Magnetization Reversal and Dynamics in Epitaxial Fe/Pt Spintronic Bilayers Stimulated by Interfacial Fe3O4 Nanoparticles.

Thomas Kehagias,George Vourlias,George P Dimitrakopulos,Isaak G Vasileiadis,Laura Mihalceanu,Evangelos Th Papaioannou,Christoph Hauser,Dimitrios Karfaridis,Camillo Ballani

doi:10.3390/ma14164354

Abstract

We have explored the impact of elevated growth and annealing temperatures on the local interfacial structure of thin Fe(12 nm)/Pt(10 nm) spintronic bilayers, epitaxially grown on MgO (100), and their correlation to magnetization reversal and dynamics. Electron-beam evaporation growth and subsequent annealing at 450 °C causes significant roughening of the MgO/Fe interface with irregular steps and multilevel (100) MgO surface terraces. Consequently, threading dislocations emerging at the step edges propagated in the Fe layer and terminated at the Fe/Pt interface, which appears pitted with pits 1.5–3 nm deep on the Fe side. Most of the pits are filled with the overlying Pt, whereby others by ferrimagnetic Fe3O4, forming nanoparticles that occupy nearly 9% of the Fe/Pt interfacial area. Fe3O4 nanoparticles occur at the termination sites of threading dislocations at the Fe/Pt interface, and their population density is equivalent to the density of threading dislocations in the Fe layer. The morphology of the Fe/Fe3O4/Pt system has a strong impact on the magnetization reversal, enhancing the coercive field and inducing an exchange bias below 200 K. Furthermore, low-temperature spin pumping and inverse spin Hall effect voltage measurements reveal that below their blocking temperature the nanoparticles can influence the spin current transmission and the spin rectification effects.

Highlights

Progress in nanofabrication techniques for magnetic materials, such as Fe, Ni, Co, and their alloys, over recent decades have enabled the well-controlled growth of nanometerthick layers and multilayers and led to many discoveries in the field of nanomagnetism and spintronics
The effort today is to efficiently enhance the spin current transport using spin Hall effect (SHE) and inverse spin Hall effect (ISHE), by manipulating interfaces between the layers and subsequently by modifying the static and dynamic interfacial effects associated with the spin-orbit coupling and the intrinsic symmetry breaking at interfaces [11]
High Resolution Transmission Electron Microscopy (HRTEM) imaging of the Fe(12 nm)/Pt(10 nm) bilayer configuration grown on MgO

Summary

Introduction

Progress in nanofabrication techniques for magnetic materials, such as Fe, Ni, Co, and their alloys, over recent decades have enabled the well-controlled growth of nanometerthick layers and multilayers and led to many discoveries in the field of nanomagnetism and spintronics. SHE can lead to spin currents that flow perpendicular to the direction of charge current via spin-dependent scattering processes (intrinsic (or) impurities) in metals with large spin-orbit coupling. The reciprocal effect, known as the inverse spin Hall effect (ISHE) [9,10], refers to the process in which a pure spin current leads to charge accumulation and development of an electromotive force in a direction transverse to the spin current. The effort today is to efficiently enhance the spin current transport using SHE and ISHE, by manipulating interfaces between the layers and subsequently by modifying the static and dynamic interfacial effects associated with the spin-orbit coupling and the intrinsic symmetry breaking at interfaces [11]

Methods

Results

Conclusion