Observations of the Novel Low-Field Microwave Absorption in ZnxCo1-xFe2-xAlxO4 Ferrites

Abstract

Nanocrystalline Zn_xCo_1-xFe_2-xAl_xO₄ with particle sizes between 6 and 13 nm were synthesized by glycol-thermal reaction under a low reaction temperature of 200 °C. XRD analysis confirmed the cubic spinel phase with no impurity phases of the as prepared compounds. Raman active photon modes observed also confirmed ferrite crystal lattice. Direct TEM measurements of particle sizes relate well with XRD data and reveal nearly spherical-shaped particle images. Electron spin resonance analysis shows the novel low-field microwave absorptions (LFMA) for the as-prepared (6 ≤ D ≤ 13 nm) compounds recorded at about zero fields. Similar signals have been observed for similar compounds produced by standard ceramic process, confirming reproducibility. The area of the LFMA signals increases with increasing Zn²⁺ and Al³⁺ concentrations and their orientations change with particle size. The presence of LFMA signals makes compounds investigated suitable for applications in low magnetic field sensors, magnetic field-controlled absorbers, spin valves, etc.