氧化物稀磁半导体材料的理论与实验研究进展

以氧化物宽禁带半导体为基体,通过掺杂磁性元素,可将非磁性半导体转变成铁磁性半导体,利用这些铁磁性半导体,能将新型的自旋电子器件集成到传统的微电子器件上,构成功能丰富的新型器件.由于稀磁半导体材料在自旋电子学中的重要作用,近年来受到广泛的关注.简要总结了有关氧化物稀磁半导体研究的发展状况;分析了制备条件对其磁性的可能影响;重点介绍了该系统中有关磁性起源的理论模型,包括双交换机制、磁极化子模型、RKKY模型等;比较了2种磁极化子理论模型,并对这些模型的适用范围进行了分析讨论.另外,还介绍了该体系微结构和磁结构的一些检测方法以及与磁性相关的输运性质、反常霍尔效应等.     

Magnetic Properties of Chalcopyrite-Based Diluted Magnetic Semiconductors

We calculated the chemical trends of transition metal-doped chalcopyrite DMS (diluted magnetic semiconductors) by the use of KKR–CPA–LDA method. The ferromagnetism was stable in V- and Cr-doped chalcopyrite DMS. In the case of Fe and Co doping, however, the spinglass-like state was realized. On the other hand, in the cases of Mn doped I-III-VI₂ and II-IV-V₂ type DMS, the ground state was ferromagnetic and spinglass-like, respectively.     

Transport and Optical Properties of Diluted Magnetic Semiconductors

We investigated the transport and optical properties of diluted magnetic semiconductors theoretically by using a simple model where carriers move in a single band. In this model the carrier feels a nonmagnetic potential at a magnetic impurity site, and its spin interacts with the localized spins of the magnetic impurities through exchange interactions. The electronic states of a carrier were calculated by using the coherent potential approximation (CPA). The magnetism was investigated by minimizing the free-energy and the electrical conductivity was calculated by using the Kubo formula. We examined the results in several typical cases which correspond to (Ga_1–xMn_x)As with x = 0.05.     

过渡金属掺杂ZnO稀磁半导体的发光特性

ZnO是一种宽带隙Ⅱ-Ⅵ族半导体,具有良好的光电耦合特性和稳定性,在光、电、磁功能集成等新型器件方面可获得重要应用.近来的研究表明,过渡金属掺杂的ZnO基半导体有望成为实现高居里温度稀磁半导体的候选材料,是目前研究的热点.总结了近几年人们在Fe、Co、Ni、Cu、Mn等过渡金属掺杂的ZnO基稀磁半导体的发光特性研究结果,讨论了过渡金属掺杂后ZnO中观察到的可见发光机制,分析认为过渡金属掺杂ZnO的可见光发射主要与这些发光过渡金属引入后所产生的缺陷有关,而紫外发光峰的变化则与过渡金属掺入后ZnO晶体质量与禁带宽度的改变相关.     

Giant Magneto-Optical Properties in Hybrid Nanostructures of Diluted Magnetic Semiconductors With Ferromagnetic Co Wires

Giant Zeeman effects of excitons were studied in hybrid nanostructures of diluted magnetic semiconductor (DMS) quantum wells (QWs) with ferromagnetic Co, where the DMS-QW wires with the width of 200 nm were sandwiched in the Co wires with the width of 400 nm. When the direction of the Co magnetization is normal to the wire plane, a magnetic field B ^⊥ _Co‐flux perpendicular to the well plane can be applied from the Co wires to all of the DMS-QW wire. In addition, the use of a Co/Pt multilayered film with the perpendicular magnetization at zero external field was examined instead of the pure Co film. The excitonic photoluminescence spectrum from the DMS-QW shows significant broadening in the hybrid structures, indicating the giant Zeeman shift of excitons induced by B ^⊥ _Co‐flux.     

退火处理Fe(Co)Al(Zr)O系薄膜磁性能的研究

采用射频磁控溅射装置在氩气氛下制备了Fe(Co)Al(Zr)O系薄膜.用X射线衍射仪、透射电镜及其选区衍射来分析薄膜的微结构.用振动样品磁强计、磁导计等测量了矫顽力Hc、饱和磁化强度Ms及磁导率等磁性参数.通过退火处理研究了Fe(Co)Al(Zr)O系薄膜的磁性能.Fe(Co)Al(Zr)O系薄膜磁各向异性是由形状各向异性引起的.     

Mn0．8Zn0．2Fe2O4／MgAl-LDHs复合材料的磁性能和磁热效应

采用共沉淀法将纳米锰锌铁氧体粒子(Mn0.8Zn0.2Fe2O4)与镁铝双金属氢氧化物(MgAl-LDHs)进行组装合成了磁性纳米镁铝双金属氢氧化物,并通过TEM,FTIR、DTA、XRD、VSM等方法对其进行表征.样品的结构分析结果表明,复合材料具有典型的核壳结构,镁铝双金属氢氧化物被赋予磁性后并没有改变其层状结构的典型特征.样品的磁学性能和磁热性能测试结果表明,铁氧体的含量对复合材料的磁性能和磁热效应起着决定性作用;MgAl-LDHs对铁氧体粒子没有显著的磁屏蔽效应,复合材料的饱和磁化强度与铁氧体的含量呈正线性相关,而复合材料的矫顽力随MgAl-LDHs含量的增加呈现先减小后增大的趋势,但整体变化幅度很小,同时MgAl-LDHs对铁氧体粒子磁热效应的影响也极小.     

Spin Carrier Exchange Interactions in (Ga,Mn)N and (Zn,Co)O Wide Band Gap Diluted Magnetic Semiconductor Epilayers

(Ga,Mn)N and (Zn,Co)O wide band gap diluted magnetic semiconductor epilayers have been investigated by magneto-optical spectroscopy. In both cases, absorption bands observed below the energy gap allow us to study the nature of the valence and spin state of the incorporated magnetic element. Exchange interactions between magnetic ions and carriers can be observed by analyzing the magnetic circular dichroism in transmission or the exciton Zeeman splitting in reflection for (Zn,Co)O. A first estimation of the exchange integrals can be given for both materials.     

SrCo0.8Fe0.2O3-δ及SrCo0.8Fe0.1Sn0.1O3-δ的热学与透氧性能研究

介绍了对SrCo0.8Fe0.2O3-δ、SrCo0.8Fe0.1Sn0.1O3-δ两种透氧膜材料相组成、热学性能及氧渗透性能的研究,发现实验中获得的SrCo0.8Fe0.2O3-δ透氧膜材料具有长期的相组成稳定性;在它的B位进一步用Sn取代部分Fe,获得名义组成SrCo0.8Fe0.1Sn0.1O3-δ样品,具有典型的双相组成特征.与单相SrCo0.8Fe0.2O3-δ相比,双相结构SrCo0.8Fe0.1Sn0.1O3-δ样品的热膨胀率降低,抗热冲击性能增加显著;同时,氧渗透性能也有一定程度的提高,如1.2mm厚的SrCo0.8Fe0.2O3-δ陶瓷膜样品在1000℃具有1.87×10-6mol·cm-2·s-1的透氧率(Po2(h)=2.09×104pa,Po2(1)=1.2×103Pa),同样条件下的SrCo0.8Fe0.1Sn0.1O3-δ样品透氧率为2.49×10-6mol·cm-2·s-1.     

Synthesis,Structural, and Magnetic Properties of Nanocrystalline Ti 0.95Co0.05O2-Diluted Magnetic Semiconductors

With a view to investigate the influence of nanometric size on the structural, surface, and magnetic properties of nanocrystalline Ti_0.95Co_0.05O₂-diluted magnetic semiconductors, prepared by a novel simple controllable peroxide-assisted reflux chemical route followed by annealing at different temperatures, a systematic investigation has been undertaken. Structural characterizations such as X-ray diffraction followed by Rietveld refinement, electron diffraction pattern, Fourier transform infrared, Raman scattering, and X-ray photoelectron spectroscopy (XPS) measurements have shown anatase phase formation in nanocrystalline Ti_0.95Co_0.05O₂ without any additional impurity phases. The modified reflux chemical route was effective in obtaining pure phase Ti_0.95Co_0.05O₂ nanoparticles. Surface morphological investigations by using transmission electron microscopy and atomic force microscopy measurements showed the predominant effect of random distribution of nanoparticles on the aggregation behavior and local microstructural changes. The deconvoluted XPS core level Co 2p spectral study manifested the oxidation state of Co as + 2 and is found to be stable with varying particle size and annealing temperature. The ferromagnetic behavior was investigated by vibrating sample magnetometer, magnetic force microscopy, and electron spin resonance measurements. These magnetization studies showed all the samples are ferromagnetic at room temperature without any magnetic clusters. The correlation between structure, surface condition of the nanoparticles and local electronic interactions, and magnetization of the samples was analyzed and explored the origin of ferromagnetism.     

Theoretical Investigation of Structural,Electronic, and Magnetic Properties of V-Doped MgSe and MgTe Semiconductors

In this study, we have explored the structural, electronic, and magnetic properties of V-doped zincblende MgSe and MgTe compounds using density functional calculations. The Wu-Cohen generalized gradient approximation is used for optimizing the structural properties, while the modified Becke and Johnson local (spin) density approximation functional has been employed to compute the electronic and magnetic properties. The spin dependent band structures, electronic density of state, and magnetic moments calculated for V-doped MgSe and MgTe semiconductors exhibit occurrence of 100 % spin polarization at the Fermi level which confirms stable half-metallic ferromagnetism in these materials. The spin-down gaps and the half-metallic gaps are analyzed in terms of V-3d and Se-4p (Te-5 p) hybridization, where it is observed that the V-3dstates play a key role in generating spin polarization and the magnetic moment in these compounds. The exchange constants N ₀ αand N ₀ β have been calculated to demonstrate the effects resulting from exchange splitting process. Furthermore, spin-polarized charge density calculation is presented for elucidating the bonding nature, while pressure dependence of total magnetic moment for three concentrations of V-doped MgSe and MgTe are also discussed.     

Boosting the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 cathode materials with Zn3(PO4)2 surface coating

Ni-rich layered oxides have been demonstrated to be promising cathode materials for high-energy–density batteries. However, most of them suffer from sluggish kinetics and structural instability, severely impeding their practical applications. Herein, the surface of LiNi_0.8Co_0.1Mn_0.1O₂ cathode is modified with ionic, conducting zinc phosphate (Zn₃(PO₄)₂) nanolayers. The nanolayers are autogenously formed from the reaction of NH₄H₂PO₄ with ZnO assisted with citric acid. The as-prepared 3 wt% Zn₃(PO₄)₂ coated sample exhibits a first discharge capacity of 203.4 mAh g^-1and excellent capacity retention for 100 cycles. The surface Zn₃(PO₄)₂ nanolayers positively impact the cell performance by scavenging HF and H₂O in the electrolyte, leading to less formation of byproducts on the surface of the cathodes, which lowers the cell resistance and polarization voltage. Our study provides a simple and efficient strategy to design and optimize promising layer-structural cathodes for LIBs.     

Annealing Induced Enhancement in Magnetic Properties of Co0.5Zn0.5Fe2O4 Nanoparticles

In this paper, cobalt zinc ferrite (Co_0.5Zn_0.5Fe₂O₄) nanoparticles (NPs) have been prepared using chemical co-precipitation method. In order to investigate the annealing induced effects on their various physical properties, the prepared samples have been annealed at 500 °C, 650 °C and 1000 °C and then compared with as-prepared sample. X-ray diffraction (XRD) patterns of as-prepared and annealed samples at various temperatures exhibit single phase spinel structure. Enhancement in crystallinity and crystallite size is observed with the increase in annealing temperature. The annealing has also greatly influence the morphology and grain size of prepared NPs. The Co_0.5Zn_0.5Fe₂O₄ NPs have shown remarkable enhancement in magnetic moment with increase in annealing temperature. The bandgap energies of Co_0.5Zn_0.5Fe₂O₄ NPs have been measured via UV Spectrometer and observed to decrease with annealing temperature. FTIR spectra of the samples reveal the presence of both high frequency and low-frequency bands due to tetrahedral and octahedral sites, which corroborate well with the XRD results. The observed characteristics of cobalt zinc ferrite NPs as a function of annealing temperature are the rising contender for many data storage and nanodevice applications. Finally, the genotoxicity of prepared nanoferrites has been checked via comet assay.     

Trends of Parallel Microstructure and Magnetic Properties Evolution in Co0.5Zn0.5Fe2O4

The present paper reports on an effort to expose and scientifically explain the microstructure–magnetic properties relationship as they evolve with increasing sintering temperature. Mechanical alloying was used to prepare cobalt–zinc ferrite nanoparticles with sintering temperature from 800 to 1,350 °C with 50 °C increment. The microstructure of the samples was observed using a field emission scanning electron microscope, and the magnetic parameters, such as the real permeability and loss factor, were measured at room temperature in the frequency range from 10 MHz to 1.0 GHz using an Agilent 4291B impedance/material analyzer. The B–H hysteresis of the samples was investigated using a MATS-2010SD Static Hysteresisgraph. From the results, the real permeability and loss factor were observed to increase up to 1,250 °C. These increases corresponded to increases in grain size and are mainly due to easier domain wall movement. However, due to zinc loss, \(\mu ^{\prime }\) and \(\mu ^{\prime \prime }\) as well as the saturation induction decreased from 1,300 to 1,350 °C. The coercivity increased up to 850 °C and decreased with increasing temperature. This increasing-to-decreasing coercivity trend corresponded well with the single- to multi-domain grain size transition marked by critical grain size at about 0.13 μm.     

脉冲激光沉积制备外延Ni_(0.8)Zn_(0.2)Fe_2O_4薄膜的应变与磁性能研究

用脉冲激光沉积设备,分别在SrTiO3(001)(STO)和MgO(001)基片上外延生长了单层Ni0.8Zn0.2Fe2O4(NZF)薄膜。经X射线衍射分析,在STO和MgO基片上制备的NZF薄膜均为单一c取向的外延薄膜,由PHI扫描可知薄膜均为四重对称结构。由NZF薄膜的倒易空间图可以计算得到在STO和MgO基片上应变分别为0.0704和-0.0124。分别对不同基片上的NZF薄膜进行磁强计测量可得,在STO基片上沉积的NZF薄膜的面内和面外饱和磁化强度分别为269.6和224.78 emu/cm3,面内和面外的矫顽场分别为2.68×104和4.78×104A/m,在MgO基片上沉积的NZF薄膜的面内和面外饱和磁化强度分别为219.11和180.75 emu/cm3,面内和面外的矫顽场分别为3.46×104和5.32×104A/m。     

Spontaneous Polarization and Magnetic Investigation Of BiXO3 (X=Co,Mn, Fe,V, Zn): First-Principle Study

Spontaneous polarization and magnetic properties of BiXO3 with X = Co, Fe, Mn, V, and Zn have been studied using the full-potential, linear augmented plane wave (FP-LAPW) method with GGA and mBJ implemented in the WIEN2K code. The investigation shows that BiXO3 with X = Co, Fe, Mn, and Zn is stable in the antiferromagnetic state while for BiVO3, the magnetic stability was shown in the ferromagnetic state. The calculation shows the existence of a charge transfer between p states of oxygen and d states of Co and Fe for X = Co and Fe. The existence of Co, Fe, Mn, and V makes BiXO3 a non-absorbent compound. However, for Zn, the structure behaves as an absorbent compound especially in the visible light. We note that the spontaneous polarization is calculated with Berry phase BI and was found very close and comparable with other works.     

尖晶石型Ni0.8Zn0.2Fe2O4纳米晶体的制备及电磁性能研究

以金属离子的柠檬酸盐为前驱体，通过sol-gel自燃烧的合成方法制备了镍锌铁氧体（Ni0．8Zn0．2Fe2O4）纳米晶体。采用FT-IR、DSC-TG、XRD、TEM波导等方法对产物以及产物的电磁性能进行了表征。结果表明，在前驱体中，金属离子与柠檬酸以络合物的形式存在，凝胶在220℃完成自燃烧反应，随着热处理温度的升高，粉体的粒径逐渐增大，纳米晶体在8-12GHz的测试条件下具有介电损耗与磁损耗，随着涂层厚度的增加，混合媒质的微波反射率逐渐增加，反射率吸收峰随着厚度的增加向低频移动。     

纳米晶Co0.8Fe2.2O4薄膜的室温和高温结构及磁性

采用溶胶-凝胶旋转包覆法在玻璃衬底上制备了CO0.8Fe2.2O4薄膜.用振动样品磁强计和X射线衍射仪对样品的磁性和结构进行了室温及高温原位测量;用X射线光电子能谱仪和原子力显微镜测量了样品的成分及表面形貌.室温测量结果表明,400%退火时,样品已生成单一的尖晶石相,随退火温度升高衍射峰增高.样品的晶粒尺寸较小(14.2～29.6 nm),有利于降低磁记录材料的晶界噪音.630%退火样品的矫顽力达到1.56 X 105A·m-1.高温原位测量发现,500%高温时线膨胀系数约为1.3 X 10-5K-1,显示样品结构的热稳定性非常好,适合于磁光记录过程.随温度升高,样品由亚铁磁性逐渐过渡到顺磁性.     

Crystal structure,oxygen permeability and stability of Ba0.5Sr0.5Co0.8Fe0.1M0.1O3−δ (M = Fe,Cr, Mn,Zr) oxygen-permeable membranes

Oxygen-permeable ceramic membrane materials of the Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) and partially Fe-substituted Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Cr, Mn, Zr) were synthesized by solid-state reaction method. These materials possess purely cubic perovskite structure with the exception of Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Mn, Zr), in which minor impurities exist. Oxygen permeability across these dense membrane disks were measured under an air/He oxygen partial pressure gradient in the temperature range of 973–1123 K. The results demonstrated that the oxygen permeation fluxes of the Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Fe, Cr, Mn, Zr) membranes increased in the following order: Fe (BSCFO) > Cr > Zr > Mn. The corresponding activation energies for oxygen permeation of Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Fe, Cr, Zr) membranes were calculated to be similar (53 ± 4 kJ/mol), which was remarkably lower than that (99 ± 3 kJ/mol) of Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Mn) membrane. In addition, good oxygen permeation stability of the Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Cr) membrane was achieved at the temperature lower than 1123 K. The X-ray diffraction (XRD) and differential thermal analysis (DTA) experiments showed that the structural stability of BSCFO could be significantly improved when Fe ions in the BSCFO material were partially substituted by Cr, Mn or Zr ions.     

Magnetic and Magnetotransport Properties of Diluted Magnetic Semiconductor (Ga,Mn)Sb Crystals

We report the magnetic and magnetotransport properties of Ga_1−x Mn _x Sb crystals grown with different Mn doping concentrations (x=0.01, 0.02, 0.03 and 0.04) by the horizontal Bridgman technique. A systematic reduction in lattice parameter with increase in Mn concentration is observed through X-ray diffraction studies. The crystals show negative magnetoresistance and anomalous Hall effect below 10 K. Anomalous Hall coefficient is negative and decreases with increasing Mn concentration. Temperature dependence on magnetization measurement shows a magnetic ordering below 10 K which could arise from GaMnSb alloy formation. Also, ferromagnetism is observed till room temperature due to the presence of MnSb clusters. Existence of MnSb clusters is verified through scanning electron microscopy. The carrier concentration increases with Mn doping and this results in decrease of resistivity. The observed magnetic and transport properties indicate the presence of ferromagnetic phase below 10 K in the studied system.