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Nanoscale Transistors
Published in Manoj Kumar Majumder, Vijay Rao Kumbhare, Aditya Japa, Brajesh Kumar Kaushik, Introduction to Microelectronics to Nanoelectronics, 2020
Manoj Kumar Majumder, Vijay Rao Kumbhare, Aditya Japa, Brajesh Kumar Kaushik
RAP is the resistance in antiparallel magnetization state which is high in value. As the GMR phenomenon is very weak, a tunnel barrier is inserted between free layers, which results in a strong change in resistance called tunnel magnetoresistance (TMR). This TMR is observed in new devices called a magnetic tunnel junction (MTJ). The TMR effect introduces the novel class of nonvolatile memory technology named as magnetoresistive random access memories (MRAMs) that store the data in the form of the resistance state of MTJ.
Physics of Nanomagnets
Published in Klaus D. Sattler, 21st Century Nanoscience – A Handbook, 2020
Ralph Skomski, Balamurugan Balasubramanian, D. J. Sellmyer
There are many magnetoresistance contributions, and a comprehensive description of these contribution goes far beyond the scope of this chapter. Ordinary magntoresistance means that a magnetic field H curves the path of conduction electrons in nonmagnetic metals and thereby creates an H2 term in the resistivity. Anisotropic magnetoresistance (AMR) occurs in magnetic materials [74] and reflects spin–orbit coupling. Pictorially, the spin perturbs the surrounding electron cloud and makes the scattering dependent on the spin direction. For example, in Figure 18.6, the resistivity depends on whether the electrons move in the x- or z-direction. Giant magnetoresistance (GMR) and grain-boundary magnetoresistance are due to rapid magnetization variations, which act as scattering centers [75]. Tunnel magnetoresistance (TMR) means spin-dependent electron tunneling through a thin insulating layer [76]. Colossal magnetoresistance (CMR) involves double exchange (Mn3+ , Mn4+) and means that the antiferromagnetic insulator LaMnO3 (La3+ Mn3+O2-3) becomes a ferromagnetic conductor in an external magnetic field H.
The Prospect of STT-RAM Scaling
Published in Xiaobin Wang, Krzysztof Iniewski, Metallic Spintronic Devices, 2017
Yaojun Zhang, Wujie Wen, Hai Li, Yiran Chen
Following the scaling of switching current, the read current of the MTJ must decrease accordingly to suppress the read disturbance. This fact will introduce another concern on the readability of STT-RAM: in a traditional current sensing STT-RAM read scheme, for instance, a read current Iread is injected into the memory cell. The generated bit-line voltage is then compared to a reference voltage to read out the MTJ resistance state. The generated sense margin, which can be measured by the voltage difference between the bitline voltage and the reference voltage, is proportional to Iread·RL·TMR. Here RL is the low MTJ resistance. TMR is tunnel magnetoresistance ratio. A certain sense margin must be maintained in STT-RAM read operations to overcome the device mismatch in the sense amplifier and keep the sensing errors at a minimum level.
Quantitative nondestructive testing of wire rope based on pseudo-color image enhancement technology
Published in Nondestructive Testing and Evaluation, 2019
In all of these methods, the location of the leakage flux due to the defect in the circumferential direction was missing. Based on a magnetic dipole model, Wu [7] applied vector superposition and field integration to analyze the signal characteristics of a rectangular induction coil as a function of sensor placement and scanning direction. They found that for the same defect, a different scanning direction resulted in different signal characteristics. The amplitude of the signal was the largest when the coil was parallel to the defect. Kim [8] employed a Hall sensor array and divided the damage into three levels; a damage level threshold was determined using a generalized extremum distribution. The relationship between the envelope and the threshold MFL signal was used as the characteristic to quantify the defect. However, the circumferential resolution of the Hall sensor array was too low to accurately locate the polar coordinate of the defect. Liu [9] compared the detection accuracy of a Helmholtz coil sensor and a tunnel magnetoresistance (TMR) sensor. They showed that the TMR sensor had the advantage of higher SNR and greater precision on the measurement of small defects, such as abrasion and broken wires. Lei [10] improved the traditional detection device using higher sensitivity giant magnetoresistance (GMR) sensors to solve the problem of low SNR caused by the small diameter and large lift-off. Wu [11] optimized the structure factor of the sensor by using an orthogonal test.
Recent advances in two-dimensional ferromagnetism: strain-, doping-, structural- and electric field-engineering toward spintronic applications
Published in Science and Technology of Advanced Materials, 2022
Sheng Yu, Junyu Tang, Yu Wang, Feixiang Xu, Xiaoguang Li, Xinzhong Wang
The 2D magnetic tunnel junction (MTJ) is composed of two separate ferromagnets as electrodes and an intermediate insulating atomic layer. Tunnel magnetoresistance is a that occurs in a MTJ via applying bias voltage. The tunneling probability depends on the electronic density of states near the Fermi energy in the ferromagnets and the thickness of the insulating barrier. When the magnetizations in two ferromagnetic electrodes are parallel, their similar distributions of the electronic density of states near the Fermi level provide more tunneling opportunities, leading to a high conductance. On the other hand, when the magnetizations of two ferromagnets are antiparallel, a mismatch of their density of states will impede the tunneling with a low conductance.
Efficient autonomous material search method combining ab initio calculations, autoencoder, and multi-objective Bayesian optimization
Published in Science and Technology of Advanced Materials: Methods, 2022
Yuma Iwasaki, Hwang Jaekyun, Yuya Sakuraba, Masato Kotsugi, Yasuhiko Igarashi
Heusler alloys are an important application of the autonomous material search systems. They have attracted much attention in recent years because they exhibit various physical properties [16–19]. One of the most attractive physical properties is half-metallicity, which has one metallic spin band and one semiconducting spin band [20]. They have been extensively studied for applications in tunnel magnetoresistance [21–24], giant magnetoresistance [25–28], and other spintronics devices [29–31]. However, since the material search space is extremely vast due to their multi-elemental nature and their disordered phases, the development of Heusler alloys is very difficult.