Ordering Phenomena in Transition Metal Oxides

Magnetotransport in Eu-based hexaborides   

EuB₆ is a low-temperature ferromagnet which exhibits a number of remarkable electronic magnetotransport phenomena, including a record high optical Kerr-rotation effect. Substituting isoelectronic Ca for Eu leads to significant changes of the electronic properties across the series of Eu_1-xCa_xB₆, including chemical and hence electronic phase separation. As a result, percolation effects provoke an anomalous enhancement of the defect-induced electrical resistivity ρ_d, particularly in the regime around the percolation limit. At low temperatures, the anomalous enhancement of ρd can be completely quenched by moderate external magnetic fields, leading to colossal negative magnetoresistance effects.