key: cord-0744752-c67dmaqs
authors: Zhang, Zhanjun
title: Study on the influence of magnesium doping on the magnetic properties of spinel Zn-Mg ferrite
date: 2020-10-02
journal: Mater Today Commun
DOI: 10.1016/j.mtcomm.2020.101734
sha: 60a69901be2c27a34bc1a40b8a3090ba050cde72
doc_id: 744752
cord_uid: c67dmaqs

Polycrystalline spinel ferrite powders of Zn(1-)(x)Mg(x)Fe(2)O(4), (x = 0.0, 0.4, 0.8, and 1.0) have been synthesized by solid-state reaction. An antiferromagnetic Néel temperature (T(N) = 25 K) point is observed in ZnFe(2)O(4,) while MgFe(2)O(4) shows a strong ferromagnetism. The magnetization value of Zn(1-)(x)Mg(x)Fe(2)O(4) increases first and then decreases with the increase of x. When x = 0.8 (Zn(0.2)Mg(0.8)Fe(2)O(4)), the value of the saturation magnetization (M(s)) reaches a maximum as 85.566 emu/g. The magnetization of Zn(1-)(x)Mg(x)Fe(2)O(4) shows a very sensitive response to the Mg(2+) concentration at the tetrahedral sites (A-sites) or the octahedral sites (B-sites). I suggest that the A-B super-exchange interaction is enhanced after Mg(2+) ions substituting Zn(2+) ions.

As an important member of ferrite family, spinel ferrite has unique attraction. For a long time, spinel ferrites have attracted the extensive interests due to their remarkable properties reflected in various applications, such as data storage devices [1] , microwave absorbing materials [2] , ferrofluid and catalysis [3, 4] , gas sensing materials [5] [6] [7] , anode materials of lithium-ion batteries [8] , magnetic hyperthermia [9] [10] [11] , optical and dielectric materials [12] , fast frequency response in soft magnetic materials and biomedical fields [13] , etc. In recent years, the research on ZnFe2O4 ferrite is fascinating. Due to its better chemical activity and thermal stability [14] , ZnFe2O4 can be used as the electro-optical devices [15] , magnetic hyperthermia materials in biomedical applications [16] , photo-catalytic systems [17] , contrast enhancers [18] , and so on. Even the latest reports claim that it can be used as the potential detection of the corona virus disease (COVID-19) by S.B. Somvanshi et al [19] . As known, the magnetic properties of such spinel ferrites strongly depend on their chemical compositions, element occupancies and substitutions. Even small amount of ions changing in the spinel ferrites can seriously impact the magnetic properties. Therefore, it is particularly important to select suitable metal cations to substitute. As a counterpart of ZnFe2O4, the MgFe2O4 is also applicable in the electronics and biomedical areas [20, 21] . Meanwhile, these two ferrites have two variant lattice structures i.e. ZnFe2O4 (normal spinel) and MgFe2O4 (inverse spinel).

Thus, a formation of mixed spinel lattice structure can give rise to superior properties than their individual parts. Furthermore, by controlling the stoichiometric ratio between zinc and magnesium, the magnetization parameters of zinc-magnesium ferrite can be fine-tuned to our expected values.

However, most of the synthesized magnetic nanoparticles are found to have mixed magnetic phases, so it is very important to understand the different magnetic phases in the synthesized materials for practical application [22] . In this paper, the microstructure, electronic valence state and magnetism of Zn-Mg ferrite are comprehensively explored and evaluated. These methods can be used to synthesize Zn-Mg ferrite such as ball milling [23] , sol gel [24] , solid state reaction [25] , hydrothermal [26] and co-precipitation [27, 28] ，etc. Considering the factors of low cost, no pollution and easy operation, the traditional solid sintering theory is used to synthesize it here. By measuring the low-temperature magnetic properties of the spinel ferrite powders, we found that the ion occupations of zinc ions and magnesium ions in the same crystal structure are very different, thus showing very different macroscopic physical properties. Therefore, further research and analysis of this kind of ferrite has attracted great interest and extensive attention of researchers.

Zn-Mg spinel ferrite (Zn1-xMgxFe2O4, x = 0.0, 0.4, 0.8, 1.0) particles were synthesized by the solid state reaction method. Fe2O3, ZnO and MgO (purity of 99.9%

for all) were used as the raw materials and mixed according to the calculated stoichiometric ratio. Then, the mixed raw materials were placed in a high-temperature J o u r n a l P r e -p r o o f sintering furnace to be gradually heated to 1373 K and sintered at this temperature for 2 hours. The specific sample preparation process is shown in Figure 1 . X-ray diffraction (XRD, Cu Kα radiation, λ = 0.15406 nm, Philips) and scanning electronic microscopy (SEM) were used to analyze the crystal structure information and reveal the surface morphology of the samples at room temperature (300 K). The prepared Zn-Mg ferrite samples were authenticated by X-ray diffraction (XRD) patterns Table 1 . As mentioned above, the samples obtained from our experiment are in accordance with the calculated stoichiometric ratio and is intrinsically effective.

The crystal structure diagram affected by Magnesium doping.

In order to facilitate the understanding of their magnetic properties, the crystal structure of the samples and the occupancy of different ions therein need to be further analyzed and discussed. As shown as Figure 3 , the positions occupied by all ions in the unit cell and the positions occupied by substituted ions (metal cations) are clearly displayed. As we known, the formula unit of a cubic spinel ferrite can be expressed as

1+x]O4, representing that the tetrahedral sites (A-sites) are occupied by the metal cations in parentheses and the octahedral sites (B-sites) are occupied by the metal cations in square brackets [13] . However, Mg 2+ ions occupy both the A-sites and B-sites in a spinel ferrite [1, 13, 29, 32] . The variational proportion of cations distribution in A-sites and B-sites will greatly affect the structure, electricity and magnetism of spinel ferrite [29, 32] . All the individual elemental spectra are fitted using XPS peak fitting software. In Figure 5 (b), the Mg1s peak is observed at 1304.1 eV with Mg 2+ in Zn0.6Mg0.4Fe2O4

ferrite. The lower energy peak attributed to A-site Mg 2+ and higher energy peak to B-site Mg 2+ [36] . It can be inferred from our experimental results that magnesium ions occupy B-site and force some iron into A-site. Figure 5( [36, 37] . This is enough to show that the magnetism of experimental sample particles is caused by the change of iron oxidation state and the occupancy rate of different cations. Figure 6 TGA curves of Zn1-xMgxFe2O4 ferrites.

In order to investigate the impact of the heat treatment on Zn1-xMgxFe2O4 samples, the thermal response recorded by TGA has been analyzed. The Table 1 . Figure 8 (b) reveals that ZnFe2O4 shows a fully paramagnetic state at 300 K, while the 'S'-like shape of hysteresis loops at 5 K as shown as Figure 8 (a Figure 8 (c) also confirm this conclusion.

Finally, the Ms of Zn1-xMgxFe2O4 will decrease for x > 0.8, which is attributed to the decrease of Fe 3+ ions of B-sites [24] .

In conclusion, the magnetic properties of Zn1-xMgxFe2O4 ( 

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper J o u r n a l P r e -p r o o f 

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