Magnetization manipulation and antiferromagnetic dynamics driven by spin current in Weyl semimetals

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

Non-technical abstract: Control of the magnetic properties in solid-state materials is key to the operation of many devices that are extensively used in daily life. Applications of such devices include data storage in computers, data encryption on credit cards, and high-frequency signal generation, to name a few. Conventionally, the control of magnetic state is obtained by using an externally applied magnetic field, but this restricts the physical footprint and operational speed of these devices. However, the control of the magnetic state in ferromagnetic and antiferromagnetic materials by other means, such as utilizing electric field or charge current, can overcome these limitations, and potentially realize more advanced nanoscale devices for generating, transmitting, and processing signals at extremely high speeds. However, the fundamental understanding of electric current-induced control and spin dynamics of the magnetic state in ferromagnetic and antiferromagnetic materials is still in its infancy. This project will study an emergent quantum solid-state material platform, namely Weyl semimetals, to demonstrate control of the magnetic state through electric charge current. In these quantum materials, the atoms are arranged in a special configuration that gives rise to unique properties, which in turn allow for an efficient control of magnetic state in ferromagnetic materials and induce spin dynamics in antiferromagnetic materials. The success of this research project will lay the foundation to build a comprehensive understanding of electric charge current-induced spin manipulation and dynamics in magnetic materials, which will have far reaching implications for the emerging field of quantum spintronics. Furthermore, this research project will provide research experience, training, and active mentorship to undergraduate students from a collaborating minority serving institution. Connections with middle school and high school teachers in the greater Pittsburgh area will be established to develop physics demonstrations with detailed lesson plans on the topics of electricity and magnetism. Technical abstract: An energy efficient and field-free manipulation of the magnetic order, i.e., net magnetization of a ferromagnet or Néel vector of an antiferromagnet, using electric field induced spin current is key to realize advanced spintronic applications that include ultra-fast magnetic memory devices, terahertz oscillators, and magnonic devices for generation, transmission, and detection of high-frequency signals. On the other hand, topological materials with lower crystal symmetries, such as Weyl semimetals, host spin-momentum locked electronic states that can lead to an efficient charge to spin transduction and a plethora of other novel phenomena that are highly relevant for quantum spintronics. This research project will utilize crystalline thin films of van der Waals based Weyl semimetals and couple them with a variety of magnetic systems to build atomically sharp superlattices for studying spin manipulation and spin dynamics. The scientific objectives of this research project are two-fold: (1) To obtain a time resolved and spatially resolved view on the underlying mechanisms of field-free spin-orbit torque switching of magnetization in semiconducting and insulating ferromagnets. (2) To study spin-current induced Néel vector dynamics in easy plane antiferromagnets and subsequent spin-pumping from antiferromagnets by exploiting out-of-plane oriented spin current in Weyl semimetals. This research objective is aimed at demonstrating the working principle of an antiferromagnetic oscillator. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.