Group of magneto-optical investigations 1

Members of the group:

• Piryatinskaya V.G., Head of the group, Candidate of Sciences (Ph.D), senior researcher.

• Bedarev V.A., Candidate of Sciences (Ph.D), senior researcher;

• Kachur I.S., Candidate of Sciences (Ph.D), senior researcher;

• Merenkov D.N., Candidate of Sciences (Ph.D), senior researcher;

• Poperezhai S.M., junior researcher;

The main field of research:

• Magneto-optical investigations of spontaneous and magnetic-field induced phase transitions, spin reorientation processes in magnetically ordered dielectrics, metallic magnetic superlattices and nanostructures.

• Magneto-optical and visual investigations of magnetically inhomogeneous states formed in the process of phase transitions.

• Optical spectroscopy of magnetic dielectrics; investigations of optical and magnetic excitations, magnetic and structural phase transitions in antiferromagnets, multiferroics, crystals with different magnetic dimensionality.

Equipment:

• Experimental magneto-optical setup for measuring linear and circular optical birefringence and visual investigation of domain structure in a visible spectral range in magnetic fields up to 50 kOe and at temperatures 5-300 K.

• Experimental magneto-optical setup for measuring polar and longitudinal Kerr effect in magnetic fields up to 50 kOe at temperatures 10-300 K at light wavelength 633 nm.

• Experimental setup for investigation of optical absorption spectra in the wavelength range 250-1200 nm at temperatures 1.7-300 K in stationary magnetic fields up to 70 kOe.

The most important results:

• Long-live photoinduced changes of the optical absorption coefficient and photoinduced linear dichroism were discovered in antiferromagnetic garnet Ca₃Mn₂Ge₃O₁₂ in the temperature range T < 180 K. The main regularities of the photoinduced processes are described in the framework of the developed model of active charges or hole polarons.

• Influence of linearly polarized light on the magnetic field induced metamagnetic phase transition was revealed in the antiferromagnetic garnet Ca₃Mn₂Ge₃O₁₂. It is established that illumination, depending on orientation of polarization plane with respect to crystallographic axes of garnet, can stimulate or suppress metamagnetic phase transition.

• Persistent photoinduced modification of the optical absorption spectrum of NaCa₂Mn₂V₃O₁₂ garnet is found. The effect reflects the valence lowering of vanadium ion under photoillumination. Photoinduced linear dichroism revealed in this crystal is anomalously strong.

• It is established that a decrease of the manganese concentration in Ca₃Ga₂Ge₃O₁₂:Mn garnets leads to an expansion of the range of existence of photoinduced effects. In particular, at a manganese concentration of about 5%, photoinduced optical absorption is observed up to room temperatures.

• Illumination of manganite films Pr_0.6La_0.1Ca_0.3MnO₃ by visual light in magnetic field at low temperatures of T < 50 K is revealed to cause increase in magnetization, decrease of electrical resistance, and stimulates a phase transition from antiferromagnetic dielectric state to ferromagnetic metallic state.

• An exciton-magnon structure including a pure exciton line and an exciton-magnon band is found in the optical absorption spectrum of quasi-two-dimensional antiferromagnet MnPS₃. It is established that in the magnetic field directed along the easy axis of the crystal, reorientation of magnetic moments of Mn²⁺ into the basal plane occurs as second order phase transition.

• In the EPR spectrum of the terbium ferroborate, the lines originating from transitions in Tb³⁺ ions which are surrounded by the growth impurities of bismuth and molybdenum were revealed. The initial splitting of the lowest quasidoublets of such Tb³⁺ ions in the crystal field and in the effective iron field was determined. Amount of centers with different types of impurities was estimated.

• Giant light scattering in the region of magnetic-field induced spin-reorientation phase transition is found in antiferromagnetic TbFe₃(BO₃)₄. The phenomenon is explained by the formation of two-phase magnetically inhomogeneous state and large Faraday effect, which is related to the magnetic subsystem of terbium ions.

• For the first time the linear birefringence induced by the electric field (Pockels effect) was detected experimentally in TmAl₃(BO₃)₄ single crystal. The electrooptical coefficient of substance is defined.

• Using magnetoanisotropic crystal TbAl₃(BO₃)₄ as an example, it was shown that the rare earth aluminum borates can be a promising coolant based on rotational magnetocaloric effect.

• Nontrivial transverse Zeeman effect is discovered in antiferromagnetic NdFe₃(BO₃)₄ crystal. The intensities of the polarized components of the Nd³⁺ Kramers doublet exhibit a nonmonotonic field dependence, and in the region of the spin-reorientation transition one of them practically disappears. A semiempirical model for description of the effect is proposed.

• Strong anisotropy of both the intensities and the energies of optical transitions of the Ho³⁺ ion depending on the direction of magnetic field in the basal plane is revealed in the absorption spectrum of the antiferromagnet HoFe₃(BO₃)₄. This phenomenon can be associated with strong magnetostriction of the crystal.

International cooperation:

• Institute of Physics of Polish Academy of Sciences, Warsaw, Poland;

• Kirensky Institute of Physics of Siberian Branch of Russian Academy of Sciences, Krasnoyarsk, Russia.