Brief Description of My Research Work
Spin transfer torque induced magnetization switching has recently attracted much interest due to its potential applications in magnetic random access memory (MRAM), fast programmable logic, high-density magnetic storage devices, magnetic sensors and in high frequency devices for tele-communications. Magnetic storage devices and magnetic sensors based on Giant Magnetoresistance (GMR) and Tunnelling Magnetoresistance (TMR) effects require high quality multilayers constructed out of ultrathin ferromagnetic and non-magnetic films. The performance of these devices strongly depend on the morphological and structural properties of the films and their physical characteristics. Among them, the crucial factor is the interlayer coupling between the two ferromagnetic layers separated by a non-magnetic spacer. Various interlayer coupling mechanisms have been reported. Among them, pinhole coupling, orange peel coupling, biquadratic coupling and RKKY coupling are important ones. These interlayer couplings play an important role in the understanding of magnetization switching mechanism and GMR of spin valves and TMR of magnetic tunnel junction structures. We have done a systematic and in-depth study about the effect of interlayer coupling that arises due to the interface roughness namely orange peel coupling and biquadratic coupling on spin transfer torque magnetization switching in trilayer and pentalayer nanopillar structures. Further, we have investigated the effect of biasing on spin transfer torque magnetization switching in the pentalayer structure, in order to reduce the switching time and critical current density required to initiate the magnetization switching. The magnetization switching dynamics of the free layer magnetization in nanopillar are basically nonlinear in nature and is governed by the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation which is a highly nontrivial vector nonlinear evolution equation. By solving this LLGS equation, we can understand the underlying magnetization dynamics. For time-independent case, LLGS equation is analytically solved and the critical current density required to switch the magnetization is calculated. Then the full LLGS equation is solved numerically by using Runge-Kutta fourth order procedure for each case and from the numerical simulations study we understood the effect of interlayer coupling and biasing on spin transfer torque switching. Our important findings are both orange peel coupling and biquadratic coupling reduces the switching time. Even though biquadratic coupling reduces the switching time, the lowest switching time is obtained through orange peel coupling. Further, we found that biasing ferromagnetic layers of the nanopillars reduce the switching time considerably. Although biasing in the case of pinned layer enhances the spin transfer torque acting on the free layer and reduces the switching time, the fastest magnetization switching is achieved in the case of free layer biasing configuration. Presently, I am working on the ways to enhancing the output power of spin torque nano oscillators (STNO) by introducing the additional spacer layer and feromagnetic layer above the trilayer structure and studying their various nonlinear dynamics phenomena.
- Working in the CSIR Project entitled “Spin Torque Nano Oscillators (STNO)” under the supervision of Prof. M. Lakshmanan.
- Worked in the emerging field of Spintronics and my research topic for Ph.D. Degree is “Effect of Interlayer Coupling and Biasing on Spin Transfer Torque Switching in Ferromagnetic Nanopillars” (2011-2017).
- Carried out a project on the topic of “Soliton Spin Excitations in Ferromagnetic Spin Systems ” during a period of two semesters (2010-2011) in the M.Phil Programme.
- Carried out a project on the topic of “Soliton in Ferromagnets” during a period of two semesters (2009-2010) in the final year of the M.Sc Programme.
Research Papers Published / Communicated
- D. Aravinthan, P. Sabareesan, and M. Daniel, Current induced magnetization switching in Co/Cu/Ni-Fe nanopillar with orange peel coupling, AIP Advances, 5, 077166 (2015).
DOI: 10.1063/1.4927546 (pdf file)
- D. Aravinthan, P. Sabareesan, and M. Daniel, Impact of biquadratic coupling on critical current density in Co/Cu/Ni-Fe nanopillar, AIP Conference Proceedings, 1728, 020443 (2016). DOI: 10.1063/1.4946494 (pdf file)
- D. Aravinthan, P. Sabareesan, and M. Daniel, Effect of biquadratic coupling on current induced magnetization switching in Co/Cu/Ni-Fe nanopillar, AIP Conference Proceedings, 1731, 130032 (2016). DOI: 10.1063/1.4948138 (pdf file)
- D. Aravinthan, P. Sabareesan, and M. Daniel, Reduction of switching time in pentalayer nanopillar device with different biasing, J. Magn. Magn. Mater., 421, 409 (2017). DOI: 10.1016/j.jmmm.2016.08.038 (pdf file)
- D. Aravinthan, P. Sabareesan, and M. Daniel, Spin transfer torque switching in pentalayer nanopillar with biquadratic coupling, J. Supercond. Nov. Magn. (2017) DOI: 10.1007/s10948-017-4517-3 (pdf file)
- D. Aravinthan, P. Sabareesan, and M. Daniel, On the effect of orange peel coupling on spin torque magnetization switching in pentalayer nanopillar (Under Review).
Presentation in Seminars / Conferences / Workshops
- Served as a Resource Person for the One day Workshop on LATEX jointly Organized by Department of Physics and Department of Mathematics, Dr.SNS Rajalakshmi College of Arts & Science(Autonomous), Coimbatore, Tamilnadu held on February 02, 2018.
- Presented a talk entitled “Impact of Biquadratic Coupling on Spin Current Induced Magnetization Switching in Pentalayer Nanopillar” in the 5th International Conference on Complex Dynamical Systems and Applications (CDSA), 2017 organized at Indian Institute of Technology Guwahati, Guwahati, India during December 04 – 06, 2017.
- Presented a talk entitled “Spin Transfer Torque Magnetization Switching in Ferromagnetic Nanopillars with Orange Peel Coupling” in the National Conference on Current Advancement in Physics organized by Department of Physics, St. John’s College, Palayamkottai, Tamilnadu, India during February 03-04, 2017.
- Presented a poster entitled “Impact of Biquadratic Coupling on Current Induced Magnetization Switching in Co/Cu/Ni-Fe Nanopillar ” in the “2016 Joint MMM – Intermag Conference” held at the Hilton San Diego Bayfront Hotel in San Diego, California, United States during January 11-15, 2016 and jointly sponsored AIP Publishing and IEEE Magnetics Society.
- Presented a poster entitled “Effect of Biquadratic Coupling on Current Induced Magnetization Switching in Co/Cu/Ni-Fe Nanopillar” in the “60th DAE Solid State Physics Symposium” held at Amity University U.P., Noida, Uttar Pradesh, India during December 21-25, 2015.
- Presented a poster entitled “Impact of Biquadratic Coupling on Critical Current Density in Co/Cu/Ni-Fe Nanopillar” in the “International Conference on Condensed Matter and Applied Physics (ICC 2015)” organized by Govt. Engineering College, Bikaner, Rajasthan, India during October 30-31, 2015.
- Presented a poster entitled “Spin Transfer Torque Switching in Pentalayer Nanopillar Having Two Pinned Layers with Biasing” in the “Physics and Applied Mathematics Researchers’ Meet – 2015” held at Indian Statistical Institute, Kolkata, India during March 18-20, 2015.
- Presented a poster entitled “Spin Transfer Torque Switching in Pentalayer Nanopillar” in the “Indo-Japan Workshop on Magnetism at Nanoscale (IJWMN-2015)” Organized by National Institute of Science Education and Research (NISER), Bhubaneswar, India during January 09-12, 2015.
- Presented a poster entitled “Impact of orange peel coupling on magnetization switching in nanopillar” in the eighth “Conference on Nonlinear Systems and Dynamics (CNSD2013)” Organized by Indian Institute of Technology(IIT), Indore, India during December 11-14, 2013.