Driving multiferroicity in BaFe₁₂O₁₉ with Tunable THz pulses, Part I: Light-induced strain

BaFe₁₂O₁₉ is an M-type hexaferrite with a strong ferromagnetic moment and high transition temperature. In addition to its superior magnetic properties, it recently has acquired great interest from the scientific community as an incipient ferroelectric, with the potential of being a multiferroic at low temperatures. Although quantum fluctuations prevent the formation of a long-range ferroelectric order even at the lowest temperatures, it has been suggested that a large enough strain can induce a ferroelectric polarization at room temperature. In a two-part talk, we discuss the possibility of optically straining BaFe₁₂O₁₉ to induce multiferroicity using THz frequency light. In this first part of the talk, we describe the generation of strong tunable narrow-band THz pulses through which we resonantly excite certain phonon modes in thin film BaFe₁₂O₁₉. We discuss the magnetic and structural response of the material to resonant excitation of these phonons using a multi-modal spectroscopic approach.