Crossover in the colossal magnetoresistance anisotropy in EuB6

Abstract

The angular dependent resistivity and magnetization have been measured on the single crystals of colossal magnetoresistance compound EuB6 at temperatures T <50 K in magnetic fields below 80 kOe. It is found that the transition from negative (NMR) to positive (PMR) magnetoresistance Δρ/ρ(H) is accompanied by the change of the transverse magnetoresistance anisotropy (MRA) while the static magnetization remains to be almost isotropic. The quantitative analysis of Δρ/ρ(ρ,H 0,T0) data (ρ is the angle between applied magnetic field and <001> axis, the rotation axis is along <110> direction) allows to estimate a field dependence of MRA charcteristic temperature T*[K]≈8+0.4H[kOe], which corresponds to the change of the largest NMR amplitude from H||<100> (T <110> (T>T*(H)). A maximal amplitude of PMR established in ferromagnetic state below 12K is detected for magnetic field applied close to <111> direction. The observed change in MRA is discussed in terms of crossover from the spin polaronic regime of charge transport in paramagnetic phase to the band conductivity in magnetically ordered state. © 2009 IOP Publishing Ltd.