The new material system consists of a superconducting microstructure, coated with an extremely thin ferromagnetic layer. An external magnetic field, applied extremely shortly, generates currents in the superconducting areas. These currents inscribe the desired magnetic patterns permanently into the ferromagnetic thin layer.
Magnetic patterns such as skyrmions or monopoles are potentially suited to store data at high speed and low energy consumption. Hitherto however it has proved to be very difficult to generate such magnetic structures in a controlled and reproducible way; likewise, it was difficult to manipulate them. A research team at the Helmholtz Research Center Berlin (HZB) around Dr. Sergio Valencia has demonstrated a method to achieve the desired results in a joint effort with a team of researchers from the Institute for Materials Science of the University of Barcelona (Spain).
The Spanish cooperation partners successfully created microstructures by applying very small dots made of yttrium barium copper oxide (YBaCuO), a high-temperature superconducting material. The team provided several samples with different dot patterns. Valencia and his team coated these microstructures with an extremely thin layer of a ferromagnetic iron-nickel alloy.
Though YBaCuO is a high-temperature superconductor, the temperatures in question are still very low: The experiments have been performed at 50 Kelvin or minus 220 degrees Celsius. The team applied a short-time magnetic field perpendicular to the plane of the materials sample. This field generated sperconducting ring currents inside the YBaCuO dots that proved to persist after the external magnetic field had been switched off. The currents generated a complex magnetic field that interacted directly with the thin layer on top.
This method makes it possible to inscribe magnetic patterns into the permalloy film on top. In this patterns, it is possible to orient all magnetic domains in a way that they point to or away from each other – which is the definition of a magnetic monopole. The team around Dr. Valencia could map the magnetic domains by means of X-ray photoelectron emssions microscopy (X-PEEM) at BESSY II.
“I am very optimistic that these patterns can be shrunk further,” Valencia said. “Thus, they could be used to implement magnetic memory devices”. He added that despite the fact that the experiments have been conducted at very low temperatures there are some hints how the magnetic structures could be stabilized at ambient temperature.
The results of the research have been published in Advanced Science.