Weak ferromagnetism and ferroelectricity in K3 Fe5 F15

Abstract

Here, we report on the observation of a weak ferromagnetic transition at TN =122 K in a K3 Fe5 F15 system which is ferroelectric and ferroelastic below Tc =490 K. The magnetization and the susceptibility continuously increase with decreasing T down to 2 K. The Mössbauer spectra show a spontaneous magnetic ordering and at least three sites corresponding to Fe2+ and Fe3+. The ratio between Fe2+ and Fe3+ is 60:40. At 6 K, there are two magnetically ordered sextets with internal fields of 585 and 263 kOe. The "slim" hysteresis loops observed are as well characteristic of weak ferromagnetism. At 122 K and at low frequencies, the system shows dielectric anomaly characteristic of magnetoelectric behavior. © 2008 American Institute of Physics.