Abstract: Magnetic interactions in Yb1−xEux alloys

Abstract

We have studied the magnetic properties of face centered cubic Yb1−xEux alloys with x = 0.05, 0.10, 0.30, and 0.40 by 151Eu Mössbauer spectroscopy, magnetization, and resistivity measurements in the temperature range from 1.5 to 300 K. At 1.5 K, the Mössbauer spectra of all samples show a well-defined magnetic hyperfine field. For x = 0.30 and 0.40 the temperature dependence of the hyperfine fields follows a Brillouin function (TM = 11.2 and 14.4 K, respectively). The magnetization versus temperature curves for these samples show broad maxima which are shifted to higher temperatures with decreasing external fields. An extrapolation to zero external field yields ordering temperatures close to those found from Mössbauer spectroscopy. The specific resistivity of these samples is quite high with a negative temperature coefficient, obeying the Mooij correlation, but no indication of the magnetic transition occurs near the ordering temperature. The Mössbauer spectra for x = 0.05 and 0.20 at temperatures above 3 K can be described only by the assumption of at least two different Eu sites distinguished by different hyperfine fields. The transition temperatures (26 and 22 K, respectively) are in good agreement with those found from resistivity and magnetization measurements. The latter show that the alloys with low Eu concentration are ferromagnetic. The concentration dependent magnetic ordering suggests a competition between short-range antiferromagnetic and long-range ferromagnetic coupling while the resistivity data indicate increased d-band occupation as Eu is added. a)Permanent address: Ames Laboratory, Iowa State University, Ames, Iowa 50011.