稀磁掺杂MnxGe1-x量子点的制备及应用

作为一种新兴的稀磁掺杂半导体材料,Mn_xGe_(1-x)量子点的自旋电子学性能在最近几年内取得了较为重大的突破。本文针对现有Mn_xGe_(1-x)量子点的稀磁掺杂制备方法及与制备方法相关联的磁电子学性能展开论述,并详细介绍了Mn_xGe_(1-x)量子点在生长过程中Mn原子与生长表面之间的相互作用、形貌转变以及迄今为止对基于这种纳米材料进行的自旋电子学应用的尝试。最后,展望了Mn_xGe_(1-x)量子点未来研究的重点和亟待解决的问题。     

Zn_(1-x)Mn_xS稀磁半导体的水热法制备及其性能

以乙二胺为修饰剂,采用水热法合成了不同掺杂比例的Zn_(1-x)Mn_xS(x=0,0.02,0.05,0.07)稀磁半导体材料,并通过XRD、FESEM、HRTEM、XEDS、光致发光光谱(PL)和振动样品磁强计(VSM)对样品的晶体结构、形貌、光学性能和磁学性能进行表征。实验结果表明:本方法制备的所有样品具有结晶良好的纤锌矿结构,没有杂峰出现;样品形貌为一维的纳米棒状,分散性良好;掺杂的Mn2+以替代Zn2+的形式进入到ZnS晶格中,随着Mn掺杂量的增加晶格常数呈现收缩趋势;样品的PL光谱存在明显的紫外发光峰、蓝光发光峰和绿光发光峰,而且峰位发生蓝移;同时一定量的Mn掺杂ZnS纳米晶在室温条件下具有铁磁性。     

AlN基稀磁半导体的研究进展

主要介绍了AlN基稀磁半导体(DMS)的研究进展,包括其发展过程、AlN基DMS的研究现状,描述了理想的AlN基DMS材料应具备的特征,并展望了其未来的研究方向.     

(Ga,Mn)As稀磁半导体的杂质动力学模拟研究

结合第一性原理计算和动力学蒙特卡罗模拟研究了稀磁半导体(Ga,Mn)As中Mn杂质的沉积动力学规律。利用第一性原理计算和爬坡弹性带方法计算了Mn杂质的跃迁势垒和结合能,并把这些能量作为动力学蒙特卡罗模拟(Ga,Mn)As微观结构演化的输入数据。结果表明在外延生长退火下长时间的微观结构演化的背后机制是Ga空位调节Mn原子在Ga子晶格上进行扩散。这种扩散会导致Mn原子的聚集,进而降低了居里温度。此外,随着退火温度的升高Mn团簇聚集的速率也更快。在高温退火下容易导致相分离。     

稀磁半导体研究的最新进展

本文系统地对于DMS的发展历史及研究现状进行了归纳总结,介绍了稀磁半导体特殊性质和机理,概述了目前DMS材料的制备方法,并对于DMS的应用前景和将来的研究方向进行了展望.     

三角反铁磁材料Mn3Z(Z=Ga,Ge,Sn)的磁性和输运性质

反铁磁材料具有零磁矩或非常小的磁矩,不易受外磁场干扰.相对于铁磁材料,反铁磁材料具有更低的能量损耗和更高的响应频率等优点,因在自旋电子学领域的实际应用方面具有巨大潜力而备受关注.作为一种兼具Kagome晶格及三角反铁磁性的特殊自旋电子学材料,六角Mn3Z(Z=Ga,Ge,Sn)合金展现出巨大的反常霍尔效应、拓扑霍尔效应...     

自燃烧法合成的ZnO基稀磁半导体纳米颗粒研究进展

稀磁半导体制备方法与磁性起源的研究是当前凝聚态物理的一项热门课题.首先介绍了自燃烧合成法的原理和优点,然后以Co和Mn掺杂ZnO为重点,总结了国内外采用自燃烧法合成的ZnO基稀磁半导体纳米颗粒晶体结构、磁性能相关的研究进展,讨论了所得纳米颗粒磁性能的内在物理机制.通过对自燃烧法合成的更宽掺杂范围ZnO基稀磁半导体纳米颗粒的研究,使我们能够更加系统地了解过渡金属掺杂ZnO材料的结构与磁性能,并探讨所得实验现象的内在物理机制.     

Bi_(12)SiO_(20)∶Mn,Cr晶体的杂质诱导光色特性

采用提拉法、电阻炉加热铂坩埚,a 轴取向生长纯的 Bi_(12)SiO_(20)和 Bi_(12)SiO_(20)∶0.05wt·%MnO_2,0.02wt·%Cr_2O_3(BSO∶Mn,Cr)晶体。电子顺磁共振谱指出:光照后激活心电荷态各自为 Mn~(5+)和 Cr~(4+);其 g 因子大小分别为2.0009和1.9616。光照前 BSO∶Mn 在410～750nm 有吸收带,并和吸收边重叠,它相应于 Mn~(5+)离子 ~3A_2→~3T_2,~3T_1跃迁,Mn~(5+)和 Mn~(4+)同时在晶体里存在。光照后,Mn~(5+)离子吸收增加。另外,BSO∶Cr 光色效应可通过 Cr~(5+)→Cr~(4+)电荷传输过程来解释。纯 BSO 晶体粉末有一个 g=2.0109峰宽为75G 的 ESR 带,这带被归为本征捕获空穴心。     

新型稀磁半导体Mn掺杂LiMgAs的光电性质

基于密度泛函理论第一性质原理平面波超软赝势法,对理想新型稀磁半导体Li_(1±y)(Mg_(1-x)Mn_x)As (x=0,0.125;y=0,0.125)进行几何结构优化,计算并分析了体系的电子结构、磁性和光学性质。结果表明,掺杂体系的磁性和电性可以分别通过Mn的掺入和Li计量数的调控来改变,掺Mn后形成Mn—As极性共价键,且引入与Mn有关的自旋极化杂质带,体系为半导体磁性材料。Li不足时,p-d杂化使体系变为半金属性,表现为100%的自旋注入,Mn—As键的重叠电荷布局最大,键长最短。而Li过量时,sp-d杂化则使体系变为金属性,居里温度最高,形成能最低,导电能力最强。对比光学性质发现,Li不足和过量时,介电函数和光吸收谱在低能区出现新峰,增强了体系对低频电磁波的吸收。掺杂体系的能量损失峰均向高能方向偏移,呈现明显的蓝移特征,且峰值急剧减小,表明其等离子共振频率显著降低,而Li过量的等离子振荡范围最宽。     

新型稀磁半导体Mn掺LiBeP的磁电性质调控

采用基于密度泛函理论的第一性原理计算方法,探究了Li1±y(Be1-xMnx)P体系的磁电性质和重叠电荷布局.结果表明,Mn的掺入使体系产生自旋极化杂质带,体系性质受Li计量数的影响,形成了较强的共价键Mn-P键,影响着整个体系的电荷分布.当Li不足时,杂质带宽度减小,净磁矩减小,此时轨道发生了sp-d杂化,体系变为半金属性.而Li填隙时,体系半金属性消失,带隙值减小,导电能力增强,但由于杨-泰勒效应的产生,使得体系净磁矩与Li空位时相当.     

Pressure-induced ferromagnetism in (In,Mn)Sb dilute magnetic semiconductor

Recent advances in III(1-x)Mn(x)V ferromagnetic semiconductors (for example in Ga(1-x)Mn(x)As) have demonstrated that electrical control of their spin properties can be used for manipulation and detection of magnetic signals. The Mn(2+) ions in these alloys provide magnetic moments, and at the same time act as a source of valence-band holes that mediate the Mn(2+)-Mn(2+) interactions. This coupling results in the ferromagnetic phase. In earlier workit was shown that the ferromagnetic state can be enhanced or suppressed by varying the carrier density. Here we demonstrate that, by using hydrostatic pressure to continuously tune the wavefunction overlap, one can control the strength of ferromagnetic coupling without any change in the carrier concentration. Tuning the exchange coupling by this process increases the magnetization spectacularly, and can even induce the ferromagnetic phase in an initially paramagnetic alloy. These results may open new directions for strain-engineering of nanodevices.     

(Ga,Mn)N : Sn Epilayers

We have prepared (Ga,Mn)N : Sn epilayers on sapphire(0001) substrates by RF-plasma assisted molecular beam epitaxy. We found that codoping with Sn enhances the incorporation of Mn into a GaN host crystal. With increasing the Sn content, the “offset” ferromagnetic magnetization component tends to disappear and the epilayers become completely paramagnetic. The effective spin number is S ≈ 2.5 without Sn, whereas it decreases to S ≈ 2.0 when Sn is incorporated. n-type conduction starts to take place when Sn contents exceed beyond the Mn contents.     

(Ga,Mn)N : Sn Epilayers

We have prepared (Ga,Mn)N : Sn epilayers on sapphire(0001) substrates by RF-plasma assisted molecular beam epitaxy. We found that codoping with Sn enhances the incorporation of Mn into a GaN host crystal. With increasing the Sn content, the offset ferromagnetic magnetization component tends to disappear and the epilayers become completely paramagnetic. The effective spin number is S 2.5 without Sn, whereas it decreases to S 2.0 when Sn is incorporated. n-type conduction starts to take place when Sn contents exceed beyond the Mn contents.     

Energy states, transport, and magnetotransport in diluted magnetic semiconductor (Ga, Mn)As with quantum well InGaAs

We investigate energy levels, thermodynamic, transport and magnetotransport properties of holes in GaAs structure with quantum well InGaAs delta-doped by C and Mn. We present self-consistent calculations for energy levels in the quantum well for different degrees of ionization of Mn impurity. The magnetoresistance of holes in the quantum well is calculated. We explain observed negative magnetoresistance by the reduction of spin-flip scattering on magnetic ions due to aligning of spins with magnetic field.     

Structure and elemental distribution of (Ga,Mn)N nanowires

(Ga,Mn)N nanowires were grown by plasma-assisted molecular beam epitaxy on p-type Si(111) substrates. Chemical composition and elemental distribution of single nanowires were analyzed by energy dispersive X-ray spectroscopy revealing an inhomogeneous Mn distribution decreasing from the surface of the nanowires toward the inner core region. The average Mn concentration within the nanowires is found to be below 1%. High-resolution transmission electron microscopy shows the presence of planar defects perpendicular to the growth direction in undoped and Mn-doped GaN nanowires. The density of planar defects dramatically increases under Mn supply.     

GaAs:Mn nanowires grown by molecular beam epitaxy of (Ga,Mn)as at MnAs segregation conditions

GaAs:Mn nanowires were obtained on GaAs(001) and GaAs(111)B substrates by molecular beam epitaxial growth of (Ga,Mn)As at conditions leading to MnAs phase separation. Their density is proportional to the density of catalyzing MnAs nanoislands, which can be controlled by the Mn flux and/or the substrate temperature. After deposition corresponding to a 200 nm thick (Ga,Mn)As layer the nanowires are around 700 nm long. Their shapes are tapered, with typical diameters around 30 nm at the base and 7 nm at the tip. The wires grow along the 111 direction, i.e., along the surface normal on GaAs(111)B and inclined on GaAs(001). In the latter case they tend to form branches. Being rooted in the ferromagnetic semiconductor (Ga,Mn)As, the nanowires combine one-dimensional properties with the magnetic properties of (Ga,Mn)As and provide natural, self-assembled structures for nanospintronics.     

Alloying (In,Mn)As and (Ga,Mn)As: Ferromagnetic (In,Ga,Mn)As Lattice-Matched to InP

An effect of alloying two ferromagnetic semiconductors (In,Mn)As and (Ga,Mn)As on the ferromagnetic properties of resultant (In,Ga,Mn)As alloys is reported. For conditions close to lattice-matching to InP substrates, y = 0.53 in (In _y Ga_1–y )_1–x Mn _x As, ferromagnetism up to Curie temperatures T _C = 100–110 K could be achieved for a Mn composition x = 0.13. Trends in the Curie temperature in (In,Ga,Mn)As are compared with (Ga,Mn)As and (In,Mn)As as a function of Mn content. Hole concentrations determined from magnetotransport, taking into account the anomalous Hall contribution to Hall resistance, gives p/Mn = 0.03 ratio to Mn composition in metallic case for x = 0.13. We mention the possible role of chemical ordering (short range) of Mn impurity atoms on hole concentration and, consequently, for the ferromagnetic properties.     

Structure and magnetic properties of (Co,Mn) co-doped ZnO diluted magnetic semiconductor nanoparticles

The ZnO, Zn_0.96Mn_0.04O, Zn_0.95Mn_0.04Co_0.01O, Zn_0.94Mn_0.04Co_0.02O and Zn_0.92Mn_0.04Co_0.04O nanoparticles were synthesized by simple chemical precipitation technique. The effects of co-doping on the structure and magnetic properties of these nanoparticles were studied. The X-rays diffraction (XRD) scans were performed in the 2θ range of 20°–80°. The XRD patterns, at 300 K, of all the pure and co-doped ZnO samples confirmed the formation of wurtzite-type structure. X-ray diffraction and transmission scanning electron microscope analysis indicated that the high spin Co²⁺ and Mn²⁺ ions were substituted for the Zn²⁺ ions at tetrahedral sites. The average size of the nanoparticles were increased from 17 to 24 nm with the increase of dopants concentration. Moreover, Energy Dispersive X-ray spectroscopy (EDX) confirmed the synthesis results. All Zn_0.96?xMn_0.04Co _x O (x?=?0.0, 0.1, 0.2 and 0.4) nanoparticles samples were observed to be paramagnetic below 300 K. However, a large increase in the magnetization was observed below 40 K. This behavior, along with the negative value of the Curie–Weiss constant obtained from the linear fit to the susceptibility data below room temperature, indicated the ferromagnetic nature of the samples. The origin of ferromagnetism is likely to be the intrinsic characteristics of the Co and Mn doped samples. The high magnetization was noted for the 1 wt% Co co-doped Mn–ZnO annealed samples as compared to other samples with Co concentration above and below this threshold concentration.     

Zn(1-x)MnxTe diluted magnetic semiconductor nanowires grown by molecular beam epitaxy

It is shown that the growth of II-VI diluted magnetic semiconductor nanowires is possible by the catalytically enhanced molecular beam epitaxy (MBE). Zn(1-x)MnxTe NWs with manganese content up to x=0.60 were produced by this method. X-ray diffraction, Raman spectroscopy, and temperature dependent photoluminescence measurements confirm the incorporation of Mn(2+) ions in the cation substitutional sites of the ZnTe matrix of the NWs.     

Rotation of Ferromagnetically Coupled Mn Spins in (Ga,Mn)As by Hole Spins

We present experimental data obtained from ferromagnetic p-(Ga,Mn)As layers that indicate the collective rotation of ferromagnetically coupled Mn spins by optically generated spin-polarized holes through the p–d exchange interaction. The rotation occurs reversibly between the in-plane and perpendicular directions, causing a large change in perpendicular magnetization without the application of a magnetic field. Pump-and-probe experiments suggest that the rotation of Mn spins take place in the picosecond time domain.