Ferrimagnetism and spin canting of ZnFe2O4 nanoparticles embedded in ZnO matrix

TL;DR

This study investigates the structural and magnetic properties of ZnFe2O4 nanoparticles in a ZnO matrix, revealing ferrimagnetism, spin canting, and superparamagnetic behavior with detailed magnetic characterization.

Contribution

It provides new insights into the ferrimagnetic ordering and spin canting in embedded ZnFe2O4 nanoparticles, highlighting their magnetic behavior at various temperatures.

Findings

Nanoparticles are ~23.4 nm in size and uniformly dispersed.

Transition from superparamagnetic to frozen magnetic state around 20 K.

Fe3+ ions at A sites align with external field, B site spins are canted by 49°.

Abstract

The structural and magnetic properties of ZnFe2O4 nanoparticles embedded in a non-magnetic ZnO matrix are presented. X-ray diffractograms and Transmission Electron Microscopy (TEM) images showed that the resulting samples are composed of crystalline ferrite nanoparticles with average crystallite size <D> = 23.4(0.9) nm, uniformly dispersed within the ZnO matrix. Magnetization data indicated a superparamagnetic-like behavior from room temperature down to T_{M} ~ 20 K, where a transition to a frozen state is observed. The M(H) curves displayed nearly zero coercive field down to TM, where a sharp increase in the H_C value is observed. The measured saturation magnetization M_S values at 200 and 2 K were M_S = 0.028(3) and 0.134(7) muB/f.u. ZnFe2O4 respectively, showing the existence of small amounts of non compensated atomic moments. M\"ossbauer measurements at low temperatures confirmed the transition to a magnetically ordered state for T < 25 K, where two magnetically split sextets develop. Whereas these two sextets show strong overlap due to the similar hyperfine fields, in-field M\"ossbauer spectra clearly showed two different Fe3+ sites, demonstrating that the sample is ferrimagnetically ordered. The two spinel sites are found to behave differently under an external field of 12 T: whereas the moments located at A sites show a perfect alignment with the external field, spins at B sites are canted by an angle alpha_B = 49(2){\deg}. We discuss the significance of this particle structure for the observed magnetic behavior.