Abstract
The electron spin degree of freedom can provide the functionality of “nonvolatility” in electronic devices. For example, magnetoresistive random access memory (MRAM) is expected as an ideal nonvolatile working memory, with high speed response, high write endurance, and good compatibility with complementary metal-oxide-semiconductor (CMOS) technologies. However, a challenging technical issue is to reduce the operating power. With the present technology, an electrical current is required to control the direction and dynamics of the spin. This consumes high energy when compared with electric-field controlled devices, such as those that are used in the semiconductor industry. A novel approach to overcome this problem is to use the voltage-controlled magnetic anisotropy (VCMA) effect, which draws attention to the development of a new type of MRAM that is controlled by voltage (voltage-torque MRAM). This paper reviews recent progress in experimental demonstrations of the VCMA effect. First, we present an overview of the early experimental observations of the VCMA effect in all-solid state devices, and follow this with an introduction of the concept of the voltage-induced dynamic switching technique. Subsequently, we describe recent progress in understanding of physical origin of the VCMA effect. Finally, new materials research to realize a highly-efficient VCMA effect and the verification of reliable voltage-induced dynamic switching with a low write error rate are introduced, followed by a discussion of the technical challenges that will be encountered in the future development of voltage-torque MRAM.
Highlights
The evolving information society has triggered the rapid spread of advanced technologies, such as Artificial Intelligence (AI), Advanced Safety Vehicle (ASV), and IoT (Internet of Things), and this has led to further industrial innovation
The utilization of the voltage-controlled magnetic anisotropy (VCMA) effect is a promising approach to realizing voltage-torque magnetoresistive random-access memory (MRAM)
Bi-stable magnetization switching has been demonstrated while using precessional dynamics that are induced by the VCMA effect
Summary
The evolving information society has triggered the rapid spread of advanced technologies, such as Artificial Intelligence (AI), Advanced Safety Vehicle (ASV), and IoT (Internet of Things), and this has led to further industrial innovation. The energy that is required to maintain magnetic information, i.e. the thermal stability, is about 60 kBT (green line in Figure 1), which means that we have a large energy gap between data writing and retention, in the order of 105 This difference mainly comes from unwanted energy consumption due to ohmic dissipation of the electric-current flow. If we employ the spin-orbit interaction coefficient of Co, λCo = 5 meV, the induced change in the PMA energy is estimated to be 0.039 ± 0.023 mJ/m2 when the applied electric-field is switched from +0.2 V/nm to −0.2 V/nm. By the spin-flip terms is greater than the PMA energy decrease by the spinconserIvnegdetneerrmals,.in low-symmetry systems, such as interfaces, the atomic electron orbital may possess an electric quadrupole moment. A demonstration of a high speed response is required to confirm whether they originate from the purely-electronic VCMA effect or not
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