The nature of the exchange interaction in eub 6 from the concentration dependence of the electron paramagnetic resonance linewidth in m xeu 1−xb 6

Abstract

A comparative study of the variation in the electron paramagnetic resonance (EPR) linewidth ΔH with x in the systems M x Eu 1− x E 6 (M  Sr, La) was carried out. In the strontium-containing solid solution an increase in x leads only to a decrease in the size of the Eu 2+ clusters, i.e. to a magnetic dilution. In this case, ΔH varies as const. (l − x) 1 2 . According to the Anderson-Weiss model, ΔH( x) can be expressed in terms of the second moment M 2( x) of the single line and an exchange field H e ( x): ΔH ≈ M 2( x)/ H e ( x). When M 2( x) is due to dipole-dipole interactions, it varies as (1 − x) M 2(0) with x < 0.9. Therefore for H e ( x) we obtain H e(x) = (1 − x) 1 2 H′ e where H′ e is a constant. This result supports the hypothesis that the exchange interaction in EuB 6 is due to the presence of current carriers. When M  La, the shape of the ΔH( x) curve differs noticeably from that considered above. This is due to the presence of loosely bound 5d electrons introduced into the lattice with the lanthanum ions. The participation of these electrons in the exchange narrowing of the EPR line cannot be described within the framework of a simple Ruderman-Kittel-Kasuya-Yosida model.