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Stoumpos, Constantinos C.,Frazer, Laszlo,Clark, Daniel J.,Kim, Yong Soo,Rhim, Sonny H.,Freeman, Arthur J.,Ketterson, John B.,Jang, Joon I.,Kanatzidis, Mercouri G. American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.21
<P>The synthesis and properties of the hybrid organic/inorganic germanium perovskite compounds, AGeI<SUB>3</SUB>, are reported (A = Cs, organic cation). The systematic study of this reaction system led to the isolation of 6 new hybrid semiconductors. Using CsGeI<SUB>3</SUB> (<B>1</B>) as the prototype compound, we have prepared methylammonium, CH<SUB>3</SUB>NH<SUB>3</SUB>GeI<SUB>3</SUB> (<B>2</B>), formamidinium, HC(NH<SUB>2</SUB>)<SUB>2</SUB>GeI<SUB>3</SUB> (<B>3</B>), acetamidinium, CH<SUB>3</SUB>C(NH<SUB>2</SUB>)<SUB>2</SUB>GeI<SUB>3</SUB> (<B>4</B>), guanidinium, C(NH<SUB>2</SUB>)<SUB>3</SUB>GeI<SUB>3</SUB> (<B>5</B>), trimethylammonium, (CH<SUB>3</SUB>)<SUB>3</SUB>NHGeI<SUB>3</SUB> (<B>6</B>), and isopropylammonium, (CH<SUB>3</SUB>)<SUB>2</SUB>C(H)NH<SUB>3</SUB>GeI<SUB>3</SUB> (<B>7</B>) analogues. The crystal structures of the compounds are classified based on their dimensionality with <B>1</B>–<B>4</B> forming 3D perovskite frameworks and <B>5</B>–<B>7</B> 1D infinite chains. Compounds <B>1</B>–<B>7</B>, with the exception of compounds <B>5</B> (centrosymmetric) and <B>7</B> (nonpolar acentric), crystallize in polar space groups. The 3D compounds have direct band gaps of 1.6 eV (<B>1</B>), 1.9 eV (<B>2</B>), 2.2 eV (<B>3</B>), and 2.5 eV (<B>4</B>), while the 1D compounds have indirect band gaps of 2.7 eV (<B>5</B>), 2.5 eV (<B>6</B>), and 2.8 eV (<B>7</B>). Herein, we report on the second harmonic generation (SHG) properties of the compounds, which display remarkably strong, type I phase-matchable SHG response with high laser-induced damage thresholds (up to ∼3 GW/cm<SUP>2</SUP>). The second-order nonlinear susceptibility, χ<SUB>S</SUB><SUP>(2)</SUP>, was determined to be 125.3 ± 10.5 pm/V (<B>1</B>), (161.0 ± 14.5) pm/V (<B>2</B>), 143.0 ± 13.5 pm/V (<B>3</B>), and 57.2 ± 5.5 pm/V (<B>4</B>). First-principles density functional theory electronic structure calculations indicate that the large SHG response is attributed to the high density of states in the valence band due to sp-hybridization of the Ge and I orbitals, a consequence of the lone pair activation.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-21/jacs.5b01025/production/images/medium/ja-2015-01025x_0013.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b01025'>ACS Electronic Supporting Info</A></P>
이종구조 MnAs 박막의 자기적 특성 및 증착 후 열처리가 미치는 영향
송종현(J. H. Song),J. B. Ketterson 한국자기학회 2009 韓國磁氣學會誌 Vol.19 No.4
We have studied physical properties of MnAs thin films grown by Molecular-Beam Epitaxy as well as their postgrowth annealing effects. The samples grown at 600 ℃ show the preferred crystal orientation of type-B independent of substrate whereas type-A is observed for the samples grown at below 200 ℃. The sample grown at 600 ℃ on GaAs(001) substrate is magnetized to only one direction even on the easy axis of magnetization. The magnetic properties are vastly enhanced after post-growth annealing for both MnAs/Si(001) sample with no ferromagnetism and ferromagnetic MnAs/GaAs(001) grown at 200 ℃.
Magnetic Properties of Ge/MnAs Digital Heterostructure
Lee, J.J.,Kim, M.Y.,Song, J.H.,Cui, Y.,Ketterson, J.B. IEEE 2007 IEEE transactions on magnetics Vol.43 No.6
<P>Magnetic properties of Ge/MnAs digital heterostructure grown by molecular beam epitaxy are reported. A Ge (1 nm)/MnAs (0.15 nm) digital heterostructure exhibited ferromagnetic ordering below 335 K. More importantly, the Ge (1 nm)/MnAs (0.15 nm) heterostructure shows an n-type conductivity and an anomalous Hall effect at room temperature. Concurrently, the magnetic phase stabilities of the Ge (1 nm)/MnAs (0.15 nm) digital heterostructure have been investigated using the highly precise all-electron full-potential linearized augmented plane-wave (FLAPW) method within the generalized gradient approximation (GGA). A total energy calculations reveal that the ferromagnetic coupling between the Mn atoms is energetically favored over the antiferromagnetic (100) and (110) coupling. The Ge (1 nm)/MnAs (0.15 nm) digital heterostructure also showed a possible half-metallic ferromagnetic phase with a 0.25 eV band gap for the minority spin channel, which indicates a promising possible spintronic application</P>
Nonreciprocal spin-wave propagation in YIG/GGG: a limit on the DMI parameter
Trossman J.,Lim Jinho,Ketterson J. B.,Bang Wonbae 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.4
Materials with low damping, such as Yttrium Iron Garnet (YIG), are of interest in connection with spintronic devices. A promising structure for information storage is the Skyrmion, a domain wall quasi-particle. It has been shown that the stabilization of a Skyrmion can be energetically favorable with the addition of spin–orbit coupling (SOC) through the Dzyaloshinskii–Moriya Interaction (DMI). This interaction should be largest in metals, but still present in insulators. To produce spintronic devices using YIG, we must evaluate the DMI interaction inherent in the substrate used to grow the YIG, which is generally Gadolinium Gallium Garnet (GGG). In this paper, we measure nonreciprocal spin-wave propagation in a thick YIG flm to place a limit on the DMI parameter in a YIG/GGG bilayer.