Switching Anomalous Hall and Nernst Responses by Nonmagnetic N Occupation at Fixed Noncoplanar Mn Antiferromagnetic Order

In the world of modern electronics, controlling the flow of electricity is usually a matter of managing magnetism. Most devices rely on ferromagnets, materials like iron that have a strong, unified magnetic pull, to steer electrons. However, a different class of materials called antiferromagnets offers a tantalizing alternative. In these substances, the tiny magnetic moments of atoms point in opposite directions, canceling each other out so that the material has no net magnetic pull. This makes them invisible to external magnets and resistant to interference, while still allowing for incredibly fast internal switching speeds. For decades, scientists believed that because these materials lacked a net magnetic field, they could not generate certain useful electrical effects that usually require magnetism. Recent discoveries have challenged this view, showing that if the internal magnetic arrangement is complex enough, these "invisible" magnets can still produce electrical currents that flow sideways, a phenomenon known as the anomalous Hall effect. The big question now is how to turn this effect on and off without physically twisting the magnetic structure, which is difficult to do.

A team of researchers has found a way to switch these electrical responses on and off simply by changing which atoms sit in the empty spaces of a crystal lattice, leaving the magnetic structure completely untouched. They focused on a specific family of manganese-based crystals. Imagine a rigid, three-dimensional grid made of manganese atoms, arranged in a complex, non-flat pattern where the magnetic directions point in and out of the plane like the spokes of a wheel. This magnetic arrangement is the engine that drives the electrical effects. The researchers created a controlled series of simulations using three different versions of this grid: one with no extra atoms, one with a specific amount of nitrogen atoms filling the gaps, and one with a full layer of nitrogen. Crucially, they forced all three versions to have the exact same size and the exact same magnetic arrangement. The only difference was how many nitrogen atoms occupied the empty spots within the crystal structure.

The results revealed a surprising and precise control mechanism. When the nitrogen atoms were absent, the electrical response was zero. When the nitrogen atoms were added to fill specific gaps, the electrical response suddenly appeared, reaching a significant strength. When the nitrogen atoms were added even further to fill every possible gap, the electrical response vanished again. This created a distinct "zero, then finite, then zero" pattern. The researchers discovered that the nitrogen atoms act as a symmetry switch. In the empty and fully filled states, the crystal possesses a high degree of symmetry that forces the electrical contributions from different parts of the material to cancel each other out perfectly, like two people pulling on a rope with equal force in opposite directions, leaving the rope still. However, in the intermediate state, the nitrogen atoms break just enough of this symmetry to stop the cancellation, allowing a net electrical current to flow.

The study showed that in this intermediate state, the material generated a specific electrical conductivity of -126 S/cm and a thermal voltage response of 0.77 V/mK. These numbers represent a robust signal that can be harnessed for technology. The key insight is that the magnetic order itself never changed; the manganese atoms kept pointing in the same directions throughout the experiment. Instead, the non-magnetic nitrogen atoms altered the rules of the crystal's geometry. By occupying specific sites, they removed certain rotational symmetries that previously forced the electrical effects to cancel out, while keeping the inversion symmetry intact. This allowed the underlying magnetic complexity to finally express itself as a measurable electrical signal.

This work establishes that non-magnetic atoms can serve as an independent control knob for electronic transport in compensated antiferromagnets. It proves that one does not need to reorient the magnetic spins to switch these effects on or off; one only needs to adjust the crystallographic occupation of the empty spaces. This finding opens a new path for designing future spintronic devices, where the flow of information could be toggled by subtle changes in atomic composition rather than bulky magnetic fields. The researchers demonstrated that the presence of non-magnetic atoms alone is not enough to guarantee a response; it is the specific way those atoms break the crystal's symmetry that determines whether the electrical current can flow. By isolating this effect through careful theoretical modeling, the study provides a clear blueprint for how to engineer materials that are both magnetically silent and electrically active.