A gentle squeeze may be enough to change how an unusual magnetic material behaves, according to new research from Rice University.
Scientists discovered that applying a small amount of pressure to a crystal made of iron and sulfur can simultaneously weaken its tiny magnetic signal and change the way electricity flows through it.
The finding could help researchers better understand a relatively new class of materials called altermagnets and potentially find new ways to control them in future electronics.
Altermagnets combine characteristics of two familiar types of magnetic materials. Ordinary magnets, known as ferromagnets, produce an external magnetic field because many of their internal magnetic moments point in the same direction.
In antiferromagnets, neighboring magnetic moments point in opposite directions, largely canceling each other out.
Altermagnets also have magnetic moments that mostly cancel each other. However, they can still influence moving electrons in unusual and potentially useful ways.
In the new study, published in Advanced Materials, researchers investigated a hexagonal form of iron sulfide, known as FeS. Although most of its magnetism cancels out, the material retains a very small magnetic moment.
FeS also displays an unusual electrical behavior called the anomalous Hall effect. Normally, an external magnetic field can cause electrons moving through a material to shift sideways, creating a voltage across it. In FeS, however, this sideways voltage can appear even without an external magnetic field.
The Rice researchers wanted to understand whether this electrical behavior was connected to the material’s tiny leftover magnetism.
They built a device that gently squeezed the FeS crystal from one direction while they measured its magnetic and electrical properties. As the pressure increased, the small magnetic signal weakened. At the same time, the unusual sideways electrical voltage also decreased.
Importantly, the material’s much stronger underlying magnetic structure remained largely unchanged.
To find out what was happening inside the crystal, the researchers used neutron beams at Oak Ridge National Laboratory. These experiments revealed that pressure did not destroy or fundamentally rearrange the magnetic structure. Instead, it changed the balance between different possible magnetic orientations within the crystal.
FeS has several nearly equal ways in which its magnetic moments can be arranged. Because very little energy separates these different states, even a modest mechanical squeeze can make certain orientations more common than others.
The close relationship between the magnetic and electrical changes also provides clues about the origin of the anomalous Hall effect in FeS. One possible explanation involves details of how electrons move through the material’s electronic structure. The new results do not reject this explanation, but they show that the electrical effect closely follows the tiny magnetic moment, suggesting the two share a common physical origin.
The discovery could eventually have implications for spintronics, a technology that uses electron magnetism, or “spin,” to store and process information.
Being able to adjust magnetic and electrical properties simply by applying mechanical strain could provide engineers with another way to control future spintronic devices. Such technologies could potentially operate with less unwanted magnetic interference and lower energy consumption.
For now, the experiment gives scientists something equally valuable: a simple new tool for uncovering how these unusual magnets actually work.
