Browsing by Author "Yi, Di"

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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.
Tailoring Magnetoelectric Coupling in BiFeO3/La0.7Sr0.3MnO3 Heterostructure through the Interface Engineering
(2019-03-15)
Yi, Di
;
Yu, Pu
;
Chen, Yi-Chun
;
Lee, Hsin-Hua
;
He, Qing
Electric field control of magnetism ultimately opens up the possibility of reducing energy consumption of memory and logic devices. Electric control of magnetization and exchange bias are demonstrated in all-oxide heterostructures of BiFeO3 (BFO) and La0.7Sr0.3MnO3 (LSMO). However, the role of the polar heterointerface on magnetoelectric (ME) coupling is not fully explored. Here, the ME coupling in BFO/LSMO heterostructures with two types of interfaces, achieved by exploiting the interface engineering at the atomic scale, is investigated. It is shown that both magnetization and exchange bias are reversibly controlled by switching the ferroelectric polarization of BFO. Intriguingly, distinctly different modulation behaviors that depend on the interfacial atomic sequence are observed. These results provide new insights into the underlying physics of ME coupling in the model system. This study highlights that designing interface at the atomic scale is of general importance for functional spintronic devices.
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.