Surface morphological changes and magnetic properties of Sc-substituted Y3Fe5O12 epitaxial films deposited on the GGG substrate

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.     

Curie temperatures of Y3Fe5O12/Gd3Fe5O12 superlattices

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.     

Synthesis and magnetic properties of Sm–Y3Fe5O12 nanoparticles

Garnet nanoparticles Y_3−xSm_xFe₅O₁₂ 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 Y_3−xSm_xFe₅O₁₂ (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.     

Y3-xBixFe5O12的晶体生长

本文讨论了Y₂O₃-Fe₂O₃-Bi₂O₃-PbO·0.2B₂O₃赝四元系相图的得出与运用;用Bi₂O₃-PbO-B₂O₃做助熔剂,获得了磁性石榴石Y_3-xBi_xFe₅O₁₂单晶(0≤x≤1.2);还论述了Bi-YIG晶体内Bi含量与助熔剂熔液成份的关系。 关键词：     

First principles study of structural,phonon, optical,elastic and electronic properties of Y3Al5O12

Structural, phonon, optical, elastic and electronic properties of Y₃Al₅O₁₂ have been investigated by means of the first principles method with the Cambridge Serial Total Energy Package (CASTEP) code based on the density functional theory. The calculated lattice parameters, valence charge density, bond length and single crystal elastic properties at zero pressure are in good agreement with the available experimental data. The close agreement with the experimental values provides a good confirmation of the reliability of the calculations. Optical, elastic and phonon properties of Y₃Al₅O₁₂ under pressures are performed. The results that are obtained show the changes of optical and elastic properties under the influence of applied pressure, and proving the dynamical stability of YAG are destructed when applied pressure up to 7 GPa. Moreover, polycrystalline elastic moduli are deduced according to the Reuss assumption. Those elastic constants provide important parameters that describe reliability of both physical model and engineering application at the atomistic level. The result of the density of states explains the nature of the electronic band structure.     

Luminescence properties of Cr:Y3Al5O12 nanocrystals

The Cr³⁺-doped Y₃Al₅O₁₂ (YAG) nanocrystalline powders were prepared by the Pechini method. The structural and phase evolution studies were performed using X-ray powder diffraction (XRD) method. The TEM images were taken in order to characterize the grain size and morphology of the Cr:YAG nanocrystals. Their excitation and luminescence spectra were investigated. It was found that luminescence properties of the Cr:YAG nanocrystals were strongly affected by size of the particles. With increasing the grain size the electron-phonon coupling decreases whereas the crystal-field strength increases.     

Weak field magnetic transition in Tb3Fe5O12

A jump like magnetic transition is observed at relatively weak field in Tb₃Fe₅O₁₂ when the magnetic field is applied along the hard axis and no transition is observed with the field applied along the easy axis. We believe that this evolution is related to the ”Umbrella” type magnetic structure known to exist in Tb₃Fe₅O₁₂ at low temperatures.     

Y3Fe5-xMnxO12的磁结构和磁性能

对多晶Y₃Fe₃Fe_5-xMn_xO₁₂(x=0.05和0.09),得到300K下的中子衍射曲线。发现当x=0.05时,Mn³⁺离子占据16a和24d位置的几率分别为0.72和0.28;当x=0.09时,Mn³⁺离子全部占据16a位置;还得到两种组分16a和24d位置各自的磁矩值。在外磁场(800—10KOe)下测量Y₃Fe_5-xMn_xO₁₂(x=0—0.11)的磁化曲线,温度范围是1.5—300K。得到饱和磁矩值;并利用趋近饱和定律确定1.5K下的磁晶各向异性常数k₁值,发现|k₁|值随含锰量增加而减小。 关键词：     

Optical characteristics of Cr and Nd codoped Y3Al5O12 ceramics

The optical characteristics of Cr³⁺ and Nd³⁺ codoped Y₃Al₅O₁₂ (YAG) ceramics are measured. These measurements are done using two pumping sources, a 808 nm laser diode (LD) and a Xe short-arc lamp, to simulate solar radiation. The specimens used are 0.1%Cr³⁺/1.0%Nd³⁺ and 3.0%Cr³⁺/1.0%Nd³⁺ (atomic%) codoped YAG ceramics. A Nd:YAG crystal doped with 1.0%Nd³⁺ is used as a reference. The saturation intensities of the Cr/Nd:YAG ceramics pumped by the LD are the same as that of the Nd:YAG crystal, while they are higher when they are pumped by the Xe lamp. The saturation intensities are for the 0.1% Cr-doped ceramic and for the 3.0%Cr-doped ceramic. The small signal gains of the 0.1%Cr-doped and 3.0%Cr-doped ceramics are measured and found to be 1.8 times and 7.0 times higher than that of Nd:YAG for the same intensity of solar pumping, respectively. The quantum efficiency of energy transfer from Cr³⁺ to Nd³⁺ is estimated to be 0.88±0.09 for the 0.1%Cr-doped ceramic and 0.67±0.08 for the 3.0%Cr-doped ceramic.     

Synthesis and laser patterning of Bi-doped Y3Fe5O12 crystals in germanosilicate glasses

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.     

High heat generation ability in AC magnetic field for nano-sized magnetic Y3Fe5O12 powder prepared by bead milling

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.     

Saturation magnetic moment at 0°K of PrY2Fe5O12 and NdY2Fe5O12 garnets

The higher saturation magnetic moment of PrY₂Fe₅O₁₂ as compared to NdY₂Fe₅O₁₂ is explained with the aid of magnetic moments obtained from Direc's theory and a definition distinguishing ionicity from valency.     

垂直各向异性Ho3Fe5O12薄膜的外延生长与其异质结构的自旋输运

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(Gd_0.63Y_2.37Sc₂Ga₃O₁₂,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.     

Study on dielectric and magnetic properties of Ho3Fe5O12 ceramics

Ho₃Fe₅O₁₂ ceramics with garnet structure were prepared by the solid-state reaction method. The results revealed the existence of Fe²⁺ ions have intensive influence on dielectric and magnetic properties of Ho₃Fe₅O₁₂ ceramics, which could be further confirmed by oxygen treatment. With a magnetic field lower than 10 kOe, the ME coefficient reaches 33 ps m⁻¹ at room temperature. And the ME coupling was further verified by dielectric anomaly near Néel temperature.     

Energy transfer and luminescent properties of Ce, Cr co-doped Y3Al5O12

The phosphors in the system Y_3−xAl_5-yO₁₂:xCe³⁺,yCr³⁺ were synthesized by solid-state reactions and their photoluminescence properties were investigated. These phosphors have absorption in the visible light region and give luminescence in the far-red region (∼688 nm), which are suitable for the application in the device of luminescent solar concentrator (LSC). In these phosphors, Ce³⁺ located at Y³⁺ site can effectively transfer its absorbed energy to Cr³⁺ at Al³⁺ site.     

Solution-combustion synthesis of Tb-doped Y3Al5O12 nanoparticles

Nano-sized YAG:Tb powder phosphors were prepared by a solution-combustion method, using the general inorganic salts as starting materials. The X-ray diffraction (XRD) measurements showed that the precursor can be well-crystallized at 900 °C. As-prepared particles have sizes mostly in the range between 30 and 100 nm as obtained by scanning electron microscope (SEM) and transition electron microscope (TEM). Selected area electron diffraction (SAED) patterns proved that the larger particles are monocrystalline. The effects of annealing temperature and Tb-doping concentration on the luminescence intensity were studied.     

Y3Al5O12的热输运性质的第一性原理研究

基于密度泛函微扰理论（DFPT）结合模守恒赝势方法进行晶格动力学模拟.得到了钇铝石榴石（YAG）的声子态密度、分波声子态密度和声子的色散谱.利用第一Brillouin区的特殊点取样方法,计算了YAG的比热容和布局数平均的声子群速度.在非谐相互作用下,利用Fermi黄金公式结合第一Brillouin区的特殊点取样方法,得出了YAG非谐声子平均自由程.综合考虑了两种声子散射机制,得到了YAG陶瓷的热导率.结果表明,对于YAG陶瓷,在低温时,晶界散射将对热阻起主要作用;在高于一定温度时,三声子相互作用对热阻的贡献将占主导地位.同时也从理论上证明了Sato等提出的在室温以上,YAG陶瓷与单晶的热导率的差异可以忽略的观点.所得到的热导率、比热容随温度的变化与实验结果很好地符合.     

The optical properties and laser characteristics of Cr and Nd co-doped Y3Al5O12 ceramics

We have fabricated Cr³⁺ and Nd³⁺ co-doped YAG (Cr;Nd:YAG) ceramics, and investigated their optical properties and laser characteristics. The Cr;Nd:YAG has two broad absorption bands at around 440 nm (⁴A₂→⁴T₁) and 600 nm (⁴A₂→⁴T₂) respectively, caused by Cr³⁺ ions. In the case of pumping at 440 nm, the maximum effective lifetime of the Cr;Nd:YAG was 737 μs with a 0.1 at% Cr³⁺ and 1.0 at% Nd³⁺ co-doped YAG sample. Cr³⁺ ions take a role of an effective sensitizer to convert the UV light of flashlamp. For single-shot laser operation, a 10.4 J output energy at 1064 nm was obtained with 0.1 at% Cr³⁺ and 1.0 at% Nd³⁺ co-doped YAG ceramic rod with a laser efficiency of 4.9%. The laser efficiency was found to be more than twice that of a 1.0 at % Nd³⁺:YAG ceramic rod.     

Metal-like to insulator transition in Lu3Fe5O12

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 _eg$e_g$ electrons. The change in the slope at 343 K in the DC conductivity plot also proves the MIT. The dependence of Z^′${\mathrm{Z}}^{\prime }$ on temperature and Z^″${\mathrm{Z}}^{″}$ on frequency clearly substantiates the presence of localized electrons up to 343 K and delocalized electrons above 343 K.