Fast, solid-state voltage-control of magnetism in thin films of ferromagnetic SmCo5 and ferrimagnetic DyCo5

• Applicant: Dr. Xinglong Ye
• Subject Area: Synthesis and Properties of Functional Materials ; Experimental Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 528530757

Controlling magnetism and magnetic properties by applying small voltages have been vigorously pursued in magneto-electric actuation, spintronics, information processing and data storage due to its ultralow power consumption. However, in ferromagnetic metals and alloys, which are core materials in important technologies, the control of magnetic properties has been limited to the scale of atomic layers in surface/interface due to strong electric field screening and the change of magnetism are usually small. Recently, we proposed the concept of controlling magnetism through electrochemically-driven insertion/extraction of hydrogen atoms into/from interstitial sites of metal structure. The uniqueness of this concept lies in controlling the absorption and desorption of electrically neutral hydrogen atoms by means of electrochemical potentials. In the preliminary studies, we show that by applying voltages of 1 V, the magnetocrystalline anisotropy and coercivity of Sm-Co permanent magnets in micrometer-sized powders can be reversibly altered by more than 1 T, two to three orders of magnitudes more than achieved by electrostatic charging and magneto-ionics. In this project, we will further develop this very promising approach and address the following challenges. Firstly, the aqueous electrolyte that provides hydrogen atoms will be difficult to be integrated into devices. Secondly, the dynamics of the tuning process and the mechanism behind the huge change of magnetic properties remain unclear. Thirdly, can we generalize this newly-developed approach to ferrimagnetic materials and tune even antiferromagnetic exchange interactions? Targeting these challenges, in this project we will first dispense with the use of aqueous electrolyte and develop the solid-state electrochemical system to realize the voltage-control of hydrogen insertion/extraction in a completely solid-state system. Further, we will implement our approach to thin films of Sm-Co system and study the dynamics of voltage-assisted magnetization reversal. Using in-situ magneto-optic Kerr effect microscopy, in-situ anomalous hall effects and in-situ X-ray magnetic circular dichroism, we will then investigate the mechanism behind the huge change of anisotropy and coercivity. Finally, we will generalize our approach to thin films of ferrimagnetic systems, with DyCo5 as the representative, and explore the voltage-driven modulation of antiferromagnetic 4f-5d-3d exchange interactions, compensation temperatures and coercivity. With the successful completion of the project, we expect to achieve fast, all-solid-state and substantial manipulation of magnetic properties in both ferromagnetic and ferromagnetic 3d-4f system by applying small voltages.

• DFG Programme: Research Grants
• Co-Investigators: Professor Dr. Oliver Gutfleisch; Konstantin Skokov, Ph.D.