Study of ferromagnetism and the semiconductor-metal transition in EuB6 by Ca substitution (original) (raw)

Abstract

ABSTRACT We present structural, magnetic susceptibility \chi(T) and electrical resistivity rho(T) data for single crystals in the Eu_xCa_1-xB6 series. The lattice constant in this series decreases linearly from 4.1854 Åfor EuB6 to 4.1534 Åfor CaB6 following Vegard's law. The paramagnetic Curie temperature, theta, as determined from fitting the high temperature data assuming Curie Weiss behavior \chi = C(T-theta)-1 decreases rapidly with decreasing Eu concentration from 15.1 K for pure EuB6 to 4.5 K for Eu_0.8Ca_0.2B_6. For Eu concentrations below x=0.2, theta decreases linearly to zero, indicating ferromagnetic interactions for all Eu concentrations. A sharp peak in rho(T) is observed at the ordering temperature Tc for Eu concentrations down to 0.2. Lowering the Eu concentration further leads to a rho(T) which increases monotonically with decreasing T down to 4 K and a decrease of partial rho/partial T with decreasing x. The highest rho values at 4 K are observed for Eu_0.35Ca_0.65B6 with a temperature dependence of rho(T) similar to what is observed in CaB6 prepared using excess Ca. However, samples with Eu concentrations below x=0.35 again show a weaker T-dependence and lower values of rho at 4 K.

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