A. Kadigrobov

Giant lasing effect in magnetic nanoconductors

We propose a new principle for a compact solid-state laser in the 1–100 THz regime. This is a frequency range where attempts to fabricate small-size lasers up to now have met severe technical problems. The proposed laser is based on a new mechanism for creating spin-flip processes in ferromagnetic conductors. The mechanism is due to the interaction of light with conduction electrons; the interaction strength, being proportional to the large exchange energy, exceeds the Zeeman interaction by orders of magnitude. On the basis of this interaction, a giant lasing effect is predicted in a system where a population inversion has been created by tunneling injection of spin-polarized electrons from one ferromagnetic conductor to another—the magnetization of the two ferromagnets having different orientations. Using experimental data for ferromagnetic manganese perovskites with nearly 100% spin polarization, we show the laser frequency to be in the range 1–100 THz. The optical gain is estimated to be of order 107 cm−1, which exceeds the gain of conventional semiconductor lasers by 3 or 4 orders of magnitude. A relevant experimental study is proposed and discussed.

Thermoelectrical manipulation of nanomagnets

We investigate the interplay between the thermodynamic properties and spin-dependent transport in a mesoscopic device based on a magnetic multilayer (F/f/F), in which two strongly ferromagnetic layers (F) are exchange-coupled through a weakly ferromagnetic spacer (f) with the Curie temperature in the vicinity of room temperature. We show theoretically that the Joule heating produced by the spin-dependent current allows a spin-thermoelectronic control of the ferromagnetic-to-paramagnetic (f/N) transition in the spacer and, thereby, of the relative orientation of the outer F-layers in the device (spin-thermoelectric manipulation of nanomagnets). Supporting experimental evidence of such thermally-controlled switching from parallel to antiparallel magnetization orientations in F/f(N)/F sandwiches is presented. Furthermore, we show theoretically that local Joule heating due to a high concentration of current in a magnetic point contact or a nanopillar can be used to reversibly drive the weakly ferromagnetic spacer through its Curie point and thereby exchange couple and decouple the two strongly ferromagnetic F-layers. For the devices designed to have an antiparallel ground state above the Curie point of the spacer, the associated spin-thermionic parallel to antiparallel switching causes magnetoresistance oscillations whose frequency can be controlled by proper biasing from essentially dc to GHz. We discuss in detail an experimental realization of a device that can operate as a thermomagnetoresistive switch or oscillator.

Model for spin-polarized transport in perovskite manganite bicrystal grain boundaries

We have studied the temperature dependence of low-field magnetoresistance and current-voltage characteristics of a low-angle bicrystal grain boundary junction in perovskite manganite

Spin controlled nanomechanics induced by single-electron tunneling

{\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}

Novel laser based on magnetic tunneling

thin film. By gradually trimming the junction we have been able to reveal the nonlinear behavior of the latter. With the use of the relation

Triplet superconducting proximity effect in inhomogeneous magnetic materials

{M}_{\mathrm{GB}}\ensuremath{\propto}{M}_{\mathrm{bulk}}\sqrt{{\mathrm{MR}}^{*}}

Resonant transmission of normal electrons through Andreev states in ferromagnets

we have extracted the grain-boundary magnetization. Further, we demonstrate that the built-in potential barrier of the grain boundary can be modeled by

Influence of spin waves on transport through a quantum-dot spin valve

{V}_{\mathrm{bi}}\ensuremath{\propto}{M}_{\mathrm{bulk}}^{2}\ensuremath{-}{M}_{\mathrm{GB}}^{2}.

Resonant tunneling through Andreev levels

Thus our model connects the magnetoresistance with the potential barrier at the grain-boundary region. The results indicate that the band-bending at the grain-boundary interface has a magnetic origin.

Coulomb blockade of spin-dependent shuttling

We consider dc-electronic transport through a nanowire suspended between normal- and spin-polarized metal leads in the presence of an external magnetic field. We show that magnetomotive coupling between the electrical current through the nanowire and vibrations of the wire may result in self-excitation of mechanical vibrations. The self-excitation mechanism is based on correlations between the occupancy of the quantized electronic energy levels inside the nanowire and the velocity of the nanowire. We derive conditions for the occurrence of the instability and find stable regimes of mechanical oscillations.