The phenomenon of magnetism is widely used in electronics and memory devices. Both areas attract the attention of a large circle of scientists due to their highest practical value. It is obvious that the boundaries of possibilities and materials used constantly need to be expanded. Japanese scientists were able to make a breakthrough by discovering unique magnetic properties in materials that were not thought to exhibit them.
Search for interactions between antiferromagnetism, band topology, and strong electron interactions. Image credit: Ray et al 2025
Magnetic materials in the form of ferromagnets with ordered electron spins are capable of demonstrating the anomalous Hall effect. The usual Hall effect occurs in an external magnetic field when current is passed through a magnetic sample. In the case of the anomalous Hall effect, the field in the sample (the potential difference at its ends or voltage) occurs in the magnetic material even without an external magnetic field.
No one expected such a phenomenon in the case of antiferromagnets. The spins in such materials are disordered and compensate each other when oriented in the opposite direction. However, even in antiferromagnets, signs of the anomalous Hall effect were found. This means that a new class of materials with its own unique properties can be used as magnetic memory, which potentially promises to improve the characteristics of memory devices. Now it is necessary to thoroughly understand this phenomenon and provide a fundamental scientific basis – this is exactly what scientists from Japan have done.
«”An anomalous Hall effect has been previously reported in a certain class of collinear antiferromagnets,” the researchers say. “However, the observed signals were extremely weak. Identifying an anomalous Hall effect without magnetization was of great scientific and technological interest.”
«One of the main goals of our research project was to create a coherent scientific picture based on our observations, the authors of the new paper state. “Each step required careful interpretation, especially because of the structural irregularities characteristic of transition metal dichalcogenide (TMD) systems.”
The scientists used a family of materials called transition metal dichalcogenides as two-dimensional building blocks. By inserting magnetic ions between the atomic layers, the researchers could control the movement and interactions of electrons. The modified three-dimensional structure exhibited new behavior that was not possible in its two-dimensional form. Only then were the researchers able to measure the anomalous Hall effect over a wide range of temperatures and magnetic fields.
In addition, the US scientists provided evidence in the form of microscopic images of samples confirming the collinear antiferromagnetic structure of the material. The results were then compared with theoretical analysis and calculations performed by a group of scientists from the University of Tokyo.
The results obtained are the first convincing experimental evidence of the anomalous Hall effect observed in collinear antiferromagnets. Since the anomalous Hall effect is traditionally believed to be associated with magnetization, its detection in such materials indicates phenomena that go beyond the standard understanding. The researchers suggest that this is due to the unique structure of the electron bands of the material, which causes the appearance of the so-called “virtual magnetic field” and enhances the anomalous Hall effect in the absence of magnetization. The work will be continued, since a full understanding of the physics of this process has not yet been achieved.