共查询到20条相似文献,搜索用时 15 毫秒
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Ferromagnetism,variable range hopping,and the anomalous Hall effect in epitaxial Co:ZnO thin film 下载免费PDF全文
A series of high quality single crystalline epitaxial Zn 0.95 Co 0.05 O thin films is prepared by molecular beam epitaxy.Superparamagnetism and ferromagnetism are observed when the donor density is manipulated in a range of 10 18 cm 3-10 20 cm 3 by changing the oxygen partial pressure during film growth.The conduction shows variable range hopping at low temperature and thermal activation conduction at high temperature.The ferromagnetism can be maintained up to room temperature.However,the anomalous Hall effect is observed only at low temperature and disappears above 160 K.This phenomenon can be attributed to the local ferromagnetism and the decreased optimal hopping distance at high temperatures. 相似文献
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Room-temperature anomalous Hall effect and magnetroresistance in (Ga, Co)-codoped ZnO diluted magnetic semiconductor films 下载免费PDF全文
This paper reports that the(Ga,Co)-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition.Room-temperature ferromagnetism is observed for the as-grown thin films.The x-ray absorption fine structure characterization reveals that Co 2+ and Ga 3+ ions substitute for Zn 2+ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin.The ferromagnetic(Ga,Co)-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room temperature.The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed. 相似文献
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An obvious weak localization correction to anomalous Hall conductance(AHC) in very thin CoFeB film is reported.We find that both the weak localization to AHC and the mechanism of the anomalous Hall effect are related to the CoFeB thickness.When the film is thicker than 3 nm,the side jump mechanism dominates and the weak locaUzation to AHC vanishes.For very thin CoFeB films,both the side jump and skew scattering mechanisms contribute to the anomalous Hall effect,and the weak localization correction to AHC is observed. 相似文献
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The resistive switching characteristics of Au/ZnTe/ITO structure with polycrystalline ZnTe film as resistive switching layer is investigated. Macroscopically, 100 bipolar switching cycles under the direct current (dc) voltages were carried out and the conduction states can retain for several hours. Microscopically, reading and writing operations can be achieved on ZnTe film with Au top electrode replaced by conductive Atomic Force Microscopy (c-AFM) tip. The I–V characteristic in low resistance state (LRS) is linear in the whole range of voltage. The I–V characteristic in high resistance state (HRS) is linear in the low voltage while it obeys Schottky emission in the high voltage, and Schottky barrier height is symmetric in the positive and negative voltage. During linear I–V characteristic voltage range, the electrons transport between adjacent point defects via Mott variable range hopping. The higher hopping distance and higher activation energy in HRS contribute to the higher resistance value in HRS compared with LRS. Impedance spectroscopy in HRS and LRS both behave as a semicircle, which accords with the semiconductor-like characteristic of conductive point defects. Photoluminescence (PL) spectroscopy indicates the decisive role of deep level defects in conduction. This study confirms the intrinsic resistive switching characteristic of ZnTe film and provides a new choice for intrinsic non-oxides material in nonvolatile memory application. 相似文献
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Universal spin-dependent variable range hopping in wide-band-gap oxide ferromagnetic semiconductors 下载免费PDF全文
This paper proposes a universal spin-dependent variable
range hopping theoretical model to describe various experimental
transport phenomena observed in wide-band-gap oxide ferromagnetic
semiconductors with high transition metal concentration. The
contributions of the `hard gap' energy, Coulomb interaction,
correlation energy, and exchange interaction to the electrical
transport are considered in the universal variable range hopping
theoretical model. By fitting the temperature and magnetic field
dependence of the experimental sheet resistance to the theoretical
model, the spin polarization ratio of electrical carriers near the Fermi
level and interactions between electrical carriers can be
obtained. 相似文献
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采用直流磁控溅射法在玻璃基片上制备了Pt底层的Co/Ni多层膜样品, 对影响样品垂直磁各向异性的各因素进行了调制, 通过样品的反常霍尔效应系统的研究了Co/Ni多层膜的垂直磁各向异性. 结果表明, 多层膜中各层的厚度及周期数对样品的反常霍尔效应和磁性有重要的影响. 通过对多层膜各个参数的调制优化, 最终获得了具有良好的垂直磁各向异性的Co/Ni多层膜最佳样品Pt(2.0)/Co(0.2)/Ni(0.4)/Co(0.2)/Pt(2.0), 经计算, 该样品的各向异性常数Keff 达到了3.6×105 J/m3, 说明样品具备良好的垂直磁各向异性. 最佳样品磁性层厚度仅为0.8 nm, 样品总厚度在5 nm以内, 可更为深入的研究其与元件的集成性. 相似文献
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We re-visit the anomalous sign reversal problem in the Hall effect of the sputtered Nb thin films. We find that the anomalous sign reversal in the Hall effect is extremely sensitive to a small tilting of the magnetic field and to the magnitude of the applied current. Large anomalous variations are also observed in the symmetric part of the transverse resistance Rxy. We suggest that the surface current loops on superconducting grains at the edges of the superconducting thin films may be responsible for the Hall sign reversal and the accompanying anomalous effects in the symmetric part of Rxy. 相似文献
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Under a strong magnetic field,the quantum Hall(QH) effect can be observed in two-dimensional electronic gas systems.If the quantized Hall conductivity is acquired in a system without the need of an external magnetic field,then it will give rise to a new quantum state,the quantum anomalous Hall(QAH) state.The QAH state is a novel quantum state that is insulating in the bulk but exhibits unique conducting edge states topologically protected from backscattering and holds great potential for applications in low-power-consumption electronics.The realization of the QAH effect in real materials is of great significance.In this paper,we systematically review the theoretical proposals that have been brought forward to realize the QAH effect in various real material systems or structures,including magnetically doped topological insulators,graphene-based systems,silicene-based systems,two-dimensional organometallic frameworks,quantum wells,and functionalized Sb(111) monolayers,etc.Our paper can help our readers to quickly grasp the recent developments in this field. 相似文献
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Based on first-principles calculations, a two-dimensional (2D) van der Waals (vdW) bilayer heterostructure consisting of two topologically trivial ferromagnetic (FM) monolayers CrI3 and ScCl2 is proposed to realize the quantum anomalous Hall effect (QAHE) with a sizable topologically nontrivial band gap of 4.5 meV. Its topological nature is attributed to an interlayer band inversion between the monolayers and critically depends on the symmetry of the stacking configuration. We further demonstrate that the topologically nontrivial band gap can be increased nearly linearly by the application of a perpendicular external pressure and reaches 8.1 meV at 2.7 GPa, and the application of an external out-of-plane electric field can also modulate the band gap and convert the system back to topologically trivial via eliminating the band inversion. An effective model is developed to describe the topological phase evolution in this bilayer heterostructure. This work provides a new candidate system based on 2D vdW materials for realization of potential high-temperature QAHE with considerable controllability. 相似文献
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Thickness dependence of the anomalous Hall effect in disordered face-centered cubic FePt alloy films 下载免费PDF全文
The anomalous Hall effect in disordered face-centered cubic(fcc) FePt alloy films is experimentally studied. The longitudinal resistivity independent term of the anomalous Hall conductivity(AHC) increases and approaches saturation with increasing film thickness. The contribution of side jump scattering is suggested to decrease monotonically with increasing film thickness, which can be ascribed to the variation of the surface scattering with the film thickness. The sign of the skew scattering contribution to the AHC is opposite to that of the intrinsic contribution in the system. 相似文献
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Our recent research achievements in the perpendicular magnetic anisotropy (PMA) properties of the CoFeB sand- wiched by MgO and tantalum layers are summarized. We found that the PMA behaviors of Ta/CoFeB/MgO and MgO/CoFeB/Ta thin films are different. The larger PMA in the latter film is related to the lower magnetization of CoFeB deposited on MgO. Furthermore, we have demonstrated a large anomalous Hall effect in perpendicular CoFeB thin fihn. Our results show large anomalous Hall resistivity, large longitudinal resistivity, and low switching field can be achieved, all at the same time, in the perpendicular CoFeB thin film. Anomalous Hall effect with high and linear sensitivity is also found in an MgO/CoFeBFFa thin film with a thick MgO layer, which opens a door tbr future device applications of perpendicular ferromagnetic thin films. 相似文献
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Quantum Hall effect (QHE), as a class of quantum phenomena that occur in macroscopic scale, is one of the most important topics in condensed matter physics. It has long been expected that QHE may occur without Landau levels so that neither external magnetic field nor high sample mobility is required for its study and application, Such a QHE free of Landau levels, can appear in topological insulators (TIs) with ferromagnetism as the quantized version of the anomalous Hall effect, i.e., quantum anomalous Hall (QAH) effect. Here we review our recent work on experimental realization of the QAH effect in magnetically doped TIs. With molecular beam epitaxy, we prepare thin films of Cr-doped (Bi,Sb)2Te3 TIs with well- controlled chemical potential and long-range ferromagnetic order that can survive the insulating phase. In such thin films, we eventually observed the quantization of the Hall resistance at h/e2 at zero field, accompanied by a considerable drop in the longitudinal resistance. Under a strong magnetic field, the longitudinal resistance vanishes, whereas the Hall resistance remains at the quantized value. The realization of the QAH effect provides a foundation for many other novel quantum phenomena predicted in TIs, and opens a route to practical applications of quantum Hall physics in low-power-consumption electronics. 相似文献
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Yi-Ming Dai 《中国物理 B》2022,31(9):97302-097302
In a quantum Hall effect, flat Landau levels may be broadened by disorder. However, it has been found that in the thermodynamic limit, all extended (or current carrying) states shrink to one single energy value within each Landau level. On the other hand, a quantum anomalous Hall effect consists of dispersive bands with finite widths. We numerically investigate the picture of current carrying states in this case. With size scaling, the spectrum width of these states in each bulk band still shrinks to a single energy value in the thermodynamic limit, in a power law way. The magnitude of the scaling exponent at the intermediate disorder is close to that in the quantum Hall effects. The number of current carrying states obeys similar scaling rules, so that the density of states of current carrying states is finite. Other states in the bulk band are localized and may contribute to the formation of a topological Anderson insulator. 相似文献
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Room temperature FM was observed in pristine ZnO thin films grown by pulsed laser deposition on Al2O3 substrates. It seems to originate from other defects but not oxygen vacancies. Magnetization of thinner films is much larger than that of the thicker films, indicating that defects are mostly located at the surface and/or the interface between the film and the substrate. Data on the Fe:ZnO and Mn:ZnO films show that a transition-metal doping does not play any essential role in introducing the magnetism into ZnO. In the case of Mn doping, the magnetic moment could be very slightly enhanced. Hall effect measurements reveal that an incorporation of Mn does not change the carrier type, but decreases the carrier concentration, and increases the Hall mobility, resulting in more resistive Mn:ZnO films. Since no anomalous Hall effect was observed, it is understood that the observed FM is not due to the interaction between the free-carrier and the Mn impurity. 相似文献
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具有垂直磁各向异性的磁性纳米结构是自旋转移力矩器件的重要研究内容, 本文采用反常霍尔效应系统地研究了磁控溅射法制备的[CoFeB/Pt]n多层膜的垂直磁各向异性. 当CoFeB的厚度小于0.6 nm时, 可以在[CoFeB/Pt]n多层膜中观察到清晰的垂直磁各向异性, 其垂直磁各向异性强烈依赖于CoFeB和Pt层厚度及多层膜周期数. 当多层膜周期数n ≥ 5时, 出现零剩磁现象. 另外, [CoFeB/Pt]n多层膜的矫顽力均小于2 kA·m-1, 有望作为垂直自由层的重要侯选材料应用于垂直磁纳米结构中. 相似文献
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Tbx(Ni0.8Fe0.2)1-x films with x≤0.14 are fabricated and the anomalous Hall effect is studied.The intrinsic anomalous Hall conductivity and the extrinsic one from the impurity and phonon induced scattering both increase with increasing x.The enhancement of the intrinsic anomalous Hall conductivity is ascribed to both the weak spin–orbit coupling enhancement and the Fermi level shift.The enhancement of the extrinsic term comes from the changes of both Fermi level and impurity distribution.In contrast,the in-plane and the out-of-plane uniaxial anisotropies in the Tb Ni Fe films change little with x.The enhancement of the Hall angle by Tb doping is helpful for practical applications of the Hall devices. 相似文献