Effect of defects in the rare-earth sublattice of the Kondo insulator YbB 12 on its spectral characteristics and magneti
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Effect of Defects in the Rare-Earth Sublattice of the Kondo Insulator YbB12 on Its Spectral Characteristics and Magnetic Susceptibility P. A. Alekseeva,b*, A. V. Kuznetsovb, P. S. Savchenkova,b, A. P. Menushenkovb, and N. Yu. Shitsevalovac a
National Research Centre “Kurchatov Institute,” pl. Akademika Kurchatova 1, Moscow, 123182 Russia b
c
National Research Nuclear University “MEPhI,” Kashirskoe sh. 31, Moscow, 115409 Russia
Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Kiev, 03680 Ukraine *e-mail: [email protected] Received January 8, 2017
Abstract—The results of measuring the static and dynamic magnetic susceptibilities of several series of samples, which are based on the YbB12 Kondo insulator and are substituted in the rare-earth sublattice, are analyzed. Substitution is performed by nonmagnetic isoelectronic Lu ions; magnetic isoelectronic Tm ions; and nonisoelectronic nonmagnetic Y, Sc, and Zr ions. The static susceptibility is measured by a SQUID magnetometer in weak fields, and the dynamic susceptibility is determined from inelastic neutron scattering data. The magnetic properties are simulated using the spectral function found from neutron experimental data. A one-to-one correspondence is established between the influence of an impurity on the initial neutron spectrum and the temperature dependence of the static susceptibility. The results obtained allow one to analyze the relation between the magnetic properties and the electronic structure of the compounds of the given class.
DOI: 10.1134/S1063776117060061
1. INTRODUCTION As follows from the physical properties of YbB12, it is a typical Kondo insulator, i.e., a compound with strong electron–electron correlations. The ground state of this compound is represented by a narrow-gap semiconductor because of a certain balance between the hybridization of f electrons with conduction band electrons, as well as between the effects of crystal field and exchange interaction. This compound is characterized by a magnetic excitation spectrum with a singlet ground state and a gap, and the rare-earth (RE) ion is characterized by a weak degree of valence instability. There is a number of reliable experimental facts regarding the structure and the temperature evolution of the magnetic excitation spectrum (which is determined by the imaginary part of dynamic magnetic susceptibility χ"(Q, E, T), where Q and E are the momentum transfer and the energy transfer, respectively) and the formation of a gap in the density of states near the Fermi level when temperature decreases [1–4]. The value of χ"(Q, E, T) can be experimentally found from scattering function S(Q, E, T) determined
by inelastic neutron scattering [5]. In general form, this function is determined by the expression 2
⎛g r ⎞ χ ''(Q, E ,T ) S (Q, E ,T ) = 1 ⎜ N e ⎟ , 2π ⎝ μ B ⎠ 1 − exp(−E / k BT )
(1)
where
χ ''(Q, E ,T ) = πχ '(Q,0,T )P (Q, E ,T )E ,
(2)
E is the energy transfer in a neutron ex
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