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Who we Are 

SimuMag - small company located in Bozeman, Montana, USA.

Montana
 
Director: Prof. Valentin Grachev.
 
Research experience

·        Many years of research work in the study of defects in solids, the theory of EPR, NMR and ENDOR, low-symmetry effects in resonance spectra, hidden symmetry in the spin- and other Hamiltonians.

·        Development of methods to obtain the physical information about defects, crystal properties near impurities and bulk crystal properties from EPR, NMR and ENDOR data. Method of the determination of band structure in non-conductive crystals on the basis of ENDOR data.

·        Revision of the radiospectroscopy background: the case of non-cubic general spin-Hamiltonians, which contain implicitly an inseparable combination of parameters and are practically unsuited for the description of EPR, NMR or ENDOR, because of the impossibility of unique determination of coupled parameters. An additional hidden gauge symmetry was found and a method of the elimination of all superfluous operators was proposed to obtain the correct spin-Hamiltonian.

·        Treatment and interpretation of experimental results obtained by EPR, ENDOR, X-ray analysis, high-resolution electron microscopy and other methods. Together with experimenters and crystal growers it was found that lithium niobate grown from the melt with an addition of potassium, LN(K) has completely different properties in comparison with conventional congruent crystals. LN(K) is practically free of intrinsic defects, what causes tremendous resolution enhancement of many spectroscopic methods and new physical properties of such crystals. Our discovery led to a booming of interest to this material and originated new life for lithium niobate.

·        Development of efficient procedures and computer programs for the simulation and treatment of observed EPR, NMR and ENDOR spectra with different ratio of parameters of Zeeman, exchange, hyperfine and quadrupole interactions (exact numerical diagonalization of spin-Hamiltonian matrix).

·        Development of models for the description of electrical properties of porous multiphase superconducting materials (high TC powders and ceramics) on the base of percolation theory.

·       Development of programs for exact numerical calculations of physical properties of homogeneous (AAAA…) and heterogeneous (ABCD…) magnetic clusters with isotropic (Heisenberg), strongly anisotropic (Ising) and intermediate interactions. Analytical investigation of low-symmetry effects in low-dimensional clusters.

·        Microtheory of hyperfine interaction of electrons in paramagnetic center with surrounding nuclei and the theory of ENDOR frequencies and intensities in the presence of external influences (pressure, electric field, temperature).

·      Systematization and generalization of investigations of crystal defects in the review "ENDOR in non-metallic crystals" published in soviet journal "Successes of Physical Sciences" and in the monography "Electric effects in radiospectroscopy" (Moscow: Nauka, 1981).

·        Investigation of low-symmetry effects and spectrum peculiarities, which arise at the transitions from para- to ferroelectric or ferroelastic phases, relations between the critical temperature dependencies of spectrum characteristics and the order parameter of ferroelastics.

·        Development of new version of Jahn-Teller effect theory for trigonal crystals to describe EPR spectra of Ni+ and Cu2+ in lithium niobate.

·        Interpretation of many new EPR, NMR, ENDOR and optical spectra in crystals and disordered materials: radiation defects in piezoelectric TeO2 and superionic Li2B4O7, intrinsic and extrinsic defects in ferroelectric LiNbO3  and incipient ferroelectric KTaO3, ferroelastic BiVO4, the donors in the semiconductors like Si, SiC, alloy Si1-xGex, free hole, gadolinium and gadolinium-hole complexes in the layered semiconductors GaSe and so on. The characteristics of several dozens of paramagnetic centers were obtained.

 

Program history 

First programs for the treatment of EPR spectra of Vk-centers in alkali-halides were written by V.Grachev (together with Yu.Semenov) in 1974 for big electronic computer BESM-6.

Now the "Visual EPR" programs are successfully used in many laboratories of  Czech Republic, France, Germany, Hungary, Italy, Japan, Korea, Poland, Russia, Sweden, The Netherlands, Ukraine, USA etc.