Field-dependent low-field enhancement in effective paramagnetic moment with nano-scaled Co3O4

TL;DR

This study investigates how the paramagnetic moment of nano-scaled Co3O4 particles varies with applied magnetic field, revealing reversible structural inversion between normal and inverse spinel forms that significantly impacts magnetic properties.

Contribution

It demonstrates field-dependent reversible structural inversion in Co3O4 nanoparticles, linking magnetic behavior to structural changes not previously characterized in such detail.

Findings

Effective paramagnetic moment increases at low fields

Structural inversion between normal and inverse spinel states

Reversible change in lattice structure with applied magnetic field

Abstract

Paramagnetic (PM) properties of columnar cobaltosic oxide (Co3O4) nanoparticles, about 75 nm in diameter, have been investigated by magnetization measurements at T > TN = 39 K. In zero or low applied field, the effective PM moment per formula unit (FU), Mu_eff, enhances significantly from the bulk value of 4.14 Mu_B/FU. It decreases asymptotically from 5.96 Mu_B/FU at Happ = 50 Oe down to 4.21 Mu_B/FU as the applied field increases to Happ = 10 kOe. The field dependent PM properties are explained by a structural inversion, from the normal spinel (spin-only moment ~ 3.9 Mu_B/FU) to the inverse spinel structure (spin-only moment ~ 8.8 Mu_B/FU). The structural inversion is reversible with the variation of the applied field. The lattice structure becomes almost 100% normal spinel in the high field exceeding 10 kOe, as revealed by the magnitude of the effective PM moment. The reversible, field dependent structure inversion is an important property with promising application potential. It is interesting for the future investigations.