mesoporous Co3O4 from LP-FDU-12 via Nanocasting Route and Effect of Wall/Pore Size on Their Magnetic Properties

“…Bulk Co 3 O 4 has a spinel structure with Co 3+ ions occupying the B sites (octahedral) and the Co 2+ ions occupying the A sites (tetrahedral) and is antiferromagnetic (AFM) below 40 K, whereas it is paramagnetic (PM) above that temperature. , However, the magnetic measurements of mesoprous Co 3 O 4 samples show that the magnetic behaviors are mainly effected by the uncompensated surface spins. Mesoporous Co 3 O 4 samples were prepared using SBA-15, ,, KIT-6, ,,,, and SBA-16 , as hard silica templates and have been studied using magnetometry. In these studies, different types of mesoporous silicas were used as a hard template for the syntheses: the Co 3 O 4 replica of SBA-15 consists of nanowires with an average diameter of about 8 nm and the nanowires surface disorder the exchanges bias field changes systematically .…”