Magnetic phase transitions and anomalous transport properties in Ca-doped Eu Hexaborides

Abstract

The temperature- and field-dependent magnetization M(T, H), electrical resistivity rho(T, H), and Hall resistivity rho(xy) (T, 11) were measured for single crystals of a series of compounds Eu1-xCaxB6 (x =0.0, 0.2, 0.4, 0.6, and 0.9). The ferromagnetic transition temperature of EuB6 (T-c = 12 K) was suppressed with small doping of Ca for Eu0.8Ca0.2B6 (T-c = 5.5 K) as evidenced by M(T) and a sharp drop in p(T). On the other hand, an antiferromagnetic transition was observed, rather than ferromagnetic transition, for Eu0.6Ca0.4B6 (T-N = 4.5 K) and Eu0.4Ca0.6B6 (T-N =3 K). At the same time, a rapid increase of rho(T) was found at low temperatures (T less than or equal to 10 K). The upturn of rho(T) was suppressed with increasing applied magnetic field. From an analysis of the Hall resistivity rho(x,y) the anomalous increase of rho(T) and its suppression were found to be due to the dramatic variations in the charge carrier density n(e f f) (T, H) and the Hall mobility mu(H) (T, R).