Features of the formation of magnetic moments of Tm³⁺ and Yb³⁺ rare-earth ions in LuB₁₂ cage glass

Abstract

The features of the formation of the magnetic moments of Tm³⁺ and Yb³⁺ ions in a metallic matrix of LuB₁₂ cage glass have been studied in measurements of the magnetization and specific heat in the temperature range of 1.9–300 K in magnetic fields up to 90 kOe. It has been shown that a paramagnetic response from the localized moments of isolated ions Tm³⁺ (7.6μ_B) and Yb³⁺ (4.5μ_B) is observed at temperatures of 150–300 K. A transition to the cage glass phase at low temperatures (T ≪ T* ∼ 60 K) is accompanied by disordering in the system of rare-earth ions and by formation of many-body states near Tm³⁺ and Yb³⁺ ions. At low temperatures near T _m in low magnetic fields, the appearance of an additional spin polarization, which is suppressed with an increase in the field, has been observed. The effective moments and g-factors of Tm and Yb obtained in high fields imply both the binding of a small fraction of magnetic ions to antiferromagnetic dimers and the Γ₆ ground state of the ² F _7/2 multiplet of the ytterbium ion. A scenario alternative to the Kondo-type behavior has been proposed to explain the nature of many-body states and the appearance of the spin polarization in rare-earth dodecaborides.