Open questions in dynamic magnetism

Vivien Zapf (National High Magnetic Field Laboratory, Los Alamos)

I will present recent results in dynamic magnetism that require better experimental tools to understand them. At the National High Magnetic Field Laboratory in Los Alamos we measure magnetic and other thermodynamic properties in magnetic field sweep rates that cover eleven orders of magnitude from superconducting magnets up through single turn magnets with pulse speeds of 10⁸ T/s. As a consequence we sometimes uncover new dynamic magnetic ordering phenomena, and wish we had tools like neutron diffraction in -- or following -- pulsed magnetic fields to achieve a microscopic understanding.

I will start by discussing how slow magnetic dynamics can be generated spontaneously by geometric frustration. In a recently-discovered class of frustrated magnets, the evolution of magnetic states in applied magnetic fields can depend on the speed or protocol in which the magnetic field is applied. I will cover the implications we observe for new magnetic hysteresis mechanisms and magnetoelectric coupling.

I will then discuss the Kibble-Zurek mechanism . this is a theory that predicts that all 2^nd order phase transitions traversed at finite speed will generate topological defects . provided this effect is not swamped by ordinary ferromagnetic domains. Some interesting evidence exists for this in Bose-Einstein Condensates, superconductors and hexagonal ferroelectrics. I will discuss what it would take to test the Kibble Zurek mechanism in antiferromagnets.

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Last modified 21-March-2015 by website owner: NCNR (attn: )