Персона: Алексеев, Павел Александрович
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Институт лазерных и плазменных технологий
Стратегическая цель Института ЛаПлаз – стать ведущей научной школой и ядром развития инноваций по лазерным, плазменным, радиационным и ускорительным технологиям, с уникальными образовательными программами, востребованными на российском и мировом рынке образовательных услуг.
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- ПубликацияТолько метаданныеDramatic impact of intermediate-valence impurity on induced magnetism in singlet ground state system PrNi(2020) Clementyev, E. S.; Lazukov, V. N.; Savchenkov, P. S.; Alekseev, P. A.; Савченков, Павел Сергеевич; Алексеев, Павел Александрович© 2020 Elsevier B.V.We studied the influence of La (nonmagnetic) and Ce (intermediate valence) impurities on the ferromagnetic ordering temperature Tc of compounds RE1-x(La,Ce)xNi (RE = Pr, Gd). The ordering temperature Tc was measured in a wide range of impurity concentration. Crystal electric field (CEF) splitting for the PrNi and Pr0.25Ce0.75Ni was defined by neutron spectroscopy measurements. The strong difference in the influence of La and Ce on Tc of PrNi and GdNi based systems has been obtained. The introduction of a spin-fluctuating intermediate valence impurity in PrNi leads to a dramatic increase in the area of the ordered state on the phase diagram, due to an increase in Tc, compared to the impact of La-impurity over the entire concentration range. The dependence of Tc on the Ce concentration for the Pr1-xCexNi was calculated within the framework of the model of microscopic states. The essential modification of the CEF splitting by the Ce impurity appears to be the decisive factor affecting Tc wherein the Ce ion carries zero static magnetic moments similar to the La case. The latter explains the identical dependencies of the ordering temperature on the impurity concentration observed in systems with a long-range order of local magnetic moments Gd1-xLaxNi and Gd1-xCexNi.
- ПубликацияТолько метаданныеNeutron magnetic form factor in studies of f-electron instability(2025) Alekseev, P. A.; Lazukov, V. N.; Savchenkov, P. S.; Алексеев, Павел Александрович; Савченков, Павел Сергеевич
- ПубликацияТолько метаданныеInduced magnetism and “magnetic hole” in singlet ground state system PrNi(2019) Clementyev, E. S.; Lazukov, V. N.; Savchenkov, P. S.; Alekseev, P. A.; Савченков, Павел Сергеевич; Алексеев, Павел Александрович© 2019 Elsevier B.V.The phenomenon of “induced magnetic ordering” for the local magnetic moments with singlet ground state in a periodical lattice is considered for the prototype intermetallic rare-earth compound PrNi ordered ferromagnetically at temperature TC = 21 K. Within the framework of a realistic model the energy dispersion relations are obtained for the magnetic excitations above Tc along the high symmetry directions. The “soft mode” behaviour observed for the acoustic magnetic excitation along (q 0 0) direction is reproduced. The influence of the substitution of isovalent nonmagnetic La for Pr1−xLaxNi on the temperature of ferromagnetic ordering is investigated. The linear decrease of the ordering temperature TC down to zero value in increasing of the La concentration up to x = 0.5 is observed and described by the model.
- ПубликацияТолько метаданныеEvidence of Homogeneous Intermediate Valence Coexisting with Long-range Magnetic Order in EuCu2(Si,Ge)2(2021) Savchenkov, P. S.; Sidorov, V. A.; Guo, J.; Sun, L.; Alekseev, P. A.; Алексеев, Павел Александрович© 2021, Pleiades Publishing, Inc.The phase diagram of the intermediate valence system EuCu2Ge2 is investigated by measuring the temperature dependencies of the heat capacity and the electrical resistance as a function of pressure up to 15 GPa. Transition to the magnetic ordered state is observed at pressures up to 9 GPa. It is established that for EuCu2Ge2 system the effects of the hydrostatic and chemical (substitution of Ge for Si) pressure on Eu-valence are equivalent from the point of view of the transition to the antiferromagnetic ordered ground state. The coexistence of the homogeneous intermediate valence state and long-range magnetic order in EuCu2(Si,Ge)2 has been confidently established. The magnetic phase diagram is presented as a function of Eu average valence. The probable background for the formation of the magnetically ordered intermediate valence state of Eu is considered. There is an indication that it develops on the basis of competition of the two magnetic configurations of Eu, in some analogy with the case of TmSe intermediate valence system.
- ПубликацияТолько метаданныеCooperative and Local Features of the Spin Gap Formation in the Kondo Insulators YbB12 and CeFe2Al10(2022) Lazukov, V. N.; Savchenkov, P. S.; Alekseev, P. A.; Алексеев, Павел Александрович© 2022, Pleiades Publishing, Ltd.Abstract: The formation of the excitation spectra of the ground state for Kondo insulators like YbB12, CeFe2Al10 has been studied and analyzed in terms of correspondence between cooperative and local effects. Experimental results concerning different types of substitutions for the rare earth and d-metal sublattices are discussed on the basis of model calculations. It is shown how the transformation from Kondo insulator to heavy fermions occurs in the f-electron excitation spectra of CeFe2Al10.
- ПубликацияОткрытый доступUncommon Magnetism in Rare-Earth Intermetallic Compounds with Strong Electronic Correlations(2023) Savchenkov, P. S.; Alekseev, P. A.; Савченков, Павел Сергеевич; Алексеев, Павел АлександровичRare-earth intermetallic compounds are characterised by the presence of a long-range magnetic order due to the interaction of local magnetic moments periodically located within the crystal lattice. This paper considers the possibility of forming an ordered state in cases where there is no opportunity to observe the local moment of the f-electronic shell in a traditional sense. These are, first of all, systems with a singlet ground state, as well as systems with fast spin fluctuations caused by a homogeneous intermediate-valence state of a rare-earth ion. Extensive experimental studies of these effects using neutron diffraction, neutron spectroscopy, and high-pressure studies of the magnetic phase diagram are presented and analysed, and the corresponding microscopic model representations are discussed. In particular, the possible origin of long-range magnetic order in mixed-valence compounds is analysed.