Ponomarev Boris Konstantinovich

Position: Leading research scientist. Address: Institute of solid state physics, RAS, 142432, Chernogolovka, Moscow district, Russia. Location: 121 ETK. Fax: 7-096-524-9701 (from abroad). 8-2-524-9701 (from Moscow and Moscow district). 8-096-524-9701 (from other Russia regions and former USSR countries). e-mail: ponom@issp.ac.ru

Research interest:

1.Magnetic and magneto-elastic properties of heavy rare earth metals.

In the sixties years of the last century the great interest was attracted to the rare earth metals and their compounds. It was due to their unusual magnetic properties – very large paramagnetic susceptibility and extremely high magnetic anisotropy. Usual magnetic equipment of that period with the magnetic fields of ~50 kOe was not enough for the investigations of those metals. High magnetic fields of 100 kOe and more were necessary to saturate the magnetization of havy rare earth metals.

B. K. Ponomarev worked out the original experimental equipment to measure the magnetization, the magnetic anisotropy constants and the magnetostriction in pulsed magnetic fields up to 150 kOe at the temperature range (78 – 350)K. B. K. Ponomarev was the first investigator who measured the torque in the pulsed magnetic field.

The magnetization, the magnetic anisotropy and the magnetostriction of the single crystal samples of Gd, Tb, Dy, Ho and Er metals were investigated. The effect of the elongation of the spontaneous magnetic moment of the crystal due to its rotation from the easy magnetic direction to the heavy one was observed. The magnetic anisotropy constants were measured. The peculiarities of the magnetic properties of heavy rare earth metals were explained by the existence of the nonzero angular moment in rare earth ions. It was shown that the effective exchange field theory is sufficient for the description of the magnetic order in heavy rare earth metals and their compounds.

2. The duality of the state of the magnetic carriers in the traditional 3d-magnetic materials. The applicability of the theory of the effective field .

The peculiarity of the way of the development of the magnetic science was in that the first ferromagnetic materials – iron, cobalt, nickel and so on - were essentially collective systems and the first theory of the magnetic order – the Weiss molecular field theory - was developed for essentially individual magnetic carriers.

Naturally this theory was very far from the real behavior of 3d-ferromagnetics known at that time. Due to this disagreement very many researchers did not accept the effective field approximation as the satisfactory tool for the description of the ferromagnetism.

Many researchers noted, that the carriers of the magnetic moments in 3d-ferromagnetics should be itinerant. But the neutron experiments showed that the carriers of the magnetic moments in nickel were evidently localized near their atoms. This was the origin of the hypothesis of the dual nature of the magnetic moments in 3d-ferromagnetics.

B. K. Ponomarev saw the quite satisfactory agreement of this theory with the experimental results for heavy rare earths. He paid attention on the theory of the magnetic order that was developed by Stoner and Wohlfarth on the base of the effective field approximation for the magnetic carriers with the Fermi statistic.

He worked out the experimental equipment for magnetic measurements in pulsed fields up to 400kOe at temperatures up to 700K (in the collaboration with V. G. Tissen). The measurements of the magnetization of nickel in high fields and at high temperatures showed that the effective field theory with the Fermi statistic describes the magnetic properties of nickel quite satisfactory. So it was shown that the effective field theory is a very good tool if one uses the right statistic.

This experiment solved also the problem of the duality of the state of the magnetic carriers in the 3d-metals. The explanation was that the main thing is not the spatial localization or delocalization but the width of the energy band of the carriers. The band can be wide enough comparatively to the exchange interaction to apply the band theory and all the same the spatial localization can be strong enough to produce the distinctive maximum on the neutron pattern.

These investigations stimulated the development of the approach of the rigid band theory for the description of the magnetic properties of the hydrides of the 3d-metals obtained in the laboratory of the physics of high pressure.

3.Magneto-electric interactions.

B. K. Ponomarev discovered the nonlinear magneto-electric effect in paramagnetic ferroelectric rare earth molybdates family (in collaboration with B. S. Red'kin, C. A. Ivanov and V. N. Kurlov). These are the first group of substances in which the spontaneous electric polarization can be reversed using only the magnetic field without applying the electric field.

He observed the intensive green photoluminescence in terbium molybdate under the blue laser irradiation (in the collaboration with V. D. Negrii). It was accompanied by the appearing of large photo-voltage (about 30 Volts).

He observed two types of the photo-induced electric voltage in rare earth molybdates – due to exciting of rare earth ions and due to ionizing them.

4.The ferro-electric domain contrast under the electron irradiation.

He observed the spontaneous reversal of the ferroelectric domain contrast induced in terbium molybdate by the electron beam in the electron microscope (in the collaboration with L. S. Kokhanchik) and derived the theory of the double electric layer explaining the effect.

5.Spontaneous currents in rare earth molybdates under the high pressure.

B. K. Ponomarev showed experimentally that the high hydrostatic pressure (about 20 kilobars) induces in rare earth molybdates the redistribution of the charge density that should be taken into account while identifying the phase transition.

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