Scientists were able to increase the velocity of the domain wall in microwaves through mechanical defects
Scientists from the Immanuel Kant Baltic Federal University have discovered how the defects in ferromagnetic (able to magnetize under certain conditions) microwires and magnetic fields on both ends affect the speed of domain walls — boundaries between areas with different directions of magnetic moments. The study has shown that the speed at which the walls move in the areas with mechanical defects of the wire may increase multiple to the number of these defects, with the field of scattering of terminal domains also accelerating the movement. The data collected would be beneficial for creating more and accurate medical device products, electronic devices and security systems. The study is published in Intermetallics magazine.
Ferromagnetic microwires are thin wires of few micrometers in diameter made of different metals, such as iron, nickel, copper and their alloys. They are manufactured by the Taylor-Ulitovskiy method — its essence consists in an ultrafast cooling of metallic melt that is coated in glass. The glass casing protects the metallic nucleus from corrosion (chemical destruction) and makes the material biocompatible. Thus, such microwires may be used in biomedical devices.
Magnetic microwires are magnetically soft, meaning that they can be quickly magnetized reversely under the action of a small magnetic field. At the same time, the material may quickly alternate between the two steady magnetization conditions: when the magnetic moments are aligned in one particular direction or in opposite directions to each other. The magnetization process takes place due to an extremely fast motion of a domain wall — boundaries between magnetic domains (zones) with different direction of magnetization. In this case, the response time of the device depends on the speed of the domain wall. However, motion control of the domain walls remains a challenge because it is affected by a lot of factors.
Scientists from the Baltic Federal University of Immanuel Kant (Kaliningrad) together with colleagues from University of the Basque Country (Spain) investigated how inhomogeneities in material and additional magnetic fields affect the velocity of the domain wall in iron-based microwires. To do this, the authors used the induction method that allows to precisely measure the speed and acceleration of the domain walls.
For the first time he researchers have identified three domain walls' movement modes: slowed-down, when the domain walls' velocity declines as it moves along the microwire; uniform, when the speed remains constant; and accelerated, at which the domain wall's velocity increases. These modes were found by scientists in different areas of the same microwire, which indicates a strong influence of inhomogeneities and defects on the domain walls' movement.
In their work, the scientists investigated microwires with different ratios of diameters of metallic nucleus and glass coating. It turned out that such defects as mechanical defects of glass coating or local internal inhomogeneities of metallic core fundamentally alter the domain wall's velocity. Specifically, in areas with defects it increases by 1.5 times.
In addition, scientists identified that the fields that form at the ends of the microwire also alter the speed of the domain walls by tens of meters per second, what is important to consider in the design of high-precision control devices, such as sensors of magnetic fields.
The results of the study are important for developing new sensory devices based on the mechanism of domain walls' movement. Understanding how it is affected by the defects and parasitic fields will allow to create faster and more reliable sensors for use in medicine, electronics and security systems.
"Our results open new opportunities to controlling the movement of domain walls in magnetic microwires. This knowledge will help design devices with decreased response time and increased sensitivity", — says Valeriy Savin, junior researcher of REC "Smart materials and biomedical applications" at Immanuel Kant Baltic Federal University.
"Relying on the basic experimental studies in the field of magnetism of ferromagnetic microwires, we have identified three types of domain wall's movement — slowed-down, uniform and accelerated, — and presented a generalized model of domain wall's speed settings in microwires, taking into account the effect of mechanical defects, in our project. This research may lead to reduced response time of sensitive devices that are based on the mechanism of domain walls' movement" — concludes Valeria Kolesnikova, junior researcher of REC "Smart materials and biomedical applications" at Immanuel Kant Baltic Federal University.
More information:
doi.org/10.1016/j.intermet.2025.108726
Provided by Immanuel Kant Baltic Federal University