Magnetic properties of multiferroic Pb5Fe3F19

Abstract Fluoride ferroelectrics containing 3d transition metal ions are potential single-phase multiferroics. Pure phase Pb5Fe3F19 powders are prepared by the solid-state reaction, which is confirmed by the X-ray diffraction with isostructure to Pb5Cr3F19. X-ray photoelectron spectroscopy confirms that Fe ions are in the valence state of +3. Ferroelectricity is confirmed by the observation of amplitude and phase hysteresis loops by piezoresponse force microscopy at room temperature. Two anomalies are observed at TN1 of 78 K and TN2 of 21 K in the temperature dependent magnetization (M−T) curves, which is due to the onset of two antiferromagnetic transitions. The bifurcation between the zero-field cooled and field cooled M−T curves at temperatures below TN1 of 78 K is attributed to competition of the complicated antiferromagnetic exchange coupling between the neighboring Fe3+ ions, leading to the magnetic relaxation. Small hysteresis with negligible coercivity can be observed in the field dependent magnetization curves below TN1. The magnetization and coercivity are significantly enhanced with further decreasing temperature, indicating the weak ferromagnetism. The observed ferromagnetism might be due to the magnetoelectric coupling between the ferroelectric polarization and magnetization, leading to the spin canting of the antiferromagnetic coupling between neighboring Fe3+ ions. The magnetoelectric coupling is confirmed by the observation of magnetodielectric effect, which is due to the strong magnetic and structural coupling.