Nikitin Sergei Aleksandrovich

Doctor of Physics and Mathematics (1983), Professor (1988).
Head of the laboratory of amorphous and crystalline alloys of rare earth metals.

Reseach interests:
Physics of magnetics, magnetic phase transitions, magnetic properties of rare earth compounds.

Direction of reseach:
Experimental study of the magnetic properties of rare earth alloys and compounds.

Number of publications: more than 250.

Main results of science activity:

Magnetic phase transitions, magnetostricton and magnetoresistance in rare earth metals have been studied. The effect of giant magnetostriction have been found in rare earth metals.

Theoretic and experimental study was made of the low temperature anomalies and particularities of physical properties for various rare earth ferrimagnetic compounds. Magnetization of ferromagnetics near Curie point bas been investigated by means of thermodynamics theory of second order phase transitions. Rare earth alloys with high saturation induction were found. Effective exchange fields and exchange contributions in hyperfine fields on gadolinium and iron nuclears in intermetallic compounds of rare earth and iron.

A study was made of magnetic properties, concentration and temperature dependencies of magnetostriction, magnetic anisotropy, thermal dilatation, conductivity, galvanomagnetic and magnetocaloric effects in single crystals of rare earth alloys. The relation between magnetic properties and electron structure has been established. The scattering of conductive electrons was found on quadrupole moments of 4f- electron shells of rare-earth ions. It was shown that giant magnetostriction is due to interaction of orbital moment of 4f- electron shell with crystalline field. It was concluded that the antiferromagnetism - ferromagnetism transition in rare earth metals and alloys results from the magnetoelastic interaction. Three-critical point on magnetic phase diagram was found in dysprosium and rare earth alloys. Thermodynamic theory and experimental study was carried out of magnetic phase transition near Curie temperature in rare earth metals in the field along hard magnetic axes. It was shown that this transition is connected with the change of such magnetic characteristics as magnetization and reorientation angle.

Giant magnetocaloric effect has been found in rare earth metals, Fe-Rh alloy and a series of intermetallic compounds. Giant elastocaloric effect was found in the range of magnetic phase transition in Fe-Rh alloy. Pressure effects on magnetization have been measured in single crystals of rare earth metals and alloys. The reason ofn magnetoelastic effects has been explained.

Magnetic order was considered in amorphous rare earth - 3d- transition metal alloys. It was shown that the main particularities of process arises from specific exchange interaction and random magnetic anisotropy. The field and temperature dependencies of Young's modulus were measured in rare earth single crystals. It was shown that the experimental trends obtained near the ferromagnetic transition can be interpreted within the approach based on the theory of second order phase transition.

Spin-reorientation phase transitions in RFe11Ti single crystals have been studied. The effect of rare earth sublattice on magnetic anisotropy in these compounds has been determined. The magnetic order in R(Fe,Co)(Si,Ge) compounds has been investigated. The new ferromagnetic and antiferromagnetic RTi(Ge,Si) and RSc(Ge,Si) with high magnetic ordering temperatures have been found. The dependence of paramagnetic Curie temperature on 3d- electron concentration in R(Mn,Ti)Si compounds have been determined, which indicated the itinerant character of magnetism in these compounds. The effects of the hydrogen and nitrogen on the magnetocrystalline anisotropy (MCA) and magnetostriction of R2Fe17 and RFe11Ti compounds have been studied. It was determined that the change of the first MCA constant of rare earth sublattice was in agreement with the sign of the Stevens factors of R ions for all investigated compounds. As it was shown by our results, the values and signs of these effects depend essentially on interaction of an aspherical distribution of the 4f- electrons and conductive electrons charge density with crystalline fields.

Several Publications:

1) K.P.Belov, M.A.Belianchikova, R.Z.Levitin, S.A.Nikitin. Rera earth ferro- and antiferromagnetics. Nauka, Moscow, 1965, p.319.
2) S.A.Nikitin. Magnetic properties of rare earth metals and their alloys. MSU, 1989, p.247.
3) A.S.Andreenko, K.P.Belov, S.A.Nikitin, A.M.Tishin. Magnetocaloric effect in rare earth magnets. UFN, 1989, v.158, N4, p.553-579.
4) A.S.Andreenko, S.A.Nikitin. Magnetic properties of amorphous rare earth - transition metal alloys. UFN, 1997, v.167, N6, p.605-622.
5) Nikitin S.A., Ovtchenkov E.A., Tereshina I.S., Verbetski V.N., Salamova A.A. Magnetocrystalline anisotropy and magnetostriction of H and N modified of R2Fe17 compounds (R=Y, Tb, Dy, Ho, Er). J. Magn.Magn.Mater., 1999, v.195, p.464-469.

Prize-winner of State USSR Award (1984), Soros Professor (1995, 1998).

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