Relation between switching time distribution and damping constant in magnetic nanostructure

Jung-Hwan Moon,Chun-Yeol You,Tae Young Lee

doi:10.1038/s41598-018-31299-4

Abstract

It is widely known that the switching time is determined by the thermal stability parameters and external perturbations such as magnetic field and/or spin polarized current in magnetic nano-structures. Since the thermal stability parameter and switching time are crucial values in the design of spin-transfer torque magnetic random access memory, the measurement of the switching time is important in the study of the switching behavior of ferromagnetic nano-structures. In this study, we focus on the distribution of the switching time. Within the limit of a large energy barrier, a simple analytical expression between damping constant and anisotropy field with switching time distribution is obtained and confirmed by numerically solving the Fokker-Planck equation. We show that the damping constant and anisotropy field can be extracted by measuring the full width half maximum of the switching time distribution in the magnetic nano-structure devices. Furthermore, the present method can be applied to not only single nano-structure, but also inhomogeneous nano-structure arrays.

Highlights

Statistical distributions of measurable physical quantities always have significant physical meanings
The peak position and full width half maximum (FWHM) of ferromagnetic resonance (FMR) spectra are related with the magnetic energy and the Gilbert damping constant[2], More generally, in any kind of resonance experiment such as one using an RLC circuit or a damped harmonic oscillator, the peak position, and the peak width always has important physical meanings
It is revealed that (i) the FWHM is inversely proportional to the external field, (ii) the damping constant can be extracted from the FWHM, and (iii) the effective anisotropy field can be obtained from the intercept of the relation between reduced external field and FWHM

Summary

Introduction

Statistical distributions of measurable physical quantities always have significant physical meanings. The thermally activated switching time of magnetic nano-structures is determined by the Néel-Arrhenius equation[22] through the thermal stability parameter and the attempt frequency[23]. Determination of the exact damping constant of each nano-sized MTJ cell will be important in the study of STT-MRAM.

Results

Conclusion