Element-specific contributions to improved magnetic heating of theranostic CoFe2O4 nanoparticles decorated with Pd

S Fatemeh Shams,Detlef Schmitz,Margret Giesen,Mohammad Reza Ghazanfari,Florin Radu,Carolin Schmitz-Antoniak,Chen Luo,Kai Chen,Eugen Weschke,Alevtina Smekhova

doi:10.1038/s41598-021-95189-y

Abstract

Decoration with Pd clusters increases the magnetic heating ability of cobalt ferrite (CFO) nanoparticles by a factor of two. The origin of this previous finding is unraveled by element-specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) combined with atomic multiplet simulations and density functional theory (DFT) calculations. While the comparison of XAS spectra with atomic multiplet simulations show that the inversion degree is not affected by Pd decoration and, thus, can be excluded as a reason for the improved heating performance, XMCD reveals two interrelated responsible sources: significantly larger Fe and Co magnetic moments verify an increased total magnetization which enhances the magnetic heating ability. This is accompanied by a remarkable change in the field-dependent magnetization particularly for Co ions which exhibit an increased low-field susceptibility and a reduced spin canting behavior in higher magnetic fields. Using DFT calculations, these findings are explained by reduced superexchange between ions on octahedral lattice sites via oxygen in close vicinity of Pd, which reinforces the dominating antiparallel superexchange interaction between ions on octahedral and tetrahedral lattice sites and thus reduces spin canting. The influence of the delocalized nature of Pd 4d electrons on the neighboring ions is discussed and the conclusions are illustrated with spin density isosurfaces of the involved ions. The presented results pave the way to design nanohybrids with tailored electronic structure and magnetic properties.

Highlights

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The values of the Slater integrals were reduced to 90% of the atomic value
Hybrid Hartree–Fock density functional theory calculations were performed with Perdew–Burke–Ernzerhof (PBE)[42] and Fock exchange and PBE correlation functional according to: EXC = EXPBE + a EXF − EXPBE + ECPBE

Summary

Introduction

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliat. For the case of Co2+ ions, the crystal fields are smaller because of the lower charge of the cation. We used 10Dq = + 1.1 eV and 10Dq = − 0.6 eV for the octahedral and tetrahedral case, respectively.

Results

Conclusion