Voltage-Controlled Magnetic Anisotropy in Fe1-xCox/Pd/MgO system

The effect of insertion layer on the perpendicular magnetic anisotropy and its electric-field-induced change at Fe/MgO interface: a first-principles investigation

The development of ultralow power and high density nonvolatile magnetic random access memory stimulates the search for promising materials in magnetic tunnel junction with large voltage-controlled magnetic anisotropy (VCMA) efficiency. In this work, we investigate the 4dand 5dtransition metal interlayer effect on perpendicular magnetic anisotropy (PMA) and VCMA at Fe/MgO interface by using first-principles calculations. Large PMA more than 11 mJ m-2is found at Fe/MgO interface with Pt insertion layer and the mechanism for PMA is clarified based on the second order perturbation theory. Furthermore, we find that the magnitude and the sign of VCMA efficiency are varied by introducing different insertions at Fe/MgO interface. The Re and Os interlayers lead to a sizable increase in both of the PMA and the VCMA coefficient. Our findings may further emphasize the essential importance of the interface structure on PMA and VCMA and may offer new material platforms for low-power consumption spintronic devices.

Ligand-induced activation of ERK1/2 signaling by constitutively active Gs-coupled 5-HT receptors

5-HT₄R, 5-HT₆R, and 5-HT_7AR are three constitutively active G_s-coupled 5-HT receptors that have key roles in brain development, learning, memory, cognition, and other physiological processes in the central nervous system. In addition to G_s signaling cascade mediated by these three 5-HT receptors, the ERK1/2 signaling which is dependent on cyclic adenosine monophosphate (cAMP) production and protein kinase A (PKA) activation downstream of G_s signaling has also been widely studied. In this study, we investigated these two signaling pathways originating from the three G_s-coupled 5-HT receptors in AD293 cells. We found that the phosphorylation and activation of ERK1/2 are ligand-induced, in contrast to the constitutively active G_s signaling. This indicates that G_s signaling alone is not sufficient for ERK1/2 activation in these three 5-HT receptors. In addition to G_s, we found that β-arrestin and Fyn are essential for the activation of ERK1/2. Together, these results put forth a novel mechanism for ERK1/2 activation involving the cooperative action of G_s, β-arrestin, and Fyn.

Recent Progress in the Voltage-Controlled Magnetic Anisotropy Effect and the Challenges Faced in Developing Voltage-Torque MRAM

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.