Resistance Paints the Secret Angles of a Magnetic Dance ⚡ экспресс
Spin Hall effect (SMR) measurements allow probing the surface spin structure of magnetic insulators via the resistance dependence ΔR ∝ cos[2(α-α0)], where α is the angle between the current and the in-plane external magnetic field. Previously, α0=0° was observed for ferromagnets, and α0=90° for antiferromagnets. In this work, Pt bilayers with single-domain epitaxial thin films of the multiferroic BiFeO3 were studied. Signals of the same type were recorded, but with an unexpected deviation: α0 can substantially differ from 0° and 90°, showing significant variations from sample to sample. This strong discrepancy from the expected field dependence of SMR indicates unknown microscopic mechanisms. The goal is to report this anomaly and stimulate further research.
Using a method similar to spectroscopy (magnetic sensing), scientists pass a current through a multilayer film and observe the orientation of the microscopic magnetic arrows inside. Previously, everything was predictable: in some materials, the arrows aligned only along the current, in others—strictly across it. But in bismuth ferrite with a platinum coating, a glitch occurred. As the external magnet rotated, the resistance changed as if each arrow forgot the common alignment and chose its own angle—10°, 37°, 72°.
By measuring the magnitude of this chaotic signal, researchers hope to understand the cause of the entropic disorder. The solution promises the memory of the future: data will be stored not in bytes, but in twisted vortices of the magnetic field. By the way, bismuth ferrite is a two-in-one: it's both a magnet and an electric accumulator, changing properties at the slightest flip.
🎯 Bismuth ferrite is a multiferroic: it combines ferromagnetism and ferroelectricity, working as two materials in one.