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 Tc. The X-band and 216 GHz Cr3+ electron paramagnetic resonance (EPR) spectra as well as the magnetic susceptibility and Mossbauer data show the existence of two magnetic relaxor type transitions around 37 and 17 K. The K39 magic angle sample spinning NMR, EPR, and the Mossbauer 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 Mossbauer spectra shows that the Fe2+ ion is in a high spin state.