Room temperature ferromagnetic property of Fe-Y (Fe: Y-6.5) composite oxide nano-cluster via an extremely easy and scalable method

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Abstract

A novel Fe-Y composite oxide (Fe: Y-6.5) nanocluster was synthesized by self-assembly approach. The α-Fe2O3 and cubic-Y2O3 nanocrystalline with diameter around 10 nm are homogeneously assembled to form a cluster architecture which are constituted of Fe6.5Y composite oxide particles. Additional oxygen vacancies are introduced with cubic-Y2O3, and the oxygen vacancies as Fe3+–Vo–Y3+ between α-Fe2O3 and cubic-Y2O3 nanocrystalline are generated by self-assembly process. Magnetic hysteresis loops recorded by vibrating sample magnetometry at 273 K display a ferromagnetic order, related to the fact that Fe3+–Vo–Y3+ act as defect centers in the bound magnetic polaron model for Fe-Y composite oxide nanomaterial. The ferromagnetic properties are proportional to oxygen vacancy contents, and maximum magnetization (Mm) value of the nano-cluster reaches 5.14 A·m2/g.

Graphical abstract

Fe-Y (Fe: Y-6.5) composite oxide nanocluster with high intensity of oxygen vacancies was obtained by in-situ self-assembly methods. The effect of oxygen vacancy defect produced by crystal disorder on collective room temperature magnetic properties of Fe-Y oxide system was studied. The obtained results show that the Fe-Y composite oxide nanomaterial display a ferromagnetic order at 273 K, related to the fact that Fe3+–Vo–Y3+ acts as defect centers in the bound magnetic polaron model.

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Introduction

Due to the combination of tunable magnetic properties and ease of functionalization, iron oxide nanoparticles (INPs) have attracted much attention for various applications.1, 2, 3, 4, 5 Among iron oxide, α-Fe2O3 is stable for application, friendly for environment, and inexpensive for produce.6, 7, 8, 9, 10 In principle, α-Fe2O3 has antiferromagnetic behavior under the Morin temperature, when pure α-Fe2O3 has been observed with weak ferromagnetic behavior at room temperature in previous studies.11 Magnetic properties of INP depend strongly on their size, composition and shape.12, 13, 14 According to the bound magnetic polaron (BMP) model, localized carriers are mediated by oxygen vacancy (Vo) which acts as defect center, and affects the magnetic behavior of material. Furthermore, the magnitude of magnetism can be controlled by the density and constituted of defect centers such as oxygen vacancy.15, 16, 17, 18 Meanwhile, interactions between the nanocrystalline could be found in magnetic nanomaterial, and affect the magnetic behavior of the nanomaterial in various aspects.19, 20, 21 Thus, it is important to understand the influence caused by generated structural defects on the magnetic behavior of α-Fe2O3 nanomaterials.

Doping with transition metal ion into α-Fe2O3, is an effective approach to introducing structural vacancy defects and influencing the magnetic behavior of nanomaterial. When Cu2+, Zn2+, Eu2+ cations create oxygen vacancies and magneto-crystalline anisotropic effects for α-Fe2O3, Mr and Hc of the α-Fe2O3 nanoparticles increase significantly.22,23 Nevertheless, for one aspect, structural oxygen vacancy defects could be produced by crystal disorder with in situ formation of secondary nanocrystalline24; For another aspect, mesoscopic and uncontrollable structural defects could be introduced by of self-assembled preparation approach.19,20,25, 26, 27 Thus, in situ introducing secondary nanocrystalline by self-assembled method could be a potential and active approach to influencing the magnetic behavior of α-Fe2O3 system. Y2O3 nanoparticle is an excellent oxygen-activated material, which provide a lot of oxygen vacancies on its surface.28 Because the Y-O vacancy pair of Y2O3 observably reduces the vacancy formation energy, more vacancies can be drawn by formation of the Y-O vacancy pair and constitute stable vacancy clusters. Therefore, Y2O3 can accommodate high concentration of vacancies.29 Thus, Y2O3 nanoparticle is a favorable candidate which can act as a secondary nanocrystalline introducing additional oxygen vacancies to Fe2O3 nanomaterials.

The aim of this work is to investigate the formation of crystal disorder generated by Fe2O3 with in situ Y2O3 as secondary nanocrystalline via self-assembly method, and the effect of oxygen vacancy defect produced by crystal disorder on collective room temperature magnetic properties of Fe-Y oxide system. To achieve this aim, three type nanomaterials: Fe-Y (Fe: Y-6.5) composite oxide nano-cluster (FYONC), Fe2O3 nanoparticle, and Y2O3 nanoparticle were synthesized in the same self-assembly method, respectively, and the nano oxides were characterized by HR-TEM, SEM, XRD, XPS, VSM and EPR.

Section snippets

Preparation of materials

All the chemicals and reagents in this work were used directly as purchased and used without further purification, except for water that was deionized and used as a solvent.

FYONC precursor was synthesized by reverse precipitation method with Fe(NO3)3·6H2O (0.45 mol/L, AR), Y(NO3)3·6H2O (0.07 mol/L, AR) as ferrum and yttrium source, NH4HCO3 (1.25 mol/L, AR) as precipitant, and cetyl trimethyl ammonium bromide (0.011 mol/L, AR) as surfactant. Fe2O3 precursor was synthesized by reverse

Results and discussion

The microstructural morphology of nano-oxide was scanned by FE-SEM. Fig. 1(a, b) exhibit the particle-like cluster morphology of FYONC sample which was annealed from precursor at 823 K, and the particle-like cluster had a uniform size distribution of 100 nm, when cluster aggregated with ∼20 nm particle. Fig. 1(c, d) exhibit the particle morphology of Fe2O3 sample which were annealed from precursor at 823 K, and the particle-like cluster had a uniform size distribution of 20–50 nm. Fig. 1(a, b)

Conclusions

We synthesized Fe-Y (Fe: Y-6.5) composite oxide nanocluster (FYONC) with high intensity of oxygen vacancies in easy morphology control and low-cost self-assembling process. The formation mechanism of structural property and ferromagnetic behavior was studied. The self-assembled FYONC exhibits good room-temperature ferromagnetism. The presence of ferromagnetism in samples can be clarified by the defect mediated mechanism of BMP model, when Fe3+–Vo–Y3+ as defect center forms in the lattice of

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    Foundation item: Project supported by National Key R&D Program of China (2017YFB0305801) and the Joint Funds of NSFC-Liaoning (U1508213).

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