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Intrinsic Phase Shift and Novel Dynamic Magnetization States of a Spin Torque Oscillator under ac Current Injection

Published online by Cambridge University Press:  21 March 2011

Yan Zhou ,
Johan Persson  and
Johan Akerman
Yan Zhou
Affiliation:
Microelectronics and Applied Physics, Information and Communication Technology, Electrum 229, Stockholm, 16440, Sweden
Johan Persson
Affiliation:
Microelectronics and Applied Physics, Information and Communication Technology, Electrum 229, Stockholm, 16440, Sweden
Johan Akerman
Affiliation:
Microelectronics and Applied Physics, Information and Communication Technology, Electrum 229, Stockholm, 16440, Sweden
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Abstract

We report on a preferred phase shift ΔΦ0 between a spin torque oscillator (STO) and an ac current (Iac) injected at the intrinsic frequency (fSTO) of the STO. In the in-plane precession mode (IP) the STO adjusts to a state where its resistance (or voltage) lags Iac about a quarter of a wave length (ΔΦ0 = 87°−94°). In the IP mode ΔΦ0 increases somewhat with the dc current. As the precession changes into the Out-Of-Plane (OOP) mode, ΔΦ0 jumps by about 180°, i.e. the STO resistance now precedes Iac by about a quarter of a wave length (|ΔΦ0| = 86°). At the IP/OOP boundary, the ac current mixes the two oscillation modes and both periodic and chaotic oscillations are observed. As a consequence of mixing, subharmonic terms appear in the STO signal. ΔΦ0 can furthermore be tuned by changing one or more of the anisotropy field, the demagnetizing field or the applied field. At the IP/OOP boundary, Iac mixes the two oscillation modes. The intrinsic ΔΦ0 will impact any circuit design based on STO technology and will e.g. have direct consequences for phase locking in networks of serially connected STOs.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 998: Symposium J – Nanoscale Magnetics and Device Applications , 2007 , 998-J02-02
Copyright
Copyright © Materials Research Society 2007

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