Xueyun Zhou

Jiujiang University, Qianjin, Zhejiang Sheng, China

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Publications (26)48.37 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Ce9Fe91 films with different thickness were fabricated by a rf magnetron sputtering method. The critical thickness tc for spin reorientation transition has been determined to be approximately 90 nm using the stripe domain model and magnetic force microscope. Above tc, the films exhibit Bloch stripe domain structure and a superhigh resonance frequency at 6 GHz is found for the ∥ stripe configuration. However, below tc, the films possess an in-plane uniaxial anisotropy caused by order interface tension between the film and substrate, and the resonance frequency breaks through the Snoek limit.
    Physica Status Solidi (A) Applications and Materials 08/2014; · 1.53 Impact Factor
  • Dongsheng Yao, Xueyun Zhou, Shihui Ge
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    ABSTRACT: Raman scattering has been used to study the influence of cobalt, an effective dopant to obtain SrTiO3 magnetic oxide, on the lattice dynamics of SrTiO3. It is found that Co doping increases the lattice defects and induces a Raman vibration mode of 690cm−1. On the other hand, the ferromagnetism dependence on the x and annealing temperature was clearly and coherently observed in SrTi1−xCoxO3 (x=0, 0.01, 0.03 and 0.05) nanoparticles. It is found that the ferromagnetism of SrTi1−xCoxO3 nanoparticles is weakly related to crystal deformation and oxygen vacancies in SrTiO3. So, F-center model can explain the origin of the ferromagnetism in the prepared Co-doped SrTiO3 samples. At the same time, the finding of large room-temperature ferromagnetism (1.6emu/g) in this system would stimulate further interest in the area of more complicated ternary oxides.
    Applied Surface Science 01/2011; 257(22):9233-9236. · 2.54 Impact Factor
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    ABSTRACT: Excellent soft magnetic properties and appropriate uniaxial magnetic anisotropy field have been achieved in a wide metal volume fraction (x) range for as-deposited ( Fe <sub>65</sub> Co <sub>35</sub>)<sub>x</sub>( SiO <sub>2</sub>)<sub>1-x</sub> granular films fabricated by magnetron sputtering. With decreasing x from 0.86 to 0.53, the coercive force of easy axis H <sub> ce </sub> decreases clearly and shows the minimum value ( H <sub> ce </sub>=0.85 Oe ) at x=0.53 . More importantly, not only nanoscale grain-size D contributing to small coercivity is proved, but also a D<sup>3</sup> dependence of H <sub> ce </sub> is observed in the range of 0.53<x<0.86 , which is similar to the results of Suzuki etal reported for nanocrystalline alloys. Based on the random anisotropy model of Suzuki and Herzer, the grain-size D dependence of coercivity H <sub> ce </sub> in our metal-insulator granular film system was analyzed. Analyze results indicate that strong coherent uniaxial anisotropy which dominates over the random anisotropy <K<sub>1</sub>> of magnetic grains obtained by the random anisotropy model can be responsible for the D<sup>3</sup> dependence of the coercivity H <sub> ce </sub> . In addition, in the range of 0.42<x<0.53 , H <sub> ce </sub> (as well as H <sub> eh </sub> ) increases with increasing x and then the - D dependence of H <sub> ce </sub> deviates greatly from the D<sup>3</sup> law, which is ascribed to the decrease in intergranular exchange coupling due to the increase in SiO <sub>2</sub> insulator layer.
    Journal of Applied Physics 05/2010; · 2.21 Impact Factor
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    ABSTRACT: The electrical and ferromagnetic properties of (In0.9−xTbxSn0.1)2O3 and (In0.99−yTb0.01Sny)2O3 films fabricated by sol–gel method have been investigated. All the films show room temperature ferromagnetism. The magnetic moment per Tb ion of (In0.9−xTbxSn0.1)2O3 films first increases and then decreases with the increasing Tb content. The variation of conductivity with Tb content is coincident with that of the magnetic moment. Furthermore, the conductivity and magnetic moment variations with Sn content y in (In0.99−yTb0.01Sny)2O3 films also have the similar trend. These results imply that the ferromagnetism may originate from the carrier-mediated mechanism.
    Applied Surface Science 01/2010; 256(20):6013-6017. · 2.54 Impact Factor
  • Dongsheng Yao, Shihui Ge, Xueyun Zhou
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    ABSTRACT: A series of (Fe65Co35)x(SiO2)(1−x) nano-granular films with different volume fraction x are fabricated by magnetron co-sputtering technique. The structure, magnetic and high frequency properties are investigated systematically by using X-ray diffraction, transmission electronic microscopy, vibrating sample magnetometer, resistivity and complex permeability measurements. Study results indicate that the films consist of Fe65Co35 magnetic metal particles uniformly embedded in an insulating SiO2 matrix. (Fe65Co35)x(SiO2)(1−x) films exhibit large magnetic anisotropy field Hk and excellent soft magnetic properties in a wide x range from 0.80 to 0.52 with coercivity Hc smaller than 18 Oe. A minimum Hc value of 7.8 Oe is obtained for the sample with x=0.60 whose electrical resistivity ρ reaches 2220 μ Ω cm and the magnetic anisotropy field Hk is as high as 185 Oe. Especially, for the result of complex permeability measurement of the samples, very high ferromagnetic resonance (FMR) frequency is obtained. For the typical sample with x=0.60, the FMR frequency reaches 4.9 GHz, implying a very high cut-off frequency for high frequency applications, and the real part μ′ of its complex permeability exceeds 60 below 3.8 GHz while the imaginary part μ″ is very small until f>2.0 GHz. These good high frequency properties imply that (Fe65Co35)x(SiO2)(1−x) granular films are promising for applications in high frequency range. The good soft magnetic properties are ascribed to the exchange coupling among magnetic particles, which is discussed in this paper.
    Physica B Condensed Matter 01/2010; 405(5):1321-1324. · 1.28 Impact Factor
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    ABSTRACT: (Fe)0.73(Sm2O3)0.27 nano-granular films with thicknesses varying from 46nm to 220nm were fabricated by a RF magnetron sputtering method. The static and dynamic magnetic properties of these films on thickness dependence have been investigated in detail. High-resolution transmission electron micrograph shows that the films consist of Fe granules and crystalline Sm2O3 matrix. The results reveal that there is a critical thickness tc around 65nm in the (Fe)0.73(Sm2O3)0.27 nano-granular films. Below tc, the films possess an in-plane uniaxial anisotropy and lower Hc. Above tc, the films exhibit a small perpendicular anisotropy, higher Hc and stripe domains, and the stripe period increases with increasing film thickness. The dynamic permeability spectra measured over the frequency range of 0.1–7GHz display one resonance peak for all thicknesses. The spectrum of the film with thickness below tc can be ascribed to the uniform coherent spin procession. Above tc, the increasing film thickness leads to an monotonously increase of the permeability (imaginary part), and a shift of resonance frequency towards the low frequency and a decrease of resonance linewidth for the films with thickness larger than 120nm.
    Journal of Alloys and Compounds 01/2010; 506(1):109-114. · 2.73 Impact Factor
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    ABSTRACT: A series of (Fe<sub>65</sub>Co<sub>35</sub>)x(B<sub>2</sub>O<sub>3</sub>>)<sub>1-x</sub> nano-granular films with different metal volume fractions x were fabricated by magnetron sputtering. High resolution transmission electron micrographs show that the film consists of bcc Fe<sub>65</sub>Co<sub>35</sub> particles uniformly embedded in an amorphous insulating B<sub>2</sub>O<sub>3</sub> matrix with particle size around a few nanometers. With the decrease in x from 0.66 to 0.55, the films exhibit coercivity H<sub>C</sub> not exceeding 16 Oe, along with high resistivity. Especially for the sample with x=0.61, coercivities in hard and easy axes are 3 and 13.4 Oe, respectively, 4piM<sub>S</sub>=12.5 kG, and rho reaches 2.38times10<sup>3</sup> muOmegaldrcm. The dependence of complex permeability mu = mu'-jmu'' on frequency shows that the real part mu' is more than 170 below 1.5 GHz and ferromagnetic resonance frequency reaches 2.65 GHz. The good soft magnetic property is ascribed to the exchange coupling among magnetic granules. The investigation of the DeltaM-H curve evidences the existence of this inter-granule interaction.
    IEEE Transactions on Magnetics 07/2009; · 1.42 Impact Factor
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    ABSTRACT: Sn1−xMnxO2 (x ≤ 0.11) thin films were fabricated by sol–gel and spin-coated method on Si (1 1 1) substrate. X-ray diffraction revealed that single-phase rutile polycrystalline structure was obtained for x up to about 0.078. Evolution of the lattice parameters and X-ray photoelectron spectroscopy studies confirmed the incorporation of Mn3+ cations into rutile SnO2 lattice. Optical transmission studies show that the band gap energy (Eg) broadens with the increasing of Mn content. Magnetic measurements revealed that all samples exhibit room temperature ferromagnetism (RTFM), which is identified as an intrinsic characteristic. Interestingly, the magnetic moment per Mn atom decreases with the increasing Mn content. The origin of RTFM can be interpreted in terms of the bound magnetic polaron model.
    Applied Surface Science 06/2009; 255(18):7981–7984. · 2.54 Impact Factor
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    ABSTRACT: Zn1−xNixO (x=0, 0.05, and 0.1) nanorod arrays were prepared by hydrothermal method. Morphology and structure analysis indicate that the nanorods have single-crystalline wurtzite structure, and no metallic Ni or NiO phase exists. Room temperature ferromagnetism (RTFM) was observed in the Zn0.9Ni0.1O nanorods. In addtion, photoluminescence spectra of Zn1−xNixO (x=0, 0.05, 0.1 and 0.2) samples exhibit near band edge UV emissions and orange-red emissions. And the orange-red emission is confirmed to have originated from the interstitial oxygen defects.
    Journal of Alloys and Compounds 01/2009; 470(1):47-50. · 2.73 Impact Factor
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    ABSTRACT: The structure and magnetic properties of Sn <sub>1-x</sub> V <sub>x</sub> O <sub>2</sub> (x=0.02–0.22) thin films fabricated on Si (111) substrate using a sol-gel method and spin coating technique have been investigated. All the samples have pure rutile polycrystalline structure and exhibit room temperature ferromagnetism. The magnetic moment per V reaches 2.92μ<sub>B</sub> for the Sn <sub>0.98</sub> V <sub>0.02</sub> O <sub>2</sub> film and drops rapidly as V content is increased. X-ray photoelectron spectroscopy study reveals that vanadium is in V <sup>4+</sup> chemical state. Various annealing treatments were performed to explore the origin of the ferromagnetism. It is found that the ferromagnetism of Sn <sub>0.98</sub> V <sub>0.02</sub> O <sub>2</sub> film disappears after annealing in a rich-oxygen atmosphere and occurs again after annealing in a low vacuum condition. Furthermore, an annealing in Sn vapor leads to the decrease in ferromagnetism. These results confirm that the oxygen vacancies play a critical role in introducing ferromagnetism of Sn <sub>1-x</sub> V <sub>x</sub> O <sub>2</sub> films; therefore, the origin of the ferromagnetism in our samples can be understood in the framework of the bound magnetic polaron model.
    Journal of Applied Physics 01/2009; · 2.21 Impact Factor
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    ABSTRACT: Diluted magnetic semiconductors (DMSs) have been intensively studied recently due to the application in spintronics. Sn1−xCrxO2 thin films with x=0.016–0.18 were fabricated by sol–gel method and spin-coated on Si (111) substrates. X-ray diffraction (XRD) patterns show that all samples have pure rutile structure, and no Cr clusters or Cr oxides were detected. X-ray photoelectron spectrum (XPS) reveals that Cr ions in our samples have a chemical valence of 3+. The magnetic measurements were performed by vibrating sample magnetometer. All samples exhibit room temperature ferromagnetism (RTFM) and the magnetic moment per Cr ion drops rapidly with the increase of Cr content because antiferromagnetic super-exchange interaction takes place within the neighbour Cr3+ ions through O2− ions for the samples with higher Cr doping. The origin of room temperature ferromagnetism (RTFM) has been interpreted in terms of a bound magnetic polaron (BMP) model. The further annealing experiment results show that the oxygen vacancies play a crucial role in producing ferromagnetism in Sn1−xCrxO2 films.
    Journal of Alloys and Compounds 01/2009; 475(1):60-63. · 2.73 Impact Factor
  • Applied Surface Science 01/2009; 255(18):7981-7984. · 2.54 Impact Factor
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    ABSTRACT: To investigate whether oxygen vacancies play an important role in the origin of ferromagnetism in undoped nanosized metal oxides, CeO<sub>2-x</sub> nanopowders were prepared using sol-gel method, and anneal studies under various atmosphere were carried out on samples. The room temperature ferromagnetism in the samples was enhanced after being hydrogenated at 320degC in a forming gas (Ar90%+H<sub>2</sub>10%) and weakened after reheating the sample in air. These variations of the magnetization have been observed for additional cycles by alternately heating in air and Ar/H<sub>2</sub>. Raman spectroscopy study reveals that hydrogenation leads an increase in the amount of oxygen vacancies in these H<sub>2</sub> -annealed samples. It is demonstrated that this observed ferromagnetism is intrinsic and affected by the oxygen vacancies which are produced by hydrogenation but reduced by oxidation. A correlation of ferromagnetism with concentration of oxygen vacancies is obtained in CeO<sub>2-x</sub> nanopowders.
    IEEE Transactions on Magnetics 12/2008; · 1.42 Impact Factor
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    ABSTRACT: We have studied room-temperature ferromagnetism (RTFM) in Sn<sub>1</sub> <sub>-</sub> <sub>x</sub>Co<sub>x</sub>O<sub>2</sub> powders and films fabricated by the sol-gel method. Our X-ray diffraction, high-resolution transmission microscopy, and X-ray photoelectron spectroscopy results show that all the samples have a pure rutile structure, and Co ions have a chemical valence of 2+. In addition, the magnetic moment per Co ion drops rapidly with the increase of Co content. Interestingly, Sn <sub>1</sub> <sub>-</sub> <sub>x</sub>Co <sub>x</sub>O <sub>2</sub> films spin-coated on a Si (111) substrate have much larger magnetic moment than powder samples, because film samples have larger domain volumes, which may induce stronger long-range magnetic exchange coupling.
    IEEE Transactions on Magnetics 11/2008; · 1.42 Impact Factor
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    ABSTRACT: The Co-doped ZnO powders were synthesized by sol–gel method, and treated at different temperatures (673–873 K) in the presence or absence of NH3 atmosphere for 0.5 and 2 h, respectively. X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) show that better crystal structure can cause larger ferromagnetism and the second phase (Co3O4) is the reason for saturation magnetization decrease of the sample sintered at higher temperature in air. XPS and nuclear magnetic resonance (NMR) prove the existence of Co2+ ions in the Zn0.9Co0.1O and the absence of Co clusters, indicating intrinsic ferromagnetism of the samples treated in air. However, strong ferromagnetism of the samples annealed in NH3 is ascribed to cobalt nitride formed during annealing.
    Physica B Condensed Matter 09/2008; 403(18):3336–3339. · 1.28 Impact Factor
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    ABSTRACT: Co-doped Sn O <sub>2</sub> thin films were fabricated by sol-gel method. All the samples have pure rutile polycrystalline structure and exhibit room temperature ferromagnetism (RTFM). Sn <sub>1-x</sub> Co <sub>x</sub> O <sub>2-δ</sub> films spin coated on Si (111) substrate have larger magnetic moment than those on Si (amorphous) substrate. X-ray photoelectron spectra reveal that cobalt exists as Co <sup>2+</sup> in samples and <sup>57</sup> Co spin-echo nuclear magnetic resonance experiment did not find Co clusters. Interestingly, the magnetic moment per Co atom decreases with the increase in Co content. The results of the annealing at oxidizing and vacuum atmospheres show that oxygen vacancies play a crucial role in producing ferromagnetism, implying that the origin of RTFM can be understood by a bound magnetic polaron model.
    Journal of Applied Physics 08/2008; · 2.21 Impact Factor
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    ABSTRACT: ( Fe <sub>65</sub> Co <sub>35</sub>)<sub>x</sub>( SiO <sub>2</sub>)<sub>1-x</sub> granular films with various volume fraction (x) of Fe <sub>65</sub> Co <sub>35</sub> alloy were fabricated by magnetron sputtering, and the interaction between granules was explored by δM(H) plots. Research results show that δM(H) is positive for the samples in a wide range of 0.42≪x≪0.86 , indicating that exchange coupling exists among granules. Further research revels that δM(H)<sub> max </sub> increases gradually with decreasing x , reaching the maximum value at x=0.57 , then decreases after x≪0.57 . Since δM(H)<sub> max </sub> can effectively reflect the intensity of exchange coupling, the intergranular exchange coupling also increases first, then decreases as x decreases. The microstructure is analyzed with help of the high-resolution transmission electron microscopy, and results show that the variation of exchange coupling with metal volume fraction x is dominated by the change of microstructure of samples. The microstructure of the sample with x=0.57 satisfy the optimization for realizing exchange coupling, leading to excellent soft magnetic properties.
    Journal of Applied Physics 08/2008; · 2.21 Impact Factor
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    ABSTRACT: A series of ( Fe <sub>65</sub> Co <sub>35</sub>)<sub>x</sub>( MgF <sub>2</sub>)<sub>1-x</sub> films with different metal volume fraction x was fabricated by magnetron sputtering. High resolution transmission electron micrographs show that the film consists of bcc Fe <sub>65</sub> Co <sub>35</sub> particles uniformly embedded in an amorphous insulating MgF <sub>2</sub> matrix with particle size around a few nanometers. The research results reveal that high sputtering power (200 W) leads to the occurrence of FeCo fluorides, which are harmful to soft magnetic properties. For the samples fabricated using 60 W, good soft magnetic properties have been obtained in a wide x range (x=0.9-0.55) , with H<sub>c</sub> not exceeding 10 Oe, along with high resistivity. In particular, for the sample with x=0.62 , coercivities in hard and easy axes are 0.6 and 7.2 Oe, respectively, 4πM<sub>s</sub>=11.5 kG , and ρ reaches 2.53 m Ω  cm . The dependence of complex permeability μ=μ<sup>′</sup>-jμ<sup>″</sup> on frequency shows that the real part μ<sup>′</sup> is more than 100 below 1.0 GHz and ferromagnetic resonance frequency reaches 2.35 GHz. The excellent soft magnetic property is ascribed to the exchange coupling among magnetic granules.
    Journal of Applied Physics 07/2008; · 2.21 Impact Factor
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    ABSTRACT: Sn1−xMnxO2 (x ≤ 0.11) thin films spin-coated on Si (1 1 1) substrate were fabricated by sol–gel method. X-ray diffraction revealed that single-phase rutile polycrystalline structure was obtained for x up to about 0.078. Evolution of the lattice parameters and X-ray photoelectron spectroscopy studies confirmed the incorporation of Mn3+ cations into rutile SnO2 lattice. Magnetic measurements revealed that all Sn1−xMnxO2 thin films exhibit ferromagnetism at room temperature, which is identified as an intrinsic characteristic. Magnetization data showed that the average magnetic moment per Mn atom decreased and the coercivity increases with increasing Mn content. The origin of room temperature ferromagnetism can be understood in terms of the percolation of the bound magnetic polaron. Our experimental results prove that the sol–gel method is an effective method for fabrication of transition metal doped SnO2 nanostructures with room temperature ferromagnetism by chemical synthesis.
    Applied Surface Science 01/2008; · 2.54 Impact Factor
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    ABSTRACT: A series of (Fe65Co35±2)x–(SiO1.7±0.2)1−x nano-granular films with various metal volume fractions (x) were fabricated by rf sputtering. In a wide range, excellent soft magnetic properties have been achieved. In the x range from 0.7 to 0.48, the films exhibit small coercivity Hc not exceeding 4Oe and high electrical resistivity ρ up to 1.15×104μΩcm. And a minimum Hc value of 1.65Oe was obtained for the sample of x=0.57 with ρ=2.86×103μΩcm. At a frequency lower than 2.0GHz, the real part μ′ of complex permeability of this sample is more than 170 and the FMR frequency is as high as 2.6GHz, implying a high cut-off frequency for high frequency applications. With decreasing Fe65Co35±2 volume fraction, the resistivity of films increases remarkably and the grain size decreases obviously. At the same time, the coercivity Hc decreases with grain size decreasing, which is consistent with the conclusion resulted from random anisotropy model quoted by Herzer. Study on Henkel plots shows that intergranular ferromagnetic exchange coupling exists among grains and is important for realizing soft magnetic properties.
    Applied Surface Science 01/2008; 254(8):2556-2561. · 2.54 Impact Factor

Publication Stats

53 Citations
48.37 Total Impact Points

Institutions

  • 2010–2011
    • Jiujiang University
      Qianjin, Zhejiang Sheng, China
  • 2008–2009
    • Lanzhou University
      Kao-lan-hsien, Gansu Sheng, China
    • Northeast Institute of Geography and Agroecology
      • State Key Laboratory of Magnetism
      Beijing, Beijing Shi, China