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- 저자 : Koplak, O.V. (검색결과 4 건)
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Talantsev, A,Lu, Y,Fache, T,Lavanant, M,Hamadeh, A,Aristov, A,Koplak, O,Morgunov, R,Mangin, S IOP 2018 Journal of Physics, Condensed Matter Vol.30 No.13
<P>Two synthetic antiferromagnet bilayer systems with strong perpendicular anisotropy CoFeB/Ta/CoFeB and Pt/Co/Ir/Co/Pt have been grown using sputtering techniques. For both systems two types of magnetization transitions have been studied. The first one concerns transitions from a state where magnetizations of the two magnetic layers are parallel (<I>P</I> state) to a state where magnetizations of the two layers are aligned antiparallel (<I>AP</I> state). The second one concerns transitions between the two possible antiparallel alignments (<I>AP</I>+ to <I>AP</I>−). For both systems and both transitions after-effect measurements can be understood in the frame of nucleation—propagation model. Time derivative analysis of magnetic relaxation curves and mapping of the first order reversal curves at different temperature allowed us to demonstrate the presence of different pinning centers, which number can be controlled by magnetic field and temperature.</P>
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Effect of Co layer thickness on magnetic relaxation in Pt/Co/Ir/Co/Pt/GaAs spin valve
Morgunov, R.B.,L'vova, G.L.,Talantsev, A.D.,Koplak, O.V.,Fache, T.,Mangin, S. North-Holland Pub. Co 2018 Journal of magnetism and magnetic materials Vol.459 No.-
<P><B>Abstract</B></P> <P>Long magnetic relaxation (up to few hours) between stable magnetic states was analyzed in Pt/Co/Ir/Co/Pt/GaAs heterostructures of different Co layers thickness. The experimental data were compared to a large variety of theoretical models amongst which the <I>Fatuzzo-Labrune</I> one seems to be the more relevant. The contributions from domain nucleation and domain wall motion to magnetic relaxation of the spin valves were separated and evaluated. The increase of Co layer thickness suppresses the domain nucleation and enhances the domain wall propagation. The obtained data provide an understanding of the limitations of switching time in the spin valves of large area necessary for GMR biosensors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> In Pt/Co/Ir/Co/Pt/GaAs heterostructures, magnetic relaxation obeys <I>Fatuzzo-Labrune</I> formalism. </LI> <LI> Contributions of reversal phase and domain walls to the magnetic relaxation of the spin valves were distinguished. </LI> <LI> Reversal phase and domain walls contributions to the magnetic relaxation depend on Co layer thickness. </LI> </UL> </P>
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Kushch, L. A.,Sasnovskaya, V. D.,Dmitriev, A. I.,Yagubskii, E. B.,Koplak, O. V.,Zorina, L. V.,Boukhvalov, D. W. The Royal Society of Chemistry 2012 Dalton Transactions Vol.41 No.44
<P>A new high symmetry Mn<SUB>12</SUB> oxocarboxylate cluster [Mn<SUB>12</SUB>O<SUB>12</SUB>(CN-<I>o</I>-C<SUB>6</SUB>H<SUB>4</SUB>CO<SUB>2</SUB>)<SUB>12</SUB>(CH<SUB>3</SUB>CO<SUB>2</SUB>)<SUB>4</SUB>(H<SUB>2</SUB>O)<SUB>4</SUB>]·8CH<SUB>2</SUB>Cl<SUB>2</SUB> (<B>1</B>) with mixed carboxylate ligands is reported. It was synthesized by the standard carboxylate substitution method. <B>1</B> crystallizes in the tetragonal space group <I>I</I>4<SUB>1</SUB>/<I>a</I>. Complex <B>1</B> contains a [Mn<SUB>12</SUB>O<SUB>12</SUB>] core with eight CN-<I>o</I>-C<SUB>6</SUB>H<SUB>4</SUB>CO<SUB>2</SUB> ligands in the axial positions, four CH<SUB>3</SUB>CO<SUB>2</SUB> and four CN-<I>o</I>-C<SUB>6</SUB>H<SUB>4</SUB>CO<SUB>2</SUB> in equatorial positions. Four H<SUB>2</SUB>O molecules are bonded to four Mn atoms in an alternating up, down, up, down arrangement indicating a 1 : 1 : 1 : 1 isomer. The Mn<SUB>12</SUB> molecules in <B>1</B> are self-assembled by complementary hydrogen C–H⋯N bonds formed with participation of the axial <I>o</I>-cyanobenzoate ligands of the adjacent Mn<SUB>12</SUB> clusters. The lattice solvent molecules (CH<SUB>2</SUB>Cl<SUB>2</SUB>) are weakly interacted with Mn<SUB>12</SUB> units that results in solvent loss immediately after removal of the crystals from the mother liquor. The electronic structure and the intramolecular exchange parameters have been calculated. Mn 3d bands of <B>1</B> are rather broad, and the center of gravity of the bands shifts down from the Fermi level. The overlap between Mn 3d bands and 2p ones of the oxygen atoms from the carboxylate bridges is higher than in the parent Mn<SUB>12</SUB>-acetate cluster. These changes in the electronic structure provide a significant difference in the exchange interactions in comparison to Mn<SUB>12</SUB>-acetate. The magnetic properties have been studied on a dried (solvent-free) polycrystalline sample of <B>1</B>. The dc magnetic susceptibility measurements in the 2–300 K temperature range support a high-spin ground state (<I>S</I> = 10). A bifurcation of temperature dependencies of magnetization taken under zero field cooled and field cooled conditions observed below 4.5 K is due to slow magnetization relaxation. Magnetization <I>versus</I> applied dc field exhibited a stepwise hysteresis loop at 2 K. The ac magnetic susceptibility data revealed the frequency dependent out-of-phase (<I>χ</I><SUB>M</SUB>′′) signals characteristic of single-molecule magnets.</P> <P>Graphic Abstract</P><P>New high symmetry Mn<SUB>12</SUB> SMM with four CH<SUB>3</SUB>CO<SUB>2</SUB> and four CN-<I>o</I>-C<SUB>6</SUB>H<SUB>4</SUB>CO<SUB>2</SUB> ligands in equatorial positions and eight CN-<I>o</I>-C<SUB>6</SUB>H<SUB>4</SUB>CO<SUB>2</SUB> in axial ones is synthesized and characterized. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2dt31173a'> </P>
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