Browsing by Author "Farhan, Alan"

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Complex strain evolution of polar and magnetic order in multiferroic BiFeO3 thin films
(2018-09-21)
Chen, Zuhuang
;
Chen, Zhanghui
;
Kuo, Chang-Yang
;
Tang, Yunlong
;
Dedon, Liv R.
Electric-field control of magnetism requires deterministic control of the magnetic order and understanding of the magnetoelectric coupling in multiferroics like BiFeO3 and EuTiO3. Despite this critical need, there are few studies on the strain evolution of magnetic order in BiFeO3 films. Here, in (110)-oriented BiFeO3 films, we reveal that while the polarization structure remains relatively unaffected, strain can continuously tune the orientation of the antiferromagnetic-spin axis across a wide angular space, resulting in an unexpected deviation of the classical perpendicular relationship between the antiferromagnetic axis and the polarization. Calculations suggest that this evolution arises from a competition between the Dzyaloshinskii-Moriya interaction and single-ion anisotropy wherein the former dominates at small strains and the two are comparable at large strains. Finally, strong coupling between the BiFeO3 and the ferromagnet Co0.9Fe0.1 exists such that the magnetic anisotropy of the ferromagnet can be effectively controlled by engineering the orientation of the antiferromagnetic-spin axis.
Manipulating magnetoelectric energy landscape in multiferroics
(2020-06-05)
Huang, Yen-Lin
;
Nikonov, Dmitri
;
Addiego, Christopher
;
Chopdekar, Rajesh, V
;
Prasad, Bhagwati
Magnetoelectric coupling at room temperature in multiferroic materials, such as BiFeO3, is one of the leading candidates to develop low-power spintronics and emerging memory technologies. Although extensive research activity has been devoted recently to exploring the physical properties, especially focusing on ferroelectricity and antiferromagnetism in chemically modified BiFeO3, a concrete understanding of the magnetoelectric coupling is yet to be fulfilled. We have discovered that La substitutions at the Bi-site lead to a progressive increase in the degeneracy of the potential energy landscape of the BiFeO3 system exemplified by a rotation of the polar axis away from the < 111 > (pc) towards the < 112 > (pc) discretion. This is accompanied by corresponding rotation of the antiferromagnetic axis as well, thus maintaining the right-handed vectorial relationship between ferroelectric polarization, antiferromagnetic vector and the Dzyaloshinskii-Moriya vector. As a consequence, La-BiFeO3 films exhibit a magnetoelectric coupling that is distinctly different from the undoped BiFeO3 films. BiFeO3 has a wide application but the impact of rare-earth substitution for the evolution of the coupling mechanism is unknown. Here, the authors reveal the correlation between ferroelectricity, antiferromagnetism, a weak ferromagnetic moment, and their switching pathways in La-substituted BiFeO3.