[12.01월] 장현명 교수 연구실
Artificially Imposed Hexagonal Ferroelectricity in Epitaxially Constrained Thin-Film Heterostructure
J. Am. Chem. Soc. 3, 134, 1450–1453 (2012)
Multiferroics have received a great deal ofattention because of their fascinating physics of orderparametercross-couplings and their potential for enablingnew device paradigms. Considering the rareness ofmultiferroic materials, we have been exploring the possibility of artificially imposing ferroelectricity by structurally tailoring antiferromagnets in thin-film forms.
YbFeO3 (YbFO hereafter), a family of centrosymmetric rare-earth orthoferrites, is known to be nonferroelectric (space group Pnma). Here we report that a YbFO thin-film heterostructure fabricated by adopting a hexagonal template surprisingly exhibits nonferroelastic ferroelectricity with the Curie temperature of 470 K. The observed ferroelectricity is further characterized by an extraordinary
two-step polarization decay, accompanied by a pronounced magnetocapacitance effect near the lower decay temperature, ∼225 K. According to first-principles
calculations, the hexagonal P63/mmc−P63mc−P63cm consecutive transitions are primarily responsible for the observed two-step polarization decay, and the ferroelectricity originates from the c-axis-oriented asymmetric Yb 5dz2−O 2pz orbital hybridization. Temperature-dependentmagnetization curves further reveal an interesting phenomenon of spontaneous magnetization reversal at 83 K, which is attributed to the competition between two distinct magnetocrystalline anisotropy terms, Fe 3d and Yb 4f moments.