For nearly 90 years, physicists divided magnetic materials into two groups. In ferromagnets, the spins of electrons - a quantum property that acts like a tiny magnetic arrow - all point the same way and create a magnetic field. In antiferromagnets, neighboring spins point in opposite directions and cancel each other out. Now researchers led by SLAC National Accelerator Laboratory have confirmed a third type of magnetism, called altermagnetism. Their srudy is published in Science.
Altermagnets have alternating spins and no overall magnetization, like antiferromagnets. But the crystal structure surrounding the opposing spins is rotated, which breaks a symmetry that ordinary antiferromagnets have. This small difference lets altermagnets carry spin currents, flows of information based on electron spin instead of electric charge, an ability once tied to ferromagnets alone.
To prove the new phase is real, the researchers studied manganese telluride, a material long classed as an antiferromagnet. At the European Synchrotron Radiation Facility in France, they aimed circularly polarized X-rays - light whose electric field twists in a left or right handed direction - at the crystal. A chiral, or handed, material scatters the two beams differently, and manganese telluride did exactly that. Conventional antiferromagnets show no such signature. The team repeated the measurements months later and reproduced the result.
A simple squeeze changes the magnetism
In a companion finding, scientists at Oak Ridge National Laboratory gently squeezed tiny crystals of manganese telluride and iron sulfide between titanium plates. Neutron measurements at the Spallation Neutron Source showed that the pressure changed the populations of magnetic domains, regions that share one magnetic arrangement, and altered an electrical response known as the anomalous Hall effect. The two linked studies, in Physical Review X and Advanced Materials and described in an Oak Ridge news release, show that mechanical strain can tune altermagnetic behavior.
The work matters because of spintronics, a field that uses electron spin as well as charge to store and move information. Ferromagnets are easily disturbed by outside magnetic fields, while antiferromagnets are hard to read. Altermagnets combine the stability of antiferromagnets with spin currents that can be read out, and they can now be controlled with a simple squeeze. That mix could lead to faster computer memory, more energy efficient data centers, and new quantum devices.