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Anisotropic AC Magnetic Susceptibility in (Ga,Mn)As Films
Xiang Li,Sining Dong,Taehee Yoo,Xinyu Liu,Sanghoon Lee,Furdyna, Jacek K.,Dobrowolska, Margaret IEEE 2015 IEEE transactions on magnetics Vol.51 No.11
<P>We report a systematic investigation of ac magnetic susceptibility in (Ga,Mn)As films as a function of temperature and magnetic field, carried out in parallel with dc magnetization measurements. The temperature dependence of ac susceptibility χ<SUB>ac</SUB> shows anisotropic behavior: 1) a single peak in χ<SUB>ac</SUB> is observed close to T for the [11̅0] orientation of the driving ac field; 2) a single peak is also seen close to 22 K for the field along [110]; and 3) peaks at both these temperatures are observed for the field applied along [100]. A detailed analysis of the ac and dc data unambiguously indicates that the peak near T is related to the paramagnetic-to-ferromagnetic phase transition, with the ferromagnetic domains nucleating with their easy axes aligned with the [11̅0] direction, providing a clear picture of uniaxial domain behavior near T . The peak near 22 K, on the other hand, is related to the onset of biaxial domain structure in (Ga,Mn)As induced by the competition between uniaxial and cubic anisotropy. More specifically, the ac susceptibility peak near T<SUB>C</SUB> involves 180° magnetization flips along the [11̅0] easy axis of the domains, while the peak near 22 K originates from magnetization wobbling between two biaxial easy axes separated by a small angle.</P>
Time-Resolved Photoluminescence in CdSe/CdZnSe and CdSe/CdMnSe Coupled Quantum Dot Structures
오은순,D. G. Choi,J. H. Park,Jacek Furdyna,이상훈,김신,T. K. Lee 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.2I
We studied the time-resolved photoluminescence (PL) from coupled quantum dot (QD) systems (CdSe/CdZnSe and CdSe/CdMnSe) and the PL decay as functions of the magnetic field and the temperature. In the CdSe/CdMnSe system, the PL decay of the + component exhibited biexponential behavior under external fields, which indicated that a fraction of the CdSe QDs were not coupled to the CdMnSe QDs. The PL lifetimes of these structures were found to be more significantly affected by non-radiative recombination, rather than by the vertical coupling between the QDs.
Decimal Tunneling Magnetoresistance States in Fe/GaAlAs/GaMnAs Magnetic Tunnel Junction
Taehee Yoo,Sanghoon Lee,Xinyu Liu,Furdyna, Jacek K.,Dong Uk Lee,Eun Kyu Kim IEEE 2014 IEEE transactions on magnetics Vol.50 No.11
<P>We report the realization of ten stable tunneling magnetoresistance (TMR) states in a single device. To achieve ten resistance states, we have used a magnetic tunnel junction (MTJ) structure that consists of two magnetic layers, which are Fe and GaMnAs ferromagnetic layers. Owing to the two in-plane magnetic easy axes that result from strong cubic anisotropies in both Fe and GaMnAs layers, noncollinear magnetic configurations between two magnetic layers were realized, in addition to the parallel and antiparallel configurations. Such noncollinear magnetic configurations provide stable intermediate TMR values between two extreme values corresponding parallel and antiparallel configurations. The number of stable TMR values was further increased by forming multidomain structures in the MTJ structure. We demonstrate that we can obtain up to ten stable TMR values, and they can be controlled by applying the appropriate magnetic field sequences.</P>
Antiferromagnetic Interlayer Exchange Coupling in Ferromagnetic GaMnAs/GaAs:Be Multilayers
Lee, Hakjoon,Lee, Sangyeop,Choi, Seonghoon,Yoo, Taehee,Lee, Sanghoon,Liu, Xinyu,Furdyna, Jacek K. IEEE 2015 IEEE transactions on magnetics Vol.51 No.11
<P>Interlayer exchange coupling (IEC) between the GaMnAs layers in GaMnAs/GaAs:Be multilayer systems has been investigated using magnetotransport experiments. The observation of a stable antiparallel magnetization alignment state from the systems indicates the presence of antiferromagnetic (AFM) IEC between the GaMnAs layers. The transitions between parallel and antiparallel alignments of GaMnAs magnetic layers in the system were carefully investigated by measuring resistance change with increasing temperature under various bias magnetic fields. From the dependence of the transition temperature on bias fields, we have estimated the magnitude of AFM IEC and its temperature behavior of our GaMnAs/GaAs:Be multilayers.</P>