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Samardak, Alexander S.,Davydenko, Alexander V.,Ognev, Alexey V.,Jeon, Yoo Sang,Choi, Young Soo,Kim, Young Keun IOP Publishing 2016 Japanese journal of applied physics Vol.55 No.10
<P>Understanding the ferromagnetic behavior of coupled magnetic nanoparticles (NPs) in a chain structure, called a 'nanochain (NC)', will open up new routes for its practical use. Here, we report the magnetization reversal modes in isolated magnetite (Fe3O4) NPs with diameters of 100 and 200 nm, as well as those of one-dimensional (1D) self-assembled NCs consisting of these NPs. NCs consisting of 100-nm diameter NPs switched through a transverse domain wall-like motion. Meanwhile, in 200-nm diameter NPs and NCs, we observed 3D magnetic vortex states that were more energetically favorable than single domain or multidomain states. (C) 2016 The Japan Society of Applied Physics</P>
Entropy Estimation of the Position of the Barrier Dimension
Berik Akhmetov,Alexander Ivanov,Anis Gilmutdinov,Ivan Ognev,Kaiyrkhan Mukapil 제어로봇시스템학회 2015 제어로봇시스템학회 국제학술대회 논문집 Vol.2015 No.10
It is shown that large neural networks allow solving tasks that cannot classical quadratic forms in linear algebra. Thus the assessment of output entropy of neural network converters biometrics code is possible. The assessment of high-dimensional entropy is based on the symmetrization of the problem of the correlation of biometric data. Entropy of low dimension and high-dimensional entropy are differently connected with equally correlated data. For low-dimensional transformations only short-sighted algorithms, which not capable to bypass local extrema of quality are effective. The algorithms constructed on the accounting of multidimensional entropy are far-sighted, they don"t see local extrema.
Kolesnikov, A.G.,Samardak, A.S.,Stebliy, M.E.,Ognev, A.V.,Chebotkevich, L.A.,Sadovnikov, A.V.,Nikitov, S.A.,Kim, Y.J.,Cha, I.H.,Kim, Y.K. North-Holland Pub. Co 2017 Journal of magnetism and magnetic materials Vol.429 No.-
One of the major societal challenges is reducing the power consumption of information technology (IT) devices and numerous data centers. Distinct from the current approaches based on switching of magnetic single-domain nanostructures or on movement of domain walls under high currents, an original magnetic skyrmion technology offers ultra-low power, fast, high-density, and scalable spintronic devices, including non-volatile random access memory. Using data-driven micromagnetic simulations, we demonstrate the possibility of spontaneous nucleation and stabilization of different skyrmionic states, such as skyrmions, merons, and meron-like configurations, in heavy metal/ferromagnetic nanodisks with the interfacial Dzyaloshinskii-Moriya interaction (iDMI) as a result of quasi-static magnetization reversal only. Since iDMI is not easily modulated in real systems, we show that skyrmion stabilization is easily achievable by manipulating magnetic anisotropy, saturation magnetization, and the diameters of nanodisks. The state diagrams, presented in terms of the topological charge, allow to explicitly distinguish the intermediate states between skyrmions and merons and can be used for developing a skyrmionic medium, which has been recently proposed to be a building block for future spin-orbitronic devices.
Hybrid magnetic anisotropy <i>[Co/Ni]<sub>15</sub> </i>/<i>Cu/[Co/Pt]<sub>4</sub> </i> spin-valves
Kolesnikov, A.G.,Wu, Hao,Stebliy, M.E.,Ognev, A.V.,Chebotkevich, L.A.,Samardak, A.S.,Han, Xiufeng Elsevier 2018 Journal of magnetism and magnetic materials Vol.449 No.-
<P><B>Abstract</B></P> <P>Thin film multilayer heterostructures consisting of two magnetically coupled stacks, one with in-plane and the second one with out-of-plane magnetic anisotropies, are very promising hybrid magnetic anisotropy materials for spintronics. Here we present results on magnetic and magnetoresistance properties of <I>[Co/Ni]<SUB>15</SUB> </I> (in-plane)/<I>Cu/[Co/Pt]<SUB>4</SUB> </I> (out-of-plane) spin-valves with hybrid magnetic anisotropy. We demonstrate that the saturation field and magnetoresistance depend on the thickness of the copper interlayer (<I>t<SUB>Cu</SUB> </I>) and they have peak values at <I>t<SUB>Cu</SUB> </I> = 2.5 nm, where the antiferromagnetic coupling is maximum. We reveal that an indirect exchange coupling between <I>[Co/Ni]<SUB>n</SUB> </I> and <I>[Co/Pt]<SUB>m</SUB> </I> stacks decreases the magnetization switching fields making these systems suitable for low-field sensor, spin torque oscillator and bit patterned media applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hybrid anisotropy spin-valves (HAS) were systematically studied. </LI> <LI> HAS with AFM coupling have peak values of <I>H<SUB>s</SUB> </I> and <I>MR</I>. </LI> <LI> Simulated M-H and MR loops correctly describe the experimental data. </LI> <LI> AFM coupled HAS have the increased field ranges and linear dependence of MR. </LI> </UL> </P>
Magnetization reversal of ferromagnetic nanosprings affected by helical shape
Nam, Da Yeon,Samardak, Aleksei Yu.,Jeon, Yoo Sang,Kim, Su Hyo,Davydenko, Alexander V.,Ognev, Alexey V.,Samardak, Alexander S.,Kim, Young Keun The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.43
<P>Helicity, a natural property of macro-, micro-, and nano-objects, potentially offers a new dimension to mechanical and electromagnetic applications for creating emerging nanodevices, such as nanorobots, nanomagnets, nanosensors, and high-density magnetic memory. Helical magnetic nanosprings are unique objects with remarkable magnetic properties, including the absence of stray fields in remanence owing to the chiral geometry, which makes them promising for data storage devices, nanoelectromechanical systems, and biomedical usage. Here, we investigated Co and CoFe nanospring arrays electrodeposited in highly ordered nanoporous templates. We report helical-shape-driven magnetization reversal of the nanosprings in comparison with the behavior of dipolarly coupled nanowires. We reveal two magnetization reversal modes depending on the orientation of the external magnetic field: coherent rotation of magnetization in the longitudinal geometry and three-dimensional vortex domain wall motion in the transverse geometry. The experimental findings are supported by analytical calculations and micromagnetic simulations that help to explain the field-dependent spin configurations observed by magnetic force microscopy.</P>