Large anisotropic magnetoresistance in paramagnetic Fe-doped Ta4SiTe4
Large anisotropic magnetoresistance (AMR) usually relies on magnetic ordering, which fixes a preferred moment orientation and couples it to charge transport. Here, we demonstrate that pronounced AMR can instead arise from the anisotropic magnetic-field-induced polarization of dilute local moments in paramagnetic Fe-doped Ta4SiTe4, a quasi-one-dimensional van der Waals narrow-gap semiconductor. Magnetization measurements reveal Curie-like paramagnetism down to 2 K, with the c axis as the magnetic easy axis. The magnetization is described by an effective S = 1/2 model with an anisotropic g-factor ratio of g_c/g_ab = 1.43(1). With the electrical current applied along the c axis, the Fe-doped sample exhibits a large negative magnetoresistance for B//c and only a weak positive response for B//ab, whereas the undoped sample shows little magnetoresistance for either field orientation. The resulting AMR ratio reaches -33% at 8 K and 10 T and exhibits a nonmonotonic temperature dependence qualitatively captured by a minimal spin-disorder model. These results show that engineering the local environment of dilute magnetic ions provides a route to large paramagnetic AMR without long-range magnetic order, extending the materials design space for AMR beyond magnetically ordered systems.