Magnetic Properties of Zn0.8(Fe0.1,Co0.1)O Diluted Magnetic Semiconductors: Experimental and Theoretical Investigation

Structural and magnetic properties of Zn_0.8(Fe_0.1, Co_0.1)O bulk diluted magnetic semiconductor have been investigated using X-ray diffraction (XRD) and magnetic measurements. TEM (Transmission Electron Microscopy) images confirmed the high crystallinity and grain size of Zn_0.8(Fe_0.1,Co_0.1)O powder, the samples were characterized by energy dispersive spectroscopy (EDS) to confirm the expected stoichiometry. This sample has been synthesized by co-precipitation route. The study of magnetization hysteresis loop measurements infers that the bulk sample of Zn_0.8(Fe_0.1,Co_0.1)O shows a well-defined hysteresis loop at T _c (200?K) temperature, which reflects its ferromagnetic behavior. Hydrogenation treatment was used for the control of phase separation. Based on first-principles spin-density functional calculations, using the Korringa?CKohn?CRostoker method (KKR) combined with the coherent potential approximation (CPA), the ferromagnetic state energy was calculated and compared with the local-moment-disordered (LMD) state energy. The mechanism of hybridization and interaction between magnetic ions in Zn_0.8(Fe_0.1,Co_0.1)O is also investigated.     

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.     

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.     

Electronic and Magnetic Theoretical Investigation of Antiferromagnetically ErRh Layers

Self-consistent ab initio calculations, based on the DFT (Density Functional Theory) approach and using the FLAPW (Full potential Linear Augmented Plane Wave) method, are performed to investigate both electronic and magnetic properties of the ErRh layers. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two sites of Er atoms. Magnetic moments considered to lie along axes are computed. The data obtained from the ab-initio calculations are then used as input for the high-temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The exchange integrals between the magnetic atoms in the same sites are given by using mean field theory. The HTSEs of the magnetic susceptibility of ErRh antiferromagnetic spin-S through two model: Heisenberg and XY for ErRh layers, are studied to sixth order series in β=1/k _B T. The critical exponent γ associated with the magnetic susceptibility is deduced for the two models.     

First Principles Study on the Effects of Cu Doping on the Magnetic Moment and Electronic Properties of V-Doped ZnO

The CASTEP program was used to study the effects of Cu on the structure, magnetic moment and electronic properties of V-doped ZnO. The calculated enthalpies showed that the Cu atoms were inclined to stay near the V atoms. Cu neutralized the delocalized electrons in V-doped ZnO. Cu also suppressed the magnetic moments of Zn and O more than those of the V ions. The different amounts of suppression caused the moments to concentrate on the V atoms. The magnetic moments decreased in Cu and V co-doped ZnO. The suppressions of the magnetic moments and concentrations of the Cu atoms were verified with density of states calculations. The states showed that Cu increased the conduction in V-doped ZnO. The calculated spin isospheres showed that Cu improved the concentration of the magnetic moments on the V sites. The improved concentration enhanced the performance of diluted magnetic semiconductors based on V-doped ZnO. These results help in understanding the role of Cu in V-doped ZnO. They also provide a reference for preparing diluted magnetic semiconductors based on V-doped ZnO     

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.     

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.     

Electronic and Magnetic Properties of Os-Doped Rhodium Clusters: a Theoretical Study

The stability and electronic and magnetic properties of Rh_nOs (n=?2–12) clusters in their most stable configurations were systematically studied by using density functional theory (DFT) at M06L/aug-cc-pVDZ level. Calculation of the second-order difference of energies and fragmentation energies exhibited that Rh₃Os, Rh₅Os, Rh₇Os, and Rh₉Os clusters are more stable than any other clusters. The calculated HOMO-LUMO energy gaps of the Rh_nOs clusters are found to be in the range of 0.018 to 0.299 eV, implying that the metallic behavior can appear in these clusters. Accordingly, the Rh_nOs clusters can be employed as heterogeneous nanocatalysts in many chemical reactions. The local Fukui function (\(f_{k}^{-} )\) has also been calculated, and the obtained results reveal that the highest \(f_{k}^{-} \) values are predicted for the Rh atoms. Therefore, the Rh atoms in the clusters are considered the most reactive sites that undergo reactions with electrophilic reagents. The analysis of the magnetic properties of the Rh_nOs clusters shows that the total magnetic moment per atom of these clusters varies from 0.67 to 1.75 µ_B/atom. And, the PDOS analysis reveals that the d orbitals play a crucial role for the magnetism of the Rh_nOs clusters, and the contribution of the s and p orbitals is small.     

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.     

Heusler合金Co2MnAl1-xGex的电子结构、磁性和半金属性

基于密度泛函理论(DFT),使用广义梯度近似(GGA)和局域密度近似(LDA)研究了Heusler合金Co2MnAl1-xGex(x=0、0.25、0.5、0.75、1)的磁性和电子结构。随着掺杂浓度x的增加,合金的晶格常数和磁矩都线性增加,分别很好地满足Vegard和S-P规律。对于整个合金系列,随x的增加,自旋向下带带隙宽度略有减少,费米面向高能移动。由于Co2MnAl0.5Ge0.5合金的费米面恰好居于其自旋向下带带隙中部,此时合金具有最好的半金属稳定性,预期在磁隧道结器件中能实现高的自旋极化率。     

Growth and Properties of V-Doped HgSe Crystals

HgSeV crystals with a vanadium concentration ranging from 10²⁴to 10²⁶m^–3were grown, and their transport properties were investigated between 77 and 400 K in magnetic fields of up to 12.73 kA/m. The effect of long-term annealing in Se vapor on the electron concentration and mobility in the crystals was studied. The n(N _V), (T), and R _H(T) data obtained before and after annealing suggest that the V dopant produces a resonance donor level in the conduction band of HgSe at E _V 0.250–0.260 eV.     

基于第一性原理研究Heusler合金Fe2CuGa的结构和性能

采用基于密度泛函理论的第一性原理,系统研究了Heusler合金Fe2CuGa的结构、磁性、弹性性能和电子性质.计算结果表明:立方相的基态结构是铁磁态的Hg2CuTi结构.立方到四方的相变几乎是体积不变的,这是形状记忆合金的特性.奥氏体和马氏体的磁矩分别是4.48和4.56μB/f.u..另外,预测了Fe2CuGa的弹性系数.Fe2CuGa的立方结构在力学上是不稳定的而四方结构是稳定的.根据体模量和剪切模量的比值,发现Fe2CuGa在本质上是可延展的.利用态密度的方法解释了Fe2CuGa马氏体相变的来源.     

Ab Initio,Mean Field and Series Expansions Calculations Study of Structural,Electronic and Magnetic Properties of MnAs

The self-consistent ab initio calculations, based on density functional theory (DFT) approach and using full-potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the MnAs compounds. Polarized spin and spin-orbit coupling are included in calculations within the framework of the ferromagnetic state between two adjacent Mn atoms. The ferromagnetic and antiferromagnetic energies of MnAs systems are obtained. Magnetic moment considered to lie along (001) axes is computed. The obtained data from ab initio calculations are used as input for the high-temperature series expansion (HTSE) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Mn-Mn in MnAs are given using the mean field theory. The HTSEs of the magnetic susceptibility with the magnetic moments in MnAs (m _Mn) through the Ising model is given up to the tenth order series in x=J ₁(Mn-Mn)/ k _B T. The Néel temperature T _C is obtained by HTSEs of the magnetic susceptibility series combined with the Padé approximant method. The critical exponent γ associated with the magnetic susceptibility is deduced as well.     

First Principle Study of the Structural, Electronic and Magnetic Properties of MgO Nanolayers on Fe Substrate

We have investigated the structural, electronic, and magnetic properties of MgO nanolayers with two different nanolayer thicknesses (1.5 nm and 1.75 nm) on a Fe substrate. The calculated results in this paper were obtained using the density functional theory (DFT) within the generalized gradient approximation (GGA). The total energies as a function of volume are calculated and thereby the lattice parameters, bulk moduli of MgO nanolayers with two different thicknesses have been calculated. The effects of surface atoms and Fe substrate atoms on physical properties of these nanolayers have been analyzed using the calculated total and partial electron density of states in its ferromagnetic phase. The spin-polarized density of states of MgO shows that this compound is an insulator in the nonmagnetic phase. MgO nanolayers on Fe substrate are metal in the ferromagnetic phase. The magnetic properties of surface atoms and Fe substrate atoms have been investigated and compared with bulk. Furthermore, the effect of hydrostatic pressure on the total and local magnetic moment of these nanolayers has been investigated.     

Zn_(1-x)Mn_xS稀磁半导体的合成与光学性能

通过水热法制备不同掺杂浓度的Zn_(1-x)Mn_xS(x=0.00,0.02,0.05,0.07)稀磁半导体材料,研究Mn~(2+)掺杂浓度对ZnS纳米棒微观结构和光学性能的影响。采用X射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、选区电子衍射(SAED)、X射线能量色散分析谱仪(XEDS)和紫外可见吸收光谱(UV-vis)对样品的晶体结构、形貌和光学性能进行表征。结果表明:制备的所有样品均具有结晶良好的纤锌矿结构,没有杂峰出现,生成纯相Zn_(1-x)Mn_xS纳米晶。样品形貌为纳米棒状结构,分散性良好。掺杂的Mn元素进入到ZnS纳米晶中,Mn~(2+)替代了Zn~(2+),而且随着Mn掺杂量的增加晶格常数减小。同时UV-vis光谱发现样品的光学带隙增大,发生了蓝移现象。     

First-Principles Study on Structural,Electronic, and Magnetic Properties of 3d Transition-Metal Nanowires Encapsulated Inside GaN Nanotubes

We have performed the first-principles calculations on the structural, electronic, and magnetic properties of 3d transition-metal nanowires (TMNW₄s), Fe₄, Co₄, and Ni₄, encapsulated inside GaN nanotubes (GaNNTs). The results show that, all three types of the TMNW₄ encapsulated inside the narrower (6,6) and broader (8,8) GaNNTs are both exothermic. The spin polarization and magnetic moment of the TMNW₄@(8,8) systems are larger than those of the TMNW₄@(6,6) systems due to more weak restriction of the broader (8,8) GaNNT, but those of these two combined systems are smaller than those of the corresponding freestanding TMNW₄. Our results reveal that either the TMNW₄@(6,6) or TMNW₄@(8,8) systems have high spin polarization and magnetic moment and stably exist in atmosphere for long time and thus can be expected to have potential applications in building nanodevices.     

Electronic and Magnetic Properties of MnSb Compounds

The self-consistent ab initio calculations, based on density functional theory (DFT) approach and using full-potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the MnSb compounds. Polarized spin and spin-orbit coupling are included in calculations within the framework of the ferromagnetic state between two adjacent Mn atoms. The ferromagnetic energy of MnSb systems is obtained. Magnetic moment considered to lie along the (001) axes are computed. The exchange interactions between the magnetic atoms Mn–Mn in MnSb are given using the mean field theory. Obtained data from ab initio calculations are used as input for the high-temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The HTSEs of the magnetic susceptibility of the magnetic moments in MnSb (m _Mn) is given up to the tenth order series in (x = J ₁(Mn–Mn)/ k _B T). The critical temperature T _C is deduced by HTSEs of the magnetic susceptibility series combined with the Padé approximation method. The critical exponent γ associated with the magnetic susceptibility is deduced as well.     

Electronic and Magnetic Properties of MnAu Superlattices

Self-consistent ab initio calculations, based on the Density Functional Theory (DFT) approach and using full potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the MnAu superlattices. Polarized spin and spin-orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent MnAu superlattices. Obtained data from ab initio calculations are used as input for the Monte Carlo simulations to compute other magnetic parameters. On the other hand, and within the framework of Monte Carlo simulations, we examine the magnetic properties in the binary MnAu superlattices modelized by the Mn ion with spin moment, S=5/2. The considered Hamiltonian takes into account the nearest neighbor and second nearest interactions, and an external magnetic field h. The magnetization of the MnAu superlattice is calculated versus temperature for a fixed size. The magnetic hysteresis cycle is established for T=120 K. The effect of magnetization versus the second exchange interaction (J _c ) are established with absence and presence of magnetic field (h).