title: Coherent microwave generation by spintronic feedback oscillator.
abstract: The transfer of spin angular momentum to a nanomagnet from a spin polarized current provides an efficient means of controlling the magnetization direction in nanomagnets. A unique consequence of this spin torque is that the spontaneous oscillations of the magnetization can be induced by applying a combination of a dc bias current and a magnetic field. Here we experimentally demonstrate a different effect, which can drive a nanomagnet into spontaneous oscillations without any need of spin torque. For the demonstration of this effect, we use a nano-pillar of magnetic tunnel junction (MTJ) powered by a dc current and connected to a coplanar waveguide (CPW) lying above the free layer of the MTJ. Any fluctuation of the free layer magnetization is converted into oscillating voltage via the tunneling magneto-resistance effect and is fed back into the MTJ by the CPW through inductive coupling. As a result of this feedback, the magnetization of the free layer can be driven into a continual precession. The combination of MTJ and CPW behaves similar to a laser system and outputs a stable rf power with quality factor exceeding 10,000.
authors.affiliation: Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai - 400 076, India.
authors.forename: Dinesh
authors.initials: D
authors.lastname: Kumar
authors.affiliation: Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka - 560-8531, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Konishi
authors.affiliation: Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai - 600036, India.
authors.forename: Nikhil
authors.initials: N
authors.lastname: Kumar
authors.affiliation: Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka - 560-8531, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Miwa
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Ibaraki -305-8568, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Fukushima
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Ibaraki -305-8568, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Yakushiji
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Ibaraki -305-8568, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Yuasa
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Ibaraki -305-8568, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kubota
authors.affiliation: Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai - 400 076, India.
authors.forename: C V
authors.initials: CV
authors.lastname: Tomy
authors.affiliation: Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai - 600036, India.
authors.forename: A
authors.initials: A
authors.lastname: Prabhakar
authors.affiliation: Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka - 560-8531, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Suzuki
authors.affiliation: Department of Electrical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai - 400 076, India.
authors.forename: A
authors.initials: A
authors.lastname: Tulapurkar