title: Order of magnitude improvement of nano-contact spin torque nano-oscillator performance.
abstract: Spin torque nano-oscillators (STNO) represent a unique class of nano-scale microwave signal generators and offer a combination of intriguing properties, such as nano sized footprint, ultrafast modulation rates, and highly tunable microwave frequencies from 100 MHz to close to 100 GHz. However, their low output power and relatively high threshold current still limit their applicability and must be improved. In this study, we investigate the influence of the bottom Cu electrode thickness (tCu) in nano-contact STNOs based on Co/Cu/NiFe GMR stacks and with nano-contact diameters ranging from 60 to 500 nm. Increasing tCufrom 10 to 70 nm results in a 40% reduction of the threshold current, an order of magnitude higher microwave output power, and close to two orders of magnitude better power conversion efficiency. Numerical simulations of the current distribution suggest that these dramatic improvements originate from a strongly reduced lateral current spread in the magneto-dynamically active region.
authors.affiliation: Department of Materials and Nano Physics, School of Information and Communication Technology, KTH Royal Institute of Technology, Electrum 229, 164 40 Kista, Sweden. johan.akerman@physics.gu.se.
authors.forename: Seyed Amir Hossein
authors.initials: SA
authors.lastname: Banuazizi
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Sohrab R
authors.initials: SR
authors.lastname: Sani
authors.affiliation: Department of Integrated Devices and Circuits, School of Information and Communication Technology, KTH Royal Institute of Technology, Electrum 229, 164 40 Kista, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Eklund
authors.affiliation: Department of Integrated Devices and Circuits, School of Information and Communication Technology, KTH Royal Institute of Technology, Electrum 229, 164 40 Kista, Sweden.
authors.forename: Maziar M
authors.initials: MM
authors.lastname: Naiini
authors.affiliation: Department of Physics, Shahid Beheshti University, 19839 Tehran, Iran.
authors.forename: Seyed Majid
authors.initials: SM
authors.lastname: Mohseni
authors.affiliation: Department of Materials and Nano Physics, School of Information and Communication Technology, KTH Royal Institute of Technology, Electrum 229, 164 40 Kista, Sweden. johan.akerman@physics.gu.se and Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden.
authors.forename: Sunjae
authors.initials: S
authors.lastname: Chung
authors.affiliation: Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden.
authors.forename: Philipp
authors.initials: P
authors.lastname: Dürrenfeld
authors.affiliation: Department of Integrated Devices and Circuits, School of Information and Communication Technology, KTH Royal Institute of Technology, Electrum 229, 164 40 Kista, Sweden.
authors.forename: B Gunnar
authors.initials: BG
authors.lastname: Malm
authors.affiliation: Department of Materials and Nano Physics, School of Information and Communication Technology, KTH Royal Institute of Technology, Electrum 229, 164 40 Kista, Sweden. johan.akerman@physics.gu.se and Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden and NanOsc AB, Electrum 205, 164 40 Kista, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Åkerman