Alex V. Trukhanov*ab,
Munirah A. Almessierecd,
Abdulhadi Baykale,
Yassine Slimanic,
Ekaterina L. Trukhanovaab,
Daria I. Tishkevichab,
Svetlana V. Podgornayaa,
Egor Kaniukova and
Sergei V. Trukhanovab
aNational University of Science and Technology MISiS, 119049 Moscow, Russia
bScientific-Practical Materials Research Centre of NAS of Belarus, 220072 Minsk, Belarus. E-mail: truhanov86@mail.ru
cDepartment of Biophysics, Institute for Research and Medical Consultations (IRMC), Imam Abdulrahman Bin Faisal University, P. O. Box 1982, Dammam 31441, Saudi Arabia
dDepartment of Physics, College of Science, Imam Abdulrahman Bin Faisal University, P. O. Box 1982, Dammam 31441, Saudi Arabia
eDepartment of Nanomedicine Research, Institute for Research and Medical Consultations (IRMC), Imam Abdulrahman Bin Faisal University, P. O. Box 1982, Dammam 31441, Saudi Arabia
First published on 29th November 2022
The soft/soft (CoFe2O4)x:(Ni0.4Cu0.2Zn0.4Fe2O4)y (CFOx/NCZOy) nanocomposites (NCs) based on spinel ferrites were produced by the sol–gel method with varying phase's ratio (x:y = 0:1; 1:1; 2:1; 3:1; 1:3; 1:2 and 1:0). All NCs consisted of 2 single phases (initial spinels) without any impurities and the absence of chemical interaction between phases. Structural features were investigated and analyzed. The varying of the structural parameters was non-linear and correlated well with the lattice parameter for initial components. There were two maxima observed for all NCs on particle size distribution. It was demonstrated that an increase in the CFO content leads to an increase in the most probable size of the coarse fraction and a decrease in the most probable grain size of the fine fraction. An increase in the NCZO content leads to a decrease in the average size of both fine and coarse fractions. This is obviously due to the large number of defects in the NCZO crystal lattice. The high frequency electromagnetic parameters (real and imaginary parts of the permittivity and permeability, reflection losses) were analyzed in the range of 2–10 GHz. The increase of the energy losses with frequency increase was observed. The nature of the attenuation of the reflected energy associated with the electromagnetic absorption processes due to magnetic losses. Maximal values of the electromagnetic absorption were observed for CFO2/NCZO1 (−18.9 dB). This correlates with the lattice parameters of the composites. The result of the electromagnetic characteristics opens broad perspectives for practical applications such kind of NCs for antenna technology (5G technology) and for electromagnetic absorbing coatings.
When soft and hard magnetic phases do exchange coupled with each other, an exchange-spring magnet (with high Hc and high Ms) can be produced. By adjusting the microstructure between hard and soft phases, the magnetic properties of an exchange-spring magnet can be easily tuned. Therefore, they can be used for different applications. The hard phase is difficult to reverse under the lower applied field due to its large anisotropy. But the magnetization of soft grains will be sufficiently exchange-coupled with that of the neighbouring hard grains and will align in the magnetization. So an exchange-coupled magnet nanocomposite (NC) is the combination of high saturation magnetization of the soft with high coercivity of the hard phase.32 The exchange-coupling interaction between the hard and soft magnetic phases will bring about additional flexibility and an opportunity to tailor the overall properties of the materials33 and give rise to unique physical characteristics as well as superior properties, making these NCs exceptional compared to their individual component counterparts for biomedicine, spintronics, optoelectronics, and nanoelectronics applications.34
The BHmax, which is associated with remnant magnetization, Ms, and Hc of the material, shows the energy density storage capacity of magnetic material. To improve BHmax for this purpose, exchange-spring composites are beginning to be synthesized for advanced applications.35 The exchange-coupling interaction between the hard and soft magnetic phases can improve microwave absorption capability.33
Fei et al. have been successful in synthesizing CoFe2O4/Fe3O4 exchange-spring magnets using Spark Plasma Sintering (SPS) and found the appropriate sintering temperature to be 500 °C.36,37 Safi et al. studied the role of shell thickness on the exchange spring mechanism of cobalt ferrite/iron cobalt magnetic NCs and their exchange coupled NCs exhibit a significant enhancement of the maximum energy product.38 Almessiere et al. successfully synthesized39 the hard/soft CoFe2O4/(NiSc0.03Fe1.97O4)x (0 ≤ x ≤ 5) NCs via sol–gel auto-combustion technique and investigated the supercapacitor property of the products. It was observed that the device also displayed excellent stability as it was tested for 5000 charge–discharge cycles. Wang et al.40 synthesized the hard and soft magnetic NCs of CoFe2O4/Fe3O4 through a co-precipitation route. The presence of a good exchange-coupling interaction between the hard and soft magnetic phases results in a 35% and 842% higher value of (BH)max than those of the pure CoFe2O4 at 300 K and 77, respectively. In another study,34 Almessiere et al. presented the electrical and dielectric properties of rare earth substituted hard–soft ferrite (Co0.5Ni0.5Ga0.01Gd0.01Fe1.98O4)x/(ZnFe2O4)y NCs.
The objectives of the current study are to synthesize and investigate the features of the structural parameters and microwave properties under exchange coupling in functional soft/soft (CoFe2O4)x:(Ni0.4Cu0.2Zn0.4Fe2O4)y (x:y = 0:1; 1:1; 2:1; 3:1; 1:3; 1:2 and 1:0) or CFOx/NCZOy NCs based on nanosized spinel ferrites CoFe2O4 (CFO) and Ni0.4Cu0.2Zn0.4Fe2O4 (NCZO) with varying ratio (x:y).
Fig. 1 Features of the crystal structure of the CFOx/NCZOy composites. (a) Crystal structure of the spinel-like ferrite with SG: Fdm. (b) XRD patterns of the CFOx/NCZOy composites. |
Fig. 2 Main structural parameters of the CFOx/NCZOy composites from XRD data analysis. (a) Average size of crystallite. (b) Lattice parameter a. (c) Volume of the unit cell V. |
Fig. 3 SEM images (left column) and particle size distributions (right column) of the CFOx/NCZOy composites. (a) CFO3/NCZO1. (b) CFO2/NCZO1. (c) CFO1/NCZO1. (d) CFO1/NCZO2. (e) CFO1/NCZO3. |
Average particle size analysis for each composite was performed by a standard statistical method using SmartSEM software as in ref. 43. An area of at least 250 μm2 was used to analyze each sample. Particle size distributions are shown for each sample over the SEM images in Fig. 3. All samples are characterized by the presence of two maxima. Thus, the two values of most probably particle sizes were determined for each sample. For better understanding of the microstructure we provide HRTEM images and electron diffraction pattern for CFO1/NCZO1 on Fig. 4.
The dependence of the most probable size on the spinel ratio is shown in Fig. 5.
Fig. 5 Change in the most probable particle size for fine and coarse phases depending on the CFO and NCZO phase ratio in the CFOx/NCZOy composites. |
The results showed that the particle size of the coarse fraction nonlinearly decreases from 1.61 to 1.33 μm. The particle size of the fine fraction varies from 0.37 to 0.56 μm. Moreover, an increase in the CoFe2O4 content leads to an increase in the most probable size of the coarse fraction and a decrease in the most probable grain size of the fine fraction. An increase in the NCZO content leads to a decrease in the average size of both fine and coarse fractions. This is probably due to the large number of defects in the crystal lattice of the complex NCZO spinel, which prevents the growth of particles.
Fig. 6 shows the change in the ratio of coarse and fine fractions with a decrease in the CFO and an increase in the NCZO spinel content. An almost linear increase in the proportion of the fine fraction and a corresponding decrease in the proportion of the coarse fraction were observed.
Fig. 6 Changes in the proportion of fine and coarse phases depending on the ratio between CFO and NCZO components of the CFOx/NCZOy composites. |
Thus, it can be concluded that CFO spinel promotes the growth of coarse grains with an average size of 1 to 2 μm, and the addition of NCZO in nanocomposites causes the formation of particles with an average size of 380–560 nm.
Fig. 7 Permittivity behavior vs. frequency for the CFOx/NCZOy composites in the range 2–10 GHz. (a) Real part of the permittivity – ε′. (b) Imaginary part of the permittivity – ε′′. |
The values of the ε′ for the initial components CFO and NCZO were in the range of 1.85–2.23 and 1.96–2.49, respectively. The real permittivity of CFO and NCZO decreased rapidly in the frequency ranges of 2–5 and 2–8 GHz, respectively. The features of electrical polarization in materials can explain it. The decrease in real permittivity can be attributed to a decrease in the intensity of charge carrier interaction on grain boundaries. This is an interesting fact that at the lower frequencies (<3 GHz) the behavior of the real permittivity correlates well with the chemical composition of the CFOx/NCZOy. It means that ε′ values for composites were between the values for initial spinels. We have found a synergistic effect with a frequency increase when the additivity principle is violated. This is manifested in the fact that the permittivity value for CFOx/NCZOy NCs was much lower than for the initial components.
This was especially evident at frequencies above 5 GHz (Fig. 7a). The values for CFOx/NCZOy composite materials were in the range, which is noticeably lower than for the original spinels. This behavior may be due to a decrease in the interphase polarization intensity. Similar behavior can be found for imaginary permittivity (Fig. 7b). A rapid increase of the ε′′ from 0.70 to 0.31 and from 0.74 to 0.17 was observed in CFO and NCZO, respectively. Moreover, the values for CFOx/NCZOy NCs were in the range, which is noticeably lower than for the original spinels. As it was mentioned above, the imaginary part of permittivity shows us the energy losses in materials. If in the range of 1 GHz to 1 THz the imaginary part of permittivity is higher than the real part, it corresponds to high-energy losses in materials due to electrical nature. In the present case, the ε′′ values were lower than ε′.
Fig. 8 depicts the behavior of the permeability (real permeability ε′ on Fig. 8a and imaginary permeability ε′′ on Fig. 8b, respectively). Almost all CFOx/NCZOy NCs, as well as initial CFO and NCZO spinels, demonstrated a monotonic decrease in the real part of the permeability. It can be associated with the features of the magnetization processes in magnetic materials. The values of the ε′ for CFOx/NCZOy NCs as well as initial CFO and NCZO spinels were in the range of 1.63–0.02. There was no observed correlation between the composition and real permeability vs. frequency. The opposite behavior was found for imaginary permeability vs. frequency in this range. All composite samples demonstrated a rapid increase of ε′′. The values of the ε′′ for initial components CFO and NCZO were in the range of 0.11–0.35 and 0.18–0.37, respectively. It was observed that the rapid increase of the imaginary permeability occurred in the frequency range of 5–6 GHz for all samples. The increase in the imaginary permeability lets us assert that the energy losses in CFOx/NCZOy composites increase with frequency.
Fig. 8 Permeability behavior vs. frequency for the CFOx/NCZOy composites in the range 2–10 GHz. (a) Real part of the permeability – μ′. (b) Imaginary part of the permeability – μ′′. |
Fig. 9 shows the behavior of the energy losses for reflection vs. frequency. The value of energy losses for all CFOx/NCZOy NCs is negative. This corresponds to the attenuation of the energy of the reflected wave. We should emphasize that all samples demonstrated an increase in losses (as a module) as frequency increased. This correlates well with the μ′′(F) behavior. We can conclude that the nature of the attenuation of the reflected energy is associated with the electromagnetic absorption processes due to magnetic losses. The values of the energy losses for initial components CFO and NCZO were in the range −13.2…−15.4 dB and −12.3…−14.7 respectively. We need to highlight that the values of the energy losses for CFOx/NCZOy composites were larger in comparison with the initial spinels. Thus, CFOx/NCZOy composites with the ratios 1:1; 3:1; 1:3; and 1:2 have similar behavior and values of the energy losses that were in the range of −13.0…−17.7 dB. Maximal values of the energy losses due to electromagnetic absorption were observed for CFO2/NCZO1 or 2:1 (−18.9 dB). This corresponds to the attenuation of the reflected electromagnetic energy by almost 2 orders of magnitude in comparison with the incident energy.
No. | Ratio between phases CoFe2O4/(Ni0.4Cu0.2Zn0.4)Fe2O4 | Acronym where CoFe2O4 – CFO, (Ni0.4Cu0.2Zn0.4)Fe2O4 – NCZO |
---|---|---|
1 | CoFe2O4 (1:0) | CFO or (1:0) |
2 | (Ni0.4Cu0.2Zn0.4)Fe2O4 (0:1) | NCZO or (0:1) |
3 | CoFe2O4:(Ni0.4Cu0.2Zn0.4)Fe2O4 (1:1) | CFO1/NCZO1 or (1:1) |
4 | CoFe2O4:(Ni0.4Cu0.2Zn0.4)Fe2O4 (1:2) | CFO1/NCZO2 or (1:2) |
5 | CoFe2O4:(Ni0.4Cu0.2Zn0.4)Fe2O4 (1:3) | CFO1/NCZO3 or (1:3) |
6 | CoFe2O4:(Ni0.4Cu0.2Zn0.4)Fe2O4 (2:1) | CFO2/NCZO1 or (2:1) |
7 | CoFe2O4:(Ni0.4Cu0.2Zn0.4)Fe2O4 (3:1) | CFO3/NCZO1 or (3:1) |
For CoFe2O4
Co2+ + 2Fe3+ + 4O2− → CoFe2O4 | (1) |
For (Ni0.4Cu0.2Zn0.4)Fe2O4
0.4Ni2+ + 0.2Cu2+ + 0.4Zn2+ + 2Fe3+ + 4O2− → (Ni0.4Cu0.2Zn0.4)Fe2O4 | (2) |
X-ray diffraction investigations were performed using a Rigaku diffractometer in the range of 20°–70° (Benchtop Miniflex in Cu-Kα radiation). The refinement of the XRD patterns was done using FullProf software. The features of the structural parameters (unit cell constant (a), volume (V) and average size of crystallite) were determined by the Rietveld method.1,3 Microstructural parameters (average particle and crystallite size, particle size distribution) were investigated using SEM (scanning electron microscope FEI Titan ST). The SEM images analysis was done to calculate the average particles size and their distribution. The average particle size was estimated using the following equation:45
(3) |
Electrodynamic parameters were measured in the range of 2–10 GHz. It was used as a co-axial method for measuring S11 and S21 parameters. The impedance of the co-axial line was evaluated using the following equation:
(4) |
The frequency-dependent (in the range of 1–20 GHz) S-parameters were measured by an Agilent network analyzer. The Nicholson–Ross–Weir method (NRW) was used to determine the reflection losses (in dB) following the relation:
(5) |
This journal is © The Royal Society of Chemistry 2022 |