E. A. Vilkov

sd-Exchange emission in ferromagnetic junctions

The spin-injection emission in a ferromagnetic junction at terahertz frequencies is theoretically analyzed. It is demonstrated that the efficiency of the emission caused by the sd-exchange interaction of the injected spin in which the electromagnetic field is involved strongly depends on the orientation angle of the magnetization of the active region relative to the magnetization direction of the injecting region. The fact that the calculated radiation frequency and power are close to the experimental results shows that the sd-exchange emission must be taken into account in the interpretation of the observed terahertz emission in magnetic junctions.

Spin-injection radiation of terahertz waves in ferromagnetic structures

We propose and discuss the mechanisms of terahertz sd exchange radiation during transmission of the spin-polarized current in a structure from a thin steel rod pressured to an ultrathin ferromagnetic film. The two mechanisms considered are quantum transitions between the quasi-Fermi levels in the film near the rod and precession of injected spins around the film magnetization.

Spin-injection stimulated emission of terahertz waves in magnetic junctions

The stimulated emission of terahertz radiation in magnetic junctions at room temperature resulting from the current injection of nonequilibrium spins is observed. Contacts between two ferromagnetic layers as well as between a ferromagnetic and an antiferromagnetic layer are investigated. The current produces the population inversion of spin energy levels. As the system is placed in a cavity, positive feedback and stimulated emission appear. The development of a dominant emission peak and onset of electromagnetic turbulence are observed.

Detection and generation of submillimeter and terahertz modes in ferromagnet-antiferromagnet junctions

Spin-polarized current can tilt magnetic sublattices in an antiferromagnetic layer of a ferromagnet-antiferromagnet junction without imposing any external magnetic field. Thus, the current can induce magnetization in the antiferromagnetic layer. This effect seemingly took place in experiments on the observation of terahertz emission at the precession frequencies of current-induced magnetization. In this work, the mechanisms of motion of the induced magnetization, as well as the possibility of detection and generation of radiation emitted during such motion, are suggested and discussed. The notion of spin-injection antiferromagnetic resonance is introduced.

A spin-injection terahertz generator based on the metatransition monolithic structure

The possibility of generation of terahertz electromagnetic waves by the current in a planar structure composed of metalferromagnetic nanoparticles imbedded into an antiferromagnetic medium, is considered.

sd-Exchange electron spin resonance in a ferromagnetic metal

The possibility of resonance absorption in the terahertz range caused by the sd-exchange interaction at the incidence of an electromagnetic wave on a ferromagnetic metal has been predicted. The absorption coefficient has been calculated. It has been shown that the resonance frequency is determined by the magnetization of a ferromagnet and the absorption coefficient additionally depends on the orientation of the magnetization with respect to the plane of polarization of the wave.

Frequency tuning of the spin-injection radiation in the magnetic contact junction

The frequency tuning of the terahertz radiation of spin-injection oscillator based on magnetic contact junction that is formed by contacting ferromagnetic metal layers with different magnetizations is analyzed. Under the current-induced spin injection from one magnetic layer (injector) to another (working) layer, the interval of radiation frequencies is determined by the current density in the magnetic contact, the mismatch angle of the magnetizations of injector and working layer, and the equilibrium spin polarization. The wide-range tuning of terahertz frequencies of the spin-injection radiation can be implemented using variations in the above parameters.

Stimulated terahertz emission

The observation of the stimulated terahertz radiation in magnetic junctions at the room temperature resulting from the current injection of nonequilibrium spins is reported. Contacts between two ferromagnetic layers and between a ferromagnetic and an antiferromagnetic layer are investigated. As the current is increased, first, a narrow isolated radiation peak at terahertz frequencies is observed, which is analogous to the laser peak; then, the peak broadens and its intensity increases by more than an order of magnitude.

Spin-Injection Stimulated Radiation of Terahertz Waves in Magnetic Junctions (“Twaser” Action)

We report on apparently the first observation of terahertz stimulated radiation in magnetic junctions due to nonequilibrium spins injected by current at room temperatures. The contact between ferromagnetic layers is investigated and so the contact between ferromagnetic and antiferromagnetic layers. The current flowing in the structure creates an inversed population of spin energy levels. After a placing of such a structure in a resonator positive feedback and stimulated emission appears. When current is growing, we observe the relatively narrow (in frequencies) peak - analogous to laser generation but at terahertz frequencies. For the higher currents we observe the picture of electromagnetic turbulence.

Spin Injection Mechanisms for Radiation and Detection of Terahertz Waves Based on Magnetic Nano Junction

Spin injection mechanisms for radiation and detection of terahertz waves based on magnetic nano junction are considered. High efficiency of terahertz radiation is theoretically explained and the method of the detection of this radiation is offered. The device of the spin injected terahertz radiators is presented.