Y. Q. Ma

Anhui University, Luchow, Anhui Sheng, China

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Publications (63)169.69 Total impact

  • S. Huang · Y.Q. Ma · S.T. Xu ·
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    ABSTRACT: Well-dispersed uniform cobalt ferrite nanoparticles were synthesized by thermal decomposition of a metal-organic salt in organic solvent with a high boiling point, and characterized by XRD, TEM and detailed magnetic measurements. The moments of CoFe2O4 nanoparticles consist of the core and canted surface moments below 200 K, and the exchange-coupling between the surface and core spins enhanced the remanence (Mr) to saturation (Ms) magnetization ratio (Mr/Ms) at the temperature of 10 K. Interestingly, the anomalous memory effect was observed in a broad temperature range which can be attributed to the relaxation of surface spins below 200 K and the one from the moments of magnetically ordered entity larger than one particle above 200 K.
    Solid State Communications 12/2015; 224:1-4. DOI:10.1016/j.ssc.2015.09.013 · 1.90 Impact Factor
  • X. Sun · Y.Q. Ma · Y.F. Xu · S.T. Xu · B.Q. Geng · Z.X. Dai · G.H. Zheng ·
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    ABSTRACT: The dispersive and uniform CoFe2O4 nanoparticles were synthesized by thermal decomposition of metal organic salt in organic solvent with high boiling point, and subsequently reduced in H2 ambient for 1.5, 4 and 8 h to obtain the CoFe2O4/CoFe2 composite. The M(H) loops of all composites were measured at 10, 50, 100, 150, 200, 250, 300 and 390 K, respectively. The jumps around the zero magnetic field in M(H) loops below 200 K signify that no exchange-coupling takes place between soft and hard species. At 10 K, the maximum Hc and Mr/Ms ratio are 16 kOe and 0.81 for the sample reduced for 1.5 h, the much larger value than that previously observed. When the measuring temperature increases, the Hc value monotonously decreases to 1.8, 1.7, 1.2 kOe, and correspondingly the Mr/Ms ratio decreases to 0.55, 0.45 and 0.40 at T = 300 K for samples reduced for 1.5, 4 and 8 h, respectively; these higher values at room temperature has not been obtained previously in CoFe2O4/CoFe2 composites as far as we know. We suggest that it is important to keep high anisotropy and weak dipolar interaction for improving Hc and Mr/Ms and that the Mr/Ms will be further improved if the exchange coupling was really realized between soft and hard magnets. Further investigations are in process.
    Journal of Alloys and Compounds 10/2015; 645. DOI:10.1016/j.jallcom.2015.05.009 · 3.00 Impact Factor
  • X. Sun · Y.Q. Ma · S.T. Xu · Y.F. Xu · B.Q. Geng ·
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    ABSTRACT: Abstract Well-dispersed uniform NiFe2O4 nanoparticles (NPs) with an average particle size of 15.4 nm were synthesized by thermal decomposition of a metal-organic salt, and then were diluted in a SiO2 matrix via a sol-gel method with different concentration. The magnetization (M) dependence of NiFe2O4/SiO2 on the temperature (T) and on the applied magnetic field (H) was systematically characterized by the Quantum Design superconducting quantum interference device (SQUID) PPMS system. The results of M ~ H/T divide the magnetic properties between 10 K and 300 K into two regions: the low temperature blocked-particle regime below the blocking temperature TB and the interacting superparamagnetic (ISP) regime above TB. In the ISP regime, all samples deviate from the ideal Langevin superparamagnetic behavior due to the effective anisotropy induced by the stress, surface spins and interparticle dipolar interaction. The Raman spectra indicate that the stress in all samples exhibits the vibration behavior, which leads to the effective anisotropy and hence coercivity vibration.
  • B.Q. Geng · Y.Q. Ma · S.T. Xu · Y.F. Xu · X. Sun · Z.X. Dai · G.H. Zheng ·

  • B.Q. Geng · Y.Q. Ma · Y.F. Xu · S.T. Xu · X. Sun · G.H. Zheng · Z.X. Dai ·
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    ABSTRACT: In order to clarify the intrinsic reason for the smaller remanence (Mr)-to-saturation (Ms) magnetization ratio Mr/Ms than that expected by the Stoner–Wohlfarth model in CoFe2O4/CoFe2 nanoparticles in the previous report, we first prepared well-dispersed CoFe2O4 nanoparticles, and then they were diluted in the SiO2 matrix followed by reduction in H2 as far as possible to exclude or reduce disadvantageous variables (such as the growth and aggregation of particles and the exchange coupling between soft magnetic particles in the process of reducing) affecting magnetic properties. Such an idea has not been taken into account before to our knowledge. The analyses on the magnetic results indicate that the CoFe2O4/CoFe2 nanoparticles herein reported are a pure dipolar system, in which the coercivity (Hc) and Mr/Ms ratio are very sensitive to the anisotropy and the strength of dipolar interaction. These results signify that it is important to maintain the CoFe2O4/CoFe2 nanoparticles with higher anisotropy and weaker dipolar interaction for improving Mr/Ms and Hc. This suggestion was further confirmed by our another result wherein an Mr/Ms value of 0.64 was obtained even though no exchange coupling was observed in the CoFe2O4/CoFe2 nanoparticles, and further work is in process. Graphical abstract: Numerous efforts have devoted to improve the values of Ms and Mr/Ms by compositing hard CoFe2O4 (CFO) ferrite with soft CoFe2 (CF) alloy, which unfortunately give the low Mr/Ms value (<0.5) even in presence of the exchange coupling. Key issues involve the preparation of CFO/CF composite. Previously the preparation of CFO/CF undergoes the synthesis of CFO and the subsequent reducing in the H2 ambient, as shown in Figure (a), while in this work well dispersed CFO nanoparticles were first prepared , and then diluted in the SiO2 matrix followed by reducing in H2 to exclude or reduce disadvantageous variables, such as the growth and aggregation of particles and the exchange coupling between soft magnetic particles in the process of reducing, as shown in Figure (b). Our results suggest that higher anisotropy and weaker dipolar interaction favor the larger Mr/Ms value, as shown in Figure (c).[InlineMediaObject not available: see fulltext.]
    Journal of Nanoparticle Research 07/2015; 17(7). DOI:10.1007/s11051-015-3087-1 · 2.18 Impact Factor
  • S T Xu · Y Q Ma · G H Zheng · Z X Dai ·
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    ABSTRACT: Well-dispersed uniform cobalt ferrite nanoparticles were synthesized by thermal decomposition of a metal-organic salt in organic solvent with a high boiling point. Some of the nanoparticles were diluted in a SiO2 matrix and then the undiluted and diluted samples were characterized and their magnetic behavior explored. The undiluted and diluted samples exhibited maximum coercivity Hc of 23 817 and 15 056 Oe at 10 K, respectively, which are the highest values reported to date, and the corresponding ratios of remanence (Mr) to saturation (Ms) magnetization (Mr/Ms) were as high as 0.85 and 0.76, respectively. Interestingly, the magnetic properties of the samples changed at 200 K, which was observed in magnetic hysteresis M(H) loops and zero-field cooling curves as well as the temperature dependence of Hc, Mr/Ms, anisotropy, dipolar field, and the magnetic grain size. Below 200 K, both samples have large effective anisotropy, which arises from the surface spins, resulting in large Hc and Mr/Ms. Above 200 K, the effective anisotropy decreases because there is no contribution from surface spins, while the dipolar interaction increases, resulting in small Hc and Mr/Ms. Our results indicate that strong anisotropy and weak dipolar interaction tend to increase Hc and Mr/Ms, and also clarify that the jumps around H = 0 in M(H) loops can be attributed to the reorientation of surface spins. This work exposes the underlying mechanism in nanoscale magnetic systems, which should lead to improved magnetic performance.
    Nanoscale 03/2015; 7(15). DOI:10.1039/c5nr00582e · 7.39 Impact Factor
  • Y.F. Xu · Y.Q. Ma · S. T. Xu · F. L. Zan · G. H. Zheng · Z. X. Dai ·
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    ABSTRACT: By controlling the phase distribution and interfacial conditions, the composites of (soft)Ni0.6Zn0.4Fe2O4/(hard) SrFe12O19 ferrites were prepared with different mass ratios fs of soft magnet. The coercivity mechanism was analyzed according to the theory for melt-spun and sintered magnets. Using the modified Brown׳s equation, we derive the exchange coupling coefficient αex that can be quantificationally expressed as αex=α0 exp(−fs/f0) with α0 and f0 being constants, which has not been reported before as far as we know.
    Materials Letters 09/2014; 131:203-205. DOI:10.1016/j.matlet.2014.05.187 · 2.49 Impact Factor
  • Y.F. Xu · Y.Q. Ma · S.T. Xu · F.L. Zan · G.H. Zheng · Z.X. Dai ·
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    ABSTRACT: All samples were synthesized via supercritical (390 degrees C) and low-temperature (190 degrees C) hydrothermal methods followed by annealing at 1000 degrees C, and contained both SrFe12O19 and alpha-Fe2O3 phases as reported in literature. The magnetic properties sensitively depended on the relative content of each phase, which was generally attributed to phase homogeneity and microstructural characteristics in literature as far as we know. In this paper, we observed a double-peak behavior in the curve of irreversible susceptibilities chi(irr) versus an external magnetic field H, which was assigned to the cation vacancies and their distribution. The coercivity of the sample almost changed linearly with the average value of magnetic fields at which the chi(irr) (H) peak located. Therefore, we conclude that the magnetic parameters, at least the coercivity, are mainly determined by cation vacancies which have usually been neglected before in SrFe12O19.
    Materials Research Bulletin 09/2014; 57:13–18. DOI:10.1016/j.materresbull.2014.05.017 · 2.29 Impact Factor
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    ABSTRACT: We investigated the effects of Ag added Sr0.9La0.1TiO3 ceramics prepared via a hydrothermal method and sintering. The results indicate that Ag addition is an efficient way to enhance its thermoelectric properties. The maximum thermoelectric figure-of-merit, ZT, is 0.20 at 955 K for x=0.15 sample.
    Journal of Low Temperature Physics 02/2014; 174(3-4). DOI:10.1007/s10909-013-0965-8 · 1.02 Impact Factor
  • D. Zou · Y.Q. Ma · S. B. Qian · B. T. Huang · G. H. Zheng · Z. X. Dai ·
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    ABSTRACT: Eu3+-doped yttrium borate samples were prepared via a hydrothermal method using borate or tributyl borate as B3+ sources, with and without carbon nanotubes as templates. The morphology of the samples is easily altered by varying the carbon nanotube template, B3+ source and post-annealing treatment. Photoluminescence measurements indicate that the color purity of samples is clearly improved by template-assisted synthesis. Furthermore, with tributyl borate as the B3+ source, CIE coordinates of (0.67, 0.33), very similar to the (0.665, 0.334) coordinates for the commercial red phosphor Y2O2S:Eu3+, can be obtained. Finally, an extra Eu3+-O-2 excitation band is observed for samples made by template-assisted synthesis. The underlying mechanism is discussed in detail. (c) 2013 Elsevier B.V. All rights reserved.
    Journal of Alloys and Compounds 01/2014; 584:471-476. DOI:10.1016/j.jallcom.2013.09.065 · 3.00 Impact Factor
  • F. L. Zan · Y.Q. Ma · Q. Ma · Y.F. Xu · Z. X. Dai · G. H. Zheng ·
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    ABSTRACT: Precursor powders, containing mainly CoFe2O4 and Co(OH)(2), have been hydrothermally synthesized and then annealed in either air to obtain a ferrimagnetic CoFe2O4/antiferromagnetic Co3O4 composite, or H-2 ambient to reduce the precursors to Co/Fe alloy. Giant exchange bias (H-E = 2233 Oe) and significant coercivity enhancement (H-C = 10153 Oe) were observed below the Neel temperature of Co3O4 in samples annealed in air, resulting from the exchange coupling between ferrimagnetic CoFe2O4 and antiferromagnetic Co3O4 phases. By reducing precursor powders in H-2 ambient, a solid solution of Fe and Co (Co3Fe7) was obtained; the average atomic moment for Co3Fe7 is 2.4 mu(B), larger than that of separated Fe or Co. We also show that the magnetic parameters can be sensitively tuned by varying processing conditions, which may be useful for obtaining the desired magnetic performance. (c) 2013 Elsevier B.V. All rights reserved.
    Journal of Alloys and Compounds 12/2013; 581:263-269. DOI:10.1016/j.jallcom.2013.07.062 · 3.00 Impact Factor
  • D. Zou · Y.Q. Ma · S.B. Qian · G.H. Zheng · Z.X. Dai · G. Li · M.Z. Wu ·
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    ABSTRACT: YBO3:Eu3+ phosphors with different morphologies such as flower-like, spherical-like and cake-like have been hydrothermally synthesized without any additives by simply adjusting the B3+ sources, stirring speeds and initial solution pH values. During the hydrothermal reaction, stirring with suitable speed can reduce particle size and obtain more uniform size distribution. The emission intensity can be distinctly enhanced by stirring and post-annealing due to the micro-structural improvement and better crystallization. Interestingly, the weak acidity (pH = 6) in the initial solution or post-annealing enhances the emission in the wavelength range of visible light, and weakens the emission around 700 nm due to weakened distortion of the outside surroundings of Eu3+, which is useful in Plasma Display Panel (PDP) application.
    Journal of Alloys and Compounds 10/2013; 574:142–148. DOI:10.1016/j.jallcom.2013.04.079 · 3.00 Impact Factor
  • Source
    G. H. Zheng · Z. H. Yuan · Z. X. Dai · H. Q. Wang · H. B. Li · Y. Q. Ma · G. Li ·
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    ABSTRACT: Ruddlesden-Popper (RP) phase (Sr0.9La0.1)3Ti2O7/xAg (x=0, 0.05, 0.10, 0.15) are systematically investigated with regard to their phase composition and thermoelectric transport properties. The XRD results show that all oxide samples are of two phases and they have layered microstructure. The electrical conductivity is found to be increased simultaneously. And the absolute Seebeck coefficient decreases firstly and then increases Ag addition, which leads to (Sr0.9La0.1)3Ti2O7/xAg (x=0.10) sample possesses optimum power factor. The total thermal conductivity lowers with Ag addition. The dimensionless figure of merit, ZT, reaches 0.12 for x=0.10. These results suggest that a proper of metal element Ag addition would be an effective way improving thermoelectric performance of (Sr0.9La0.1)3Ti2O7 system.
    Journal of Low Temperature Physics 06/2013; 173(1-2). DOI:10.1007/s10909-013-0885-7 · 1.02 Impact Factor
  • F.L. Zan · Y.Q. Ma · Q. Ma · G.H. Zheng · Z.X. Dai · M.Z. Wu · G. Li · Z.Q. Sun · X.S. Chen ·
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    ABSTRACT: CoFe2O4/Co0.7Fe0.3 nanocomposite permanent magnets have been synthesized in one step by a hydrothermal method at reaction temperatures of 80, 120, 140, 160 and 180 °C and characterized by XRD, SQUID, SEM, (HR)TEM, and SAED. All samples consisted of octahedral CoFe2O4 particles and spherical-like Co0.7Fe0.3 particles. The maximum magnetization and coercivity were 191 emu/g and 1311 Oe, respectively, values not previously observed for the CoFe2O4/Co0.7Fe0.3 system. This maximum magnetization was attributable to the larger mass ratio of Co0.7Fe0.3 to CoFe2O4, which were in intimate contact. Magnetic dipolar interaction plays a crucial role in magnetic properties and leads to the reduction of the magnetization and the Mr/Ms ratio. The coercivity of all samples exhibited complex variation with reaction temperature and its mechanism may deserve further investigation.
    ChemInform 04/2013; 553:79–85. DOI:10.1016/j.jallcom.2012.11.120
  • F. L. Zan · Y. Q. Ma · Q. Ma · G. H. Zheng · Z. X. Dai · M. Z. Wu · G. Li · Z. Q. Sun · X. S. Chen ·
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    ABSTRACT: The title nanocomposite permanent magnets are hydrothermally synthesized from a mixture of CoCl2, (NH4)2Fe(SO4)2, sodium citrate, NaOH, and H2O (autoclave, 80—180 °C, 24 h).
    ChemInform 04/2013; 44(15):no-no. DOI:10.1002/chin.201315006
  • G. H. Zheng · Z. X. Dai · Y. Q. Dong · F. L. Zan · D. Zou · Y. Q. Ma · G. Li ·

    Material Research Innovations 11/2012; 16(6):438-441. DOI:10.1179/1433075X12Y.0000000039 · 0.83 Impact Factor
  • G.-H. Zheng · Z.-X. Dai · Y.-Q. Dong · Y.-Q. Ma · G. Li ·
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    ABSTRACT: The effects of Al doping at Mn sites in manganites La 0·9Te0·1MnO3 have been studied by preparing the series La0·9Te0·1Mn 1-xAlxO3 (0·05≤x≤0·20). All samples can be indexed by rhombohedral lattice with the space group R3̄C. Upon Al doping, both the Curie temperature TC and magnetisation M are suppressed. The resistivity measurements indicate that there exists a weak metal-insulator transition for the sample with x=0·05, with an increase in the doping level, the metal-insulator transition disappears and the resistivity increases. Thermopower S(T) exhibits a maximum at TS, which is close to TC, for all samples. By fitting the S(T) and ρ(T) curves, it is found that the temperature dependences of both S(T) and ρ(T) in the high temperature paramagnetic region follow the variable range hopping mechanism for all samples. Thermal conductivity k(T) values decrease with the increasing Al doping level. The results are discussed according to the destruction of the Mn2+-O-Mn3+ double exchange interaction and the disorder effect due to the Al doping.
    Material Research Innovations 11/2012; 16(6):400-405. DOI:10.1179/1433075X11Y.0000000061 · 0.83 Impact Factor
  • G. H. Zheng · Z. X. Dai · Y. Q. Dong · Y. Y. Zhang · Y. Q. Ma · H. Zhang · G. Li ·
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    ABSTRACT: Systematical studies of resistivity ρ(T), thermopower S(T), and thermal conduction κ(T) have been performed on the electron-doped manganites La0.9Te0.1Mn1−x Cr(Al) x O3 (0.05≤x≤0.20). The Cr005 and Al005 samples exhibit an insulator-metal transition in the ρ(T) curves, however, other samples present insulating behaviors in the whole measured temperature. The S(T) data increases with decreasing temperature and develop a peak at TSPT_{S}^{P} for all samples, with decreasing temperature further, another characteristic temperature TsmT_{s}^{m} is observed. The fits of ρ(T) and S(T) data in the high temperature region are presented, and the result shows that the electron conduction is governed by the VRH mechanism for Al-doped samples and the SPC mechanism for Cr-doped ones. As to thermal conduction κ(T), it is suggested that it comes from two sides, one is the phonon-phonon scattering due to disorder and the other is the spin-phonon interaction. KeywordsThermoelectric power–Transport mechanism–Thermal conductivity
    Journal of Low Temperature Physics 10/2011; 165(1):43-54. DOI:10.1007/s10909-011-0390-9 · 1.02 Impact Factor
  • G He · Z Q Sun · Y Q Ma · M Z Wu · Y M Liu · S W Shi · G Li · X S Chen · L D Zhang · Z B Fang ·
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    ABSTRACT: Composition dependence of interface control, band alignment and electrical properties of HfTiON/Si grown by sputtering has been studied by spectroscopy ellipsometry (SE), x-ray photoelectron spectroscopy (XPS) and electrical measurement. Analysis from XPS has confirmed that the interfacial layer consisting of silicate and SiOx is formed unavoidably, irrespective of composition ratio. Meanwhile, reduction in band gap and asymmetric band alignment has been detected for HfTiON films with the increase in Ti composition. To meet the requirements of high-k dielectrics with the barrier height of over 1 eV, the incorporation composition ratio needs to be carefully optimized. As a result, improved C–V characteristics and reduced leakage current have been achieved from HfTiON gate dielectric MOS capacitors with optimized composition ratio of Hf:Ti = 1:1, which can be attributed to the reduction in oxygen-related traps and the obtained near-symmetric band alignment relative to Si.
    Semiconductor Science and Technology 09/2011; 26(10):105019. DOI:10.1088/0268-1242/26/10/105019 · 2.19 Impact Factor
  • W.L. Zhu · Y. Q. Ma · C. Zhai · K. Yang · X. Zhang · D.D. Wu · G. Li · G.H. Zheng ·
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    ABSTRACT: Photoluminescence properties of Sr3(VO4)2, Sr2Y2/3−yEuy(VO4)2 and Sr2Y2/3−zSmz(VO4)2 (y, z = 0, 0.1, 0.2, and 0.3) samples have been investigated. The self-activated Sr3(VO4)2 sample shows the activation and emission bands due to the charge transfer transition of VO43-. While Sr2+ is partially substituted by Y3+, Sr2Y2/3 (VO4)2 can be used as the good host material for Eu3+ and Sm3+ activator-ions. The Eu3+ and Sm3+ ions doped Sr2Y2/3(VO4)2 can be effectively excited by the near UV light with wavelengths of 300 nm, and emit red light around 617 and 604 nm, respectively. Specially, for Sr2Y2/3−yEuy(VO4)2, Y3+ substitution quite enhances the emission intensity and quenching concentration of Eu3+. For example, Sr2Y0.56Eu0.1(VO4)2 has higher emission intensity than Sr2.85Eu0.1(VO4)2 without Y3+, and even much higher than Y1−xEuxVO4 which has been extensively used. Our results suggest that Sr2Y2/3−yEuy(VO4)2 samples may be good candidate for a new phosphor to convert the UV pump light into visible wavelength bands.
    Optical Materials 06/2011; 33(8):1162-1166. DOI:10.1016/j.optmat.2011.01.019 · 1.98 Impact Factor

Publication Stats

675 Citations
169.69 Total Impact Points


  • 2006-2015
    • Anhui University
      Luchow, Anhui Sheng, China
    • Chinese Academy of Sciences
      • Key Laboratory of Organic Solids
      Peping, Beijing, China
  • 2004-2006
    • Hefei Institute of Physical Sciences, Chinese Academy of Sciences
      Luchow, Anhui Sheng, China