P. D. Kim

Optically driven conductivity and magnetoresistance in a manganite-based tunnel structure

In the multilayer structure, La0.7Sr0.3MnO3/depleted manganite layer/MnSi, the photovoltaic effect has been discovered. The depleted manganite layer in the structure is dielectric and serves as a potential barrier between the ferromagnetic conducting La0.7Sr0.3MnO3 and MnSi layers by the formation of a magnetic tunnel junction. The photoinduced changes in the transport properties of the magnetic tunnel structure have been observed in the current-in-plane geometry. The changes are reversible and saturate at radiation power densities over 30?mW?cm?2. The photovoltaic effect has a threshold character: it reveals only at h? > 1.17?eV. Most likely, the effect of optical radiation is related to the formation of electron?hole pairs due to interband absorption of light in the dielectric layer. A photocurrent through the tunnel junctions separating the conducting layers causes a redistribution of the current channels between the conducting layers, which influences the conductivity and the magnetoresistance of the structure.

On the low-frequency resonance of magnetic vortices in micro- and nanodots

The resonance motion of the magnetization of thin cylindrical and parallelepiped micro- and nanodots has been studied theoretically and experimentally. Analytical expressions for the external-field dependence of the resonance frequency of the vortex-structure oscillations have been derived taking into account the inertial and damping coefficients. The external-field dependence of the damping parameter has been found theoretically. The influence of the effective mass of a magnetic vortex on its low-frequency dynamics has been discussed.

Collective dynamics of magnetic vortices in an array of interacting nanodots

The lift of the degeneracy of the resonance frequency of motion of the core of a magnetic vortex in a square array of nanodots has been experimentally detected. The appearance of a frequency multiplet has been theoretically explained. It has been shown that a reason for the lift of degeneracy can be the magnetostatic interaction between nanodots.

Magnetic ordering in multilayer monoatomic Co/Cu films

Abstract The magnetic properties of monoatomic (∼0.3 nm) cobalt layers were studied in multilayer Co/Cu and Co/SiO 2 systems and in a three-layer Cu/Co/Cu film structure. The saturation magnetization M and nuclear spin-spin relaxation times T 2 were measured as functions of the copper layer thickness d Cu . Also the frequency spectra of spin-echo signals from 59 Co nuclei were measured. The main result obtained was experimental evidence for the effect of copper conduction electrons on magnetic ordering in cobalt, which is strongly dependent on d Cu . For d Cu = 0.2–0.3 nm, multilayer structures with monoatomic Co layers exhibit three-dimensional (spatial) properties. As d grows, their properties transform first into quasi-two-dimensional ones, and further into such states when they are probably determined by the quantum size effect for each individual Co layer.

The antitumor effect of magnetic nanodisks and DNA aptamer conjugates

Here we describe a method of forming large arrays (up to 109 pieces) of free magnetic Ni-nanodisks 50 nm thick coated on both sides with layers of 5 nm thick Au. The antitumor effect of the magnetic nickel gold-coated nanodisks and DNA aptamer conjugates was evaluated in vivo and in vitro. Under the influence of rotating magnetic field, the studied nanodisks can cause the death of Ehrlich ascites carcinoma cells.

On the resonant state of magnetization in array of interacting nanodots

Abstract Development of the interpretation of the phenomenon of the lift of the magnetic resonance frequencies degeneracy caused by the magnetostatic interaction in assemblies of nanodisks has been done. The difference of the resonance behavior of magnetic vortexes in a round and rectangular nanodots has been studied experimentally and explained.

Observation of nonmonotonic oscillatory interlayer exchange coupling in Co∕Cu∕CoO films with varying Cu spacer thickness

We report our experimental observation of interlayer exchange coupling phenomena in CoO∕Cu∕Co trilayers with systematic variation of Cu spacer layer thickness as well as temperature. It has been found that there exists a clear indication of nonmonotonically varying oscillatory interlayer exchange coupling. The amplitude of oscillation increases, reaches to the maximum, and decreases with increasing Cu spacer thickness from 1 to 16 atomic layers for all temperature ranges between 70 and 200K.

Co/Pt multilayer structures on the crystal MgO and Si substrate as a media for perpendicular magnetic recording

In this work, the crystal structure and hysteretic magnetic properties of equiatomic single-crystal CoPt/MgO films prepared by magnetron sputtering and their modifications after heat treatment are studied. A perpendicular magnetic anisotropy is obtained in annealed films in a film thickness range of 2 < d ≤ 16 nm. The correlation between the magnitude of magnetocrystalline anisotropy constant of CoPt films and the order parameter of the L10 superstructure of these alloys is ascertained. The influence of the single-crystal MgO substrate on the structure and magnetic properties of the films of equiatomic CoPt alloys is also investigated.

Observations of domain structure of Co/Cu/Co sandwiches with wedge-shaped Cu spacer via magneto-optical Kerr effect

In this paper, magneto-optical Kerr effect was used to investigate the interaction between magnetic layers in Co/Cu/Co sandwiches with Cu spacer layer sputtered as a wedge. Various domain structures were observed to depend on wedge gradient orientation relative to an easy magnetization axis. When the easy axis of the Co layers was normal to the wedge gradient, the exchange coupling oscillation period was measured as approximately 8.5 A.

Magnetization Dynamics in Two-Dimensional Arrays of Square Microelements

The collective magnetization motion in an array of magnetostatically interacting ferromagnetic square elements is studied theoretically and experimentally. Dispersion laws are obtained for collective modes for some particular cases of the distribution of the topological charges πT of magnetic vortices in particles. Resonance curves are plotted with allowance for dissipation for various values of πT. An experimental investigation of the ferromagnetic resonance in a two-dimensional array of particles qualitatively supports the calculation results.