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

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

doi:10.3390/ma14164354

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

Materials (Basel). 2021 Aug 4;14(16):4354. doi: 10.3390/ma14164354.

Authors

Thomas Kehagias¹, Dimitrios Karfaridis¹, Camillo Ballani², Laura Mihalceanu³, Christoph Hauser², Isaak G Vasileiadis¹, George P Dimitrakopulos¹, George Vourlias¹, Evangelos Th Papaioannou²

Affiliations

¹ Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.
² Institute of Physics, Martin-Luther University Halle-Wittenberg, 06120 Halle, Germany.
³ Department of Physics, Technical University of Kaiserslautern, 67663 Kaiserslautern, Germany.

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.

Keywords: HRTEM; ISHE; XPS; dislocation pipe diffusion; magnetic measurements; magnetite nanoparticles; magnetization reversal; spin pumping; spintronic bilayers.