David Lederman, Department of Physics, University of California, Santa Cruz
Multiferroic materials, where ordering of different types co-exist (e.g., ferroelectricity and magnetism), are being intensively studied due to their possible applications in various electronic devices. Most of these materials studied to date are complex oxides. However, complex fluorides also have the ability form complex compounds which are also multiferroic , even though they have not been studied extensively to date. In this talk, I will discuss efforts to synthesize these materials in thin film form, using molecular beam epitaxy, and to characterize the ferroelectric and magnetic properties. In particular, we have studied the BaCoF4 compound, where ferroelectricity and antiferromagnetic ordering coexist, and where strain induced by the substrate can generate weak ferromagnetism . I will also discuss fluoride perovskites, in particular NaMnF3, where the ABF3 structure is analogous to the ABO3 structure in complex oxides. However, in the NaMnF3 compound, it is theoretically predicted that the A-site is the atom involved in ferroelectric displacement, and therefore magnetoelectricity, if it exists, should be enhanced . I will show that NaMnF3 indeed orders antiferromagnetically at low temperatures, with indications of weak ferromagnetism, and that it is ferroelectric or a ralaxor ferroelectric, depending on the film quality . Finally, I will discuss the prospects of generating magnetoelectric responses (where magnetic fields can alter the ferroelectric response and electric fields can cause a magnetic response) in these materials.