Browsing by Author "Liu, Jian"

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A Strain-Driven Antiferroelectric-to-Ferroelectric Phase Transition in La-Doped BiFeO3 Thin Films on Si
(2017-09-01)
Chen, Deyang
;
Nelson, Christopher T.
;
Zhu, Xiaohong
;
Serrao, Claudy R.
;
Clarkson, James D.
A strain-driven orthorhombic (O) to rhombohedral (R) phase transition is reported in La-doped BiFeO3 thin films on silicon substrates. Biaxial compressive epitaxial strain is found to stabilize the rhombohedral phase at La concentrations beyond the morphotropic phase boundary (MPB). By tailoring the residual strain with film thickness, we demonstrate a mixed O/R phase structure consisting of O phase domains measuring tens of nanometers wide within a predominant R phase matrix. A combination of piezoresponse force microscopy (PFM), transmission electron microscopy (TEM), polarization electric field hysteresis loop (P-E loop), and polarization maps reveal that the O-R structural change is an antiferroelectric to ferroelectric (AFE-FE) phase transition. Using scanning transmission electron microscopy (STEM), an atomically sharp O/R MPB is observed. Moreover, X-ray absorption spectra (XAS) and X-ray linear dichroism (XLD) measurements reveal a change in the antiferromagnetic axis orientation from out of plane (R-phaSe) to in plane (O-p hase). These findings provide direct evidence of spin-charge-lattice coupling in La-doped BiFeO3 thin films. Furthermore, this study opens a new pathway to drive the AFE-FE O-R phase transition and provides a route to study the O/R MPB in these films.
Si nanocrystal memory devices self-assembled by in situ rapid thermal annealing of ultrathin a-Si on SiO2
(2007)
Chen, Jian-Hao
;
Lei, Tan-Fu
;
Landheer, Dolf
;
Wu, Xiaohua
;
Liu, Jian
Si-nanocrystal memories have been fabricated using the thermal agglomeration of an ultrathin (0.9-3.5 nm) amorphous Si (a-Si) film. The a-Si was deposited by electron beam evaporation followed by in situ annealing at 850 C for 5 min. Hemispherical nanocrystals were obtained with a dot density up to 3.9 x 10(11) cm(-2), and a stored charge density of 4.1 x 10(12) cm(-2) (electron + hole) was achieved. The data retention characteristics of nanocrystal-embedded devices have shown a 1 V memory window after 100 h. Well-separated Si nanocrystals with a 23-32% surface-coverage ratio have been successfully demonstrated. The process compatibility of the proposed technique was also discussed. (C) 2007 The Electrochemical Society.
Tuning the Competition between Ferromagnetism and Antiferromagnetism in a Half-Doped Manganite through Magnetoelectric Coupling
(2013-09-18)
Yi, Di
;
Liu, Jian
;
Okamoto, Satoshi
;
Jagannatha, Suresha
;
Chen, Yi-Chun
We investigate the possibility of controlling the magnetic phase transition of the heterointerface between a half-doped manganite La0.5Ca0.5MnO3 and a multiferroic BiFeO3 (BFO) through magnetoelectric coupling. Using macroscopic magnetometry and element-selective x-ray magnetic circular dichroism at the Mn and Fe L edges, we discover that the ferroelectric polarization of BFO controls simultaneously the magnetization of BFO and La0.5Ca0.5MnO3 (LCMO). X-ray absorption spectra at the oxygen K edge and linear dichroism at the Mn L edge suggest that the interfacial coupling is mainly derived from the superexchange between Mn and Fe t(2g) spins. The combination of x-ray absorption spectroscopy and mean-field theory calculations reveals that the d-electron modulation of Mn cations changes the magnetic coupling in LCMO, which controls the enhanced canted moments of interfacial BFO via the interfacial coupling. Our results demonstrate that the competition between ferromagnetic and antiferromagnetic instability can be modulated by an electric field at the heterointerface, providing another pathway for the electrical field control of magnetism.