E.P. Nikolaeva

Room temperature magnetoelectric control of micromagnetic structure in iron garnet films

The effect of magnetic domain wall motion induced by electric field is observed in epitaxial iron garnet films grown on (210) and (110) gadolinium-gallium garnet substrates. The displacement of the domain wall changes to the opposite at the reversal of electric field polarity, and it is independent of the magnetic polarity of the domains. Dynamic observation of the domain wall motion in 400 V electric pulses gives the domain wall velocity of about 50 m/s. The same velocity is achieved in a magnetic field pulse of about 50 Oe. This type of magnetoelectric effect is implemented in single phase material at room temperature.

Nucleation of magnetic bubble domains in iron garnet films by means of an electric probe

The possibility of the local nucleation of magnetic bubble domains from a single-domain state in an arbitrary region of a iron garnet film ((210) crystallographic orientation) by means of an electrically charged tip electrode has been experimentally demonstrated. The size of magnetic bubble domains nucleated near the contact point between the probe and sample depends on the magnitude of a DC voltage supplied to the probe. After the removal of the voltage, magnetic bubble domains move away from the probe, decreasing to the equilibrium radius.

Electric Field Driven Magnetic Domain Wall Motion in Iron Garnet Films

The room temperature magnetoelectric effect was observed in epitaxial iron garnet films that appeared as magnetic domain wall motion induced by electric field. The films grown on gadolinium-gallium garnet substrates with various crystallographic orientations were examined. The effect was observed in (210) and (110) films and was not observed in (111) films. Dynamic observation of the domain wall motion in 800 kV/cm electric field pulses gave the domain wall velocity in the range 30÷50 m/s. Similar velocity was achieved in magnetic field pulse about 50 Oe.

The Influence of the Magnetic Field on Electrically Induced Domain Wall Motion

Domain walls in iron garnet films demonstrate magnetoelectric properties that manifest themselves as a displacement induced by inhomogeneous electric field. In this paper the results of the study of electric field induced domain wall dynamics and its dependence on external magnetic field are presented. The measured velocity of the electrically induced domain wall motion increased by an order with the magnetic field applied perpendicular to the domain wall plane. The numerical simulation shows that the observed behaviour of the domain wall can be explained by magnetic field induced modification of its internal micromagnetic structure and enhancement of the electric polarization associated with the wall.

Modification of the domain wall structure and generation of submicron magnetic formations by local optical irradiation

Experimental and theoretical investigations are made of the generation of vertical Bloch lines in a magnetic iron garnet film exposed to pulsed optical radiation. High-speed photography and anisotropic dark-field microscopy are used to study characteristic features of the generation of Bloch lines and domain structure relaxation processes after the local action of a laser pulse. Optimum optical irradiation parameters to ensure the controlled generation of Bloch lines are established. A theoretical model is developed which links the generation of Bloch lines to the migration of domain walls induced by local changes in the distribution of the degaussing fields caused by a reduction in magnetization with temperature at the optical radiation focusing point. The experimental results indicate that the controlled formation of magnetic structures smaller than or of the order of 0.1 μm by local optical irradiation is quite feasible.

Electric-field-driven magnetic domain wall as a microscale magneto-optical shutter

Nowadays, spintronics considers magnetic domain walls as a kind of nanodeviсe that demands for switching much less energy in comparison to homogeneous process. We propose and demonstrate a new concept for the light control via electric field applied locally to a magnetic domain wall playing the role of nanodevice. In detail, we charged a 15-μm-thick metallic tip to generate strong non-uniform electric field in the vicinity of the domain wall in the iron garnet film. The electric field influences the domain wall due to flexomagnetoelectric effect and causes the domain wall shift. The resulting displacement of the domain wall is up to 1/3 of domain width and allows to demonstrate a novel type of the electrically controlled magneto-optical shutter. Polarized laser beam focused on the electric-field-driven domain wall was used to demonstrate the concept of a microscale Faraday modulator. We obtained different regimes of the light modulation – linear, nonlinear and tri-stable – for the same domain wall with corresponding controllable displacement features. Such variability to control of domain wall’s displacement with spatial scale of about 10 μm makes the proposed concept very promising for nanophotonics and spintronics.

Spin Flexoelectricity and New Aspects of Micromagnetism

The coupling between the strain gradient and electric polarization is known as flexoelectricity in dielectrics materials. In case of magnetic media it takes the form of electric polarization induced by spin modulation and vice versa. This spin flexoelectricity causes new physical phenomena of micromagnetism such as electric field driven magnetic domain wall motion and electrical control of magnetic vortices in magnets as well as clamping of the magnetic domain walls at the ferroelectric ones in multiferroics.

Magneto-optical light modulator with local domain wall manipulation

We consider a scheme of Faraday magneto-optical light modulator with local magnetization control via magneto-electric effect. Our earlier researches of bismuth-substituted iron garnets films showed the giant domain wall (DW) displacement in electric field of charged tip due to magneto-electric effect [1, 2]. The displacement gives the opportunity to the local magnetization switching on the spatial scales about few microns.

New mechanisms of optical writing/reading in magnetic media

Optical detection of magnetic features of 0.1 µm or less in size, as well as their generation and motion due to laser shots, is described. The physical effects discovered make it possible to implement the basic functions of a memory device (writing, shift in a storage register, and reading) by purely optical means. These effects can form a basis for designing novel ultra-high-density solid-state memories with optical access and control.