Role of SiO2 coating in multiferroic CoCr2O4 nanoparticles

M. Kamran,Asmat Ullah,Y. Mehmood,H. Krenn,K. Nadeem

doi:10.1063/1.4973732

M. Kamran, Asmat Ullah + Show 3 more

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https://doi.org/10.1063/1.4973732

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Abstract

Effect of silica (SiO2) coating concentration on structural and magnetic properties of multiferroic cobalt chromite (CoCr2O4) nanoparticles have been studied. The nanoparticles with average crystallite size in the range 19 to 28 nm were synthesised by sol-gel method. X-ray diffraction (XRD) analysis has verified the composition of single-phase cubic normal spinel structure of CoCr2O4 nanoparticles. The average crystallite size and cell parameter decreased with increasing SiO2 concentration. TEM image revealed that the shape of nanoparticles was non-spherical. Zero field cooled/field cooled (ZFC/FC) curves revealed that nanoparticles underwent a transition from paramagnetic (PM) state to collinear short-range ferrimagnetic (FiM) state, and this PM–FiM transition temperature decreased from 101 to 95 K with increasing SiO2 concentration or decreasing crystallite size. A conical spin state at Ts = 27 K was also observed for all the samples which decreased with decreasing average crystallite size. Low temperature lock-in transition was also observed in these nanoparticles at 12 K for uncoated nanoparticles which slightly shifted towards low temperature with decreasing average crystallite size. Saturation magnetization (Ms) showed decreasing trend with increasing SiO2 concentration, which was due to decrease in average crystallite size of nanoparticles and enhanced surface disorder in smaller nanoparticles. The temperature dependent AC-susceptibility also showed the decrease in the transition temperature (Tc), broadening of the Tc peak and decrease in magnetization with increasing SiO2 concentration or decreasing average crystallite size. In summary, the concentration of SiO2 has significantly affected the structural and magnetic properties of CoCr2O4 nanoparticles.

Highlights

Multiferroic materials show simultaneously ferroelectric and ferromagnetic ordering that exhibit unprecedented physical properties due to coupling between magnetic and electric order parameters.[1]Due to potential uses of multiferroic, they have recently gained much attention in dynamic random access memories, electromagnetic sensors, telecommunication systems, data storage media and spintronics.[2,3,4,5] Despite their applications, multiferroic are few and exploration of new multiferroic materials is of great importance for the emerging technology
X-ray diffraction (XRD) studies confirm the formation of single phase normal spinel CoCr2O4 nanoparticles and average crystallite size lies in the range of 19 – 28 nm for different SiO2 concentration
Uncoated CoCr2O4 nanoparticles with y = 0 % undergo a ferrimagnetic transition at Tc = 101 K, which decreases to 95 K with increasing SiO2 concentration up to 80%

Summary

INTRODUCTION

Multiferroic materials show simultaneously ferroelectric and ferromagnetic ordering that exhibit unprecedented physical properties due to coupling between magnetic and electric order parameters.[1]. The unit cell of CoCr2O4 consists of 32 oxygen, 16 chromium and 8 divalent transition metal ions. It is a ferrimagnetic (FiM) system that undergoes long range order at lock in temperature state at TF = 14 – 15 K, spiral spin state at Ts = 27 K and collinear short range FiM state at Tc = 93-97 K.7–10. We will focus on the effect of SiO2 coating concentration on the structural and magnetic properties of CoCr2O4 nanoparticles

EXPERIMENT

RESULTS AND DISCUSSION

CONCLUSIONS