基于GaAs的新型稀磁半导体材料(Ga,Mn)As

介绍了一种基于 Ga As的新型稀磁半导体材料 ( Ga,Mn) As,包括 ( Ga,Mn) As的制备方法、结构特性、磁性质及磁输运性质。最后 ,展望了 ( Ga,Mn) As的应用前景     

巨磁电阻(GMR)传感器芯片技术背景简介

<正>1988年,法国巴黎大学Fert研究小组在纳米结构的磁性多层膜中,发现膜电阻随外加磁场发生巨大变化的现象,较传统的磁各向异性磁电阻(AMR)大一个数量级以上,称之为巨磁电阻(GMR)效应。其物理机制与传导电子自旋散射相关。     

我国(Ga,Mn)As磁性半导体研究取得进展

7月9日,《物理评论快报》(Phys.Rev.Lett.111,027203 2013)报道了中科院半导体研究所半导体超晶格国家重点实验室赵建华研究组及合作者在(Ga,Mn)As/Co2FeAl双层膜铁磁界面耦合和磁邻近效应方面取得的最新研究成果。(Ga,Mn)As兼具铁磁体和半导体的性质,过去十多年里受到了高度关     

低温退火对稀磁半导体(Ga,Mn)As性质的影响

利用低温分子束外延技术在GaAs(001)上外延生长出厚度为500nm的稀磁半导体(Ga,Mn)As薄膜. 双晶X射线衍射证明其为闪锌矿结构，晶格参数为0.5683nm，据此推导出其Mn含量为7%. 磁测量结果揭示其铁磁转变温度为65K. 观察了低温退火处理对(Ga,Mn)As磁性质的影响，发现生长后退火处理显著提高了其铁磁转变温度，可以达到115K.     

低温退火对稀磁半导体(Ga,Mn)As性质的影响

利用低温分子束外延技术在GaAs(001)上外延生长出厚度为500nm的稀磁半导体(Ga,Mn)As薄膜.双晶X射线衍射证明其为闪锌矿结构,晶格参数为0.5683nm,据此推导出其Mn含量为7%.磁测量结果揭示其铁磁转变温度为65K.观察了低温退火处理对(Ga,Mn)As磁性质的影响,发现生长后退火处理显著提高了其铁磁转变温度,可以达到115K.     

低温退火对稀磁半导体(Ga,Mn)As性质的影响

利用低温分子束外延技术在GaAs(001)上外延生长出厚度为500nm的稀磁半导体(Ga,Mn)As薄膜.双晶X射线衍射证明其为闪锌矿结构,晶格参数为0.5683nm,据此推导出其Mn含量为7%.磁测量结果揭示其铁磁转变温度为65K.观察了低温退火处理对(Ga,Mn)As磁性质的影响,发现生长后退火处理显著提高了其铁磁转变温度,可以达到115K.     

(Ga,Mn,As)/GaAs的发光谱

利用低能双离子束外延技术 ,在 4 0 0℃条件下生长样品 (Ga,Mn,As) / Ga As.样品光致发光谱出现三个峰 ,即1.5 0 4 2 e V处的 Ga As激子峰、1.4 875 e V处的弱碳峰和低能侧的一宽发光带 .宽发光带的中心位置在 1.35 e V附近 ,半宽约 0 .1e V.在 84 0℃条件下对样品进行退火处理 ,退火后的谱结构类似退火前 ,但激子峰和碳杂质峰的峰位分别移至 1.5 0 6 5 e V和 1.4 894 e V,同时低能侧的宽发光带的强度大大增加 .这一宽发射带的来源还不清楚 ,原因可能是体内杂质和缺陷形成杂质带 ,生成 Mn2 As新相 ,Mn占 Ga位或形成 Ga Mn As合金     

In Ga As/Ga As超晶格的界面研究

In_xGa_(1-x)As/Ga As之间晶格失配度与X成线性关系,其最大值为7％。因而当外延层厚度大于临界厚度时在界面会产生微缺陷,这些缺陷对其材料性能有很大影响。因此对In x Ga_(1-x)As Ga As界面研究就显得很重要。本工作就GaAs衬底上MBE生长In_(0.2)Ga_(0.8)As/Ga As超晶格样品进行平面,断面的TEM研究。实验结果表明超晶格平整,均匀,只看到位错一种微缺陷。GaAs衬底内位错。表面机械损伤会在超晶格层内引入位错。在In Ga As Ga As界面上失配位错情况如图1所示。图1a为[110]方向衬象,可见界面上位错线及露头(箭头所示)倾转约30,在图1b中看到位错网络,箭头所示位错为1a中所示的露头。     

低能离子束制备(Ga,Gd,As)薄膜

室温条件下 ,用离子束外延设备制备 ( Ga,Gd,As)样品 ,X射线衍射 ( XRD)结果表明除了 Ga As衬底峰 ,没有发现其他新相的衍射峰。俄歇电子能谱 ( AES)分析了样品中元素随深度的变化 ,不同样品中元素的分布有着不同的特点。并运用原子力显微镜 ( AFM)研究了样品表面的形貌特点 ,表明样品表面的粗糙度与 Gd注入过程中在样品表面沉积的多少有关。运用交变梯度磁强计 ( AGM)对薄膜进行磁性分析 ,结果表明有的样品在室温条件下出现铁磁性 ,但金属钆本身具有室温铁磁性 ,因而需要进一步分析。     

稀磁半导体(Ga1-xFex)As的磁性及稳定性

运用第一性原理下的LMTO-ASA方法研究稀磁半导体(Ga1-xFe x )As( x ＝1,1/2,1/4和1/8)的电子结构、磁性及其稳定性.计算了Fe掺杂浓度的变化对(Ga1-xFe x )As的磁性及稳定性的影响.     

Magnetostatic wave propagation in YIG double layers

Calculations are presented for the magnetostatic surface wave propagation characteristics in single-crystal yttrium-iron-garnet (YIG) double layers with arbitrary direction of magnetization. The induced uniaxial magnetic anisotropy field is assumed to be different in the two layers; hence, the magnetization in one layer is aligned at an angle with respect to the magnetization direction in the other layer. The magnetostatic field interactions between layers depend on the angle between the two magnetization directions and on the separation between the two YIG layers. The wave propagation directions and time delays in each layer can be strongly affected by the use of an applied magnetic field and the magnetostatic coupling between the two layers, as well as by the uniaxial anisotropy energy in each layer     

Magnetization oscillations in a ferromagnet/nonmagnetic metal/ferromagnet nanostructure under the action of the spin-polarized current

Oscillations of magnetization of a ferromagnetic disk included in the ferromagnet/nonmagnetic metal/ferromagnet nanostructure under the action of the spin-polarized current are studied in the macrospin approximation. Conditions for switching and oscillations of magnetization are determined for four cases of the magnetic crystallographic anisotropy near the transition instability region depending on the ratio between disk dimensions and current density. It is shown that the region of disk magnetization instability corresponds to the minimum values of the current density that are necessary for excitation of the oscillations or switching of magnetization. Depending on the value and direction of the anisotropy and the relaxation parameter, the frequency of the observed oscillations varies within 0.1–30 GHz.     

Magnetic Anisotropy of Cr7Ni Spin Clusters on Surfaces

The problem of the experimental and theoretical determination of magnetic anisotropy in isolated molecular spin clusters is addressed here. To this end, the case of molecular Cr₇Ni rings sublimated in ultrahigh vacuum conditions and assembled in an ordered fashion on Au(111) surface is addressed and investigated using X‐ray magnetic dichroism (XMCD) and theoretical calculations. Fixing the experimental conditions at a temperature T = 8 K and a magnetic field of 5 T, the angular‐dependence of the dichroic signal reveals an easy‐axis anisotropy for the Ni magnetization along the direction perpendicular to the ring while the magnetization of the whole Cr₇Ni molecule is preferentially aligned within the ring plane. These features are well reproduced by spin Hamiltonian simulations, which reflect the character of the S = 3/2 first excited multiplet, dominating at T = 8 K and 5 T. Density functional theory (DFT) calculations show that local spin orbit interactions determine an easy axis anisotropy at the Ni site while the Cr magnetic moment turns out to be more isotropic. This is the first direct observation of the interplay between the single ion and the overall magnetic anisotropy in complex (polynuclear) molecular systems.     

Structure and soft magnetic properties of Fe-Co-Ni-based multicomponent thin films

Soft magnetic thin films with suitable uniaxial anisotropy and high saturation magnetization are required for high frequency applications, since the ferromagnetic resonance frequency (f_FMR) is proportional to the multiplication of the saturation magnetization and anisotropy magnetic field. In this study, multicomponents of Fe-Co-Ni-based soft magnetic thin films were deposited on the Si substrate by radio frequency (RF) magnetron sputtering with various Ar/N₂ ratios at room temperature. The composition, crystal structure, surface morphology, and magnetic domain were analyzed. Without nitrogen doping, the domain of the magnetic thin film was arranged randomly. The effect of N₂ content in the thin film on the magnetic properties was evaluated and further discussed. Magnetic properties, including saturation magnetization (M_s) and coercivity (H_c), were determined. The saturation magnetization of the undoped magnetic thin film was around 1.3 T. However, when the nitrogen was added, the magnitude of the anisotropy field could reach 30 Oe, while the saturation magnetization was around 1 T. It is expected that the derived magnetic thin film is a promising candidate for potential usage in high frequency inductors.     

Omnidirectional Control of Large Electrical Output in a Topological Antiferromagnet

Control of magnetization direction is essential for the wide application of ferromagnets; it defines the signal size of memory and sensor. However, the magnetization itself causes a dilemma. While its size matters to obtain strong responses upon its reversal, the large magnetization concomitantly suppresses the range of its directional control because of the demagnetizing field. On the other hand, realization of the desired magnetic anisotropy requires careful engineering of crystalline and interfacial effects to overcome the demagnetization barrier. Thus, it would be ideal if one could find alternative magnets that carry no magnetization but strong responses. The discovery of a topological metallic state in the antiferromagnet Mn₃Sn is significant; they host a large Berry curvature in momentum space, enabling the observation of disproportionately large transverse responses such as anomalous Hall and Nernst effects, the key functionalities for replacing ferromagnets in the magnetic devices. Here, the experimental realization of omnidirectional control of the large responses in an antiferromagnet is reported. In particular, it is demonstrated that the absence of shape anisotropy enables the omnidirectional control, and lifts the shape constraint in designing the magnetic devices. This work lays the technological foundation for developing simple-structured high-performance devices including multi-level memory and heat flux sensor.     

Magnetic structure and magnetoresistance of patterned epitaxial iron thin films: The influence of shape and magnetocrystalline anisotropy

A magnetic-force-microscopy investigation is conducted into the influence of the shape and magnetic anisotropy on the magnetic structure and the mode of magnetization reorientation in epitaxial iron thin films patterned by subtractive techniques. Magnetic anisotropy is found to have a strong influence on the magnetic structure. With an applied field directed along a specimen, the latter is in a single-domain state when oriented parallel to the easy axis of magnetization, and is in a multidomain state when oriented perpendicular to the easy axis, the domain magnetic moments being parallel to the easy axis in both cases. The magnetic structure appears as a streaky pattern. Magnetization reorientation proceeds by domain-wall motion in both cases. The tanks do not change the mechanism of magnetization reorientation in the rectangular part, yet they ensure a single-domain state at lower magnetic flux densities. The results should offer some scope for using epitaxial iron thin films of suitable shape and crystallographic orientation in spin-valve injectors or detectors.     

A Strain‐Mediated Magnetoelectric‐Spin‐Torque Hybrid Structure

Magnetization dynamics induced by spin–orbit torques in a heavy‐metal/ferromagnet can potentially be used to design low‐power spintronics and logic devices. Recent computations have suggested that a strain‐mediated spin–orbit torque (SOT) switching in magnetoelectric (ME) heterostructures is fast, energy‐efficient, and permits a deterministic 180° magnetization switching. However, its experimental realization has remained elusive. Here, the coexistence of the strain‐mediated ME coupling and the SOT in a CoFeB/Pt/ferroelectric hybrid structure is shown experimentally. The voltage‐induced strain only slightly modifies the efficiency of SOT generation, but it gives rise to an effective magnetic anisotropy and rotates the magnetic easy axis which eliminates the incubation delay in current‐induced magnetization switching. The phase field simulations show that the electric‐field‐induced effective magnetic anisotropy field can reduce the switching time approximately by a factor of three for SOT in‐plane magnetization switching. It is anticipated that such strain‐mediated ME‐SOT hybrid structures may enable field‐free, ultrafast magnetization switching.     

Ferrites with Planar Anisotropy at Microwave Frequencies

Materials with an easy plane of magnetization (planar anisotropy) have recently been discovered. The large anisotropy field that tends to keep the magnetization in the easy plane reduces the field required to cause ferromagnetic resonance, which makes the material promising for microwave applications. Equations are derived for the susceptibility, taking into account losses and a finite medium. Propagation in a longitudinal and transverse static field is considered. The location of a slab in a rectangular waveguide for minimum loss in the forward direction, and the use of the material as a phase shifter, are discussed. Experimental microwave data on some materials are given, and also data on an isolator and phase shifter incorporating these materials.     

GdFeCo/AlN/DyFeCo静磁耦合多层薄膜磁化方向转变的研究

对 Gd Fe Co/Al N/Dy Fe Co静磁耦合多层薄膜变温磁化方向变化进行了研究。结果表明读出层 Gd Fe Co随温度上升从平面磁化转变成垂直磁化 ,转变过程中受饱和磁化强度 (Ms)和有效各向异性常数影响 ,但主要受饱和磁化强度 (Ms)的影响。在高温时读出层的磁化强度很小 ,退磁场能减小 ,在静磁耦合作用下 ,使 Gd Fe Co读出层的磁化方向发生转变 ,而且磁化方向的转变在较小的温度范围内变化较快。