ACS Nano, 2018

Magnetization Ratchet in Cylindrical Nanowires

Cristina Bran, Eider Berganza, Jose A. Fernandez-Roldan, Ester M. Palmero, Jessica Meier, Esther Calle, Miriam Jaafar, Michael Foerster, Lucia Aballe, Arantxa Fraile Rodriguez, Rafael P. del Real, Agustina Asenjo, Oksana Chubykalo-Fesenko, and Manuel Vazquez

DOI: 10.1021/acsnano.8b02153

The unidirectional motion of information carriers such as domain walls in magnetic nanostrips is a key feature for many future spintronic applications based on shift registers. This magnetic ratchet effect has so far been achieved in a limited number of complex nanomagnetic structures, for example, by lithographically engineered pinning sites. Here we report on a simple remagnetization ratchet originated in the asymmetric potential from the designed increasing lengths of magnetostatically coupled ferromagnetic segments in FeCo/Cu cylindrical nanowires. The magnetization reversal in neighboring segments propagates sequentially in steps starting from the shorter segments, irrespective of the applied field direction. This natural and efficient ratchet offers alternatives for the design of three-dimensional advanced storage and logic devices.

We welcome Laura H. Lewis, Distinguished University and Cabot Professor of Chemical Engineering and  Professor of Mechanical and Industrial Engineering at Northeastern University (E.E.U.U.). She will be with us until the end of July

We welcome Juan Pablo Mesa Taborda (student of Mechanical Engineering) and Alex Jiménez (student of Chemical Engineering) from Northestern University at the United States. They are carrying out scientific internship till the end of July.

Nanotechnology 29 (2018) 065301

Antidot patterned single and bilayer thin films based on ferrimagnetic Tb–Co alloy with perpendicular magnetic anisotropy

N A Kulesh , M Vázquez, V N Lepalovskij and V O Vas’kovskiy

Hysteresis properties and magnetization reversal in TbCo(30 nm) and FeNi(10 nm)/TbCo(30 nm) films  with nanoscale antidot lattices are investigated to test the effect of nanoholes onthe perpendicular anisotropy in the TbCo layer and the induced exchange bias in the FeNi layer.The antidots are introduced by depositing the films on top of hexagonally ordered porous anodicalumina substrates with pore diameter and interpore distance fixed to 75 nm and 105 nm,respectively. The analysis of combined vibrating sample magnetometry, Kerr microscopy andmagnetic force microscopy imaging measurements has allowed us to link macroscopic and local magnetization reversal processes. For magnetically hard TbCo films, we demonstrate the tunability of magnetic anisotropy and coercive field (i.e., it increases from 0.2 T for the continuous film to 0.5 T for the antidot film). For the antidot FeNi/TbCo film, magnetization ofFeNi is confirmed to be in plane. Although an exchange bias has been locally detected in the FeNi layer, the integrated hysteresis loop has increased coercivity and zero shift along the field axis due to the significantly decreased magnetic anisotropy of TbCo layer.

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