{"title":"Chaotic Dynamics in Spin Torque Nano-oscillator Driven by Voltage Feedback","authors":"Meenakshi Sravani, Swapnil Bhuktare","doi":"10.1007/s10948-025-06980-1","DOIUrl":null,"url":null,"abstract":"<div><p>Non-linear dynamics, including auto-oscillations, chaotic dynamics, and synchronization, are integral to physical and biological applications and can be excited in spintronic devices. In this study, we are interested in exploring the excitation of chaos using voltage feedback in a spin torque nano-oscillator using a Magnetic Tunnel Junction (MTJ). According to the Poincaré-Bendixson theorem, chaos cannot arise in a two-dimensional system of MTJ featuring two dynamic variables describing the zenith and azimuth angles of magnetization. Hence, we prefer the feedback system as it creates a multi-dimensional system, making it interesting to explore the emergence of chaos in such systems. Such feedback is achieved by utilizing a 3-terminal device consisting of an MTJ with an in-plane pinned layer (PL) and an out-of-plane free layer (FL) geometry. When a DC current above the critical threshold is applied, the FL’s oscillating magnetization generates an AC output voltage through the Tunnel Magneto Resistance (TMR) effect. A fraction of this voltage, fed back after a delay, modulates the FL’s anisotropy via voltage controlled magnetic anisotropy (VCMA) effect, potentially driving chaotic dynamics or oscillator death based on the feedback delay and gain of the feedback circuit. The observed chaotic regime has been studied by evaluating the Lyapunov exponent, bifurcation diagrams, Fourier spectral analysis, and reconstruction of the trajectory in embedding phase space. Such observed chaotic dynamics can find practical applications in random number generators and physical reservoir computing.</p></div>","PeriodicalId":669,"journal":{"name":"Journal of Superconductivity and Novel Magnetism","volume":"38 3","pages":""},"PeriodicalIF":1.6000,"publicationDate":"2025-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Superconductivity and Novel Magnetism","FirstCategoryId":"101","ListUrlMain":"https://link.springer.com/article/10.1007/s10948-025-06980-1","RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"PHYSICS, APPLIED","Score":null,"Total":0}
引用次数: 0
Abstract
Non-linear dynamics, including auto-oscillations, chaotic dynamics, and synchronization, are integral to physical and biological applications and can be excited in spintronic devices. In this study, we are interested in exploring the excitation of chaos using voltage feedback in a spin torque nano-oscillator using a Magnetic Tunnel Junction (MTJ). According to the Poincaré-Bendixson theorem, chaos cannot arise in a two-dimensional system of MTJ featuring two dynamic variables describing the zenith and azimuth angles of magnetization. Hence, we prefer the feedback system as it creates a multi-dimensional system, making it interesting to explore the emergence of chaos in such systems. Such feedback is achieved by utilizing a 3-terminal device consisting of an MTJ with an in-plane pinned layer (PL) and an out-of-plane free layer (FL) geometry. When a DC current above the critical threshold is applied, the FL’s oscillating magnetization generates an AC output voltage through the Tunnel Magneto Resistance (TMR) effect. A fraction of this voltage, fed back after a delay, modulates the FL’s anisotropy via voltage controlled magnetic anisotropy (VCMA) effect, potentially driving chaotic dynamics or oscillator death based on the feedback delay and gain of the feedback circuit. The observed chaotic regime has been studied by evaluating the Lyapunov exponent, bifurcation diagrams, Fourier spectral analysis, and reconstruction of the trajectory in embedding phase space. Such observed chaotic dynamics can find practical applications in random number generators and physical reservoir computing.
期刊介绍:
The Journal of Superconductivity and Novel Magnetism serves as the international forum for the most current research and ideas in these fields. This highly acclaimed journal publishes peer-reviewed original papers, conference proceedings and invited review articles that examine all aspects of the science and technology of superconductivity, including new materials, new mechanisms, basic and technological properties, new phenomena, and small- and large-scale applications. Novel magnetism, which is expanding rapidly, is also featured in the journal. The journal focuses on such areas as spintronics, magnetic semiconductors, properties of magnetic multilayers, magnetoresistive materials and structures, magnetic oxides, etc. Novel superconducting and magnetic materials are complex compounds, and the journal publishes articles related to all aspects their study, such as sample preparation, spectroscopy and transport properties as well as various applications.