Sayantika Bhowal
Recently, a new class of antiferromagnets, also known as altermagnets, has been proposed that exhibit non-relativistic spin-splitting in contrast to the conventional antiferromagnets with degenerate up and down spin-polarized bands. Taking the example of prototypical non-relativistic spin-split centrosymmetric antiferromagnet rutile MnF2, in my talk, I will show that the non-relativistic spin-splitting is conveniently described in terms of the ferroic ordering of magnetic octupoles. Using density-functional and model calculations, we show that the magnetic octupole is the lowest-order ferroically ordered magnetic quantity in this case, and so is the natural order parameter for the transition into the magnetically ordered state. They provide a unified description of the broken time-reversal symmetry and the non-relativistic spin splitting as well as a platform for manipulating the latter and account for other phenomena, such as piezomagnetism, characteristic of this class of antiferromagnets. Unusually for antiferromagnets, we show that the magnetic octupoles cause a non-zero magnetic Compton scattering, providing also a route for their direct experimental detection.
Reference:
Bhowal and N. A. Spaldin, arXiv:2212.03756 (2022).