Controlling Magnetic Interactions: Antiferromagnetic to Ferromagnetic Order
Switching a material from antiferromagnetic (AFM) to ferromagnetic (FM) order is the maximum change of macroscopic magnetism that one can generate. Several systems display intrinsic competition between these types of order, thus enabling control of the state via external conditions such as electric field, pressure, strain, temperature, etc. This talk will focus on two systems that exhibit an AFM to FM transition, and will discuss the underlying physics driving the competitive nature of the coupling. The magnetoelectric EuTiO3 (ETO) changes its magnetic order from AFM to FM through phonon softening induced by biaxial strain. With an appropriate strain state, the energy difference between the two interactions gets small so that the magnetic state can be altered by an external electric field.
By compressively straining the ETO film, the antiferromagnetic order becomes frustrated with the application of an electric field above 1.8 kV/cm. Inter-metallic FeRh films have attracted growing interest in the last decade because its potential application in heat-assisted magnetic recording. This material exhibits a temperature- or field-induced first-order magnetic transition from AFM order to FM order above the room temperature with structural and electronic transitions. I present the magnetic behavior of Rh 4d states through the transition using x-ray resonant magnetic scattering at the Rh L2 edge concurrently with the structural evolution by x-ray diffraction. The structural transition measures a lower temperature than the Rh ferromagnetic transition. This confirms that the structural transition is driven by a magnetically frustrated state due to the onset of Rh 4d magnetic moments.