Department of Physics of Defective Solid Solutions
Alternate Head of the Department: Alexandr A.Shemyakov, candidate of physico-mathematical sciences (062) 311-69-19
Directions of Scientific Researches: Defects of the crystal lattice of a point and cluster types and its influence on magnetic and transport properties of metal-oxide solid solutions of the perovskite and spinele structure and with a determined composition-structure-properties interrelation in mesoscopic inhomogeneous magnetics. Superfine interactions on the nuclei of dia- and paramagnetic ions in S- and D-states. The phenomenon of electron exchange between unequally valence ions of manganese, iron and chromium in manganese perovskites, oxide and hal’kohenide spineles.
The investigation techniques: nuclear magnetic resonance of 55Mn, 57Fe, 53Cr, 63,65Cu, 59Co, 67Zn, 7Li, 27Al, 89Y, 139La, 17O and others by the method of a spin echo over the frequency range 5 – 650 MHz, X-ray method (low- and high-temperature), magnetic resonance – determination of magnetization and Curie temperature, resistance and magnetoresistance in the field up to 6 kE at ô = 77–400 ë.
Basic Results
It has been found out that actual perovskite and spinele structures have subtraction defects simultaneously in the cationic and anionic sublattices. There has been determined the defect formation mechanism in the processes of synthesis and sintering of manganite-lanthanum perovskites consisting in cyclic changes of the oxygen content and manganese valences when heating, annealing and cooling samples. Because of this, an increase of the concentration of cationic and anionic vacancies takes place, and in case of the manganese excess a more complex defects of the cluster type occur.
There has been detected and explained the effect of a dynamic narrowing of the NMR-spectrum of ions Mn3+(÷) in lithium ferrite conditioned by relaxation processes in the orbital Ian Teller subsystem. It is shown that with a rise of temperature there takes place an equalization of the Ian Teller state populations resulting in a decrease of the quadrupole splitting of separate lines and in a narrowing of the whole absorption line.
In hal’kohenide spineless there has been detected a phenomenon of electron exchange between unequally valence chromium ions leading to a spin density averaging on their nuclei.
Applied researches
Development of radio-absorbing materials and highsensitive magneto resistive current sensors.
Scientific cooperation
Donetsk National University (Donetsk, Ukraine), the Institute “Monokrystall” (Khar’kov, Ukraine), the NPF “Ferrokeram” (Belaya Tserkov’, Ukraine), the Institute of Physics of the Polish Academy of Sciences (Poland).
Selected publications
1. V.Ya.Mitrofanov, F.Ya.Fishman, A.A.Shemyakov. The effect of a dynamic narrowing of the NMR-spectrum of Ian Teller ions Mn3+ in lithium ferrite. Zhurnal experimental’noi I teoretichesloi fizik i61(7), 570 (1995).
2. V.P.Paschenko, S.I.Khratsev, A.A.Shemyakov e.a Nonstoicheometry, defectivity of the structure and properties of manganite-lanthanum magnetoresistive materials La1-xMn1+xO3±δ. Nonorganic materials 35 (12), 1509 (1999).
3. V.P.Pashchenko, A.A.Shemyakov, V.K.Prokopenko et all. Effect of substitution of Mn by Cr on the 55Mn NMR and magnetoresistance in La0,6Sr0,2Mn1,2-xCrxO3 (0≤x≤0,2). Journal of Magnetism and Magnetic Materials 220, 52 (2000)
4. S.S.Kucherenko, V.P.Paschenko, P.I.Polyakov, V.A.Shtaba, A.A.Shemyakov. Pressure, temperature and magnetic field influence on resistance and magnetoresistive effect of the manganite-lanthanum ceramics and film La0,7Mn0,3O3-δ. Fizika nizkih temperatur 27, 1370 (2001).
5. V.P.Paschenko, N.I.Nosanov, A.A.Shemyakov, V.K.Prokopenko.A high-sensitive magnetoresistor. Invention patent UA 45153 á. Bull. N3 (2002).
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