Magnetic properties of multiferroic K3Cr2Fe3F15

The local electronic and structural as well as the macroscopic magnetic properties of K3Cr2Fe3F15 have been studied between room temperature and 4 K. The system has been found to be isostructural with ferroelectric and weakly ferrimagnetic K3Fe5F15 above the ferroelectric transition temperature T-c. The X-band and 216 GHz Cr3+ electron paramagnetic resonance (EPR) spectra as well as the magnetic susceptibility and Moumlssbauer data show the existence of two magnetic relaxor type transitions around 37 and 17 K. The K-39 magic angle sample spinning NMR, EPR, and the Moumlssbauer data further demonstrate the existence of two nonequivalent Fe, Cr, and K sites in the unit cell as well as the presence of rapid exchange at higher temperatures. The observation of the Fe2+ EPR and Moumlssbauer spectra shows that the Fe2+ ion is in a high spin state