New Production Process Makes Technology Better and Less Expensive

Nanomagnets play a key role in modern information technologies. They facilitate fast data storage, precise magnetic sensors, novel developments in spintronics, and, in the future, quantum computing. The foundations of all these applications are functional materials with particular magnetic structures that can be customized on the nanoscale and precisely controlled.

In the past, Dr. Rantej Bali and his colleagues at HZDR’s Institute of Ion Beam Physics and Materials Research had already developed processes for imprinting materials with tiny magnetic structures in varying geometries because the nature of the respective magnetic nanostructures determines how the material behaves in the application. Now the team has taken a crucial step forward: “We have managed to produce vertically aligned nanomagnets using a relatively simple material. This could make all technologies that are dependent on nanomagnets better and less expensive,” reports Bali.

In most materials, electron spins tend to lie horizontally along the surface and not point outward. This severely restricts applications. Now the researchers have been able to demonstrate that by drastically reducing the size of the magnetic fields the spins can be forced to stand out vertically from the material’s surface. Although conventional methods achieve similar behavior, they need raw materials with complex crystal structures or combine different materials in thin layers, making this method complicated and expensive. This new development is quite different: “Both the materials and the manufacture are inexpensive and suitable for most magnetic application scenarios,” explains Bali.

The secret is in the reduction: ion beam magnetic engraving

The researchers used a thin metallic film of iron-vanadium alloy as their raw material. In their disordered form, the atoms of this material initially exhibit only weak magnetism. But this all changes when they are bombarded with a highly focused ion beam. The principle behind this is that when a beam with a diameter of just two nanometers hits the material, it reorganizes the atoms locally into a crystal lattice. The ions effectively push the atoms into place in the lattice. In the ordered, crystalline state, the material becomes ferromagnetic. Thus, bit by bit, miniscule magnetic fields are created in the film. While the precise physical mechanism is as yet unknown, it is clear that this process allows magnetic nanostructures to be produced in almost any geometry and size.

Unlike in earlier attempts, this time, the researchers reduced the width of the nanostrips until they finally obtained extremely thin magnetic fields just 25 nanometers wide. Contrary to their expectation, they discovered that the nanometer-sized areas in the very thin strips suddenly stood out vertically from the surface.

Vertical nanomagnets are more efficient

Vertically aligned nanomagnets are advantageous for a number of reasons: first, they can be accommodated much more compactly. This increases the data storage density of hard disks, for example, and supports the trend towards ever more miniaturized components. Second, they make the materials more efficient, for instance in spintronics which uses not only the electrons’ charge but also their spin for signal transport. When electric current flows through the material, vertical moments exert a greater torque on the electrons than parallel moments. Quantum computers can also benefit from vertically aligned nanomagnets to distinguish between the two possible ground states of a qubit, which correspond to an upward or downward magnetic alignment, and to control them with high sensitivity.

“To put it very simply, it’s rather like a game of cards. If you put down all the cards next to each other on the table, they need quite a lot of space. Instead, if you stand them up, it saves a lot of space. One card, standing up, responds much more sensitively to stimuli than one lying down. The same is true of the nanomagnets’ response to external magnetic stimuli,” illustrates Bali.

Experimental and theoretical proof

In order to understand the results of their experiments even better, the researchers conducted further tests to observe how magnetic domains form in material. These are areas in which all magnetic moments are aligned in the same direction. When two opposite domains collide, the magnetization must change direction within the domain wall, the narrow boundary area only a few nanometers wide. The result is that the magnetic moments align themselves vertically.

Read the original article on Helmholtz-Zentrum Dresden-Rossendorf (HZDR).