E. Z. Meilikhov

Quantum size effect transition in percolating nanocomposite films

We report on unique electronic properties in Fe-SiO2 nanocomposite thin films in the vicinity of the percolation threshold. The electronic transport is dominated by quantum corrections to the metallic conduction of the Infinite Cluster (IC). At low temperature, mesoscopic effects revealed on the conductivity, Hall effect experiments and low frequency electrical noise (random telegraph noise and 1/f noise) strongly support the existence of a temperature-induced Quantum Size Effect (QSE) transition in the metallic conduction path. Below a critical temperature related to the geometrical constriction sizes of the IC, the electronic conductivity is mainly governed by active tunnel conductance across barriers in the metallic network. The high 1/f noise level and the random telegraph noise are consistently explained by random potential modulation of the barriers transmittance due to local Coulomb charges. Our results provide evidence that a lowering of the temperature is somehow equivalent to a decrease of the metal fraction in the vicinity of the percolation limit.

Hall effect in insulating Fe/SiO2 magnetic granular films

Abstract We present the results of the anomalous Hall effect investigations under the hopping transport regime. The Hall effect and magnetic measurements were performed in Fe/SiO2 nanocomposites at the insulator side of percolation transition. Unlike magnetic metals, in studied materials Hall effect is determined by non-direct electron tunneling between granules. The Hall effect dependence on the Fe content is non-monotonous and is in agreement with the Shklovskii, Dykhne theoretical predictions for the Hall effect in percolating systems.

Selective Removal of Atoms as a New Method for Manufacturing of Nanostructures for Various Applications

The paper demonstrates a possibility for effective modification of the thin-film material’ chemical composition, structure and physical properties as result of selective removal of atoms by the certain energy ion beam. One of the most promising results of this effect consists in developing the new technology for 3D micro-and nano-structures production for various applications.

Ferromagnetism in heterostructures based on a dilute magnetic semiconductor

Ferromagnetism of magnetic impurity atoms located in the barrier regions of various heterostructures (solitary heterojunction, single quantum well, double quantum well, or superlattice) is considered theoretically. The indirect magnetic interaction of impurities occurs via charge carriers localized in quasi-two-dimensional conducting channels of these structures due to “penetration” of the wavefunction of charge carriers into the barrier regions. The wavefunctions defined analytically in the triangular potential model are virtually the same as in “exact” numerical calculations (joint solution of the Poisson and Schrödinger equations). The corresponding Curie temperatures are determined, which may attain approximately 500 K in Ga1 − xMnxAs-based structures according to calculations.

Quasi-two-dimensional diluted magnetic semiconductors with arbitrary carrier degeneracy

In the framework of the generalized mean field theory, conditions for arising the ferromagnetic state in a two-dimensional diluted magnetic semiconductor and the features of that state are defined. RKKY-interaction of magnetic impurities is supposed. The spatial disorder of their arrangement and temperature alteration of the carrier degeneracy are taken into account.

Magnetic properties of two-dimensional random systems of Ising dipoles

Abstract Within the framework of the generalized mean-field theory, two-dimensional random systems of point Ising magnetic dipoles of both fluid and lattice type are considered. In the former case, the precise expression for the distribution function of random magnetic fields is found, the impossibility of ferromagnetic ordering established and the susceptibility of the system in a paramagnetic state is calculated. In the latter case, it has been shown that the ground state of the system of Ising dipoles placed in randomly filled sites of two-dimensional square lattice, depends on the fraction p of the filled sites: at p > p c =0.63, the system is ferromagnetic, otherwise—paramagnetic. The transition between those states is of percolation nature. Temperature dependencies of the magnetization in the ferromagnetic phase and susceptibility of the system in the paramagnetic phase have been found.

Long-term relaxation of magnetoresistance in a granular ferromagnet

Long-term relaxations (of the logarithmic type) are revealed in the tunnel magnetoresistance of Fe/SiO2 nanocomposites, which are due to variation of the magnetization of the nanocomposites. Good qualitative agreement between experimental results and the recently developed concepts of the behavior of magnetization of granular ferromagnets [7] proves that the revealed relaxations are associated with the spin-glass nature of the magnetic state of such systems. It is further demonstrated that it is, in principle, impossible to observe such relaxations using the anomalous Hall effect (proportional to magnetization) because of physical reasons, i.e., mesoscopic fluctuations of the Hall voltage as a result of the magnetic field effect and variation of magnetization.

Cumulative growth of minor hysteresis loops in the Kolmogorov model

The phenomenon of nonrepeatability of successive remagnetization cycles in Co/M (M = Pt, Pd, Au) multilayer film structures is explained in the framework of the Kolmogorov crystallization model. It is shown that this model of phase transitions can be adapted so as to adequately describe the process of magnetic relaxation in the indicated systems with “memory.” For this purpose, it is necessary to introduce some additional elements into the model, in particular, (i) to take into account the fact that every cycle starts from a state “inherited” from the preceding cycle and (ii) to assume that the rate of growth of a new magnetic phase depends on the cycle number. This modified model provides a quite satisfactory qualitative and quantitative description of all features of successive magnetic relaxation cycles in the system under consideration, including the surprising phenomenon of cumulative growth of minor hysteresis loops.

Nonuniform RKKY Magnetism in Thin Films/Wires

Mean-field continual model of Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetism in thin films and wires is considered. The spatial distribution of the magnetization is described by the nonlinear integral equation. The magnetization distribution over the film thickness or the wire diameter is close, correspondingly, to the parabolic or Gaussian one. The dependence of the Curie temperature on the film thickness, and temperature dependencies of the average film and wire magnetizations are determined.

Selective Removal of Atoms as Basis for Ultra-High Density Nano-Patterned Magnetic and Other Media

The paper demonstrates a possibility for effective modification of the thin-film material’ chemical composition, structure and physical properties as result of selective removal of atoms by the certain energy ion beam. One of the most promising results of this effect is a production of devices with nanostructured high-density patterned magnetic media.