Influence of phase ratio on structural, magnetic, and microwave characteristics of hard/soft SrEr0.01Cr0.01Fe11.98O19/NiFe2O4 magnetic nanocomposites

Abstract

Hard/soft (H/S) SrEr0.01Cr0.01Fe11.98O19/NiFe2O4 magnetic nanocomposites (MNCs) with different H/S ratios (2/1; 1.5/1; 1/1; 1/1.5; and 1/2) were produced by one-pot sol-gel auto-combustion approach. The structure and morphology were characterized by XRD, SEM, TEM, and HR-TEM, respectively. The magnetic characteristics of hard/soft (H/S) SrEr0.01Cr0.01Fe11.98O19/NiFe2O4 nanocomposites with different H/S ratios (2/1; 1.5/1; 1/1; 1/1.5; and 1/2) were examined via M-H measurements (magnetization versus magnetic field) at 300 and 10 K, and M-T measurements (magnetization vs. temperature), which revealed the ferrimagnetic behavior of different NCs. Kinked M-H loops have been observed at the vicinity of 0 Oe at both temperatures. dM/dH curves displayed also double peaks. These results indicated the occurrence of competition between intergranular exchange coupling and dipolar interactions. It was noticed that the level of intergranular dipolar interactions is diminishing with the rising soft magnetic phase. As a result, an increase in saturation magnetization (M-s) and remanence (M-r) was observed with the rise of the soft magnetic phase, whereas the coercivity (H-c) is reducing. Microwave properties (frequency dispersions of the main electromagnetic characteristics-real and imaginary parts of the permittivity and permeability) were examined in the range of frequencies up to 16 GHz. Using the standard model, main electromagnetic characteristics were determined from S-parameters for investigated samples. It was demonstrated that the ratio between soft and hard magnetic phases in functional composites can influence such microwave characteristics as reflection losses as well as electromagnetic absorption. Obtained results open broad perspectives for real applications of such types of composites in the field of electromagnetic absorbing materials.