首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The magneto-optical Kerr effects (MOKE) of epitaxial Y3Fe5O12/Gd3Ga5O12 (YIG/GGG) garnet superlattices grown on (1 1 1)GGG previously by pulsed laser deposition (PLD) were measured. A series of superlattices were investigated with the thickness of the ferrimagnetic YIG layer varied from six unit cells to only one unit cell while keeping the Curie paramagnetic GGG fixed at one unit cell. It was demonstrated that the ellipsometric technique employing photoelastic modulators (PEM) is sensitive enough to measure the MOKE signals of these ultrathin oxide samples. The Curie temperatures, determined by MOKE, are fit with a power law, yielding a shift exponent λ = 3.1 ± 1.2.  相似文献   

2.
Garnet nanoparticles Y3−xSmxFe5O12 were fabricated by a sol–gel method. The XRD patterns of all the samples have only peaks of the garnet structure and the sizes range from 34 to 67 nm. Results of VSM show that the saturation magnetization of Y3−xSmxFe5O12 (0<x3) decreases on increasing the Sm concentration x evidently. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the nanoparticle size is increased.  相似文献   

3.
New germanosilicate glasses giving the crystallization of yttrium iron garnet Y3Fe5O12 (YIG) and Bi-doped YIG, 23Na2O-xBi2O3-(12−x)Y2O3-25Fe2O3-20SiO2-20GeO2 (mol%), are developed, and the laser-induced crystallization technique is applied to the glasses to pattern YIG and Bi-doped YIG crystals on the glass surface. It is clarified from the Mössbauer effect measurements that iron ions in the glasses are present mainly as Fe3+. It is suggested from the X-ray diffraction analyses and magnetization measurements that Si4+ ions are incorporated into YIG crystals formed in the crystallization of glasses. The irradiations (laser power: 32-60 mW and laser scanning speed: 7 μm/s) of continuous wave Yb:YVO4 fiber laser (wavelength: 1080 nm) are found to induce YIG and Bi-doped YIG crystals, indicating that Fe3+ ions in the glasses act as suitable transition metal ions for the laser-induced crystallization. It is suggested that YIG and Bi-doped YIG crystals in the laser irradiated part might orient. The present study will be a first step for the patterning of magnetic crystals containing iron ions in glasses.  相似文献   

4.
采用提拉法生长了Yb3+掺杂量分别为5.4at%, 16.3at%, 27.1at%, 53.6at%和100at%的Yb:Y3Al5O12晶体.系统地表征和分析了Yb3+掺杂量对晶体吸收光谱和荧光光谱的影响.随着Yb3+掺杂量的增加,各峰值吸收系数呈线性增加的趋势.应用Smakula公式计算了各吸收峰对应的振荡强度,并分析了Yb3+掺杂量对振荡强度的影 关键词: 吸收光谱 荧光光谱 自吸收 浓度猝灭  相似文献   

5.
Polycrystalline Lu3Fe5O12, prepared using the solid state reaction method, has Fe in the mixed valence state as inferred from the X-ray photoelectron spectroscopy. A spectral change in the impedance plot at 343 K is attributed to metal-like to insulator transition (MIT), which is analyzed in terms of localized and delocalized egeg electrons. The change in the slope at 343 K in the DC conductivity plot also proves the MIT. The dependence of ZZ on temperature and ZZ on frequency clearly substantiates the presence of localized electrons up to 343 K and delocalized electrons above 343 K.  相似文献   

6.
通过尿素分解法,把三价铬离子掺入到钇铝石榴石Y3Al5O12中,采用共沉淀法制备出绿色颜料。扫描电镜测试表明产物颗粒直径在200 nm左右,用XRD测试复合氧化物的结晶相行为,确定主相是钇铝石榴石相,用紫外可见漫反射光谱测试掺杂离子的配位状态和电子跃迁行为,用色度学测试氧化物颜色特征。将复合氧化物颜料颗粒与高分子聚丙烯共混,熔体纺丝,并通过北京同步辐射X射线CT对制得的纤维加以测试,结果表明复合氧化物颜料在高分子基质中得到良好的分散。这种颜料性能稳定,对环境友好,为实现无水印染技术奠定基础,减少纺织印染工业中所排放的污水。  相似文献   

7.
Sm3Fe5O12 thin films of various thicknesses were grown on a (0 0 1)-oriented Gd3Ga5O12 substrate by pulsed laser deposition. The crystal structure of the films was strongly dependent on film thickness. The lattice was strained for thinner films due to a lattice mismatch between the film and substrate. This lattice strain was relaxed when the film thickness exceeded a critical thickness of around 660 Å. It is suggested that the epitaxial strain induces uniaxial magnetic anisotropy with an out-of-plane magnetic easy axis.  相似文献   

8.
Y3Al5O12:Ce3+ (YAG:Ce) and Tb3Al5O12:Ce3+ (TAG:Ce) both show the typical Ce3+ ion luminescence of the allowed Ce3+ d–f transition. Eu3+ codoping, however, reveals different results for both matrices: in YAG:Ce,Eu, only the luminescence of the Ce3+ ion occurs by excitation within the Ce3+ absorption bands. Here, the Eu3+ luminescence cannot be sensitized by the Ce3+ ion. But in TAG:Ce,Eu, both Ce3+ and Eu3+ luminescence are measured at several excitation wavelengths: an excitation within the Tb-sublattice results in both Ce3+ and Eu3+ luminescence, which is not surprising as an energy transfer from Tb3+ to Ce3+ and Eu3+ is well known in literature. In addition, an excitation in the lowest 5d level of Ce3+ delivers Eu3+ luminescence at room temperature. This means that the Ce3+ ion can be used as a sensitizer in the TAG lattice that transfers its energy via the Tb sublattice to the activator Eu3+.  相似文献   

9.
The paper is dedicated to investigation of the Mn2+ luminescence in Tb3Al5O12 (TbAG) garnet, as well as the processes of excitation energy transfer between host cations (Tb3+ ions) and activators (Mn2+ and Mn2+-Ce3+ pair ions) in single crystalline films of TbAG:Mn and TbAG:Mn,Ce garnets which can be considered as promising luminescent materials for conversion of LED's radiation. Due to the effective energy transfer between TbAG host and activator, Mn2+ ions in TbAG possess the bright orange luminescence in the bands peaked at 595 nm with a lifetime of 0.64 ms which are caused by the 4T16A1 radiative transitions. The simultaneous process of energy transfer is realized in TbAG:Mn,Ce: (i) from Tb3+ to Mn2+ ions; (ii) from Tb3+ cations to Ce3+ ions and then partly to Mn2+ ions through Tb3+ ion sublattice and Ce-Mn dipole-dipole interaction.  相似文献   

10.
The magnetic susceptibility of the garnet-type single crystal Tm3Al5O12 exhibits the typical Van Vleck temperature independent paramagnetism below ≈8 K. The temperature dependence of the susceptibility over the range 2.0-300 K has been analyzed on the assumption that the cubic crystal-electric-field dominates the energy level on 3H6 (J=6) ground multiplet for Tm3+ ion having 12-electrons in 4f shell. The ground state of the 3H6 is nonmagnetic with Γ2 singlet, avoiding the Kramers doublet. The energy separation between Γ2 and the first excited state Γ(2)5 triplet is evaluated to be 68.0 K. The whole energy interval Δ between Γ2 and the highest state Γ1 in 3H6 is estimated to be 339.5 K.  相似文献   

11.
In the present work, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition depth profiles of Bi3.15Nd0.85Ti3O12 (BNT) ferroelectric thin film, which was prepared on Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrates by chemical solution deposition (CSD). It is shown that there are three distinct regions formed in BNT film, which are surface layer, bulk film and interface layer. The surface of film is found to consist of one outermost Bi-rich region. High resolution spectra of the O 1s peak in the surface can be decomposed into two components of metallic oxide oxygen and surface adsorbed oxygen. The distribution of component elements is nearly uniform within the bulk film. In the bulk film, high resolution XPS spectra of O 1s, Bi 4f, Nd 3d, Ti 2p are in agreement with the element chemical states of the BNT system. The interfacial layer is formed through the interdiffusion between the BNT film and Pt electrode. In addition, the Ar+-ion sputtering changes lots of Bi3+ ions into Bi0 due to weak Bi-O bond and high etching energy.  相似文献   

12.
Absorption and fluorescence spectra observed between 450 and 750 nm at 85 K and room temperature (300 K) are reported for Eu3+(4f6) in single-crystal Czochralski-grown garnet, Gd3Ga5O12 (GGG). The spectra represent transitions between the 2S+1LJ multiplets of the 4f6 electronic configuration of Eu3+ split by the crystal field of the garnet. In absorption, Eu3+ transitions are observed from the ground state, 7F0, and the first excited multiplet, 7F1, to multiplet manifolds 5D0, 5D1, and 5D2. The Stark splitting of the 7FJ multiplets (J=0-6) was determined by analyzing the fluorescence transitions from 5D0, 5D1, and 5D2 to 7FJ. The Eu3+ ions replace Gd3+ ions in sites of D2 symmetry in the lattice during crystal growth. Associated with each multiplet manifold are 2J+1 non-degenerate Stark levels characterized by one of four possible irreducible representations (irreps) assigned by an algorithm based on the selection rules for electric-dipole (ED) and magnetic-dipole (MD) transitions between Stark levels in D2 symmetry. The quasi-doublet in 5D1 was characterized by an analysis of the magneto-optical spectra obtained from the transitions observed between 5D1 and 7F1. A parameterized Hamiltonian defined to operate within the entire 4f6 electronic configuration of Eu3+ was used to model the experimental Stark levels and their irreps. The crystal-field parameters were determined through use of a Monte-Carlo method in which nine independent crystal-field parameters, were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental Stark levels is 5.9 cm−1. The choice of coordinate system, in which the nine are real and the crystal-field z-axis is parallel to the [0 0 1] crystal axis and perpendicular to the xy plane, is identical to the choice we used previously in analyzing the spectra of Er3+ and Ho3+ garnets.  相似文献   

13.
Single-phased polycrystalline Y3Fe5−2xAlxCrxO12 garnet samples (x=0, 0.2, 0.4 and 0.6) have been prepared by the conventional ceramic technique. Rietveld refinement of X-ray diffraction patterns of the samples shows them to crystallize in the Ia3d space group and the corresponding lattice constant to decrease with increasing Al3+ and Cr3+ contents (x). Mössbauer results indicate that Cr3+ substitutes for Fe3+ at the octahedral sites whilst Al3+ essentially replaces Fe3+ at the tetrahedral sites. This result indicates that co-doping of Y3Fe5O12 does not affect the preferential site occupancy for separate individual substitution of either Cr3+ or Al3+. The magnetization measurements reveal that the Curie temperature (Tc) monotonically decreases with increasing x while the magnetic moment per unit formula decreases up to x=0.4 and then slightly increases for x=0.6. This reflects a progressive weakening of the ferrimagnetic exchange interaction between the Fe3+ ions at octahedral and tetrahedral sites due to co-substitution. The magnetic moment was calculated using the cations distribution inferred from the Mössbauer data and the collinear ferrimagnetic model, and was found to agree reasonably with the experimentally measured value. The phenomenological amplitude crossover, characterized by the temperature T*, has also been observed in the doped YIG and briefly discussed.  相似文献   

14.
王维  祁欣  岳元 《中国物理 B》2011,20(1):17502-017502
This paper theoretically investigates the effects of crystal field and exchange interaction field on magnetic properties in dysprosium gallium garnet under extreme conditions (low temperatures and high magnetic fields) based on quantum theory. Here, five sets of crystal field parameters are discussed and compared. It demonstrates that, only considering the crystal field effect, the experiments can not be successfully explained. Thus, referring to the molecular field theory, an effective exchange field associated with the Dy--Dy exchange interaction is further taken into account. Under special consideration of crystal field and the exchange interaction field, it obtains an excellent agreement between the theoretical results and experiments, and further confirms that the exchange interaction field between rare-earth ions has great importance to magnetic properties in paramagnetic rare-earth gallium garnets.  相似文献   

15.
Nano-sized magnetic Y3Fe5O12 ferrite having a high heat generation ability in an AC magnetic field was prepared by bead milling. A commercial powder sample (non-milled sample) of ca. 2.9 μm in particle size did not show any temperature enhancement in the AC magnetic field. The heat generation ability in the AC magnetic field improved with a decrease in the average crystallite size for the bead-milled Y3Fe5O12 ferrites. The highest heat ability in the AC magnetic field was for the fine Y3Fe5O12 powder with a 15-nm crystallite size (the samples were milled for 4 h using 0.1 mm? beads). The heat generation ability of the excessively milled Y3Fe5O12 samples decreased. The main reason for the high heat generation property of the milled samples was ascribed to an increase in the Néel relaxation of the superparamagnetic material. The heat generation ability was not influenced by the concentration of the ferrite powder. For the samples milled for 4 h using 0.1 mm? beads, the heat generation ability (W g−1) was estimated using a 3.58×10−4 fH2 frequency (f/kHz) and the magnetic field (H/kA m−1), which is the highest reported value of superparamagnetic materials.  相似文献   

16.
The periodic Hartree-Fock method has been applied to calculate the electronic structure of the yttrium aluminium garnet. We report on the results of the density of state calculations, the population analysis, as well as the electric-field-gradient distribution. A comparative analysis with the related structure α-Al2O3 was done. The calculations show that the Y3Al5O12 crystal is more ionic than α-Al2O3.  相似文献   

17.
The simulation of magnetic properties in extended quantum spin networks can be done in good conditions with Ising models within Monte Carlo–Metropolis algorithms, as our systematic studies, employing original computer codes, proved. The present analysis provides interesting insights into the exchange interactions governing the magnetic behavior of the Gd3Fe5O12 system, taken as a prototype for ferrites with garnet structure. Effective exchange interaction parameters are estimated by fitting the computed with experimental compensation temperature and temperature dependence of the magnetization.  相似文献   

18.
In the present paper, phosphors with the composition Y3−x−yAl5O12:Bi3+x, Dy3+y were synthesized with solid state reactions. The luminescence properties of Bi3+ and Dy3+ in Y3Al5O12(YAG) and the energy transfer from Bi3+ to Dy3+ were investigated in detail. Bi3+ in YAG emits one broad band peaking at 304 nm which can be ascribed to the transition from excited states 3P0, 1 to ground state 1S0. Dy3+ in YAG emits two groups of peaks around 484 and 583 nm, respectively, which can be ascribed to the transitions from excited state 4F9/2 to ground states 6H15/2 and 6H13/2. The co-doping of Bi3+ enhances the luminescent intensity of Dy3+ by ∼7 times because Bi3+ can transfer the absorbed energy to Dy3+ efficiently. The mechanism of energy transfer was also discussed.  相似文献   

19.
垂直磁各向异性稀土-铁-石榴石纳米薄膜在自旋电子学中具有重要应用前景.本文使用溅射方法在(111)取向掺杂钇钪的钆镓石榴石(Gd0.63Y2.37Sc2Ga3O12,GYSGG)单晶衬底上外延生长了2—100 nm厚的钬铁石榴石(Ho3Fe5O12,HoIG)薄膜,并进一步在HoIG上沉积了3 nm Pt薄膜.测量了室温下HoIG的磁各向异性和HoIG/Pt异质结构的自旋相关输运性质.结果显示,厚度薄至2 nm的HoIG薄膜(小于2个单胞层)在室温仍具有铁磁性,且由于外延应变,2—60 nm厚HoIG薄膜都具有很强的垂直磁各向异性,有效垂直各向异性场最大达350 mT;异质结构样品表现出非常可观的反常霍尔效应和“自旋霍尔/各向异性”磁电阻效应,前者在HoIG厚度小于4 nm时开始缓慢下降,而后者当HoIG厚度小于7 nm时急剧减小,说明相较于反常霍尔效应,磁电阻效应对HoIG的体磁性相对更加敏感;此外,自旋相关热电压随HoIG厚度减薄在整个厚度范围以指数方式下降,说明遵从热激化磁振子运动规律的自旋塞贝克效应是其主要贡献者.本文结果表明HoIG纳米薄膜具有可调控的垂直磁各向异性,厚度大于4 nm的HoIG/Pt异质结构具有高效的自旋界面交换作用,是自旋电子学应用发展的一个重要候选材料.  相似文献   

20.
Sc-doped YIG films were grown on (1 1 1) oriented GGG crystalline substrate with disorientation angle within the range 0-25′. Sc3+ ion substitution was varied within the range 0.25-0.3 per formula unit. The films demonstrate different types of surface morphology versus film growth rate and substrate disorientation. Conditions for existence of these types of the surface morphology were defined. The field dependence of magnetic susceptibility at magnetization reversal in film plane and Faraday rotation at wavelength 633 nm for a magnetic field applied in perpendicular direction were measured to characterize the films grown. Films with “mirror-like” surface demonstrate a planar magnetization at room temperature.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号