Abstract

Most magnetic materials, phenomena and devices are well described in terms of the magnetic dipoles arising from the spin of their constituent electrons. There is mounting evidence, however, of intriguing magnetic behaviors that can’t be explained in terms of electron spin dipole moments; these behaviors are often attributed to “hidden order” since their origin is difficult to decipher with conventional experimental probes. In this talk I will discuss some unusual magnetic effects, such as electric-field induced magnetism, magnetism on apparently non-magnetic surfaces, and unconventional spin splitting of energy bands, and show that they can be understood in terms of a “hidden order” of higher-order magnetic multipoles, beyond the magnetic dipole. While there are clear experimental signatures of such hidden multipolar order, and it is captured nicely in our computer simulations, attempts at direct measurement have so far proved elusive, and I will close with a plea for better ideas.

If you wish to meet the speaker, please contact ap2076@cam.ac.uk to be added to their visit schedule.