Non-equilibrium effects in the magnetic behavior of Co_3O_4 nanoparticles

TL;DR

This study investigates the unique non-equilibrium magnetic properties of Co_3O_4 nanoparticles, revealing atypical behaviors such as unshifted ZFC peaks and negligible aging effects, and tests the applicability of Fisher's relation for these particles.

Contribution

It provides a detailed analysis of the magnetic behavior of Co_3O_4 nanoparticles, highlighting their unique properties and validating Fisher's relation in this context.

Findings

ZFC magnetization peak coincides with bifurcation temperature and does not shift under magnetic fields.

Aging effects are negligible in both FC and ZFC protocols.

Memory effects are observed only in FC protocol.

Abstract

We report detailed studies on non-equilibrium magnetic behavior of antiferromagnetic Co_3O_4 nanoparticles. Temperature and field dependence of magnetization, wait time dependence of magnetic relaxation (aging), memory effects and temperature dependence of specific heat have been investigated to understand the magnetic behavior of these particles. We find that the system shows some features characteristic of nanoparticle magnetism such as bifurcation of field cooled (FC) and zero field cooled (ZFC) susceptibilities and a slow relaxation of magnetization. However, strangely, the temperature at which the ZFC magnetization peaks coincides with the bifurcation temperature and does not shift on application of magnetic fields up to 1 kOe, unlike most other nanoparticle systems. Aging effects in these particles are negligible in both FC and ZFC protocol and memory effects are present only in FC protocol. We estimate the N\'eel temperature by using Fisher's relation as well as directly by measurement of specific heat, thus testing the validity of Fisher's relation for nanoparticles. We show that Co3O4 nanoparticles constitute a unique aniferromagnetic system which develops a magnetic moment in the paramagnetic state because of antiferromagnetic correlations and enters into a blocked state above the N\'eel temperature.