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Sae Hwan Chun,
Yi Sheng Chai,
Byung-Gu Jeon,
Hyung Joon Kim,
Yoon Seok Oh,
Ingyu Kim,
Hanbit Kim,
Byeong Jo Jeon,
So Young Haam,
Ju-Young Park,
Suk Ho Lee,
Jae-Ho Chung, Jae-Hoon Park,
Kee Hoon Kim
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ABSTRACT: We find the realization of large converse magnetoelectric (ME) effects at room temperature in a magnetoelectric hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then reaches up to 0.62μ(B)/f.u. in an electric field of 1.14 MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be approximately described by an effective free energy with a distinct set of ME coefficients.
Physical Review Letters 04/2012; 108(17):177201. · 7.37 Impact Factor
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Kyung-Tae Ko,
Min Hwa Jung,
Qing He,
Jin Hong Lee,
Chang Su Woo,
Kanghyun Chu,
Jan Seidel,
Byung-Gu Jeon,
Yoon Seok Oh,
Kee Hoon Kim,
Wen-I Liang,
Hsiang-Jung Chen,
Ying-Hao Chu,
Yoon Hee Jeong,
Ramamoorthy Ramesh, Jae-Hoon Park,
Chan-Ho Yang
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ABSTRACT: 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 Néel temperature of the multiferroic compound BiFeO(3) 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.
Nature Communications 01/2011; 2:567. · 7.40 Impact Factor
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Sae Hwan Chun,
Yi Sheng Chai,
Yoon Seok Oh,
Deepshikha Jaiswal-Nagar,
So Young Haam,
Ingyu Kim,
Bumsung Lee,
Dong Hak Nam,
Kyung-Tae Ko, Jae-Hoon Park,
Jae-Ho Chung,
Kee Hoon Kim
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ABSTRACT: We show that low field magnetoelectric (ME) properties of helimagnets Ba0.5Sr1.5Zn2(Fe1-xAlx)12O22 can be efficiently tailored by the Al-substitution level. As x increases, the critical magnetic field for switching electric polarization is systematically reduced from approximately 1 T down to approximately 1 mT, and the ME susceptibility is greatly enhanced to reach a giant value of 2.0x10{4} ps/m at an optimum x=0.08. We find that control of the nontrivial orbital moment in the octahedral Fe sites through the Al substitution is crucial for fine-tuning the magnetic anisotropy and obtaining the conspicuously improved ME characteristics.
Physical Review Letters 01/2010; 104(3):037204. · 7.37 Impact Factor
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Jung Ho Yu,
Xinyu Liu,
Kyoung Eun Kweon,
Jin Joo,
Jiwon Park,
Kyung-Tae Ko,
Dong Won Lee,
Shaoping Shen,
Kritsanu Tivakornsasithorn,
Jae Sung Son, Jae-Hoon Park,
Young-Woon Kim,
Gyeong S. Hwang,
Margaret Dobrowolska,
Jacek K. Furdyna,
Taeghwan Hyeon
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ABSTRACT: Doping of semiconductor nanocrystals by transition-metal ions has attracted tremendous attention owing to their nanoscale spintronic applications. Such doping is, however, difficult to achieve in low-dimensional strongly quantum confined nanostructures by conventional growth procedures. Here we demonstrate that the incorporation of manganese ions up to 10% into CdSe quantum nanoribbons can be readily achieved by a nucleation-controlled doping process. The cation-exchange reaction of (CdSe)13 clusters with Mn2+ ions governs the Mn2+ incorporation during the nucleation stage. This highly efficient Mn2+ doping of the CdSe quantum nanoribbons results in giant exciton Zeeman splitting with an effective g-factor of ~600, the largest value seen so far in diluted magnetic semiconductor nanocrystals. Furthermore, the sign of the s–d exchange is inverted to negative owing to the exceptionally strong quantum confinement in our nanoribbons. The nucleation-controlled doping strategy demonstrated here thus opens the possibility of doping various strongly quantum confined nanocrystals for diverse applications.
Nature Material 11/2009; 9(1):47-53. · 32.84 Impact Factor
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ABSTRACT: Single crystals of multiferroic cobalt chromite Co(Cr2−xCox)O4 have been grown via several methods to have different Co3+ doping levels (x = 0.0, 0.14, and 0.18). Under magnetic fields, all the crystals display electric polarization reversal below their spiral spin ordering temperatures. We find that both saturated electric polarization and magnetization under magnetic fields increase significantly with the increase in x. This result can be qualitatively explained by a broken balance between at least two electric polarization contributions existing in CoCr2O4 and is expected to be useful in tailoring electric polarization in similar kinds of multiferroics.
Applied Physics Letters 01/2009; 94(4):042505-042505-3. · 3.84 Impact Factor
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Kwangjin An,
Nohyun Lee,
Jongnam Park,
Sung Chul Kim,
Yosun Hwang,
Je-Geun Park,
Jae-Young Kim, Jae-Hoon Park,
Myung Joon Han,
Jaejun Yu,
Taeghwan Hyeon
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ABSTRACT: We synthesized uniformly sized, pencil-shaped CoO nanorods by the thermal decomposition of a cobalt-oleate complex, which was prepared from the reaction of cobalt chloride and sodium oleate. The diameters and lengths of the CoO nanorods were easily controlled by varying the experimental conditions, such as the heating rate and the amount of Co-oleate complex. The X-ray diffraction pattern revealed that the CoO nanorods have an extraordinary wurtzite ZnO crystal structure. These uniformly sized nanorods self-assembled to form both horizontal parallel arrangements and perpendicular hexagonal honeycomb superlattice structures. Reduction of the nanorods by heating under a hydrogen atmosphere generated either hcp Co or Co(2)C nanorods. Characterization of the CoO nanorods using X-ray absorption spectroscopy, X-ray magnetic circular dichroism spectroscopy, and magnetic measurements showed that they contain a small fraction of ferromagnetic Co impurities.
Journal of the American Chemical Society 09/2006; 128(30):9753-60. · 9.91 Impact Factor
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Jongnam Park,
Eunwoong Lee,
Nong-Moon Hwang,
Misun Kang,
Sung Chul Kim,
Yosun Hwang,
Je-Geun Park,
Han-Jin Noh,
Jae-Young Kim, Jae-Hoon Park,
Taeghwan Hyeon
Angewandte Chemie International Edition 04/2005; 44(19):2873-7. · 13.45 Impact Factor
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ABSTRACT: We successfully synthesized monodisperse chromium nanoparticles from the thermolysis of a Fischer carbene complex.
Chemical Communications 02/2005; · 6.17 Impact Factor
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ABSTRACT: The development of nanocrystals has been intensively pursued, not only for their fundamental scientific interest, but also for many technological applications. The synthesis of monodisperse nanocrystals (size variation <5%) is of key importance, because the properties of these nanocrystals depend strongly on their dimensions. For example, the colour sharpness of semiconductor nanocrystal-based optical devices is strongly dependent on the uniformity of the nanocrystals, and monodisperse magnetic nanocrystals are critical for the next-generation multi-terabit magnetic storage media. For these monodisperse nanocrystals to be used, an economical mass-production method needs to be developed. Unfortunately, however, in most syntheses reported so far, only sub-gram quantities of monodisperse nanocrystals were produced. Uniform-sized nanocrystals of CdSe (refs 10,11) and Au (refs 12,13) have been produced using colloidal chemical synthetic procedures. In addition, monodisperse magnetic nanocrystals such as Fe (refs 14,15), Co (refs 16-18), gamma-Fe(2)O(3) (refs 19,20), and Fe(3)O(4) (refs 21,22) have been synthesized by using various synthetic methods. Here, we report on the ultra-large-scale synthesis of monodisperse nanocrystals using inexpensive and non-toxic metal salts as reactants. We were able to synthesize as much as 40 g of monodisperse nanocrystals in a single reaction, without a size-sorting process. Moreover, the particle size could be controlled simply by varying the experimental conditions. The current synthetic procedure is very general and nanocrystals of many transition metal oxides were successfully synthesized using a very similar procedure.
Nature Material 12/2004; 3(12):891-5. · 32.84 Impact Factor
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ABSTRACT: Uniform-sized MnO nanospheres and nanorods were fabricated by the thermal decomposition of Mn−surfactant complexes. The particle sizes of the nanospheres were varied from 5 to 40 nm by changing the surfactant. The shape of the particles could be controlled by varying the experimental conditions. The synthesized MnO nanorods have diameters ranging from 7 to 10 nm, and lengths ranging from 30 to 140 nm. Structural characterization using X-ray powder diffraction, X-ray absorption spectroscopy, and high-resolution transmission electron microscopy revealed that the nanoparticles are core/shell structures with a MnO core and a thin Mn3O4 shell. The MnO nanoparticles exhibited very interesting magnetic properties. For example, the MnO nanorods with dimensions of 7 nm × 33 nm showed two blocking temperatures at 35 and 280 K, respectively.
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