Abstract
This study focused on the impact of Ga–Gd co-substitution on the structural, magnetic features and hyperfine interactions of nanosized NiCuZn spinel ferrites [Ni
0.4
Cu
0.4
Zn
0.2
Ga
x
Gd
x
Fe
2-2x
O
4
(
x
≤ 0.04) NSFs] synthesized via sonochemical approach using ultrasonic irradiation. X-ray powder pattern (XRD) analyses confirmed cubic spinel structures of products. Crystallites and particle sizes of all samples are found to be between 9–14 nm and 18–22 nm, respectively. The NSF morphology and chemical composition were investigated by transmission and scanning electron microscope (TEM and SEM) along with energy-dispersive X-ray (EDX). The cation distribution of all ions was evaluated by Mossbauer spectroscopy. The high spin Fe
3+
ions determined the isomer shift (I.S.) values. For lower rare-earth dopant ratios, we found that Gd
3+
ions occupy B sites, while Ga
3+
ions reside in A sites, and thereafter, some Ga
3+
ions start to enter B sites. Magnetometry measurements were used to evaluate the effect of magnetic field (
H
) and temperature (
T
) on the magnetization of products. For each sample, both coercivity (
H
c
) and saturation magnetization (
M
s
) increase when the
T
decreases below ambient temperature. All substituted samples display
M
s
values higher than those of non-substituted ones; however,
H
c
values diminish for
x
content up to 0.02 and thereafter enlarge. Different magnetization measurements revealed superparamagnetic-to-ferromagnetic transition below the blocking temperature (
T
B
).