Inside a magnet, there are regions where all the atomic magnets point in the same direction. Between such regions lies a narrow transition zone where the magnetization direction gradually rotates. This zone is called a domain wall. Previously, it was considered massless: give it a push, and it stops immediately. But new experiments show that the wall has inertia. It cannot instantly speed up or slow down.

Inertia makes the wall resemble a heavy ball. If you push it with a magnetic field or a stream of electrons, it rolls differently than a light ball would. The scientists built a model in which the wall has mass. It turned out that with a strong push, it accelerates faster than usual. And if you remove friction, the motion becomes chaotic, like an electron in a crystal.

This discovery is useful for racetrack memory. There, information is stored in the positions of domain walls that race along a thin wire. If walls accelerate faster, data can be read and written more quickly. However, chaos in the absence of friction is a challenge: you need to precisely control the motion.

So, a magnetic wall is not just a line on a map of magnetic fields. It is a massive object that can be accelerated, like a sled down a hill. The better we understand its inertia, the faster future memory devices will work.