Browsing by Author "Kim, Kee Hoon"

Now showing 1 - 4 of 4

Concurrent transition of ferroelectric and magnetic ordering near room temperature
(2011-11-01)
Ko, Kyung-Tae
;
Jung, Min Hwa
;
He, Qing
;
Lee, Jin Hong
;
Woo, Chang Su
Strong spin-lattice coupling in condensed matter gives rise to intriguing physical phenomena such as colossal magnetoresistance and giant magnetoelectric effects. The phenomenological hallmark of such a strong spin-lattice coupling is the manifestation of a large anomaly in the crystal structure at the magnetic transition temperature. Here we report that the magnetic Neel temperature of the multiferroic compound BiFeO3 is suppressed to around room temperature by heteroepitaxial misfit strain. Remarkably, the ferroelectric state undergoes a first-order transition to another ferroelectric state simultaneously with the magnetic transition temperature. Our findings provide a unique example of a concurrent magnetic and ferroelectric transition at the same temperature among proper ferroelectrics, taking a step toward room temperature magnetoelectric applications.
Flexible Multiferroic Bulk Heterojunction with Giant Magnetoelectric Coupling via van der Waals Epitaxy
(2017-06-01)
Amrillah, Tahta
;
Bitla, Yugandhar
;
Shin, Kwangwoo
;
Yang, Tiannan
;
Hsieh, Ying-Hui
Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate damping effect still remains a major hurdle in realizing the ultimate magneto electric coupling. To overcome this obstacle, an alternative strategy of fabricating a self-assembled ferroelectric-ferrimagnetic bulk heterojunction on a flexible muscovite via van der Waals epitaxy is adopted. hi this study, we investigated the magnetoelectric coupling in a self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) bulk heterojunction epitaxially grown on a flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedded in a ferrimagnetic CFO matrix. Moreover, due to the weak interaction between the flexible substrate and bulk heterojunction, the interface is incoherent and, hence, the substrate damping effect is greatly reduced. The phase-field simulation model also complements our results. The magnetic and electrical characterizations highlight the improvement in magnetoelectric coupling of the BFO-CFO bulk heterojunction. A magnetoelectric coupling coefficient of 74 mV/cm.Oe of this bulk heterojunction is larger than the magnetoelectric coefficient reported earlier on flexible substrates. Therefore, this study delivers a viable route of fabricating a remarkable magnetoelectric heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance.
Quantitative determination of anisotropic magnetoelectric coupling in BiFeO(3)-CoFe(2)O(4) nanostructures
(2010-08-02)
Oh, Yoon Seok
;
Crane, S.
;
Zheng, H.
;
Chu, Y. H.
;
Ramesh, R.
The transverse and longitudinal magnetoelectric susceptibilities (MES) were quantitatively determined for (001) heteroepitaxial BiFeO(3)-CoFe(2)O(4) nanostructures. Both of these MES values were sharply enhanced at magnetic fields below 6 kOe and revealed asymmetric line shapes with respect to the dc magnetic field, demonstrating the strain-induced magnetoelectric effect. The maximum transverse MES, which reached as high as similar to 60 mV/cm Oe, was about five times larger than the longitudinal MES. This observation signifies that transverse magnetostriction of the CoFe(2)O(4) nanopillars is enhanced more than the bulk value due to preferred magnetic domain alignment along the [001] direction coming from compressive, heteroepitaxial strain. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3475420]
Quantitative determination of anisotropic magnetoelectric coupling in BiFeO3-CoFe2O4 nanostructures
(2010-08-02)
Oh, Yoon Seok
;
Crane, S.
;
Zheng, H.
;
Chu, Y. H.
;
Ramesh, R.
The transverse and longitudinal magnetoelectric susceptibilities (MES) were quantitatively determined for (001) heteroepitaxial BiFeO3-CoFe2O4 nanostructures. Both of these MES values were sharply enhanced at magnetic fields below 6 kOe and revealed asymmetric line shapes with respect to the dc magnetic field, demonstrating the strain-induced magnetoelectric effect. The maximum transverse MES, which reached as high as similar to 60 mV/cm Oe, was about five times larger than the longitudinal MES. This observation signifies that transverse magnetostriction of the CoFe2O4 nanopillars is enhanced more than the bulk value due to preferred magnetic domain alignment along the [001] direction coming from compressive, heteroepitaxial strain. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3475420]