The rapid increase in energy consumption related to digital technologies is a major global challenge. In magnetic data storage media, such as hard dics drives, information is stored through a specific alignment of magnetization in microscopic areas. The direction of magnetization is usually adjusted by electric currents or local magnetic fields –these magnetic fields are also generated by electrical currents in microcoils. In both cases, the electric current leads to energy loss by Joule heating. Therefore, the control of magnetization by electric fields is a promising approach to reduce the energy consumption of magnetic data technologies. So far, however, electric field control of magnetization requires high voltages or is restricted to low temperatures.
An international research team lead by the Massachusetts Institute of Technology (MIT) and with participation of Prof. Karin Leistner and Dr. Jonas Zehner (Professorship of Electrochemical Sensors and Energy Storage at the Institute of Chemistry at Chemnitz University of Technology, previously members of the research group Magneto-ionics and Nanoelectrodeposition at the Leibniz Institute for Solid State and Materials Research (IFW) Dresden)) now demonstrates 180° magnetization reversal by low voltage based on magneto-ionic effects. This result has the potential to open a pathway to dramatically reduced global power consumption of modern data storage.
As a new approach towards voltage-induced magnetization switching, the research team took advantage of the specific properties of ferrimagnets. Ferrimagnets offer a multi-sublattice configuration with sublattice magnetizations of different magnitudes opposing each other. The net magnetization arises from the addition of the sublattice contributions. For ferrimagnetic gadolinium-cobalt (GdCo) the researchers could demonstrate that the relative sublattice magnetizations can be reversibly toggled by voltage-induced hydrogen loading/unloading, a so-called magneto-ionic effect.
The additional functionalization of the material with an antiferromagnetic layer lead to the exchange-bias effect. This exchange bias effect pinned the magnetization direction of the sublattices. This way, during magneto-ionic switching, a 180° reversal of the net magnetization is achieved. In this case, for the first time, the local magnetization of a ferrimagnet could be reversed by purely electric fields and without an external magnetic field.
Prof. Karin Leistner and Dr. Jonas Zehner brought in their expertise on the transfer of magneto-ionic control to exchange bias systems. „My group intensively studies the combination of magneto-ionic systems with aniferromagnetic layers and we are by now experts in the magneto-ionic control of exchange bias,” explains Prof. Karin Leistner. In his doctorate time at the IFW Dresden, during a research stay at the MIT, Jonas Zehner prepared thin film systems by magnetron sputtering and optimized the thickness, composition and layer sequence for a model system to stabilize exchange bias in magneto-ionic systems. He measured the magnetic properties during hydrogen loading with a home-built magneto-optical Kerr Effect setup. The research stay at MIT was funded by the German Science Foundation (DFG) under a project lead by Prof. Karin Leistner.
The research team included scientists from MIT, IFW Dresden, TU Chemnitz, University of Minnesota, Korea Institute of Science and Technology and ALBA Synchrotron in Barcelona. The lead was taken by the material scientists Dr. Mantao Huang and Prof. Geoffrey Beach from MIT, experts in hydrogen-based magneto-ionic devices and spintronics.
Prof. Karin Leistner, Dr. Jonas Zehner und other members of the Professorship for Electrochemical Sensors and Energy Storage will continue the work on this project and the collaboration with the MIT at the TU Chemnitz.
Original publikation: M. Huang, M. U. Hasan, K. Klyukin, D. Zhang, D. Lyu, P. Gargiani, M. Valvidares, S. Sheffels, A. Churikova, F. Büttner, J. Zehner, L. Caretta, K.-Y. Lee, J. Chang, J.-P. Wang, K. Leistner, B. Yildiz and G. S. D. Beach, Voltage control of ferrimagnetic order and voltage-assisted writing of ferrimagnetic spin textures. Nature Nanotechnology
Prof. Dr. Karin Leistner
k.leistner(at)ifw-dresden.de // karin.leistner(at)chemie.tu-chemnitz.de