Enhanced ferromagnetism in BaNiF4 film

BaMF4 (M = Mn, Ni, Co, etc.) are typical multiferroic materials with above room temperature ferroelectricity, but the antiferromagnetic ordering temperature is quite low. We report the epitaxial growth of BaNiF4 films on Al2O3 substrates by pulsed laser deposition. The epitaxial growth of BaNiF4 films is confirmed by the observation of only (040), (080) and (0120) diffraction peaks in X ray diffraction patterns. Using piezoresponse force microscopy (PFM), the ferroelectricity at room temperature has been inferred from the observation of PFM hysteresis loops. The wasp-wasted hysteresis loops are clearly observed below 10 K, which is due to the weak antiferromagnetic nature of the canted spins. Clear weak ferromagnetism has been observed up to 300 K, which is considered to be due to the epitaxial strains.