Black phosphorus is a promising material to serve as the barrier of magnetic tunnel junctions (MTJs) due to the weak van der Waals interlayer interactions. In particular, the special band features of black phosphorus may bring intriguing physical characteristics. Here, we study theoretically the effect of band gap tunability of black phosphorus on the MTJs with black phosphorus barrier. It is found that, the tunneling magnetoresistance (TMR) may achieve a transition from finite value to infinity owing to the variation of the band gap of black phosphorus. Combining with the latest experimental results of the pressure-induced band gap tunability, we further investigate the pressure effect of TMR in the MTJs with black phosphorus barrier. The calculations show that the pressure sensitivity can be quite high under appropriate parameters. Physically, the high sensitivity originates from the TMR transition phenomenon. To take advantage of the high pressure sensitivity, we propose and design a detailed structure of highly sensitive pressure sensors based on MTJs with black phosphorus barrier, whose working mechanism is basically different from the convential pressure sensors. The present pressure sensors possess four advantages and benifits: (1) high sensitivity, (2) well anti-interference, (3) high spatial resolution, and (4) fast response speed. Our study may advance new research area for both the MTJs and pressure sensors.
Magnetic silicene superlattices (MSSLs) are versatile structures with spin-valley polarization and tunneling magnetoresistance (TMR) capabilities. However, the oscillating transport properties related to the superlattice periodicity impede stable spin-valley polarization states reachable by reversing the magnetization direction. Here, we show that aperiodicity can be used to improve the spin-valley polarization and TMR by reducing the characteristic conductance oscillations of periodic MSSLs (P-MSSLs). Using the Landauer-Büttiker formalism and the transfer matrix method, we investigate the spi…
Impact of current paths on measurement of tunneling magnetoresistance and spin torque critical current densities in GaMnAs-based magnetic tunnel junctions
Resistivity measurements of a few-layer black phosphorus (bP) crystal in parallel magnetic fields up to 45 T are reported as a function of the angle between the in-plane field and the source-drain (S-D) axis of the device. The crystallographic directions of the bP crystal were determined by Raman spectroscopy, with the zigzag axis found within 5° of the S-D axis, and the armchair axis in the orthogonal planar direction. A transverse magneto-resistance (TMR) as well as a classically-forbidden longitudinal magneto-resistance (LMR) are observed. Both are found to be strongly anisotropic and non-m…
The tunnel magnetoresistance (TMR) effect observed in magnetic tunnel junctions (MTJs) is commonly used in many spintronic applications because the effect can easily convert from local magnetic states to electric signals in a wide range of device resistances. In this study, we demonstrated TMR ratios of up to 631% at room temperature (RT), which is two or more times larger than those used currently for magnetoresistive random access memory (MRAM) devices, using CoFe/MgO/CoFe(001) epitaxial MTJs. The TMR ratio increased up to 1143% at 10 K, which corresponds to an effective tunneling spin polar…
A first-principles study of tunneling magnetoresistance in Fe/MgAl2O4/Fe(001) magnetic tunnel junctions
利用第一性原理计算研究了Fe/MgAl 2 O 4/Fe（001）磁性隧道结的电子结构和弹道电导随自旋的变化.计算得到的Fe/MgAl 2 O 4/Fe（001）MTJ的隧道磁电阻（TMR）比约为160%，远小于相同势垒厚度的Fe/MgO/Fe（001）MTJ的TMR比（1600%）。而在正常尖晶石MgAl 2 O 4的费米能级附近的能隙中存在δ 1对称的倏逝态，表明Fe/MgAl 2 O 4/Fe（001）MTJ中可能存在大的TMR. Fe/MgAl 2 O 4/Fe（001）MTJ的小TMR比是由于Fe电极的面内波矢量（k//）的二维（2-D）布里渊区中的带折叠效应导致的少数自旋态中的新导电沟道。由于MgAl 2 O 4的面内晶胞尺寸是bcc Fe的原始面内晶胞尺寸的两倍，边界边缘的能带被折叠，并且在MgAl 2 O 4势垒中与δ 1倏逝态耦合的少数自旋态出现在k//=0处，这显著降低了MTJ的TMR比。
We investigate the role of pseudospin structure of few-layer black phosphorus (BP) in interband tunneling properties in lateral BP junctions. We find that interband tunneling is critically dependent on junction directions because of the anisotropic pseudospin structure of BP. When the armchair direction of BP is normal to the interface, pseudospins of incident and transmitted carriers are nearly aligned so that interband tunneling is highly effective, analogous to the Klein tunneling in graphene. However, when the zigzag direction is normal to the interface, interband tunneling is suppressed b…
We theoretically investigated a method to detect a single skyrmion in a magnetic tunneling junction (MTJ) geometry. Using the tunneling Hamiltonian approach, we calculated the tunneling magnetoresistance (TMR) ratio of the skyrmion-ferromagnet bilayer system. We show the TMR ratio is determined sorely by the spin profile of the skyrmion and geometrical factor of the device, if only the system is reasonably clean such that the spectral broadening is smaller than the exchange coupling between the local and the itinerant magnetic moment. The TMR ratio in that case can amount to $30\%$ or higher w…
We report on our theoretical study of the inverse TMR effect in the spin polarized transport through a narrow channel. In the weak tunneling limit, we find the ordinary positive TMR. The TMR changes its sign as the transmission probability becomes large close to a unity. Our results might be relevant to the magnetic tunnel junction with a pinhole or a quantum point contact.
Tunneling magnetoresistance devices based on topological insulators: Ferromagnet/insulator/topological-insulator junctions employing Bi$_{2}$Se$_{3}$
本文从理论上研究了三维拓扑绝缘体Bi $_{2}$ Se $_{3}$的隧穿磁电阻（TMR）器件。基于Bi $_{2}$ Se $_{3}$的现实紧束缚模型进行理论计算。我们研究了利用Bi $_{2}$ Se $_{3}$的表面态的三维器件，以及利用薄Bi $_{2}$ Se $_{3}$条的边缘态的二维器件。我们证明了Bi $_{2}$ Se $_{3}$的材料性质允许在室温下的TMR比为1000%的量级。分析公式推导出，允许在这些设备中实现的TMR比的快速估计。该装置可用于测量自旋极化的拓扑表面状态作为替代自旋ARPES。与基于磁性隧道结的TMR器件不同，本器件避免使用其磁化需要被钉扎的第二铁磁电极。
Heavy metals with strong spin-orbit coupling (SOC) have been employed to generate spin current to control the magnetization dynamics by spin-orbit torque (SOT). Magnetic tunnel junction based on SOT (SOT-MTJ) is a promising application with efficient writing operation. Unfortunately, SOT-MTJ faces the low tunneling magnetoresistance (TMR) problem. In this work, we present an ab initio calculation on the TMR in SOT-MTJ. It is demonstrated that TMR would be enhanced by SOT-MTJ symmetry structure. The symmetrization induces interfacial resonant states (IRSs). When IRSs match identical resonances …
We theoretically study the tunnel magnetoresistance (TMR) effect in (111)-oriented junctions Co/MgO/Co(111) and Ni/MgO/Ni(111). The Co-based junction is shown to have a TMR ratio over 2000$\%$, which is one order higher than that of the Ni-based one. The high TMR ratio is attributed to the interfacial resonance effect: The interfacial $d$-$p$ antibonding states are formed close to the Fermi level in the majority-spin channel and these states in both interfaces resonate with each other. This differs essentially from the conventional coherent tunneling mechanism of high TMR ratios in Fe(Co)/MgO/…
We have studied the influence of the transverse size of a magnetic tunnel nanojunction on the magnitude of the magnetoresistance. During modeling, the size of the right contact was fixed, while the size of the left one gradually changed until they coincided. We found a sharp drop in the tunneling magnetoresistance (TMR) in nanocontacts with mismatched cross section. This can be explained by the peculiarities of the spatial distribution of the electron density, which is different for majority and minority-spin states. The discovered effect must be taken into account in the design of TMR-based n…
We report the precise control of tunneling magnetoresistance (TMR) in devices of self-assembled core/shell Fe$_3$O$_4$/Co$_{1-x}$Zn$_x$Fe$_2$O$_4$ nanoparticles ($0\leq x\leq 1$). Adjusting the magnetic anisotropy through the content of Co$^{2+}$ in the shell, provides an accurate tool to control the switching field between the bistable states of the TMR. In this way, different combinations of soft/hard and hard/soft core/shell configurations can be envisaged for optimizing devices with the required magnetotransport response.
The study of the effects of scaling on magnetic tunnel junction (MTJ) devices has become an important topic in the field of spin-based memory devices. Here, we investigate the effect of elastic dephasing on trilayer and pentalayer MTJ considered at small transverse cross-sectional areas using the non-equilibrium Green's function spin transport formalism. We consider the structures with and without dephasing effects and clearly point out as to how the tunnel magnetoresistance effect gets affected by dephasing. We attribute the trends noted by analyzing the transmission spectra and hence the cur…
Bistable valency in individual atoms presents a new approach toward single-atom memory, as well as a building block to create tunable and stochastic multi-well energy landscapes. Yet, this concept of orbital memory has thus far only been observed for cobalt atoms on the surface of black phosphorus, which are switched using tip-induced ionization. Here, we show that individual iron atoms on the surface of black phosphorus exhibit orbital memory using a combination of scanning tunneling microscopy and spectroscopy with ab initio calculations based on density functional theory. Unlike cobalt, the…
Interface-Controlled Antiferromagnetic Tunnel Junctions based on a metallic van der Waals A-type Antiferromagnet
Hefei University of Technology（合肥工业大学）；University of Science and Technology of China（中国科学技术大学）；Agency for Science Technology and Research (A*STAR)（科学与技术研究局）；Anhui University（安徽大学）；RMIT University（皇家墨尔本理工大学）
Interfacial Effects of Al-Termination on Spin Transport in Magnetic Tunnel Junctions
实验表明，Co/Al $_2$ O $_3$磁性隧道结（MTJ）中的隧道电流是正自旋极化的，这与标准隧道理论直观地预期的相反，标准隧道理论给出的自旋极化完全取决于Co层的$E_F$处的态密度（DOS）。在这里，我们报告的理论结果，给出一个积极的隧道自旋极化和隧道磁电阻（TMR）是在良好的协议与实验。从密度泛函理论（DFT）的计算，富铝界面MTJ与原子级的障碍被证明有一个积极的极化DOS界面附近。我们还提供了一个原子模型的计算，它给出了见解的正极化的来源。一个层和自旋相关的有效质量模型，使用从DFT结果提取的值，然后被用来计算隧道电流，这表明积极的自旋极化。最后，我们从隧穿自旋极化率计算了TMR，与实验结果符合得很好。
Spin-resolved electron symmetry filtering is a key mechanism behind giant tunneling magnetoresistance (TMR) in Fe/MgO/Fe and similar magnetic tunnel junctions (MTJs), providing room temperature functionality in modern spin electronics. However, the core process of the electron symmetry filtering breaks down under applied bias, dramatically reducing the TMR above 0.5 V. This strongly hampers the application range of MTJs. To circumvent the problem, resonant tunneling between ferromagnetic electrodes through quantum well states in thin layers has been used so far. This mechanism, however, is mai…
