Experimental investigation of topological excitations in magnetic tunneling junctions

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

Nontechnical Abstract: In recent years, it has been discovered that properties hidden inside certain materials can be excited electrically or magnetically, to design the next generation of electronics. Skyrmion, a nanoscale whirling magnetic pattern, is an example of such topological excitations in magnetic materials. The magnetic tunnel junction is arguably the most promising spintronics device, developed in the recent years, for data storage, sensing, and logic computation. Generally, in such applications two opposite ferromagnetic states are used to store binary data in the magnetic tunneling junctions. This experimental research develops new ways to create, probe, and manipulate the magnetic skyrmion states in the magnetic tunnel junctions. The skyrmion-based magnetic tunnel junctions are expected to consume less energy, operate at a higher speed, and be more robust against material disorder, providing a platform for significant technological advances. The project prepares graduate students for skilled research in both spintronics and microwave electronics, technical areas that are of great economic importance to our society, and well-trained physicists in these areas are in high demand. The development of a graduate level course on nano-magnetics and spintronics effectively integrates the proposed research into a teaching topic in demand, to fulfill the needs of students from multidisciplinary areas such as Physics, Electrical Engineering, Material Sciences, and Chemistry. Technical Abstract: The objective of this research is to study individual and interacting magnetic skyrmions in magnetic tunnel junctions. Current-driven spin-transfer torque, voltage controlled magnetic anisotropy, and applied magnetic field vector are used as a means to control the interplay between the Heisenberg exchange interaction, responsible for ferromagnetism, and the Dzyaloshinskii-Moriya interaction, which gives rise to stable skyrmions. A phase diagram for competing magnetic excitations is mapped out experimentally. Sub-nanosecond electrical voltage pulses are used to deterministically create and annihilate individual skyrmions. A resonant spectroscopy technique is developed to use the breathing mode of skyrmions to carry out characterizations, including energy dispersion, core size, etc. Interacting skyrmions in larger devices, as in the case of a skyrmion crystal, are studied. The implications of disorder, particularly for edge imperfection, are investigated. 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.