Liqing Pan

University of Science and Technology, Beijing, Peping, Beijing, China

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Publications (44)69.76 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The structure, magnetic phase transition and martensitic transformation of quinary Ni45Co5(Mn, In, Sn)50 Heusler alloy are investigated systematically. X-ray diffraction reveals that there are two kinds of typical structure in alloys, the martensite phase with tetragonal structure and the austenite with cubic structure. Furthermore, it is found that Mn content plays an important role in the evolution of the crystal structure of quinary alloys, making the structure of alloys transform the cubic phase to tetragonal with increasing Mn content, and the threshold of structure transformation is about the Mn content of 35%. The temperature dependence of magnetization indicates that the tetragonal phase usually exhibits a low magnetization, while the cubic corresponds to a high magnetization. Particularly, the strong coupling between magnetism and structure occurs in Ni45Co5Mn40InxSn10−x alloys, and the alloys exhibit a large magnetic entropy change of 22.5 J kg−1 K−1 in martensitic transformation, making it a good candidate for magnetic refrigeration materials.
    Journal of Alloys and Compounds 12/2014; 615:316–321. · 2.73 Impact Factor
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    ABSTRACT: We report that by heating samples the critical current density for magnetization reversal (Jc) in a single perpendicularly magnetized layer can be decreased from 2.6 × 107 A/cm2 to about 1 × 106 A/cm2 for a temperature increase of 143 K. The nonlinear dependence of Jc on the perpendicular anisotropy field indicates that the coherent magnetic switching model cannot fully explain the current-induced perpendicular switching. By considering the current-induced domain nucleation and expansion during switching, we conclude that Jc also depends on current-induced domain behavior. Moreover, by reversing the heat flow direction, we demonstrate that the thermal related spin transfer torques have little influence on the thermally assisted magnetic switching.
    Applied Physics Letters 01/2014; 105(2):022407-022407-4. · 3.52 Impact Factor
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    ABSTRACT: BaTiO3 and BaTi1-xMxO3 (M=Co, Fe) nanocrystals were prepared by hydrothermal method. X-ray diffraction analysis indicated that all of the samples were of single-phase with tetragonal perovskite structure. The BaTiO3 prepared exhibited weak ferromagnetism rather than diamagnetism, probably due to the oxygen vacancies at the surface. Paramagnetism was observed for all BaTi1-xCoxO3 samples with 0.05≤x≤0.25. The Curie-Weiss fit revealed the paramagnetic moment per Co ion were 4.09 μB, 4.12 μB, and 4.36 μB for x=0.15, 0.20, and 0.25 respectively. Room temperature hysteresis loops of the Fe-doped BaTiO3 samples were observed at the doping level x between 0.2 and 0.5. The saturation magnetization firstly increased with increasing Fe content, but gradually decreased. The divergence was observed in the temperature dependence of the field cooling (FC) and zero-FC (ZFC) magnetization curves, indicating a spin-glass behavior arising from micromagnetic state, i.e. the mixing of ferromagnetic, and antiferromagnetic phases. The observed ferromagnetism may originate from the coupling between the secondary-nearest Fe ions and the antiferromagnetism may be due to the coupling between the nearest Fe ions. The ferromagnetic coupling competes with the antiferromagnetic coupling. Therefore, the ferromagnetic properties are predominant when the Fe doping level are at a certain range.
    Journal of Magnetism and Magnetic Materials 01/2014; · 2.00 Impact Factor
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    ABSTRACT: 3-D flower like CoNi alloys nanostructures composed of nanorods have been synthesized by template free hydrothermal method at relatively low temperature (120 °C). The detailed characterizations confirm the formation of good crystalline fcc CoNi alloy, average crystallite size of 18.8 ± 1.0 nm, lattice parameter of 3.531 ± 0.01 Å, and the nearly equiatomic composition (Co50Ni50). Highly uniform flower like nano structures are built up with nanorod of diameter about 100 nm and length in range of 200–400 nm. The nanorods (building blocks of flower) have single crystalline nature with [111] preferred growth direction. The concentration of NaOH plays a vital role in formation of alloys and high concentration promotes the formation of CoNi alloy at low temperature. The concentration of NaOH also affects the morphology remarkably by changing the growth/reaction rate of CoNi nanostructures and results in hollow spheres to nanoplate flower of CoNi alloys. Based on the evolution of the morphology of the products, a step wise growth mechanism is rationally proposed for flower like nanostructures by considering the effects of kinetic parameters on growth. Magnetic measurements show Co50Ni50 flower like nanostructure have high saturation magnetization, coercivity, remanent magnetization, and high effective anisotropy constant of value 101.3 emu g−1, 210.5 Oe, 16.2 emu g−1, and 4.457 × 104 J m−3 respectively. The enhancements of coercivity and effective anisotropy constant are attributed to nanoscale effects such as shape/surface anisotropy.
    CrystEngComm 06/2013; 15(26):5314-5325. · 3.88 Impact Factor
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    ABSTRACT: The structural, dielectric, ferroelectric, and magnetic properties of bulk Fe-doped Ba0.5Sr0.5TiO3 (Ba0.5Sr0.5Ti1−xFexO3; BSTF) solids prepared by standard solid-state reaction were investigated. X-ray diffraction (XRD) patterns confirmed the tetragonal structure of BSTF samples. Rietveld refinements of XRD data revealed that the doping ions lead to unit cell expansion in three directions. Ferroelectric and ferromagnetic orders of the samples were observed simultaneously at room temperature. According to experimental and simulated results, two possible exchange coupling mechanisms exist in the BSTF systems, namely, nearest-site antiferromagnetic coupling and next-nearest-site ferromagnetic coupling. The two coupling mechanisms coexist in BSTF systems, leading to extraordinary ferromagnetic behavior.
    Journal of Magnetism and Magnetic Materials 01/2013; 325:24–28. · 2.00 Impact Factor
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    ABSTRACT: Flower like FeCo alloy nanostructures assembled with nano triangular prisms have been synthesized via template free hydrothermal method at relatively low temperature (120 °C). The concentration of NaOH plays vital role in the formation of alloy phase and morphology. The excessive amount of NaOH is determined to be responsible for formation of alloy phase during hydrothermal reaction. X-ray diffraction analysis confirms the formation of good crystalline FeCo alloy with average crystallite size of 24 nm. Energy dispersive X-ray spectroscopy and inductive coupled plasma atomic emission spectroscopy reveal the nearly equiatomic composition (Fe0.5Co0.5) of prepared flower like nanostructures. Scanning electron microscope and transmission electron microscope observations show that flower like FeCo alloy structures are composed of six nano triangular prisms. The diameter of flower like structure is in the range of 0.5–1.0 μm, and the base and height of nano triangular prism are in the range of 100–200 nm. Electron diffraction pattern shows the single crystalline nature of nano triangular prism. A step wise growth mechanism of flower like structure is proposed. Magnetic investigations show high saturation magnetization of 209 emu/g, low coercivity of 30 Oe, and remanent magnetization of 3.01 emu/g at 300 K. This nearly super-paramagnetic behavior of FeCo alloy nanostructures may be due to the crystallite size proximity to its super-paramagnetic critical size.
    Journal of Alloys and Compounds 11/2012; 550(15):423–430. · 2.73 Impact Factor
  • 2012 2nd International Conference on Applied Robotics for the Power Industry (CARPI 2012); 09/2012
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    ABSTRACT: A quantitative method to detect ferromagnetic resonance using magnetic tunnel junction structure has been developed. Experimental results reveal three distinct regions for single elliptical permalloy film of micrometer lateral size. Above the spin wave instability threshold, the experimental results show a linear response of the longitudinal magnetization component to the microwave field amplitude over a large range rather than a lock-up phenomenon appeared in macroscopic permalloy films and then a phase limiting behavior. The linear behavior can be described by the theoretical model describing subsidiary resonance.
    Applied Physics Letters 12/2011; 99(23). · 3.52 Impact Factor
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    ABSTRACT: We have demonstrated that spin wave resonance in a permalloy microstrip can be detected by an electrical method based on magnetic tunnel junction structures. The detection method promises high spatial resolution and sensitivity. Both even and odd spin wave resonance modes can be clearly observed in a permalloy microstrip. The spin wave induced voltage is proportional to the input microwave power at each resonance mode. Data analysis using the model of quantized dipole-exchange spin wave resonance suggests the edge pinning of spin wave sensitively depends on the order of the spin wave mode, as well as on the excitation frequency for modes of the higher order.
    Applied Physics Letters 11/2011; 99(19). · 3.52 Impact Factor
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    ABSTRACT: We studied the real-time evolution of magnetic dynamic and static properties of 20 nm CoFeB thin film during annealing at 380 °C. The ferromagnetic resonance linewidth quickly reduces by 30% within 300 s annealing, and monotonically increases upon longer annealing. The magnetic static coercivity shows similar trend. The underlying physical relation between linewidth and anisotropy can be connected by the two-magnon scattering theory. By doping of Nb into CoFeB films, the damping was maintained at a low value within 2000 s annealing. This method to tailor the dynamic properties of CoFeB may benefit the development of magnetics and spintronics based microwave devices.
    Applied Physics Letters 01/2011; 98(4):042506-042506-3. · 3.52 Impact Factor
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    ABSTRACT: We report here the evolution of zinc based high purity phases with novel morphologies such as Zn3N2 hollow structures, ZnO nanowires and nanopowders, as well as metallic Zn layered hexagonal microparticles at progressively increased reaction temperature of 600 °C, 700 °C, 800 °C under NH3 gas atmosphere using Zn powder precursor and keeping all other experimental parameters unchanged. Growth mechanism for Zn3N2 obtained by nitridation, ZnO by oxidation and Zn microparticles via thermal evaporation & condensation process are discussed briefly. The as-synthesized products were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). Photoluminescence (PL) studies have revealed very interesting and infrequently observed emission bands at 378 and 661 nm for Zn3N2, 359 and 396 nm for ZnO as well as 389 nm for Zn polyhedral microparticles.Graphical abstract.Highlights► Highly pure Zn based phases like Zn3N2, ZnO and Zn microparticles prepared under NH3 gas environment. ► Vapor–solid and self-catalytic processes based growth mechanisms are proposed for the products. ► PL spectra of the products exhibited very interesting and infrequently observed emission bands. ► Optical studies revealed the promise of the structures for applications in light emitting devices.
    Applied Surface Science 01/2011; 257(16):7314-7319. · 2.54 Impact Factor
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    ABSTRACT: Nanoscale Cu1−xMnxO powder is prepared by using the combustion synthesis technique with two different fuels. The structural properties of the powder are determined using Rietveld refinement of X-ray diffraction data, high-resolution transmission electron microscopy, and Fourier transform infrared spectroscopy, while its magnetic properties are analyzed by means of hysteresis loop and temperature dependence of magnetization. The results show that (1) the Cu1−xMnxO nanocrystal is of monoclinic CuO structure, with grain size of 10–30nm varying with the type of fuel, the nitrate/fuel ratio (N/F), and the Mn concentration, the doping of Mn has a little influence on the lattice parameters; (2) when the Mn concentration is higher than 7%, a small amount of impurity phase of CuMn2O4 appears and annihilates the potential cation vacancies; (3) all of the samples with x≥5% exhibit low-temperature ferromagnetism with the Curie temperature of ∼90K, which increases slightly by raising the Mn concentration; (4) the paramagnetic moment per Mn ion is around 2–4bohr magneton above the Curie temperature, which decreases with increasing Mn concentration, implying that the nearest Mn ions are antiferromagnetically coupled and the ferromagnetic order could originate from the super-exchange of next nearest Mn ions along the [101̄] direction.
    Physica B Condensed Matter 01/2011; 406(17):3180-3186. · 1.28 Impact Factor
  • Chong Bi, Liqing Pan, Mei Xu, John Q Xiao
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    ABSTRACT: Unlike previous studies that emphasize the important role of thermodynamics or surface energy on the structure stabilization of ZnS nanocrystals, we successfully controlled the crystalline structure of ZnS nanocrystals simply by tuning sulfur precursor addition rate under exactly the same other conditions. We observed the structure of as prepared ZnS nanocrystals was evolved from wurtzite into zinc blende with increasing the addition rate of sulfur precursor. The method may extend to engineer other nanomaterials with desired physicochemical properties by controlling crystalline structure. On the other hand, it also makes a new approach to understand the crucial factors that determine the growth mechanism and the crystal structure of nanomaterials in theory.
    Journal of Nanoscience and Nanotechnology 12/2010; 10(12):8452-5. · 1.15 Impact Factor
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    ABSTRACT: Fe-doped CuO ( Cu <sub>1-x</sub> Fe <sub>x</sub> O ) nanocrystals (NCs) ( x=0 , 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3) are prepared by using the urea nitrate combustion method. X-ray diffraction (XRD) analysis confirmed the monoclinic structure of CuO. Single-phase structure is obtained for the 0%–20% Fe-doped CuO, whereas for the 25% and 30% Fe-doped CuO material, secondary phase, α -Fe <sub>2</sub> O <sub>3</sub> , is presented. Rietveld refinements of XRD data revealed that with an increase in Fe doping level, there is a monotonic increase in cation vacancies in the Fe-doped samples. X-ray photoelectron spectroscopy measurements on the Cu <sub>0.98</sub> Fe <sub>0.02</sub> O sample revealed that the Cu <sup>2+</sup> sites are partly substituted by Fe <sup>3+</sup> ions. The microstructure is investigated by high-resolution transmission electron microscopy. The magnetic hysteresis loops and the temperature dependence of magnetization of the samples indicated that the samples are mictomagnetic of ferromagnetic domains originated from ferromagnetic coupling between the doping Fe ions in Cu <sub>1-x</sub> Fe <sub>x</sub> O NCs randomly distributed in the antiferromagnetic CuO matrix. The Curie temperature of the ferromagnetic phase is higher than 400 K for all Fe-doped CuO samples. The ferromagnetic behavior of the samples is discussed.
    Journal of Applied Physics 07/2010; · 2.21 Impact Factor
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    ABSTRACT: Room temperature ferromagnetic Mn <sub>0.026</sub> B <sub>X</sub> Si <sub>0.974-X</sub> bulk samples with X=0.001 , 0.005, and 0.01 were fabricated by arc melting and followed by thermal annealing at 1000 ° C . The effects of carrier density on the ferromagnetism were studied. Due to the high carrier densities, all samples showed metallic behavior. Kondo effect was observed when the temperature was below 10 K. Weakly localized carriers monotonously increased with increasing boron concentration, resulting in the enhancement of exchange coupling among Mn ions. The study indicated that the ferromagnetism originates from the hole mediated Ruderman–Kittel–Kasuya–Yosida mechanism.
    Journal of Applied Physics 06/2010; · 2.21 Impact Factor
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    ABSTRACT: Wurtzite ZnS hollow nanospheres were fabricated using PS nanospheres as templates by a facile method at relative low temperature. The prepared hollow nanospheres are uniform, monodispersed with homogeneous size of around 480nm, and spherical shape. The shell thickness of these hollow nanospheres is about 60nm, and composed of many wurtzite ZnS nanocrystals with the size of 8nm. The definite shape, thick and denser shell with higher specific surface area reveals that these hollow nanospheres will find a great deal of potential applications in environment protection, photocatalysis and so on.
    Materials Letters - MATER LETT. 01/2010; 64(15):1681-1683.
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    ABSTRACT: Raman spectra of wurtzite CoxZn1−xS nanocrystals were investigated. Two main broad Raman peaks centered at 259 and 331cm−1 were observed for low doping concentration, which are assigned to A1(TO) and E1(LO) phonon modes and had large redshift compared with that for bulk counterpart. It is suggested that such phenomena be attributed to phonon confinement effects, relaxation of the wave-vector selection rule due to doping effects. Besides two broad peaks, Raman spectra of high doping concentration exhibit five additional peaks at 229, 308, 340, 348, and 362cm−1, whose relative intensities are enhanced while frequencies keep constant with increasing Co concentration due to the small reduced mass difference.
    Chemical Physics Letters 10/2009; 481(4):220-223. · 2.15 Impact Factor
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    ABSTRACT: The ac susceptibility, electrical properties, and magnetotransport properties of the as-prepared Mn <sub>x</sub> Cu <sub>1-x</sub> O thin films (x=7%–29%) were studied in the temperature range of 2–300 K. The susceptibility measurement shows that ferromagnetic transition takes place for the samples with x≥14% below 100 K. The transport properties show the transition from variable-range-hopping to metalliclike behavior at the same transition temperature as the paramagnetism to ferromagnetism transition. The metal-insulator transition is a characteristic feature of magnetic ordering in this material.
    Journal of Applied Physics 05/2009; · 2.21 Impact Factor
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    ABSTRACT: Cobalt-doped wurtzite ZnS nanocrystals were prepared by a novel and facile synthesis method at temperatures as low as 150 °C. The structural and optical properties of prepared CoxZn1−xS (0.0025 ≤ × ≤ 0.1) nanocrystals have been characterized. X-ray diffraction patterns and high-resolution TEM images reveal pure hexagonal ZnS phase with size of about 5 nm for all CoxZn1−xS nanocrystals. Room temperature photoluminescence (PL) measurements show that the overall PL intensity is quenched with increasing Cobalt concentration. Deconvoluted PL spectra show three common peaks for pure ZnS nanocrystals, which are originated from Zn or S defect states. An additional peak at 459 nm (blue) observed in CoxZn1−xS nanocrystals is probably arising from the recombination between the shallow donor level and the new dopant level.
    Materials Chemistry and Physics. 01/2009; 116:363-367.
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    ABSTRACT: We report on the room temperature ferromagnetism in Co-doped wurtzite ZnS nanocrystals with size of about 5 nm, which gradually becomes weak as the increase of doping concentration. The coercivities for all samples maintain at about 200 Oe, and the saturation magnetic moment per Co ion decreases sharply for high doping samples. Besides ferromagnetism and paramagnetism, the temperature dependence of the susceptibility indicates the strong antiferromagnetic exchange in Co-doped wurtzite ZnS nanocrystals. X-ray diffraction, high-resolution TEM and X-ray photoelectron spectroscopy results show the ferromagnetism observed cannot be induced by secondary phases.
    01/2009;

Publication Stats

70 Citations
69.76 Total Impact Points

Institutions

  • 2002–2014
    • University of Science and Technology, Beijing
      • School of Materials Science and Engineering
      Peping, Beijing, China
  • 2013
    • China Three Gorges University
      Tung-hu, Hubei, China
  • 2005
    • University of Delaware
      • Department of Physics and Astronomy
      Newark, DE, United States