Electrical characterisation of higher order spin wave modes in vortex-based magnetic tunnel junctions

Alex S Jenkins,Paulo P Freitas,Ricardo Ferreira,Lara San Emeterio Alvarez,Vincent Cros,Samh Memshawy,Paolo Bortolotti

doi:10.1038/s42005-021-00614-3

Abstract

NiFe-based vortex spin-torque nano-oscillators (STNO) have been shown to be rich dynamic systems which can operate as efficient frequency generators and detectors, but with a limitation in frequency determined by the gyrotropic frequency, typically sub-GHz. In this report, we present a detailed analysis of the nature of the higher order spin wave modes which exist in the Super High Frequency range (3–30 GHz). This is achieved via micromagnetic simulations and electrical characterisation in magnetic tunnel junctions, both directly via the spin-diode effect and indirectly via the measurement of the coupling with the gyrotropic critical current. The excitation mechanism and spatial profile of the modes are shown to have a complex dependence on the vortex core position. Additionally, the inter-mode coupling between the fundamental gyrotropic mode and the higher order modes is shown to reduce or enhance the effective damping depending upon the sense of propagation of the confined spin wave.

Highlights

NiFe-based vortex spin-torque nano-oscillators (STNO) have been shown to be rich dynamic systems which can operate as efficient frequency generators and detectors, but with a limitation in frequency determined by the gyrotropic frequency, typically sub-GHz
There has been some recent study focussed on the overlap between STNOs and magnonics, and these include relatively diverse experiments ranging from the spin wave-mediated synchronization of nanocontact oscillators[14,15] to the emission of spin waves by magnetic vortices during vortex core displacement[16,17] and reversal[18,19], and the exploration of higherorder spin-wave modes[20,21,22,23,24,25,26,27] associated with magnetic vortices, the latter of these being the focus of this study
There are a variety of dynamic modes associated with the magnetic vortex, with the fundamental mode, known as the gyrotropic mode, characterized by an orbital motion of the vortex core around a fixed point as shown in Fig. 2a, where the magnetization along the z-axis is presented, as calculated with the Mumax[340] code

Summary

Introduction

NiFe-based vortex spin-torque nano-oscillators (STNO) have been shown to be rich dynamic systems which can operate as efficient frequency generators and detectors, but with a limitation in frequency determined by the gyrotropic frequency, typically sub-GHz. In this report, we present a detailed analysis of the nature of the higher order spin wave modes which exist in the Super High Frequency range (3–30 GHz). We present a detailed analysis of the nature of the higher order spin wave modes which exist in the Super High Frequency range (3–30 GHz) This is achieved via micromagnetic simulations and electrical characterisation in magnetic tunnel junctions, both directly via the spin-diode effect and indirectly via the measurement of the coupling with the gyrotropic critical current. Vortex core switching via spin-wave mode excitation has been demonstrated on individual nanodots both optically[24,28,29,30,31,32] and via ferromagnetic resonance[33,34], these modes have not been electrically characterized in fully integrated individual MTJs before, which is an essential step towards the realization of emerging ICT technologies

Methods

Results

Conclusion