水热法合成BaNd_xFe_（12－x）O_（19）铁氧体的研究

本文利用水热法合成了六角形磁铅石结构的ＢａＮｄｘＦｅ（１２－ｘ）Ｏ（１９）铁氧体，用Ｘ射线衍射仪、透射电子显微镜和振动样品磁强计等仪器对粉末的结构、形貌和磁学性能进行了研究，并讨论了Ｎｄ（３＋）对钡铁氧体磁学性能的影响。结果表明，Ｎｄ（３＋）可以明显提高ＢａＦｅ（１２）Ｏ（１９）粉末的矫顽力。     

La~(3+) doped LiCo_(0.25)Zn_(0.25)Fe_2O_4 spinel ferrite nanocrystals:Insights on structural,optical and magnetic properties

This paper addresses the manipulation of structural,morphology,optical and magnetic properties of LiCo_(0.25)Zn_(0.25)Fe_2 O_4 ferrite via incorporation of different proportions of La~(3+) at the expense of iron ions using a sol-gel method.The samples were characterized using the X-ray diffraction technique(XRD),Fourier transform infrared(FT-IR) spectroscopy,the energy dispersive X-ray spectra(EDX),inductively coupled plasma optical emission spectroscopy(ICP-OES),high resolution scanning electron microscopy(SEM),Brunauer-Emmett-Teller(BET) surface area analysis,ultraviolet-diffuse reflectance spectroscopy(UV-DRS),and vibrating sample magnetometer(VSM) technique.The Rietveld refinements of the samples indicate that at higher concentrations of La3+,nanostructures with dual phase,i.e.cubic spinel and orthorhombic LaFeO_3 perovskite with space group(Pbnm) appear.Optical studies show that the energy band gap(E_g) of the bare LiCo_(0.25)Zn_(0.25)Fe_2 O_4 ferrite sample(2.18 eV) reaches up to 2.47 eV at x=0.06 and above this concentration,it drops sharply to 2.00 eV.Although the saturation magnetization and the coercivity of LiCo_(0.25)Zn_(0.25)La_xFe_(2-x)O_4 are lower than that of LiCo_(0.25)Zn_(0.25)Fe_2 O_4 NPs.Overall,the superparamagnetic nature and low values of saturation magnetization and coercivity of LiCo_(0.25)Zn_(0.25)La_xFe_(2-x)O_4 NPs are suitable to be applied in transformers core.     

Magnetic properties and magnetic entropy change of perovskite manganites La_(0.9-x)Eu_xSr_(0.1)MnO_3(x=0.000,0.075) by experimental method and numerical fitting

Polycrystalline samples La_(0.9-x)EuxSr_(0.1)MnO_3(x = 0.000, 0.075) were prepared by the standard solid-state reaction method. The results show that the samples preform a characteristic of clusters spin-glass state at low temperature. The samples show a characteristic of ferromagnetism(FM) characteristic in the temperature range of 15-125 K and 15-150 K respectively; the samples show preformed clusters in the temperature range of 125-343 K and 150-325 K, respectively, the samples show paramagnetism(PM)characteristic above 343 and 325 K, respectively. The second-order transitions are found at 118 and 135 K for undoped and doped sample, respectively. When the applied magnetic field is 7 T, the maximum magnetic entropy change |△S_M| value of the samples is near the Curie temperature(Tc), and the value of|△S_M| reaches 2.76 and 3.03 J/(K kg), respectively. In addition, the relative cooling power(RCP) is found to be 425.28 and 443.53 J/kg. The numerical fitting data fit well with experimental data. These results indicate that both the samples have the potential to realize magnetic refrigeration in the high temperature region(T 77 K).     

Structure and Magnetic Properties of Nd(Fe,Mo) 12 N x Prepared by Mechanically Alloying

Ｂｅｃａｕｓｅｏｆｆｉｎｅｇｒａｉｎｓ,ｔｈｅｍａｇｎｅｔｓｐｒｅｐａｒｅｄｂｙｔｈｅｍｅｃｈａｎｉｃａｌａｌｏｙｉｎｇ（ＭＡ）ｔｅｃｈｎｉｑｕｅｈａｖｅｈｉｇｈｅｒｃｏｅｒｃｉｖｉｔｙｃｏｍｐａｒｅｄｗｉｔｈｔｈｏｓｅｐｒｅｐａｒｅｄｂｙｔｒａ...     

Effect of dysprosium substitution on magnetic and structural properties of NiFe_2O_4 nanoparticles

This work investigated the effect of dysprosium(Dy)ions on the structural,microstructural and magnetic properties of nickel nanospinelferrite,NiFe_2 O_4.The nanoparticles(NPs)of NiDy_xFe_(2-x)O_4(0.0≤x≤0.1)were prepared via the hydrothermal method.The formation of cubic phase of Ni nanoferrite was confirmed through X-ray diffraction,field emission scanning and transmission electron microscopy.Moreover,the magnetic properties of NiDy_xFe_(2-x)P_4(0.01≤x≤0.10)NPs were discussed.The magnetization versus field,M(H)curves exhibit super paramagnetic nature at room temperature and ferrimagnetic nature at low temperature(10 K).A noticeable improvement in the different deduced magnetic parameters is obtained especially for the NiDy_(0.07)Fe_(1.93)O_4(x = 0.07)product.The obtained result is mostly derived from the substitution of Fe~(3+)ions of smaller ionic radii with Dy~(3+)ions of larger ionic radii that will strengthen the super exchange interactions among nanoparticles.The calculated squareness ratios are found to be much less than 0.5,due to the effect of spin disorder in the surface regions of NiDy_xFe_(2-x)O_4(0.01≤x≤0.10)NPs.The Dy~(3+) ions substitution increases the magnetic hardness(higher values of remanence M_r,coercivity H_c,and magnetic moment n_B)of nickel nanoferrite samples.     

Preparation and magnetic properties of anisotropic Nd_2Fe_(14)B/Sm_2Co_(17) hybrid-bonded magnets

In the present work, anisotropic Nd_2 Fe_(14) B/Sm_2 Co_(17) hybrid-bonded magnets were prepared with different Nd-Fe-B contents. It is found that the particle distributions and ratios between the two magnetic phases have important roles in the magnetic properties, microstructures and thermal stability of the magnets. With increase of Nd-Fe-B content, the saturation magnetization of the anisotropic hybrid magnet increases significantly, however, coercivity decreases, and the demagnetization curves show magnetically single-phase behavior. The anisotropic Nd_2 Fe_(14) B/Sm_2 Co_(17) hybrid-bonded magnets exhibit a maximum energy product and remanence of 14.15 MGOe and 99.53 A·m~2/kg, respectively, when the NdFe-B content is 70 wt% at room temperature. Furthermore, the hybrid magnets also have better thermal stability at elevated temperatures due to the interaction between the two magnetic particles.     

Effect of wheel speed on phase formation and magnetic properties of (Nd0.4La0.6)-Fe-B melt-spun ribbons

The effect of wheel speed on phase formation and magnetic properties of (Nd_0.4La_0.6)₁₅Fe_77.5B_7.5 and (Nd_0.4La_0.6)_13.4Fe_79.9B_6.7 ribbons prepared by melt-spinning method was investigated experimentally. Based on X-ray diffraction results, all melt-spun ribbons consist of the main phase with the tetragonal 2:14:1 type structure and the minor α-Fe phase. Magnetic measurements show the maximum magnetic energy product ((BH)_max) and the remanence (M_r) increases firstly and then decreases with the increase of wheel speed, while the coercivity (H_ci) increases, resulting from the variation of the average volume fraction of the α-Fe phase and the average grain size in the melt-spun ribbons. Using Henkel plots, the interaction between the 2:14:1 phase and the α-Fe phase in the melt-spun ribbons was analyzed and the intergranular exchange coupling is manifested. Optimal magnetic properties of H_ci = 7.27 kOe, M_r = 90.94 emu/g and (BH)_max = 12.10 MGOe are achieved in the (Nd_0.4La_0.6)₁₅Fe_77.5B_7.5 ribbon with the wheel speed of 26 m/s. It indicates that magnetic properties of Nd-Fe-B melt-spun ribbons with highly abundant rare earth element La can be improved by optimizing alloy composition and preparation process.     

Effect of Dy-substitution on structural and magnetic properties of MnZn ferrite nanoparticles

This paper describes the structural and magnetic properties of Dy-substituted Mn-Zn ferrite nanoparticles. Mn-Zn-Dy ferrite nanoparticles of the composition Mn_(0.5)Zn_(0.5)Dy_xFe_(2-x)O_4(x=0.05, 0.1,0.15 and 0.2) were synthesized by a facile chemical co-precipitation method. The samples were characterized through X-ray diffraction(XRD), transmission electron microscopy(TEM), Fourier transform infrared spectroscopy(FTIR), vibrating sample magnetometer(VSM) and Curie temperature. The XRD patterns confirm the synthesis of single crystalline phase of Mn-Zn-Dy ferrite nanoparticles. Lattice parameter increases with increase in Dy-substitution which confirms the replacement of Fe~(3+) ions by Dy~(3+) ions.Crystallite size is of the order of 6-8 nm for all these samples. The particle sizes observed from TEM analysis are in good agreement with the XRD values. The magnetic measurements show superparamagnetic nature of the samples. The saturation magnetization decreases with increase in Dyconcentration and can be correlated to modifications in the A-B exchange interactions as a result of the structural modifications due to Dy-substitution. The Curie temperature for Mn_(0.5)Zn_(0.5)Fe_2 O_4 nanoparticles is 124 ℃ and decreases up to 84 ℃ with the increase in the Dy-concentration. The decrease in Curie temperature can be attributed to the weakening of the superexchange interaction between A-site and B-site as a result of Dy-substitution. The low value of Curie temperature and higher value of thermomagnetic coefficient k_T shown by these samples makes them suitable for the preparation of temperature sensitive ferrofluid for heat transfer applications.     

Tunable electronic band structure,luminescence properties and thermostability of(Gd_(1-x)La_x)_2Si_2O_7:Ce scintillator by adjusting La/Gd ratio

Mixed crystal strategy is an effective approach of improving the luminescence properties of optical materials and has been adopted widely in many systems.In this paper,the La-mixed Gd_2 Si_2 O_7:Ce polycrystalline samples were successfully synthesized by a sol-gel method.The crystal structure and luminescence properties were confirmed and discussed by XRD,UV-Vis luminescence spectra,and XEL,respectively.The vacuum ultraviolet excitation spectra and thermoluminescence glow curves were also systematically investigated and discussed at varied temperature.A combination of the first-principles calculations and optical characterization experiments was employed to study the electronic band structure of host material,revealing that the band gap is narrowed and the 5 d_1 level of Ce~(3+) shifts to higher energy as the La content increases.The luminescence the rmo-stability and activation energy were also measured and calculated.It indicates that thermo-stability is strongly dependent on the La concentration.An effective approach is developed to tune the electronic band structure,luminescence properties and thermostability of(Gd_(1-x)La_x)_2 Si_2 O_7:Ce scintillator by adjusting La/Gd ratio.     

Fabrication of Ce-doped(Gd_2Y)Al_5O_(12)/Y_3Al_5O_(12) composite-phase scintillation ceramic

In this paper, a novel Ce(Gd_2 Y)Al_5O_(12)/Ce:Y_3Al_5O_(12)(Ce:GYAG/Ce:YAG) composite scintillation ceramic was designed and fabricated by a solid-state reaction method. The phase, luminescence and scintillation properties were investigated. The Ce:GYAG/Ce:YAG composite ceramic consisting of two-phase has a broad emission band ranging from 500 to 750 nm. The total mass attenuation coefficient of Ce:GYAG/Ce:YAG is 0.3864 cm~(-1), in between those of Ce:YAG and Ce:GYAG ceramics. In addition, the composite ceramic had a high light yield of 20430 ph/MeV. By controlling the ratio of GYAG and YAG, the composite ceramic can realize a spectrum design and total mass attenuation coefficient control to meet the requirements for wide-X-ray-energy-range detectors.     

Doping effect of rare-earth (lanthanum,neodymium and gadolinium) ions on structural,optical, dielectric and magnetic properties of copper nanoferrites

Copper and rare earth-doped (RE = La, Gd, Nd) CuFe_1.85RE_0.15O₄ nanoferrites were prepared using the sonochemical method. The effective doping of rare-earth (La³⁺, Nd³⁺, Gd³⁺) ions with copper nanoferrites was confirmed by X-ray diffraction. The tetrahedral and octahedral sites of the nanoferrites were identified through the Fourier transform infrared spectra. The doping of rare-earth elements enhances the optical bandgap energy of the nanoferrites that are observed through Ultraviolet–DRS spectra. The oxidation state of the elements Cu 2p, La 3d, Nd 3d, Gd 3d, Fe 2p and O 1s was analyzed. Scanning electron microscopy images indicate a spherical morphology with agglomeration to some elongate. The values of dielectric constant and conductivity decrease considerably due to doping rare-earth ions in copper nanoferrites. Low saturation magnetization and high coercivity values of rare earth-doped copper nanoferrites are observed from the typical hysteresis curves.     

Electrochemical synthesis,structure characterization and magnetic properties of Tb_xFe_7Co_3(x=0,0.6,0.8) nanowires

Highly ordered Tb_xFe_7 Co_3(x=0,0.6,0.8) nanowires were synthesized in alumina templates by electrochemical deposition method.Here,the effects of Tb content and annealing treatment on the phase composition,morphology,crystalline structure and magnetic properties were investigated.The asdeposited Tb_0 Fe_7 Co_3 nanowires comprise Fe_7 Co_3 phase.While after adding Tb,the diffraction peaks slightly shift left,indicating the infiltration of Tb atoms into Fe_7 Co_3 phase.After annealing,Tb_0 Fe_7 Co_3 nanowires still consist of Fe_7 Co_3 phase with a slight enhancement on coercivity.While the annealed nanowires with Tb doped present a complex phase composition containing Fe3 Tb,Fe_2 Tb,Co_3 Tb,Co_(17)Tb_2,TbFeO_3 and Fe_2 O_3 phases distribute in the central portion,and Co_(0.72)Fe_(0.28) at the nanowire outer walls.The annealed Tb_xFe_7 Co_3(x=0.6,0.8) nanowires show higher magnetic performance owing to the formation of hard magnetic phases,the interfacial elastic coupling between hard and soft phases and the coherent Fe3 Tb/Co_3 Tb interface which restrain the domain wall motion.To be specific,the coercivity and remanence ratio of TbxFe_7 Co_3(x=0.6,0.8) nanowires significantly enhance with increasing Tb content.     

First-principles study of structure,mechanical and optical properties of La-and Sc-doped Y_2O_3

The electronic,mechanical and optical properties of La-and Sc-doped Y_2O_3 were investigated using firstprinciples calculations.Two doping sites of Sc and La in Y_2O_3 were modeled.The calculated values of the energy of formation show that the most energetically favorable site for a La atom in Y_2O_3 is a d-site Y atom,while for Sc a b-site Y atom is the more stable position.The calculated band gap shows a slight decrease with increasing La or Sc concentration.The calculated results for the mechanical and optical properties of Y_(2-x)R_xO_3(R = Sc or La,0x ≤ 0.1875)show that La-or Sc-doped Y_2O_3 would have enhanced strength,and thus an ability of resisting external shocks,and increased hardness and mechanical toughness.These improved mechanical properties are achieved without sacrificing the optical properties of the doped compounds.So the doping of La or Sc in Y_2O_3 is permissible in the preparation of Y_2O_3 transparent ceramics,of course,doping of La or Sc will benefit the sintering of transparent ceramics.     

Luminescent and magnetic properties of multifunctional europium(III) complex based nanocomposite

The luminescent rare earth (RE) complex based multifunctional nanocomposites offer new potential applications of multimodal imaging (magnetic resonance imaging (MRI), fluorescent bioimaging, etc.) that can be associated with therapeutic activities. In this study, we report some results obtained with novel multifunctional Fe₃O₄/Si-amine/Eu(NTA)₃ nanocomposites that are composed of europium(III) complex with 1-(2-naphthoyl)-3,3,3-trifluoroacetone ligands (NTA) (Eu(NTA)₃) and superparamagnetic Fe₃O₄ nanoparticles. These nanocomposites were functionalized with an amine group for biomedicine application. The multifunctional Fe₃O₄/Si-amine/Eu(NTA)₃ nanocomposites exhibit both good magnetic behavior of Fe₃O₄ nanoparticles as a core and strong fluorescent property of europium(III) complex. Their characterizations were analyzed by XRD, SEM, EDX and FTIR spectra. The optical properties were studied in detail by UV-VIS spectra and luminescent emission spectra. The magnetic property was estimated by VMS. The effect of concentrations of luminescent Eu(NTA)₃ complex on luminescent and magnetic properties is discussed.     

Effects of Sm-doping on microstructure,magnetic and microwave absorption properties of BiFeO_3

In this paper,polycrystalline samples of Bi_(1-x)Sm_xFeO~3(x=0,0.05,0.1,0.15) were successfully synthesized by sol-gel method.The effects of Sm concentration on the crystal structure,morphology,chemical states,magnetic properties and microwave absorption performance were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),a vibrating sample magnetometer(VSM) and a Vector network analyzer(VNA),respectively.The results show that the rare earth Sm doping causes the crystal structure to change.When x≤0.1,Bi_(1-x)Sm_xFeO_3 is the distorted rhombohedral structure with space group R3 c.With the increase of Sm doping amount to x=0.15,the phase structure of Bi_(1-x)Sm_xFeO_3 changes from rhombohedral structure to cubic structure with the space group Pm3 m.The particle size decreases with the increase of the Sm doping amount.The analysis results show that Sm doping can effectively reduce the oxygen vacancies and significantly improve its magnetic properties.The results exhibit that moderately doped rare earth Sm element can effectively improve microwave absorption properties of Bi_(1-x)Sm_xFeO_3 powders.When Sm doping amount of x is 0.1,the Bi_(0.9)Sm_(0.1) FeO_3 compound has good microwave absorption performance,and the minimum reflection loss value of Bi_(0.9)Sm_(0.1)FeO_3 powder reaches about-32.9 dB at11.7 GHz,and its effective absorption bandwidth(RL -10 dB) is 2.6 GHz with the optimal matching thickness of 2.0 mm.     

Effect of Nb~(5+) and Cu~(2+) codoping on thermal properties of Gd_2Zr_2O_7 ceramic

In this work,Nb⁵⁺and Cu²⁺were selected to partially substitute Zr4+in Gd₂Zr₂O₇for studying the phase structure,microscopic morphology and thermal properties.Gd₂(Zr_(1-3 x/2)Nb_xCU_x/2)₂O₇(x=0,0.05,0.1,0.15,0.2,0.25)ceramic materials were synthesized by high-temperature solid-state reaction method.The results show that the Gd₂(Zr_(1-3 x/2)Nb_xCu_x/2)₂O₇ceramics present cubic pyrochlore structure with clear grain boundaries and dense cell structure.And the thermal expansion coefficient of Gd₂(Zr_(1-3 x/2)Nb_xCu_x/2)₂O₇ceramics gradually decreases because of the incorporation of Nb⁵⁺and Cu²⁺into Zr-site in Gd₂Zr₂O₇.Meanwhile,its thermal conductivity decreases firstly and then increases with the doping of Nb⁵⁺and Cu²⁺,which reaches the lowest value for the composition of Gd₂(Zr_0.85Nb_0.1Cu_0.05)₂O₇.     

Influence of La-Co substitution on the structure and magnetic properties of low-temperature sintered M-type barium ferrites

La-Co substituted M-type barium ferrites (BaM) were prepared by traditional solid state method and sintered at low tem-perature (1173 K). X-ray diffraction (XRD), scanning electron microscopy (SEM) and...     

Magnetic properties and microstructure of Fe_(69.5-x)Nd_7B_(21)Nb_(2.5)Ga_x(x=0-1)alloys

The Fe_(69.5-x)Nd_7 B_(21)Nb_(2.5)Ga_x(x = 0-1)permanent magnets in the form of rods were prepared by annealing the bulk amorphous alloys.The magnetic properties,phase evolution and microstructure of the alloys were investigated systematically.It is found that the glass forming ability(GFA), microstructure and magnetic properties are sensitive to Ga content for Fe_(69.5-x)Nd_7 B_(21)Nb_(2.5)Ga_x(x = 0-1)bulk alloys.The annealed alloys are mainly composed of soft α-Fe,hard Nd_2 Fe_(14)B and nonmagnetic Nd_(1.1)Fe_4 B_4 phases.When x = 0.3,the optimally annealed magnets exhibit magnetic properties of the remanence Br = 0.63 T,intrinsic coercivity H_(cj) = 368.68 kA/m and maximum energy product(BH)_(max) = 33.73 kJ/m~3.Furthermore,magnetic field heat treatment at the temperature close to Curie temperature of Nd_2 Fe_(14)B phase was applied to the annealed Fe_(69.2)Nd_7 B_(21)Nb_(2.5)Ga_(0.3) magnet.The results of X-ray diffraction(XRD)and transmission electron microscopy(TEM)indicate that the magnetic field heat treatment can be beneficial for the precipitation of α-Fe.Thus,the B_r,H_(cj) and(BH)_(max) are enhanced by 8.7%,6.3% and 16.3%,respectively.     

First-principles study of electronic structure and optical properties of Er:Lu_2O_3

In the present computational study,we found that Er:Lu₂O₃materials have promise for application in laser applications.The crystal structure and the electronic and optical properties of Er:Lu₂O₃materials were studied using first-principle calculations under the framework of density functional theory.Based on the experimental and calculated results,the structure of Lu₂O₃was established.The calculated results show that doping by Er³⁺can effectively improve its absorption coefficient in the ultraviolet region and improve the static dielectric constant of Lu₂O₃.As the doping concentration of Er³⁺increases,the energy of the valence band electrons excited to the conduction band decreases,and the transition is more likely to occur.The absorption coefficient,reflectance,and electron energy loss spectroscopy are bathochromic shifted.The Lu_2-xEr_xO₃(02O₃.     

Growth and optical properties of Pr~(3+):La_2CaB_(10)O_(19) crystal

Pr3+ doped La2CaB10O19 crystal were grown by the top-seeded solution growth(TSSG) method.The absorption spectra,emission spectra and lifetime were measured at room temperature.The J-O parameters(Ωt,t=2,4,6),the radiative transition probabilities AJ,J',oscillator strengths PJ,J',radiative lifetime τ,fluorescence branch ratios βJ and the value of integrated emission cross section have also been calculated.Five main absorption bands,3H4 to 3P1+3P2,3P0,1D2,3F3 + 3F4 and 3F2,were observed in the absorption spect...